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Explore 939 battery concepts with interactive plots, connected ideas and explanations of how Lemonergy uses them.
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The quantities every datasheet is written in, and how they relate.
The SI unit of electric current: one coulomb of charge passing a point per second. Cell currents are quoted in amperes, or as a C-rate so cells of different size can be compared.
Unit: A
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A unit of electric charge: one ampere flowing for one hour, or 3600 coulombs. Battery capacity is rated in ampere-hours, which measure charge, not energy.
Unit: Ah Also: amp-hour
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A component that stores energy as charge on two conducting plates separated by an insulator; its voltage rises in proportion to the charge, unlike a battery’s nearly flat curve. The large DC-link capacitors at an inverter’s input draw a huge inrush current when connected to a pack, which is why a pre-charge circuit fills them first.
Q = C·V; E = ½·C·V² Unit: F (farad)
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The terminal voltage while current flows, lower than the open-circuit voltage by the polarization. It is what the system actually sees, and the difference between the two is a direct measure of the cell’s resistance.
Unit: V Also: loaded voltage, voltage under load
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The SI unit of electric charge; one ampere flowing for one second. Battery engineers prefer the ampere-hour, which is 3600 coulombs, because cells deliver their charge over hours.
Unit: C
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The rate at which charge flows through the cell and its circuit, in amperes. Outside the cell it is carried by electrons; inside, by lithium ions moving through the electrolyte.
I = dQ/dt Unit: A
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Battery temperatures are quoted in degrees Celsius, but rate laws such as Arrhenius need kelvin: add 273.15. Room temperature, 25 °C, is 298 K; the two scales share the same size of degree.
Unit: °C, K
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A battery stores and delivers direct current, flowing one way; the grid and most motors use alternating current, which reverses many times a second. An inverter converts one into the other, and every conversion loses a few percent.
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The quantity a battery’s capacity actually counts: how many electrons, or lithium ions, have passed. It is measured in coulombs or ampere-hours and is conserved, which is why charge in must equal charge out plus losses.
Unit: C, Ah
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What a battery stores and delivers: the integral of power over time, in watt-hours or joules. It is capacity times voltage, which is why two cells with equal ampere-hours can hold different energy.
E = ∫ V·I dt Unit: Wh
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The frequency-dependent generalisation of resistance, with a magnitude and a phase. A cell’s impedance separates ohmic, charge-transfer and diffusion contributions that a single DC resistance lumps together.
Unit: Ω
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The resistance a cell presents to current, from its foils, electrolyte, interfaces and the reactions themselves. It converts part of the delivered energy into heat, sets the voltage drop under load, and rises as the cell ages; a large automotive cell has about a milliohm, a small cylindrical cell tens.
Unit: mΩ Also: DC resistance, DCIR
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The SI unit of energy; one watt for one second. Battery energy is almost always quoted in watt-hours instead, and 1 Wh equals 3600 J.
Unit: J
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One thousand watt-hours, the unit for pack and system energy. An electric car carries 40–100 kWh; grid storage is quoted in megawatt-hours (1000 kWh) and factory output in gigawatt-hours per year.
Unit: kWh
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Two rules of circuit analysis: the currents flowing into any node sum to zero, and the voltages around any closed loop sum to zero. In a pack they explain why every cell in a series string carries the same current, and why cells in a parallel group share current unequally when their resistances differ.
ΣI = 0 at a node; ΣV = 0 around a loop Also: Kirchhoff’s current law, Kirchhoff’s voltage law, KCL, KVL
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Whatever draws current from the battery — a motor, an inverter, a resistor in a test. Loads are specified by current, power or resistance, and a battery’s behaviour depends on which of the three stays constant.
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One thousandth of an ampere-hour, the capacity unit used for small cells. A phone cell of 4500 mAh holds 4.5 Ah; multiplied by its nominal voltage that is about 17 Wh.
Unit: mAh
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The SI unit of electrical resistance: one volt per ampere. Cell internal resistance is about a milliohm for a large automotive cell and tens of milliohms for a small cylindrical one.
Unit: Ω
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Voltage across a resistance equals current times that resistance. Applied to a cell it predicts the voltage drop under load from the internal resistance, which is the first-order reason terminal voltage sags.
V = I × R
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Which terminal is positive and which negative. Connecting a cell or charger the wrong way round, reverse polarity, drives current backwards through it and can destroy the cell, the charger or both within seconds.
Also: reverse polarity
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The rate at which a cell delivers or absorbs energy: voltage times current, in watts. Power is limited by internal resistance and temperature long before capacity runs out.
P = V × I Unit: W
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A connection of negligible resistance between two points that should be separated, so current is limited only by the source. For a battery it may be external, across the terminals, or internal, between the electrodes inside the cell.
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The SI unit of conductance, the reciprocal of the ohm. Electrolyte conductivity is quoted in millisiemens per centimetre; a good liquid electrolyte reaches about 10 mS/cm at room temperature.
Unit: S
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The SI unit of electric potential difference: one joule of energy per coulomb of charge. A lithium-ion cell sits around 3–4 V; packs reach hundreds of volts by putting cells in series.
Unit: V
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The potential difference between a cell’s two terminals. It comes from the chemical difference between the electrodes, moves with state of charge, and sags under load because of internal resistance.
Unit: V Also: terminal voltage
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The SI unit of power: one joule per second, or in a circuit, volts times amperes. A cell delivering 20 A at 3.6 V is supplying 72 W.
P = V × I Unit: W
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A unit of energy: one watt for one hour, or 3600 joules. A cell’s nominal energy in watt-hours is its capacity in ampere-hours times its nominal voltage — 20 Ah at 3.65 V is 73 Wh.
E = Q × V Unit: Wh
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What a cell is physically made of — active materials, binders, additives, foils and tabs — and how its electrodes are put together.
An electrode given a deliberate three-dimensional geometry — laser-drilled channels, interdigitated pillars or a porous metal-foam current collector — instead of a uniform flat coating. The structure shortens the paths ions must travel through a thick electrode and enlarges the reactive surface, so a cell can keep its energy while charging faster.
Also: three-dimensional electrode, structured electrode, laser-structured electrode
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The part of an electrode that actually stores lithium — graphite on the negative side, an oxide or phosphate on the positive. It makes up most of the electrode coating; the rest is binder and conductive additive.
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The positive current collector, typically 10–15 µm thick. A thin passive film keeps it stable at the high potential of the positive electrode, where copper would corrode.
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The electrode where oxidation happens. On discharge that is the negative electrode; on charge it is the positive one. Battery makers nonetheless call the negative electrode “the anode” at all times, after its role on discharge.
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The lithium host in the negative electrode: natural or synthetic graphite in almost every lithium-ion cell today, sometimes blended with a few percent of silicon to raise capacity.
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The margin, of the order of a millimetre, by which the negative electrode extends beyond the positive electrode at every edge, so lithium leaving the cathode edge always finds graphite to enter rather than plating. The overhang slowly soaks up and gives back lithium itself, which causes small apparent capacity drifts in storage and efficiency tests.
Also: negative electrode overhang, overhang effect
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How much active material, or capacity, an electrode carries per square centimetre of foil, typically 2–5 mAh/cm². Higher loading raises energy density but lengthens the ion path, which limits fast charging.
Unit: mAh/cm², mg/cm² Also: mass loading, areal capacity
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A polymer that holds electrode particles to each other and to the foil — typically PVDF for positive electrodes and CMC with SBR for graphite. It stores no charge, so cell designers use as little as the electrode needs.
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The rigid metal case of a cylindrical or prismatic cell, usually nickel-plated steel or aluminium. It holds the stack under pressure, contains the electrolyte and, in a cylindrical cell, doubles as the negative terminal.
Also: casing, housing
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Tubular carbon a few nanometres across, added at a fraction of a percent as a conductive additive. Their length lets them bridge particles that carbon black cannot, so less additive is needed and energy density rises.
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A water-soluble cellulose derivative used with SBR as the binder system for graphite electrodes. It thickens the aqueous slurry and disperses the particles; SBR supplies the elasticity.
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The electrode where reduction happens: the positive electrode on discharge, the negative one on charge. In industry usage, “cathode” means the positive electrode and its material, whatever the cell is doing.
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The lithium-containing compound in the positive electrode — NMC, NCA, LFP or LCO powder — that supplies the cell’s cyclable lithium. It is the most expensive material in most cells and sets the nominal voltage and much of the energy density.
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The smallest complete electrochemical unit: two electrodes, a separator and electrolyte in one sealed case, with two terminals. Everything larger — module, pack, system — is cells connected together.
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The layered core of a cell — negative electrode, separator, positive electrode, separator, repeated — whether wound into a jelly roll or cut and stacked as sheets. Its layer count and thickness set the capacity, and it is the part held under stack pressure. In flow batteries and fuel cells, ‘stack’ instead means many cells clamped in series.
Also: electrode stack, electrode assembly
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A hollow metal tube placed in the core of a cylindrical cell’s jelly roll, in the hole left by the winding mandrel. It stops the winding collapsing inward and keeps a clear channel for gas to reach the vent during failure; X-ray studies of 18650 cells in thermal runaway showed unsupported cores collapsing after venting.
Also: center pin, core pin
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Fine carbon, such as carbon black or carbon nanotubes, added in small amounts to an electrode so that electrons can reach every active particle. Many active materials conduct electrons poorly on their own.
Also: carbon black, conductive carbon
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The negative current collector, typically 6–10 µm thick. Copper is used because it is stable at the low potential of a graphite electrode, where aluminium would alloy with lithium.
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The thin metal foil that carries electrons between an electrode and the external circuit — usually copper on the negative side and aluminium on the positive side.
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A solid conductor where the cell’s reaction happens, in contact with the electrolyte. A lithium-ion cell has a negative electrode and a positive electrode, each a porous coating on a metal foil.
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Layered carbon, the negative active material of nearly all lithium-ion cells. Lithium intercalates between its layers up to LiC₆, a theoretical 372 mAh/g, at a potential about 0.1 V above lithium metal.
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A disordered, non-graphitisable carbon used as the negative electrode of sodium-ion cells, where graphite barely works, and as a fast-charge additive in lithium-ion. Its open structure accepts ions without the strict layer spacing of graphite.
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Electrodes and separators wound together into a spiral. It is the inside of a cylindrical cell and of many prismatic cells; large pouch cells usually use stacked sheets instead.
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The lightest metal, with the most negative electrode potential, which is why lithium cells have the highest voltage and specific energy of any practical chemistry. Inside a lithium-ion cell it exists only as Li⁺ ions in the electrolyte and in the electrode hosts, never as metal.
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A negative electrode made of lithium metal itself. It stores about ten times more charge per gram than graphite, which is the main attraction of solid-state cells, but it is reactive and prone to uneven deposits.
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A negative active material, Li₄Ti₅O₁₂, that works at about 1.55 V above lithium, so it never plates lithium and forms almost no SEI. The price is a low cell voltage of about 2.4 V and low energy density, traded for very long life and fast charging.
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The areal capacity of the negative electrode divided by that of the positive electrode facing it, usually set at 1.05–1.15. The excess negative capacity ensures there is always a graphite site for every lithium ion on charge, which guards against lithium plating.
N/P = Q_neg / Q_pos
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The electrode at the lower potential, usually graphite on copper foil in a lithium-ion cell. It holds the lithium when the cell is charged and releases it on discharge, and industry calls it the anode.
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A family of mixed oxides, such as Nb₁₆W₅O₅₅, whose open block structures let lithium diffuse quickly even through micrometre-sized particles. Like lithium titanate it works around 1.5 V versus lithium, so it avoids lithium plating and thick SEI, but it stores more charge per litre; it is developed for cells that charge in minutes.
Also: Nb₁₆W₅O₅₅, niobium oxide anode, Wadsley–Roth phase
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A water-based binder with many carboxyl groups that bond strongly to silicon surfaces, used in silicon-rich negative electrodes where CMC/SBR cannot hold the swelling particles together.
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The fraction of a layer’s volume that is empty space. In a lithium-ion electrode the pores — roughly 20–35 % of the volume after calendering — are filled with electrolyte, which carries ions to the particles.
Unit: —
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An electrode made of active-material particles, conductive additive and binder with electrolyte-filled pores between them. Its large internal surface is where the reaction happens.
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The electrode at the higher potential: a lithium metal oxide or phosphate coated on aluminium foil. It is the lithium source when a cell is built, and industry calls it the cathode.
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The flexible case of a pouch cell: a thin aluminium layer laminated between a polyamide outer film and a heat-sealable polypropylene inner film. It is light and cheap but offers no mechanical support and can swell.
Also: aluminium laminate
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The fluoropolymer binder of dry electrode processes: under shear its particles draw out into fine fibrils that web the active material together without any solvent. It is unstable at the low potential of graphite, which complicates dry negative electrodes.
Also: polytetrafluoroethylene, Teflon
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The fluoropolymer binder used in most positive electrodes. It dissolves only in solvents such as NMP, which is why positive-electrode slurries are solvent-based and need solvent recovery in the plant.
Also: polyvinylidene fluoride
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A binder made of polymers with reversible bonds — hydrogen bonds, disulfide links or host–guest pairs — that re-form after the network tears. It targets silicon and other alloying anodes, whose particles swell by up to 300 % and crack ordinary binders; a 2013 study showed such a polymer keeping silicon microparticle electrodes cycling far longer.
Also: self-healing polymer binder, dynamic binder
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A negative electrode that uses silicon, which alloys with lithium and stores roughly ten times more charge per gram than graphite but swells by up to 300 %. Today it is blended into graphite at a few percent to limit the swelling.
Also: silicon-graphite, SiOx
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A rubber latex that gives graphite coatings their flexibility and adhesion to copper, used at about 1–2 % together with CMC. The pair lets negative electrodes be made with water instead of NMP.
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The strip of metal that connects an electrode’s foil to the cell terminal: nickel or copper on the negative side, aluminium on the positive. Tab count and width set much of a cell’s resistance and heat generation.
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The bulk density of a powder after a cylinder of it has been mechanically tapped a set number of times, as in ASTM B527. Dense, spherical NMC reaches about 2.6–2.8 g/cm³, LFP only about 0.8–1.1 g/cm³; higher tap density lets calendering reach a higher electrode density and so more energy per litre.
Unit: g/cm³ Also: tapped density
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The external conductor through which current enters and leaves the cell: the can and cap of a cylindrical cell, two posts on a prismatic cell, or the sealed foil tabs of a pouch cell.
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A negative electrode using tin, which alloys with lithium up to about Li₄.₄Sn for a theoretical 994 mAh/g, nearly three times graphite. Its volume grows by roughly 260 % on lithiation, so tin is used in composites; Sony’s 2005 Nexelion cell had an amorphous tin–cobalt–carbon anode. Tin also alloys with sodium, making it a sodium-ion candidate.
Also: Sn anode, tin-based anode, Sn–Co–C
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The electrode materials that define a lithium-ion cell, the crystal structures behind them, and the shapes cells are built in.
A very long, thin prismatic LFP cell, close to a metre in length, laid side by side so the cells themselves stiffen the pack. The format trades cell-level energy density for pack-level packing efficiency and a large cooling surface.
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A small disc-shaped cell in a crimped steel case. Besides powering watches and key fobs, it is the standard laboratory format for testing a new electrode material against lithium metal.
Also: button cell, CR2032
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A cell made by winding the electrodes into a jelly roll and sealing it in a round metal can. Sizes are named by their dimensions: a 21700 cell is 21 mm across and 70 mm long.
Also: 18650, 21700, 4680
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A cathode family in which lithium and transition-metal ions share the same crystal sites at random instead of forming ordered layers. With about 10–20 % excess lithium, percolating diffusion paths open, giving over 250 mAh/g from abundant manganese, titanium or iron instead of nickel and cobalt. Slow kinetics, voltage hysteresis and oxygen loss keep it in the laboratory.
Also: DRS, cation-disordered rock salt, cation-disordered rocksalt
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A layered oxide with 80 % or more nickel, such as NMC811 or NCA. Nickel raises capacity and lowers cobalt content, but the material is less thermally stable, more sensitive to moisture and ages faster at high voltage.
Also: Ni-rich
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The crystal structure of LCO, NMC and NCA: close-packed oxygen layers with lithium and transition-metal ions in alternate layers of octahedral sites, so lithium moves in two-dimensional sheets. The structure offers high capacity and voltage but can distort or mix cations when deeply delithiated. Sodium versions are labelled O3 or P2 by their stacking.
Also: layered transition-metal oxide, α-NaFeO₂ structure, O3 structure, P2 structure
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The original lithium-ion positive material, LiCoO₂, still used in phones and laptops for its high volumetric energy density. Cobalt cost and limited thermal stability keep it out of vehicles.
Also: lithium cobalt oxide, LiCoO₂
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A positive electrode material, LiFePO₄, giving cells a nominal voltage around 3.2 V, long cycle life and good thermal stability, but less energy per kilogram than nickel-rich oxides. Its flat voltage curve makes state of charge hard to read from voltage alone.
Also: lithium iron phosphate, LiFePO₄
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A rechargeable cell in which lithium ions shuttle between two intercalation electrodes, typically graphite and a lithium metal oxide, through a non-aqueous electrolyte. Commercialised in 1991, it dominates portable electronics, electric vehicles and new grid storage.
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A layered oxide carrying extra lithium in the transition-metal layer, typically Li₁.₂Ni₀.₁₃Co₀.₁₃Mn₀.₅₄O₂. Above about 4.5 V on the first charge, oxygen joins the redox, giving more than 250 mAh/g with little nickel or cobalt. Voltage fade, oxygen loss and a large first-cycle loss slowed adoption; GM and LG Energy Solution plan LMR cells for 2028.
Also: LRM, lithium manganese-rich, Li-rich layered oxide, OLO, LMR-NMC
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Lithium iron phosphate with part of the iron replaced by manganese, which lifts the average voltage to about 3.8 V and so the energy density by 10–20 % while keeping most of LFP’s safety and cost advantages.
Also: lithium manganese iron phosphate
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A manganese spinel positive material, LiMn₂O₄, that is cheap, safe and good at high power but suffers manganese dissolution and short life at elevated temperature. It is often blended with NMC rather than used alone.
Also: lithium manganese oxide, spinel
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A nickel-doped manganese spinel, LiNi₀.₅Mn₁.₅O₄, that works at about 4.7 V and contains no cobalt. Its high voltage stresses today’s electrolytes, which is the main obstacle to commercial use.
Also: high-voltage spinel
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An NMC with roughly 50–70 % nickel, such as NMC532 or NMC622. Charging it to higher cut-off voltages, about 4.3–4.4 V and often as single crystals, recovers much of the capacity of high-nickel grades while keeping better thermal stability, lower cost and longer life — a common compromise for mainstream EV cells.
Also: mid-Ni, high-voltage mid-nickel, NMC532, NMC622
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A layered-oxide positive material, LiNi₀.₈Co₀.₁₅Al₀.₀₅O₂ in its classic form, with aluminium in place of the manganese of NMC. It offers high specific energy and is associated with long-range electric cars built from cylindrical cells.
Also: nickel cobalt aluminium oxide
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A quaternary layered oxide that adds a little aluminium to a high-nickel NMC, typically around 90 % nickel with only a few percent cobalt. Aluminium steadies the lattice and slows degradation, much as in NCA, so the material keeps high capacity with less cobalt; LG Energy Solution supplied it for GM’s Ultium cells.
Also: nickel cobalt manganese aluminium oxide, quaternary cathode, LiNiCoMnAlO₂
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A family of layered-oxide positive electrode materials, LiNiₓMnᵧCo₁₋ₓ₋ᵧO₂, used in many electric-vehicle cells. Variants are named by their metal ratio: NMC811 has eight parts nickel to one each of manganese and cobalt.
Also: NCM, nickel manganese cobalt oxide, LiNiMnCoO₂
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The orthorhombic structure of LiFePO₄ and its relatives, in which phosphate groups lock oxygen in place and lithium lies in one-dimensional channels. Strong phosphorus–oxygen bonds make the material thermally stable and long-lived, but one-dimensional diffusion and poor electronic conductivity call for small, carbon-coated particles. LMFP substitutes manganese to raise the voltage.
Also: LiMPO₄ structure, phospho-olivine
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A cell sealed in a flexible bag of aluminium laminated with plastic, holding stacked electrode sheets in larger cells or a flattened wound roll in many small ones. It is light and easy to cool, but needs outside support and can visibly swell if gas forms inside.
Also: lithium polymer cell, LiPo
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A cell in a rigid rectangular metal case, holding either a flattened jelly roll or stacked sheets. Large prismatic cells pack tightly into battery packs.
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The working principle of a lithium-ion cell: lithium ions rock back and forth between host electrodes and are neither plated nor dissolved. Because the electrodes are only hosts, the ion count stays fixed and the cell can cycle thousands of times.
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Positive-electrode powder made of individual micron-sized crystals rather than agglomerates of many small grains. With no internal grain boundaries to crack open, it resists particle cracking and gassing and lasts longer at high voltage.
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A cubic crystal structure of formula AB₂O₄ in which, for lithium materials, lithium sits in tetrahedral sites and transition metals in octahedral ones, leaving three-dimensional channels for lithium to move. That gives good rate capability; it is the framework of LMO, high-voltage LNMO and lithium titanate. Manganese spinels suffer manganese dissolution and Jahn–Teller distortion.
Also: spinel crystal structure, AB₂O₄ structure
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A cylindrical-cell construction in which the whole uncoated edge of each foil is folded and welded to the end cap instead of one or two narrow tabs. The current path shortens from metres to millimetres, cutting resistance and heating in large-format cells.
Also: full-tab, shingled tab
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The numbers that size a cell and let two cells be compared.
Current divided by nominal capacity, in reciprocal hours. 1C on a 20 Ah cell is 20 A; 2C is 40 A. C-rate lets you compare loads on cells of different sizes.
C-rate = I / Q_nominal Unit: h⁻¹
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How long a cell lasts in years, regardless of cycling, before it reaches its end-of-life criterion. It is set by calendar aging, which runs fastest at high temperature and high state of charge.
Unit: years Also: shelf life
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The share of a pack’s mass or volume that is cells rather than housing, cooling, busbars and electronics. It is typically 60–75 % by mass; raising it is the point of cell-to-pack and cell-to-chassis designs.
Unit: % Also: gravimetric cell-to-pack ratio, GCTP
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The current a cell can supply indefinitely without exceeding its temperature limit, and the higher current it can supply for a stated few seconds. Peak ratings are only valid for the duration and starting temperature given.
Unit: A
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Charge delivered on discharge divided by charge put in on the previous charge. A healthy lithium-ion cell exceeds 99.9 %; the missing fraction is lithium lost to side reactions, so CE is an early and sensitive aging signal.
CE = Q_discharge / Q_charge Unit: %
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The number of full charge–discharge cycles a cell completes before its capacity falls to a stated fraction, usually 80 %, of its initial value under defined conditions. LFP cells reach several thousand cycles; high-energy NMC fewer.
Unit: cycles
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The manufacturer’s specification sheet for a cell: nominal capacity, nominal voltage, voltage window, continuous and peak currents, operating temperatures, dimensions, mass and cycle life, each tied to the test conditions it was measured under.
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Power divided by nominal energy, the energy-based cousin of the C-rate: a 1E discharge empties a cell’s watt-hours in one hour. Grid-storage contracts are often written in E-rates or hours of discharge rather than in amperes.
E-rate = P / E_nominal Unit: h⁻¹ Also: P-rate
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The energy a vehicle draws from its battery per kilometre, in Wh/km or kWh/100 km. A mid-size electric car uses about 150–200 Wh/km and a 12 m city bus around 1–1.5 kWh/km, more in winter when heating runs. Usable energy divided by consumption gives range, so consumption sets battery size.
Range = E_usable / consumption Unit: Wh/km Also: Wh/km, kWh/100 km, kWh/km, vehicle energy consumption
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Stored energy per unit volume, in watt-hours per litre. It is the figure that matters when space is the constraint, as in a phone or under a car floor; high-energy cylindrical cells pass 700 Wh/L.
Unit: Wh/L Also: volumetric energy density
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Energy out divided by energy in over a full cycle. It is lower than coulombic efficiency because the charge voltage sits above the discharge voltage; cells reach 95–98 %, and a full storage system 85–92 % after power electronics and cooling.
Unit: % Also: round-trip efficiency
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The total energy a battery has delivered, or charged and discharged, over its life, counted in kWh or MWh. Discharged energy divided by usable energy gives equivalent full cycles. Stationary-storage and electric-bus warranties often set a throughput limit alongside years, because aging tracks the energy cycled as well as time.
Unit: kWh, MWh Also: lifetime throughput, MWh throughput, charge throughput, Ah throughput
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Total charge throughput divided by nominal capacity, so that many shallow cycles count as the equivalent number of full ones. It lets cycle life be compared across different duty cycles.
EFC = ΣQ_throughput / (2·Q_nominal)
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t = 1 / C-rate: how long a constant current would take to transfer the full nominal capacity. A definition, not a prediction of real runtime.
t = 1 / C-rate Unit: h
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The charge a cell is rated to deliver under specified test conditions — current, temperature, rest and voltage limits — usually in ampere-hours.
Unit: Ah Also: rated capacity
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Nominal capacity times nominal voltage, in watt-hours: the headline energy figure on a datasheet. The energy actually delivered depends on the load, the temperature and how the voltage curve is weighted.
E = Q × V_nominal Unit: Wh
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A representative average voltage of a cell over a full discharge, such as 3.6–3.7 V for an oxide/graphite cell or about 3.2 V for LFP/graphite. Multiplied by capacity, it gives nominal energy.
Unit: V
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The temperature range a cell may be charged and discharged in, typically 0–45 °C for charging and −20–60 °C for discharging. Charging below 0 °C risks lithium plating; above the range the cell ages fast and may vent.
Unit: °C
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An empirical rule that delivered capacity falls as a power of the discharge current, with an exponent of 1.1–1.3 for lead–acid. For lithium-ion the exponent is close to 1, so the law is rarely used.
t = H·(C/(I·H))^k
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A log–log chart of specific power against specific energy on which each storage technology occupies a region. Capacitors sit high and left, batteries lower and right, and a single cell traces a curve as it is discharged faster.
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How much of its capacity a cell can still deliver as the C-rate rises. It is measured by discharging at a series of rates and falls faster for thick, dense electrodes and at low temperature.
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A cell’s internal resistance multiplied by its capacity, which cancels out size: ten 5 Ah, 20 mΩ cells in parallel make 50 Ah at 2 mΩ, both 100 mΩ·Ah. Lower values mean more power per unit of stored energy. Conductance divided by energy, in siemens per watt-hour, expresses the same figure of merit the other way up.
R·Q (mΩ·Ah); G/E = 1/(R·E) (S/Wh) Unit: mΩ·Ah Also: ohm-ampere-hour, mΩ·Ah, siemens per watt-hour, S/Wh
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The total time a battery stays useful in its application, set by whichever of calendar life and cycle life runs out first. Runtime, by contrast, is the time a single charge lasts under a given load.
Also: runtime
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Charge stored per gram of active material, in mAh/g. It is the figure materials scientists quote: about 150–200 mAh/g for layered oxides, 160 for LFP, 372 theoretical for graphite and about 3600 for silicon.
Unit: mAh/g
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Stored energy per unit mass, in watt-hours per kilogram. Commercial lithium-ion cells range from about 160 Wh/kg for LFP to around 270 Wh/kg for high-nickel chemistries; at pack level the figure drops by a quarter or more.
Unit: Wh/kg Also: gravimetric energy density
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Deliverable power per unit mass, in watts per kilogram; power density is the same per litre. A cell is designed for energy or for power, rarely both: thin electrodes give power, thick ones give energy.
Unit: W/kg Also: power density
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The capacity a material would deliver if every available lithium ion took part, computed from Faraday’s law and the molar mass. Practical capacity is lower because not all the lithium can be removed reversibly.
Q = n·F / (3.6·M) Unit: mAh/g
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The part of a cell’s capacity that a system actually lets it use, after the BMS reserves margins at the top and bottom of the state-of-charge window. An electric-car pack may use 90–95 % of its gross capacity.
Also: available capacity
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Average discharge voltage divided by average charge voltage over a cycle. The gap comes from resistance, overpotential and hysteresis, so voltage efficiency falls as current rises. Multiplied by coulombic efficiency it gives energy efficiency; a lithium-ion cell at moderate rate reaches about 95 %, a vanadium flow battery often only 80–90 %.
VE = V̄_discharge / V̄_charge; EE = CE × VE Unit: % Also: voltaic efficiency
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The range between a cell’s lower and upper cutoff voltages, such as 2.5–4.2 V for an NMC/graphite cell. Staying inside it is what keeps the electrodes and electrolyte from degrading quickly.
Unit: V Also: operating voltage range
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How current goes in and comes out, and the limits that stop it.
Charging whose current and voltage limits adjust in real time to what the battery can safely take — its temperature, state of charge, health or impedance — or to when it is needed. Phones that hold at 80 % overnight and finish shortly before the owner wakes are an everyday example; vehicle chargers use the same idea against lithium plating.
Also: optimised charging, optimized battery charging, intelligent charging
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A short, partial charge to add range quickly — often only into the part of the SOC window where the cell accepts high current best, typically 10–80 %. Charging above 80 % is slow on any fast charger, so frequent short top-ups are often faster than one long session.
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The standard lithium-ion charge protocol: constant current until the cell reaches its upper cutoff voltage, then that voltage held constant while the current tapers. The charge ends when the current falls to a set fraction, often C/20.
Also: constant current constant voltage
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A weak cell in a series string being driven below zero volts by its neighbours as the string is discharged past the weak cell’s empty point. It causes rapid, permanent damage, and preventing it is one reason a BMS monitors every cell.
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Driving current into a cell so that lithium ions leave the positive electrode and are stored in the negative one, raising the cell voltage. It needs an external supply at a voltage above the cell’s own.
Also: charging
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How much of the current offered to a battery it can actually absorb at a given state of charge and temperature. It falls as the battery fills and as it cools, which is why regenerative braking and fast charging are limited by the battery rather than the source.
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The power electronics that convert mains or DC supply into the controlled current and voltage a battery needs. For lithium-ion it runs the CC-CV profile within the limits the BMS communicates, and stops rather than floats when the cell is full.
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A charge or discharge at a fixed current, so capacity is simply current times time. It is the first stage of a CC-CV charge and the normal way to run a capacity test.
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A charge stage in which the terminal voltage is held at a selected limit while the current is allowed to fall. The charge added during this stage and its duration depend on the cell, initial state, voltage limit and termination current.
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Charging with a fixed-power stage, so current falls as voltage rises because current equals power divided by voltage. In a CP-CV protocol, a constant-voltage stage follows when the voltage limit is reached. A power rating alone does not establish that a charger implements this sequence.
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The terminal-voltage limit that ends a discharge, or caps a charge — in constant-current, constant-voltage (CC-CV) charging the cell is then held at that voltage until the current falls to a cutoff. A real discharge ends at the lower cutoff, which is why actual runtime can differ from the ideal duration.
Unit: V
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One discharge and one charge, in either order. A full cycle spans the whole usable capacity; a partial cycle covers only part of it, and aging tests usually report both the cycle count and the depth of discharge.
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Drawing current from a cell: lithium ions leave the negative electrode, cross the electrolyte and enter the positive one, while electrons do work in the external circuit. The voltage falls as the cell empties.
Also: discharging
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The plot of terminal voltage against delivered capacity at a given current and temperature. Its shape identifies the chemistry — LFP is flat, NMC slopes — and its area is the delivered energy.
Also: voltage curve
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A deliberate, controlled overcharge of a lead–acid battery that brings weaker cells up to full and stirs the electrolyte. It must never be applied to lithium-ion cells, which are equalised electronically by the BMS instead.
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Charging a vehicle battery in about 10–15 minutes, roughly 4C to 6C — the US Department of Energy’s research target that set the term. At these rates lithium plating, heat and electrolyte transport limit the cell, so XFC needs thin or structured electrodes, strong cooling and careful protocols.
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Charging intended to replenish a specified amount of energy or state of charge in a short time. There is no universal C-rate threshold: performance depends on cell chemistry, temperature, starting state and power limits. High current can increase heating and lithium-plating risk, requiring appropriate limits.
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The instant step in terminal voltage when current starts or stops, equal to current times internal resistance. It is lost as heat and is the reason a cell’s voltage under load sits below its open-circuit voltage.
ΔV = I × R Unit: V Also: ohmic drop, voltage sag
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The current or power a battery must deliver as a function of time in its application — a drive cycle for a car, a daily charge–discharge pattern for storage. Aging tests built on a realistic profile predict life better than constant-current cycling.
Also: duty cycle, drive cycle
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A cutoff that disconnects the load when battery voltage falls to a set point, protecting against over-discharge. In a lithium-ion pack the BMS performs it; in off-grid lead–acid systems it is a function of the charge controller.
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A loss of usable capacity in nickel–cadmium cells repeatedly recharged from the same partial state. Lithium-ion cells do not show it in any practical sense, though LFP has a small related voltage memory.
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A charge protocol with a sequence of constant-current stages, often reducing current as the cell fills. Stage transitions follow selected time, voltage, state-of-charge or other limits. Charging time and lithium-plating risk depend on the cell and control conditions; a staged profile alone does not establish an improvement.
Also: step charging, stepped CC
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A fast-charging protocol from Rachid Yazami’s group in Singapore that never imposes a fixed current: the charger applies a rising series of short constant-voltage steps separated by brief rests, and the cell draws whatever current it accepts. Each step’s current decay decides when to move on; the developers report full charges in as little as 10 minutes.
Also: nonlinear voltammetry charging, NLV charging
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Discharging below the lower cutoff voltage. Near 1.5 V the copper current collector begins to dissolve, and on the next charge it can redeposit as metal that shorts the cell, so a deeply discharged cell should not simply be recharged.
Also: deep discharge
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Charging past the upper cutoff voltage. The positive electrode over-delithiates and releases oxygen, the electrolyte oxidises and lithium plates on the negative, so an unprotected overcharge can end in thermal runaway.
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The gap between a cell’s terminal voltage under load and its open-circuit voltage. It has ohmic, charge-transfer and concentration parts, grows with current and falling temperature, and is where delivered energy is lost.
Unit: V Also: overvoltage
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Charging with current pulses separated by rests or short discharges, intended to let concentration gradients relax and reduce plating. Benefits for lithium-ion are modest and depend on the cell; it is not standard practice.
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Using a vehicle’s motor as a generator while slowing down, so braking energy charges the battery in short high-current pulses. A cold or full battery cannot accept it, which is one reason a BMS computes charge power limits continuously.
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The slow recovery of a cell’s voltage towards open-circuit voltage after current stops, as concentration gradients inside the electrodes level out. It takes minutes to hours, which is why OCV measurements need a rest period.
Also: rest
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The slow loss of stored charge while a cell is not in use. An unexpected rise can signal a leakage path or a soft internal short.
Unit: %/month
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Reconfiguring a pack with contactors so that its two halves charge in parallel at half the drive voltage. An 800 V vehicle such as the Tesla Cybertruck can then use 400 V fast chargers without a DC/DC booster; GM’s Hummer EV does the reverse, driving at 400 V and switching the halves into series to charge at 800 V.
Also: bank charging, pack splitting, series–parallel switching
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The current at which a constant-voltage charge stage is declared finished, often C/20 or C/50. A higher taper current ends the charge sooner and leaves the cell slightly less than full.
Unit: A Also: termination current, cutoff current
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Holding a battery at a small current, or a fixed voltage, to keep it full. It is standard for lead–acid and NiMH but harmful for lithium-ion, which should be left to rest once charged; lithium-ion chargers instead top up when the voltage sags.
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The difference between the open-circuit voltage reached from charging and from discharging at the same state of charge. It is small for most lithium-ion chemistries but large for LFP and silicon, and it limits how precisely voltage can give SOC.
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A stretch of the voltage curve where voltage barely changes while charge passes, because the electrode is moving between two phases at a fixed potential. LFP has one long plateau; graphite shows several small ones.
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The quantities a battery management system estimates but cannot measure directly.
A cell’s condition when new, after formation and before any service: the reference against which state of health and capacity fade are measured.
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Equalising the state of charge of cells in series, since the pack is limited by its emptiest cell on discharge and its fullest on charge. Passive balancing bleeds charge from high cells through resistors; active balancing moves it between cells.
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The spread in capacity, resistance and self-discharge between nominally identical cells, from manufacturing and from unequal temperatures in service. It is why packs need balancing and why grading matches cells before assembly.
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Estimating state of charge by integrating the measured current over time. Simple and fast, but sensor offset accumulates, so it is corrected against the OCV–SOC curve at rest or fused with it in a Kalman filter.
SOC(t) = SOC₀ − ∫ I dt / Q Also: ampere-hour counting
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Estimating SOC with a model learned from data — LSTM neural networks, support vector regression, Gaussian processes — that maps histories of voltage, current and temperature to charge. It needs no physical model, but is only as good as its training data across temperature and aging, and is harder to verify for functional safety than a Kalman filter.
Also: machine-learning SOC estimation, neural-network SOC estimation, support vector machine, SVM, LSTM
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How much of a cell’s capacity is used in a cycle. Deep cycles cause more mechanical stress in the active materials than shallow ones.
Unit: %
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Plotting the derivative of voltage with respect to charge during a slow cycle. Its peaks mark electrode phase transitions, and how they shift between cycles separates lithium inventory loss from active-material loss without opening the cell.
dV/dQ vs Q Also: dV/dQ
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Two ways to estimate a cell’s fast-changing states, such as SOC, together with its slowly drifting parameters, such as capacity and resistance. Dual estimation runs two coupled filters on different time scales, each using the other’s latest output; joint estimation stacks both into one augmented vector inside a single filter, simpler to structure but larger and harder to tune.
Also: co-estimation, dual extended Kalman filter, dual EKF
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The point at which a cell no longer meets its application’s requirement, conventionally 80 % of initial capacity or a doubling of resistance. It is a definition for warranties and tests, not a point where the cell stops working.
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The inverse of differential voltage analysis: the derivative of charge with respect to voltage, plotted against voltage. Plateaus in the voltage curve become peaks whose height and position track aging, and it can be run on data a BMS already records.
dQ/dV vs V Also: dQ/dV
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A recursive estimator that blends a model prediction with noisy measurements according to how much each is trusted. In a BMS an extended Kalman filter combines coulomb counting with a voltage model to track SOC and sometimes resistance.
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Two control-theory properties of a model: whether its internal states can be inferred from its measured outputs, and whether its inputs can steer those states. SOC is poorly observable on LFP’s flat OCV plateau, where voltage barely changes with charge, and the individual SOCs of series cells cannot be steered by pack current alone, which is why balancing exists.
Also: observability
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The characteristic relation between a cell’s open-circuit voltage and its state of charge, measured once at low current and stored in the BMS. A steep curve, as for NMC, makes SOC easy to read from voltage; LFP’s flat curve does not.
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The voltage across a cell’s terminals when no current flows and the cell has rested long enough for the voltage to settle. It depends on state of charge and temperature, and a cell whose open-circuit voltage falls unusually fast in storage may have an internal short.
Unit: V
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A recursive estimator that represents an uncertain state as a cloud of weighted samples, propagating each through the model and reweighting it against every new measurement. Unlike a Kalman filter it copes with strong nonlinearity and non-Gaussian noise, at the cost of hundreds of model runs per step, so it appears more in remaining-useful-life prognostics than in production BMS firmware.
Also: sequential Monte Carlo
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An online fitting method that updates model parameters with each new sample instead of refitting all past data. A forgetting factor set just below 1, such as 0.99, discounts old samples so the estimate follows a cell’s resistance and time constants as temperature, SOC and aging change them; the BMS then hands the parameters to its state estimator.
Also: forgetting factor
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A prediction of how many cycles, or how much time, a battery has left before reaching end of life. It is estimated from the trend of state of health, and is uncertain near a knee point where fade accelerates.
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An algorithm that reconstructs internal states such as SOC by running a model alongside the cell and correcting it with the measured voltage error. A Luenberger observer uses a fixed gain, a sliding-mode observer a switching term robust to model error, an H-infinity filter bounds the worst-case error, and an adaptive observer also updates the model parameters.
Also: Luenberger observer, sliding-mode observer, H-infinity filter, adaptive observer
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The charge a cell or pack can still hold, as a percentage of its rated or beginning-of-life capacity: the capacity half of state of health. A cell measured at 82 Ah against a 100 Ah rating has an SoQ of 82 %, and the usual 80 % end-of-life convention is written against it.
SoQ = Q_now / Q_rated × 100 % Unit: % Also: SOH-C, capacity retention
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A vehicle battery’s present usable energy, read from the on-board monitor, as a percentage of the usable energy certified when new. UN GTR 22 requires at least 80 % after 5 years or 100 000 km and 70 % after 8 years or 160 000 km; Euro 7 raises the second figure to 72 % for cars.
SOCE = E_usable,now / E_usable,certified × 100 % Unit: %
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How full a cell is, as a fraction of its available capacity. State of charge, like temperature, affects how fast a stored cell ages.
Unit: %
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Remaining energy as a fraction of total energy, which differs from state of charge because the voltage falls as a cell empties. It is the quantity behind a range estimate, and is harder to estimate than SOC.
Unit: %
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A yes-or-no, or graded, judgement of whether a battery can perform a specific task right now — crank an engine, deliver the next ten seconds of power — combining state of charge, state of health and temperature.
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A summary of how far a cell has aged, often expressed through remaining capacity or increased resistance compared with when it was new. By convention a cell has reached end of life at 80 % of its rated capacity.
Unit: %
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The maximum charge or discharge power a battery can deliver for the next few seconds without breaking a voltage, current or temperature limit. The BMS recomputes it continuously from SOC, temperature and resistance and sends it to the motor controller.
Unit: W
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The internal resistance of a cell compared with its value when new: the power half of state of health. It is quoted as a ratio or a percentage increase; a doubling of resistance is a common end-of-life criterion where power matters more than capacity, as in hybrids.
SoR = R_now / R_BOL Also: SOH-R, resistance state of health
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A temperature computed rather than measured: a thermal model fed with current, coolant temperature and the readings of nearby sensors infers the temperature of cells, or cell cores, that carry no sensor. Packs often fit one thermistor for several cells, and a large cell’s core runs hotter than its surface under load, so derating depends on such estimates.
Also: soft sensor, core temperature estimation, sensorless temperature estimation
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The cell in a series string that reaches a voltage limit first — through lower capacity, higher resistance or a different SOC — and so sets the usable capacity and power of the whole pack. Balancing can correct an SOC offset but not a capacity deficit, so one weak cell among hundreds retires the pack early unless replaced.
Also: limiting cell, weakest link
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Why a cell loses capacity and gains resistance, and the mechanisms behind it.
The energy barrier a reaction must cross, which sets how sensitive its rate is to temperature in the Arrhenius law. Fitted values for lithium-ion aging are typically 20–60 kJ/mol, and they differ for each mechanism.
Unit: kJ/mol
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The gradual, irreversible change in a cell’s capacity, resistance and safety margins over time and use. It is the sum of many chemical and mechanical mechanisms, each driven by temperature, state of charge, current and cycle depth.
Also: degradation
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A specific physical or chemical process that degrades a cell — SEI growth, lithium plating, particle cracking, transition-metal dissolution. Mechanisms are grouped into three modes: loss of lithium inventory, loss of active material and resistance increase.
Also: degradation mode
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The rule that a rate constant is proportional to exp(−Ea/RT), so a thermally activated reaction speeds up steeply with temperature. Near room temperature many degradation reactions roughly double their rate for every +10 °C.
k = A·exp(−Eₐ/RT)
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Loss of the binder’s ability to hold particles to each other and to the foil, from swelling in electrolyte, repeated strain or heat. Particles that lose contact stop storing lithium, and the coating can delaminate from the foil.
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Degradation that happens with time even when a cell is not cycled — in storage, for example. It is driven mainly by side reactions such as SEI growth and accelerates with temperature.
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The loss of charge a cell can store and deliver, for example through lithium locked into the SEI or active material that has cracked out of service.
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The counterpart of the SEI on the positive electrode: a thin layer of electrolyte oxidation products on the oxide surface. It is thinner and less stable than the SEI, and its growth contributes to impedance rise, especially at high voltage.
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Oxidation of the copper current collector when a cell is over-discharged and the negative electrode’s potential rises too high. Dissolved copper redeposits on recharge as metallic filaments that can short the separator, which is why over-discharged cells are not simply recharged.
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Degradation at one electrode caused by species produced at the other — dissolved transition metals or oxidation products from the positive electrode damaging the SEI on the negative. It is why electrode aging cannot be studied in isolation.
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Attack on the foils: aluminium pitting at high potential when the passive film fails, or copper dissolving if the negative electrode is driven above about 3.5 V vs Li/Li⁺ by over-discharge. Both raise resistance and can shed metal into the cell.
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Degradation caused by charging and discharging: mechanical strain in the particles, fresh SEI on cracked surfaces and, at high rate or low temperature, lithium plating. It scales with charge throughput and grows with depth of discharge and C-rate.
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Plated lithium metal that has lost electrical contact with the electrode, usually because SEI formed around it. It can no longer take part in cycling, so every gram of it is permanent capacity loss.
Also: inactive lithium
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Separation of the electrode coating from its current collector, or of layers within a cell, which cuts the electronic path to part of the electrode. It is caused by poor adhesion, binder degradation, gas pockets or repeated swelling.
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A tree-like metal deposit that can grow from the negative electrode through the separator, raising self-discharge or causing an internal short circuit.
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Reduction of the electrolyte at the negative electrode and oxidation at the positive, outside its stability window. A little is useful — it builds the SEI — but continued decomposition consumes lithium, dries the cell and makes gas.
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Loss of liquid electrolyte to decomposition and film growth until parts of the electrode are no longer wetted. It appears late in life as a sudden rise in resistance, and is one cause of the knee in a capacity curve.
Also: electrolyte depletion
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Formation of gases — ethylene, hydrogen, carbon monoxide and carbon dioxide — by electrolyte decomposition, mostly during formation and later under high voltage or temperature. In a pouch cell it shows as swelling; in a can it raises pressure until the vent opens.
Also: gassing
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An increase in a cell’s internal resistance as it ages. It costs voltage under load and therefore power, even while the stored charge is still there.
Also: resistance growth, power fade
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The elongation of a metal–oxygen octahedron around an ion with an unevenly filled d-shell, notably high-spin Mn³⁺. When LiMn₂O₄ is discharged below about 3 V vs Li/Li⁺, so many Mn³⁺ ions distort together that the crystal turns from cubic to tetragonal; the strain cracks particles, and Mn³⁺ disproportionation feeds manganese dissolution.
Also: Jahn–Teller effect
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The point in a capacity-versus-cycles curve where slow, roughly linear fade turns into rapid loss. It usually marks the onset of lithium plating or electrolyte dry-out, and a cell past its knee is unpredictable and should be retired.
Also: rollover, sudden death
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Oxygen escaping from the crystal of a charged layered oxide as it transforms towards spinel and rock-salt phases. At high voltage it happens slowly at particle surfaces, leaving a resistive rock-salt layer and gas; on heating, high-nickel materials release it in bulk, feeding combustion inside the sealed cell. LFP’s phosphate binds its oxygen far more strongly.
Also: oxygen release, oxygen loss
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Lithium metal depositing on the negative-electrode surface instead of intercalating into it. It is promoted by charging at low temperature or high current.
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The degradation mode in which electrode material becomes unable to store lithium: particles crack and lose electronic contact, structures collapse, or transition metals dissolve. It is tracked separately for each electrode.
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The degradation mode in which cyclable lithium is consumed by side reactions — SEI growth, plating, electrolyte decomposition — and can no longer shuttle between the electrodes. It is the dominant cause of capacity fade in most lithium-ion cells.
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Fracture of active-material particles from the volume change of repeated lithium insertion and removal. New surfaces consume electrolyte to form fresh SEI, and fragments that lose contact no longer store lithium.
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The formation of a surface film that slows further reaction. In lithium-ion cells, the SEI passivates the graphite negative electrode.
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The parasitic loop in a lithium–sulfur cell in which long-chain polysulfides, Li₂Sₙ with n from 4 to 8, dissolve into the electrolyte, diffuse to the lithium electrode, are reduced there and diffuse back. It causes self-discharge, low coulombic efficiency and loss of sulfur; lithium nitrate, which passivates the lithium surface, is the usual additive against it.
Also: shuttle effect, polysulfide shuttle effect
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A film of electrolyte reaction products on the negative-electrode particles — graphite, and also silicon or lithium metal. It protects the electrode from further reaction but grows slowly for the whole life of the cell, consuming cyclable lithium.
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The observation that SEI-driven capacity loss in storage grows roughly with the square root of time, because the growing film slows its own growth. A cell that lost 4 % in its first year will lose about 1.7 % more in the second.
Q_loss ∝ √t
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The state of charge at which a cell is kept when idle. Calendar aging rises with SOC because the negative electrode sits at a lower, more reactive potential, so cells are shipped and stored at 30–50 % rather than full.
Unit: %
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Changes in the crystal structure of a positive material as it cycles: layered oxides can rearrange into spinel or rock-salt phases at the surface, with nickel ions migrating into lithium sites. The new phases block lithium transport and raise resistance.
Also: phase transformation, cation mixing
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Growth in a cell’s thickness, reversibly as the electrodes expand on charge and irreversibly as gas and SEI accumulate. Packs allow for it with compression pads, and a sudden swell in service is a warning sign.
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Manganese, nickel or cobalt ions leaching from the positive electrode into the electrolyte, especially at high voltage and temperature or when HF is present. They migrate to the negative electrode and poison the SEI there, accelerating lithium loss.
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A gradual drop in a cell’s average discharge voltage as it cycles, distinct from capacity fade. It is a known weakness of the lithium-rich manganese cathode, whose structure migrates towards spinel-like phases, costing a few tenths of a volt over a few hundred cycles. Energy then falls even where ampere-hours hold, so it must be tracked in watt-hours.
Also: voltage decay
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How cells fail dangerously, how that is tested, and what is built in to stop it.
Deliberately driving cells and packs beyond their limits — overcharge, crush, nail penetration, external short, heating, drop — to see how they fail. Standards define each test and rank the outcome on a hazard scale from no effect to explosion.
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A test in which a cell sits in an adiabatic chamber that follows its temperature, so any self-heating is not lost to the surroundings. It measures the onset temperature, the self-heating rate and the temperature at which runaway becomes unstoppable.
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A solid foam, usually of silica, that is mostly air held in nanometre-scale pores, giving a thermal conductivity of only about 0.015–0.02 W/(m·K). Sheets a millimetre or two thick between cells slow heat transfer during a thermal event, though they must keep their insulation under the compression of swelling cells.
Also: silica aerogel, aerogel sheet
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A fuse protecting one cell rather than the pack: a necked section of the internal current collector in many automotive prismatic cells, or a thin wire bond joining each cylindrical cell to the busbar. It isolates a single shorted cell from its parallel neighbours; in some prismatic cells a pressure-driven membrane deliberately shorts the terminals on overcharge to blow it.
Also: tab fuse, cell fuse
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The highest temperature from which a cell, in its actual surroundings, can still cool back down; above it, self-heating outruns heat loss and thermal runaway follows even if the heat source is removed. Unlike the onset temperature, which is measured adiabatically, it depends on the installation: better cooling raises it, while larger cells and higher SOC lower it.
Also: critical temperature, point of no return
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Deforming a cell or pack between a platen and a round bar or sphere until the voltage drops or a set force is reached, to reproduce a crash. It checks whether the case and separator fail gracefully or cause a short.
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A pressure-activated switch in the cap of a cylindrical cell. When internal pressure rises, usually from overcharge, a disc flips and permanently breaks the current path, removing the cell from the circuit before it vents.
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Spotting a failing cell before it runs away, from the signals that precede heat: a voltage drop or abnormal self-discharge from an internal short, then vent gas, pressure and swelling, then a rising rate of temperature increase. Vehicle rules demand a warning to occupants at least five minutes before a hazard reaches the cabin, so detection cannot wait for heat.
Also: thermal runaway warning, thermal event detection
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A reaction that releases heat is exothermic; one that absorbs it is endothermic. Thermal runaway is a chain of exothermic reactions; a few cell processes, such as graphite lithiation at some stages, are mildly endothermic and cool the cell.
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A low-resistance connection between the terminals outside the cell, driving currents of hundreds of amperes. Fuses, the current interrupt device and a positive-temperature-coefficient element are the layers of protection against it.
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Connecting a charged cell’s terminals through a resistance of a few milliohms and recording temperature and outcome. The result depends as much on the cell’s own resistance and its protective devices as on its chemistry.
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A top-down safety analysis that starts from one undesired event, such as thermal runaway reaching the cabin, and breaks it into the combinations of failures that could cause it, linked by AND and OR gates. With failure rates attached it yields a probability; it complements the bottom-up FMEA and is standardised in IEC 61025.
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Systems that cool or smother a battery fire: water mist and flooding for cooling, inert gas or aerosol for enclosed storage containers. Because the cell makes its own oxygen, suppression mainly limits spread and cools neighbours rather than extinguishing the failing cell.
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A deliberate opening in a traction battery’s casing, sealed by a disc that gives way under a fire hose’s jet, so firefighters can flood the cells directly instead of cooling the outside of the pack for hours. Renault Group fits it to its electric and plug-in hybrid vehicles and in 2025 offered the design free of charge to other carmakers.
Also: Fireman Access
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The property that makes lithium-ion fires hard to fight: the carbonate solvents have flash points near room temperature, and the positive electrode releases its own oxygen when hot, so the fire does not need air. Solid and non-flammable electrolytes aim to remove this.
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Sensors in a pack or storage container that detect electrolyte vapour or hydrogen released before thermal runaway. Off-gas appears minutes before heat and smoke, which makes it the earliest practical warning.
Also: off-gas detection
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A scale, 0 to 7, for grading the outcome of an abuse test: from no effect through leakage, venting and fire to rupture and explosion. Vehicle programmes typically require that no cell test exceed level 4, venting without flame.
Also: EUCAR hazard level
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Formed when LiPF₆ electrolyte meets water, or when a fluorinated cell burns. Inside a cell traces of it attack the positive electrode and SEI; in a fire it is the most dangerous component of the vented gas.
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An unintended electronic path between the electrodes inside a cell — through a metal particle, a burr, a damaged separator or lithium deposits. It discharges the cell internally and turns its energy into local heat.
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A material that swells to many times its original thickness when heated, forming a porous char that insulates whatever lies beneath. Applied as coatings on pack lids or as pads between cells, it stays thin in normal service and expands only during a thermal event, which suits the tight spaces inside a battery.
Also: intumescent coating, intumescent pad
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Driving a steel nail through a charged cell to create a sudden internal short circuit. It is easy to run and widely cited, but its severity depends on nail size, speed and depth, and it is a poor stand-in for the small latent shorts that cause field failures.
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The mixture released when a cell vents: electrolyte vapour, hydrogen, carbon monoxide, carbon dioxide and hydrocarbons, with hydrogen fluoride. It is flammable and toxic, and gas sensors detect it before smoke or heat in a storage container.
Also: vent gas
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The temperature at which a cell begins to generate heat by itself, as the SEI starts to decompose, typically 80–120 °C. Measured in an accelerating rate calorimeter, it marks the start of the path to thermal runaway, not the runaway itself.
Unit: °C Also: self-heating onset
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Charging a cell past its upper cutoff, often to 150–200 % of nominal capacity or a fixed voltage, with protection disabled. It shows how much margin the cell has above its window and whether the vent or CID acts before runaway.
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A polymer element in series with a cell whose resistance jumps when it heats, choking an external short-circuit current. It resets as it cools, unlike a fuse, but adds resistance and does not help against internal faults.
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A built-in safety feature of polyolefin separators: around 130 °C the polyethylene layer melts and closes its pores, stopping ion flow and the current with it. It helps only if the separator does not also shrink and let the electrodes touch, so shutdown behavior is not universal.
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The state of charge at which cells leave the factory and travel, kept low to reduce both calendar aging and the energy available in an incident. Air-freight rules cap lithium-ion cells shipped alone at 30 %, and plants often target 10–20 %.
Unit: %
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An insulating sheet — aerogel, mica, ceramic fibre or intumescent material — placed between cells or modules to slow heat transfer during a thermal event and buy time for occupants to leave.
Also: fire-resistant pad, mica sheet
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Thermal runaway spreading from one cell to its neighbours through conducted heat, hot gas and flame. Pack designs are judged by whether, and how slowly, a single failing cell takes the rest with it.
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Triggering thermal runaway in one cell of a module or pack — by heater, nail or overcharge — and measuring whether and how fast it spreads. Regulations now require at least a warning period, five minutes in several markets, before the cabin is at risk.
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Self-accelerating heating in a cell: heat speeds up reactions that release more heat, until the cell vents, catches fire or ruptures. An internal short, overcharge or external heating can trigger it.
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The heat a cell releases when it fails, which exceeds its stored electrical energy because decomposition reactions add heat of their own. Calorimetry on 18650 cells has measured decomposition energy up to about twice the electrical energy, and combustion of the vented contents up to about six times, so a battery fire carries far more energy than its kWh rating.
Also: heat release in thermal runaway, total heat release
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UL’s flammability standard for plastic parts in devices and appliances. In its vertical test a strip is flamed twice for 10 s; V-0, the strictest vertical class, requires burning to stop within 10 s each time, at most 50 s in total over five strips, and no drips that ignite cotton. Cell holders and module covers commonly specify V-0.
Also: UL 94 V-0, V-0 rating, flame rating
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A scored area or a membrane in the cell can that opens at a set pressure, around ten to thirty bar for a cylindrical cell, so that gas escapes in a chosen direction instead of the case splitting at random.
Also: burst disc, rupture disc
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The controlled release of gas and vapour from a cell whose internal pressure has risen too far, through a vent designed to open before the case bursts. The vented gas is flammable and toxic, so packs route it away from occupants.
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The reactions and potentials that make a cell a battery.
An electrode mechanism in which lithium forms an alloy with the host, as it does with silicon, tin or aluminium. It stores far more lithium per atom than intercalation at the cost of volume changes of several hundred percent.
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A cell’s or layer’s resistance multiplied by its electrode area, which makes resistance comparable between cells of any size. A 100 Ah cell with 2.5 m² of electrode area and 1 mΩ of resistance has an ASR of 25 Ω·cm²; cell designers and solid-state interface researchers both work in it.
ASR = R · A Unit: Ω·cm² Also: area-specific impedance, ASI
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The kinetic law relating current density at an electrode to its overpotential: current grows exponentially with overpotential in each direction. It is the charge-transfer term in every physics-based cell model.
i = i₀[exp(α_a·Fη/RT) − exp(−α_c·Fη/RT)]
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Current that charges or discharges the electric double layer at an electrode without any chemical reaction, proportional to the rate of change of potential. In cyclic voltammetry it grows linearly with scan rate while diffusion-limited faradaic peaks grow with its square root, which is how the two are separated; double-layer capacitors rely on it entirely.
i_C = C_dl · dE/dt Also: non-faradaic current, double-layer charging current
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The difference between the positive and negative electrode potentials at equilibrium: for NMC against graphite about 3.7 V. It is set by the chemistry, and the difference in Gibbs free energy of the cell reaction per unit charge.
E = E₊ − E₋ = −ΔG / nF Unit: V Also: electromotive force, EMF
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The step in which an electron crosses the interface between electrode and electrolyte as an ion is inserted or removed. Its resistance appears as a semicircle in impedance spectra and grows as films thicken and the cell cools.
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Voltage loss that arises when reactant is consumed faster than diffusion can replace it, so the concentration at the surface differs from the bulk. It dominates at high current and low temperature and recovers slowly when current stops.
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An electrode reaction in which the host compound is broken down and reformed, as sulfur or a metal fluoride is, rather than lithium slotting into an intact structure. Conversion materials store more charge than intercalation hosts but suffer large volume change and voltage hysteresis.
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The thin region at an electrode surface where ions in the electrolyte line up against the charge on the electrode, behaving like a capacitor. It stores a little charge without any reaction and shapes the high-frequency part of an impedance spectrum.
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The potential range within which an electrolyte is neither reduced nor oxidised. Carbonate electrolytes are only stable from about 1 V to 4.3 V vs Li/Li⁺; graphite operates below that, which is why the SEI, not thermodynamics, keeps the cell alive.
Unit: V
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The potential of an electrode relative to a reference, which for lithium-ion work is lithium metal in the same electrolyte, written as V vs Li/Li⁺. Graphite sits near 0.1 V and layered oxides near 3.7–4.3 V on this scale.
Unit: V vs Li/Li⁺
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Depositing a solid, usually a metal, onto an electrode by reducing its dissolved ions. Most battery copper foil is made this way on a rotating drum, and even plating and stripping of lithium or zinc decides whether metal electrodes work; lithium plating on graphite is the same process happening where it is not wanted.
Also: electroplating, electrolytic deposition
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An electrochemical cell in which an external power source drives a reaction that would not run on its own, as in water electrolysis or aluminium production. A rechargeable battery becomes one while charging; oxidation then occurs at the positive electrode, which is why calling that electrode the cathode is strictly correct only on discharge.
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How readily a material conducts electrons. Current collectors and carbon additives supply it in an electrode because most active materials, LFP above all, conduct electrons poorly; a good electrolyte should have none, or it would self-discharge the cell.
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The route electrons take during operation: from active particle through carbon additive to the foil, out through the tab and the external circuit, and back in at the other electrode. Everything on it adds resistance.
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The change of open-circuit voltage with temperature, dE/dT, usually a fraction of a millivolt per kelvin and varying with state of charge. It sets the reversible heat a cell absorbs or releases, which can be a large share of total heat at low current.
q_rev = I·T·(dE/dT) Unit: mV/K
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The equal and opposite current flowing each way across an electrode interface at equilibrium. A high value means fast kinetics and a small overpotential; it falls steeply with temperature, which is part of why cold cells are sluggish.
Unit: A/m²
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Current carried by electron transfer in a redox reaction at an electrode, so that the charge passed and the material converted are tied together by Faraday’s law. Almost all of a battery’s capacity is faradaic; the small remainder is capacitive current that charges the double layer.
Also: faradaic process
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The charge carried by one mole of electrons, 96 485 coulombs or 26.8 ampere-hours. It links the moles of lithium that move in a reaction to the ampere-hours a cell delivers.
Unit: C/mol
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The amount of substance transformed at an electrode is proportional to the charge passed: one mole of electrons per Faraday. It converts a material’s formula into its theoretical capacity in mAh/g.
m = Q·M / (n·F)
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Any device that turns the free energy of a spontaneous redox reaction into electrical work by separating its two half-reactions onto two electrodes. A battery is one or more galvanic cells; when charged it runs as an electrolytic cell.
Also: voltaic cell, electrochemical cell
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The maximum useful work a reaction can deliver at constant temperature and pressure. For a cell it equals the charge transferred times the cell voltage, with a negative sign, which ties the thermodynamics of the materials to the voltage on the terminals.
ΔG = −nFE Unit: kJ/mol
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The oxidation or reduction occurring at one electrode, written on its own with electrons shown explicitly. The cell reaction is the sum of its two half-reactions, and the cell voltage is the difference of their potentials.
Also: half-cell reaction
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The energy gap between a molecule’s highest occupied and lowest unoccupied orbitals, used to screen electrolyte components. A solvent whose LUMO lies below the negative electrode’s Fermi level is reduced, and one whose HOMO lies above the positive electrode’s is oxidised; additives such as vinylene carbonate are chosen to reduce before the main solvent and build the SEI.
Also: HOMO, LUMO, frontier orbitals, highest occupied molecular orbital, lowest unoccupied molecular orbital
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Lithium inserting into, and leaving, the host structure of an electrode material — between graphite layers, for example — without destroying it.
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An atom or molecule carrying a net charge: a cation such as Li⁺ is positive, an anion such as PF₆⁻ negative. Ions carry current through the electrolyte, electrons carry it through the solids and the external circuit.
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How readily an electrolyte carries ions, in siemens per centimetre. Liquid carbonate electrolytes reach about 10 mS/cm at room temperature; the best sulfide solid electrolytes match that, while polymers fall far short unless heated.
Unit: mS/cm
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The route lithium ions take: out of one electrode’s particles, through the electrolyte in its pores, across the separator and into the particles of the other electrode. The electrons and ions arrive together, so the slower of the two paths limits the cell.
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The relation between an electrode’s potential and the concentrations, or activities, of the species in its half-reaction. It explains why open-circuit voltage changes with state of charge and temperature.
E = E° − (RT/nF)·ln Q
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The extra voltage, beyond the equilibrium potential, needed to drive a reaction at a given rate at one electrode. Activation overpotential pays for charge transfer, concentration overpotential for depleted reactant, and both appear as polarization at the terminals.
Unit: V
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Loss of electrons by a species. On discharge the negative electrode is oxidised as lithium leaves it as Li⁺, which is why that electrode is called the anode.
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A change of crystal structure as lithium content varies, which fixes the potential while two phases coexist. Graphite fills in stages, LFP switches between two phases across almost its whole range, and these transitions make the peaks that aging diagnostics read.
Also: staging
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A plot of cell voltage against current or current density, showing how far voltage falls below its open-circuit value as load rises. Standard for fuel cells, it shows three regions: a steep early drop from activation losses, a straight ohmic section, and a final collapse when mass transport cannot keep up. For batteries it is built from pulse tests.
Also: polarization curve, V–I curve, current–voltage curve
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The oxidised and reduced forms of one species, written oxidised/reduced, such as Fe³⁺/Fe²⁺ or Li⁺/Li, each couple with an electrode potential of its own. A cell’s voltage is the difference between the couples at its two electrodes: the FePO₄/LiFePO₄ couple sits near 3.4 V vs Li/Li⁺, which is the voltage of an LFP cell.
Also: redox pair
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A dissolved molecule that is oxidised or reduced at the electrode and then carries that charge to an active material it can reach chemically, such as solid Li₂O₂ in a lithium–air battery, cutting the charging overpotential. Overcharge-protection additives work similarly: a redox shuttle oxidises at a set potential, diffuses to the negative electrode and returns, carrying the excess current.
Also: electron shuttle, redox shuttle
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A reaction in which electrons move from one species to another: one is oxidised, the other reduced. A battery separates the two halves onto two electrodes so the electrons must travel through the external circuit.
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Gain of electrons by a species. On discharge the positive electrode is reduced as it takes up lithium ions and electrons, which is why it is called the cathode.
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A lithium ion in a liquid electrolyte travels wrapped in a shell of solvent molecules and must shed it, at an energy cost, before entering graphite. Desolvation is a large part of charge-transfer resistance, especially in the cold.
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An electrode’s potential under standard conditions, tabulated against the standard hydrogen electrode. Lithium’s −3.04 V is the most negative of any metal, which is why lithium cells have the highest voltages.
Unit: V
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The reference electrode that defines zero on the electrochemical potential scale: platinum in a solution of unit hydrogen-ion activity, bubbled with hydrogen at 1 bar. Battery work mostly uses the Li/Li⁺ scale instead, which sits 3.04 V below it, so 4.2 V vs Li/Li⁺ is about 1.16 V vs SHE.
E(vs SHE) ≈ E(vs Li/Li⁺) − 3.04 V Unit: V
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A device that stores charge in the electric double layer on high-surface-area carbon rather than in a reaction. It delivers very high power and lasts a million cycles but stores only a few watt-hours per kilogram.
Also: ultracapacitor, EDLC
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The fraction of the ionic current carried by the lithium ion rather than by the anion, about 0.3–0.4 in liquid electrolytes. A low value lets concentration gradients build up under load; single-ion solid electrolytes have a value near 1.
Unit: —
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How ions move, and the equations and models that describe a cell.
A model that predicts capacity fade and resistance growth as functions of time, temperature, SOC and throughput. Empirical models fit power laws and Arrhenius terms to test data; physics-based models simulate the SEI, plating and cracking mechanisms themselves.
Also: degradation model, lifetime model
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The common estimate of effective transport in a porous layer: multiply the bulk conductivity or diffusivity by porosity to the power 1.5. Real electrodes often deviate, so measured tortuosity is preferred when available.
D_eff = D · ε^1.5
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The rate at which concentration changes with distance, dc/dx, in mol/m⁴. It is the driving force in Fick’s law; current creates one across the electrolyte and inside each particle, and it relaxes away when current stops.
Unit: mol/m⁴
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The net movement of a species from where it is concentrated to where it is scarce, driven by random thermal motion. In a cell lithium diffuses through the electrolyte in the pores and, far more slowly, through the solid particles themselves.
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The proportionality constant D in Fick’s first law, in m²/s. It sets how fast a species spreads for a given concentration gradient.
Unit: m²/s Also: diffusivity
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A model of a specific battery, kept in step with its real counterpart by live data, used to estimate state, predict life and plan operation. The term is used loosely; a model only earns it when it is continuously updated from the asset.
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A cell model built from a voltage source for OCV, a series resistor and one or more RC pairs for the slower dynamics. Its few parameters are fitted from pulse tests, and it is what most battery management systems run in real time.
Also: Thevenin model
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J = −D dc/dx: diffusive flux is proportional to the concentration gradient and points down it. It is a constitutive law, valid at one instant; Fick’s second law follows from it when mass is conserved.
J = −D · dc/dx Unit: mol/(m²·s)
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The time-dependent diffusion equation, ∂c/∂t = D ∂²c/∂x², obtained by combining Fick’s first law with conservation of mass. It is what a cell model solves inside each particle to follow lithium concentration over time.
∂c/∂t = D · ∂²c/∂x²
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Movement of ions driven by an electric field rather than a concentration difference. In the electrolyte both migration and diffusion carry lithium; the transference number says how much of the current the lithium ions carry by migration.
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The standard physics-based lithium-ion cell model: porous-electrode theory across the cell thickness, with solid diffusion solved in a representative spherical particle at every point — hence pseudo-two-dimensional. It predicts voltage from first principles but needs dozens of parameters.
Also: pseudo-two-dimensional model, Doyle–Fuller–Newman, DFN
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The usual display of an impedance spectrum: negative imaginary part against real part, one point per frequency. Reading left to right, the ohmic intercept, one or two semicircles for interfaces and a diffusion tail each tell a different story about the cell.
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Measuring or fitting the numbers a model needs: OCV curves, diffusion coefficients, exchange current densities, thicknesses and porosities for a physics model, or resistances and time constants for a circuit model. It is usually most of the modelling effort.
Also: parameter identification
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The diameter of active-material particles, usually quoted as D50, the median, in micrometres. Small particles shorten the solid diffusion path and favour power; large ones pack densely and favour energy and stability.
Unit: µm Also: D50
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The framework, due to Newman and co-workers, that treats a porous electrode as two overlapping continua — solid and electrolyte — exchanging current everywhere through their shared surface. It underlies every physics-based lithium-ion model.
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An open-source Python package for battery modelling that implements the single-particle, Newman and several degradation models with interchangeable sub-models. It has become the common reference implementation in academic battery modelling.
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The classic equivalent circuit for one electrode interface: electrolyte resistance in series with a double-layer capacitance that shunts the charge-transfer resistance and a Warburg diffusion element. It is the template for reading an impedance spectrum.
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A resistor and capacitor in parallel, the building block of an equivalent circuit model. Each pair reproduces one time constant of the cell’s voltage response, from the seconds of charge transfer to the minutes of diffusion.
τ = R × C Also: RC element, RC branch
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A simplified version of a detailed model that keeps its dominant behaviour with far fewer states. The single-particle model is one reduction of the Newman model; others use polynomial profiles, Padé approximation or proper orthogonal decomposition. A ROM gives a BMS internal quantities, such as lithium concentration in the electrodes, that an equivalent circuit model cannot.
Also: model order reduction
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A simplified physics model that represents each electrode as one spherical particle and neglects electrolyte gradients. It runs fast enough for a BMS and is accurate at low to moderate currents.
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Lithium moving through the crystal lattice of an active-material particle, with diffusion coefficients of about 10⁻¹⁶ to 10⁻¹³ m²/s — three or more orders of magnitude slower than the 10⁻¹⁰ m²/s of the liquid. It is usually the rate-limiting step for thick electrodes and large particles.
Unit: m²/s
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Surface per gram of a powder, measured by gas adsorption and quoted as the BET area in m²/g. More surface speeds the reaction but also grows more SEI, so graphite is engineered to a modest 1–3 m²/g.
Unit: m²/g
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A model written as first-order equations for a set of internal states — such as state of charge and the voltages across RC pairs — plus an output equation for the measured terminal voltage. Kalman filters and other observers need this form, so equivalent circuit and reduced physics models are cast this way for a BMS.
ẋ = A·x + B·u; y = C·x + D·u Also: state-space representation
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How winding the path through a porous layer is, compared with a straight line through it. High tortuosity means ions travel much further than the layer is thick, which limits how fast a thick, dense electrode can be charged or discharged.
Unit: —
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The impedance of diffusion, which appears as a 45° line at the low-frequency end of a Nyquist plot. Its slope and onset frequency give a route to the diffusion coefficient.
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The steps that turn powders and foils into a finished cell, in production order.
Storing freshly formed cells for days to weeks, at room or elevated temperature, so the SEI stabilises and any cell with a latent short reveals itself through voltage drop. Not to be confused with aging as degradation over a cell’s life.
Also: high-temperature aging, storage step
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Binder carried to the top of the coating by evaporating solvent during fast drying, leaving the foil interface binder-poor. The result is weak adhesion and higher resistance; it is controlled by drying profile and slurry formulation.
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A sharp raised lip of foil, or a loose flake of coating, left at a cut electrode edge by slitting or notching. The separator is only about 10–25 µm thick, so a burr of similar height can pierce it under stack pressure and cause an internal short circuit; edges are therefore inspected and worn knives replaced before burrs grow.
Also: burrs, edge burr, slitting burr, slitter burr
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Firing the precursor with a lithium source — lithium carbonate or, for high-nickel materials, lithium hydroxide — at 700–900 °C in kilns to form the layered oxide. Atmosphere and temperature profile control the crystal quality.
Also: lithiation, sintering of CAM
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Compressing a dried electrode coating between rollers to set its thickness, density and porosity. It is one of the electrode-making steps in cell production.
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The second phase of cell production: building the electrode–separator stack by winding or stacking, welding the tabs, inserting it into the case and filling the electrolyte. Most of it happens in the dry room.
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The assembly steps that put a jelly roll or stack into its metal can and close it: insertion, welding the negative tab to the can base, beading a groove that will hold the cap, and sealing the cap by crimping or laser welding, before or after electrolyte filling depending on format. Seal quality decides whether the cell stays leak-tight for life.
Also: canning, can insertion, beading and crimping
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Choosing the chemistry, electrode loadings, porosities, N/P ratio, separator, electrolyte volume and format that together meet an energy, power, life, safety and cost target. Each choice trades against the others: thicker electrodes raise energy and lower power.
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The third phase of cell production: formation, degassing, aging and end-of-line testing. It is slow and ties up capital — cells sit for weeks — which is why shortening it is a major research goal.
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The three-phase process that turns powders and foils into finished cells: electrode making, cell assembly and cell finishing. Electrode making is a roll-to-roll chemical process; assembly is precision mechanics; finishing is electrochemistry that takes weeks.
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A room whose airborne particle count is held to a class by filtered air, overpressure and gowning, graded under ISO 14644-1: ISO class 7 allows at most 352,000 particles of 0.5 µm or larger per cubic metre. It controls particles, whereas a dry room controls moisture; cell assembly usually needs both, because one metal particle can short a cell.
Also: clean room, ISO 14644
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Applying slurry to the moving foil at a controlled wet thickness, usually with a slot die, often on both sides. Coating weight per area must be held within about one percent across the web, because every downstream property depends on it.
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Flaws in a wet or dried electrode coating. Agglomerates are clumps of poorly dispersed carbon or active material that leave lumps and starved patches; pinholes are tiny uncoated spots from air bubbles, dust or a contaminated foil. Both create local loading variations that can cause lithium plating or high resistance, so lines inspect the web optically.
Also: agglomerates, agglomerate, pinholes, pinhole
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A knife-over-roll coater whose blade is a roll ground to a comma-shaped edge, set at a precise gap above a backing roll that carries the foil. It tolerates a wide range of slurry viscosity and is common on test and pilot lines, while high-volume electrode lines mostly use slot dies for faster, more uniform coating.
Also: comma bar coater, knife-over-roll coater
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Removing the gas a cell releases during formation. A pouch cell’s extra gas pocket is opened in a dry atmosphere, emptied and sealed off; large prismatic cells often vent through their fill opening before final sealing.
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The temperature at which the water vapour in air would start to condense, the standard way of specifying dry-room humidity. A −40 °C dew point corresponds to about 0.5 % relative humidity at room temperature.
Unit: °C
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Spreading slurry by drawing it under a fixed blade, so the gap between blade edge and foil sets the wet thickness. Simple and cheap, it is the standard way to coat electrode sheets in the laboratory; production lines meter the slurry through a slot die instead, for tighter thickness control at speed.
Also: doctor blade, knife coating, blade coating, tape casting
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A way of making electrodes without solvent: the powders are mixed with a binder that draws out into fine fibres under shear, and the resulting film is pressed onto the foil. It removes the slurry, the dryer and solvent recovery.
Also: dry coating, solvent-free electrode
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A production room whose air is kept extremely dry — dew points around −30 °C to −60 °C — so that no moisture reaches the cell while the electrolyte goes in. Water would react with the salt LiPF₆ to form hydrofluoric acid.
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Evaporating the solvent from the wet coating in an oven tens of metres long. Drying too fast drives binder to the surface and weakens adhesion to the foil; it is the most energy-hungry step in the plant.
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The mass of coating per unit volume after calendering, around 1.6 g/cm³ for graphite and 3.4–3.6 g/cm³ for NMC. Higher density raises energy density but lowers porosity and slows ion transport.
Unit: g/cm³ Also: press density
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The first phase of cell production: mixing a slurry, coating it on foil, drying it, calendering to density and slitting to width. It is run as a continuous roll-to-roll line, and its consistency decides most of the final cell’s quality.
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The margins by which, on every edge, the separator extends beyond the negative electrode and the negative beyond the positive, and the placement tolerance that must preserve them. If a positive edge ever sits outside the negative, lithium plates there; if the separator falls short, the electrodes can touch. Lines check alignment by camera and X-ray.
Also: separator overhang, alignment tolerance, electrode registration
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Out-of-plane waves or folds in an electrode. In production they come from calendering, where the coated area stretches more than the bare foil edge, and from uneven web tension in winding; in service, electrode expansion can buckle a tightly wound jelly roll. Wrinkles leave uneven gaps and pressure that cause local lithium plating or separator damage.
Also: wrinkling, buckling, foil wrinkles, jelly-roll deformation
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Injecting a measured volume of electrolyte into the sealed-but-for-one-opening cell, usually under vacuum followed by pressure so the liquid is pulled into the pores. The cell then rests for wetting before formation.
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The final measurements on every finished cell — capacity, internal resistance and open-circuit voltage — used to reject faulty cells and sort good ones into matched grades.
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The lithium consumed in forming the SEI on the first charge, which never returns to the positive electrode: about 5–10 % of capacity for graphite and far more for silicon. Pre-lithiation is the way to pay this debt in advance.
Unit: % Also: initial coulombic efficiency, ICE
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The first controlled charge and discharge cycles of a newly assembled cell, during which the SEI forms. It is part of cell production, before aging and grading.
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Joining metal by plunging a rotating pin tool into the joint line and traversing it, so friction softens the material without melting it and the pin stirs the two sides together. It welds aluminium extrusions into leak-tight battery trays and seals cooling plates with low distortion and without the porosity and cracking of fusion welds.
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Casting a large vehicle structure, such as a whole front or rear underbody, in one piece on an aluminium high-pressure die-casting machine with a locking force of 6,000 tonnes or more. It replaces dozens of stamped and welded parts; in some vehicles a structural battery pack bolts in between the front and rear castings to form the floor.
Also: giga casting, megacasting, Giga Press
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A cell plant with an annual output of at least a few gigawatt-hours, enough for tens of thousands of electric cars. The term began as one company’s name for its plant and is now used for any large battery factory.
Unit: GWh/year
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Sorting finished cells into bins by capacity and resistance so a module is built from closely matched cells. Mismatched cells would force the pack to balance constantly and age its weakest cell fastest.
Also: binning, sorting
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Compressing a solid-state cell from all sides by fluid pressure, at hundreds of megapascals, so sulfide electrolyte particles deform and bond to the electrode particles. It replaces the calendering and wetting steps of a liquid cell.
Unit: MPa
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The rate at which a cell’s open-circuit voltage falls during the production aging step, in millivolts per day. A high K-value signals an internal short or contamination, and such cells are scrapped before shipment.
Unit: mV/day Also: OCV drop rate
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Cutting electrodes with a pulsed laser instead of a die, used for notching and for separating sheets. It changes shape without a new tool, at the cost of a heat-affected zone that must be kept small.
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Joining metal with a focused laser beam, used to seal cans, attach caps and connect busbars to cell terminals. It is fast and precise but sensitive to gaps and reflectivity, so copper joints need special wavelengths or beam shaping.
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Stray fragments of iron, copper, zinc or steel from raw materials, worn equipment or cutting. A particle tens of micrometres across can pierce the separator, or dissolve and regrow across it, causing high self-discharge or a latent internal short circuit — the cause of the 2006 laptop battery recalls. Magnetic filters, cleanroom discipline and K-value screening keep them out.
Also: metal particle, metallic contamination, foreign particles
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Dispersing active material, conductive carbon and binder in solvent to a uniform slurry with the right viscosity for coating. Order of addition and shear history matter: poorly dispersed carbon leaves particles electrically stranded.
Also: slurry preparation
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The water left in electrodes, separator and electrolyte, measured by Karl Fischer titration and specified in the low hundreds of parts per million or below. Water forms HF with the salt, which attacks the positive electrode and the SEI.
Unit: ppm Also: Karl Fischer titration
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Graphite mined as flake, then milled, spheroidised and coated for use as a negative active material. It is cheaper than synthetic graphite and has slightly higher capacity, with more variability between sources.
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The solvent that dissolves PVDF binder for positive-electrode slurries. It is toxic and regulated, so plants recover and distil nearly all of it; eliminating it is a main motivation for dry electrode processes.
Also: N-methyl-2-pyrrolidone
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Cutting the tab shape and the electrode sheet outline from the slit strip, mechanically or by laser, before stacking. Laser notching has no tool wear but must avoid heat damage at the edge.
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Adding extra lithium to an electrode before the cell is assembled — as lithium powder, foil or a sacrificial additive — to compensate for the lithium lost to SEI formation. It matters most for silicon-rich negative electrodes.
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The mixed nickel–manganese–cobalt hydroxide made by co-precipitation from metal sulfate solutions, before lithium is added. Its particle size and shape are set here and carried through to the finished NMC powder.
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Joining metals by clamping them between electrodes and passing a short, high current pulse, so contact resistance melts a small nugget. It joins the negative tab to the can base inside cylindrical cells and nickel strips to cell terminals in tool and e-bike packs; for copper and aluminium busbars laser welding has largely taken over, as they conduct too well to heat.
Also: resistance spot welding, spot welding
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Heating a powder below its melting point until the particles grow together into a dense solid. Oxide solid electrolytes are sintered at high temperature to give good ionic contact.
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Cutting the wide coated roll into the narrow strips a cell needs, with rotary knives. A clean edge matters: burrs can pierce the separator and cause an internal short.
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A precision coating head that extrudes slurry through a narrow slot onto the foil. It sets the coating width and thickness by pump rate and line speed, and can coat in intermittent patches to leave bare foil for tabs.
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The mixture of active material, conductive carbon, binder and solvent that is coated onto a current-collector foil to make an electrode. Positive slurries use NMP as solvent; graphite slurries are water-based.
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How an electrode slurry flows under stress, measured as viscosity against shear rate on a rheometer. A good slurry is shear-thinning: thin under the high shear of the coating head, thick at rest so particles do not settle and the wet film does not spread before it dries. Rheology is the main check that mixing produced a stable, coatable slurry.
Also: slurry viscosity, shear thinning
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The mass fraction of a slurry that is not solvent, typically 50–70 %. Higher solids means less solvent to dry off, so less energy and a shorter oven, but a thicker slurry that is harder to coat evenly.
Unit: wt %
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Condensing the NMP evaporated in the dryer and distilling it for reuse. It is required by law for emissions and makes economic sense, but adds a large plant alongside the coating line.
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Pressure applied to a cell stack, in production or in use, to keep its layers in contact. Solid-state cells depend on it, because ions can only cross where two solids touch.
Unit: MPa
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Building a cell from individual electrode sheets interleaved with separator, either sheet by sheet or by folding a continuous separator in a zigzag. It uses the volume of a rectangular case better than winding but is slower and more exacting.
Also: Z-folding, lamination
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Graphite made by heating petroleum coke or needle coke to about 3000 °C, which gives uniform, long-lived particles at a high energy cost. It is preferred for fast-charge and long-life cells.
Also: artificial graphite
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Joining the bundle of foil tabs to the terminal tab, usually by ultrasonic welding, which bonds thin foils without melting them; laser welding is used for can-to-cap and busbar joints. A weak weld raises resistance and can fail in service.
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Recording for each cell which material lots, machines and process conditions produced it, so a field failure can be traced to a batch and a recall limited to it. The EU battery passport extends this record to the cell’s whole life.
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Joining metals by pressing them together and vibrating one part at ultrasonic frequency, so friction scrubs the surfaces clean and bonds them below the melting point. It is the standard way to weld stacks of thin aluminium and copper foil.
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Baking electrode rolls or finished stacks under vacuum at 80–120 °C for many hours to drive off the last traces of water before they enter the dry room. Residual moisture would otherwise react with the electrolyte salt.
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The soaking of electrolyte into every pore of the electrodes and separator after filling. It can take hours or more; a pore left dry is electrode area that never works properly.
Also: soaking
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Rolling the two electrode strips and two separator strips together around a mandrel into a jelly roll. It is fast and well understood, and it produces the round roll of a cylindrical cell or the flattened roll of many prismatic cells.
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Connecting each cell terminal to a busbar or collector plate with a thin aluminium wire, often a few hundred micrometres thick, attached ultrasonically at both ends. The wire can be sized to act as a fuse, so a cell that shorts internally is cut off from its parallel neighbours; Tesla’s cylindrical-cell packs are the best-known example.
Also: wire bond, fusible link
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The fraction of started material that ends as saleable cells. New plants often run at 60–80 % and mature ones above 95 %; because materials dominate cell cost, each point of scrap is expensive.
Unit: % Also: scrap rate
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The measurements and test procedures that characterise a cell or pack, from capacity and pulse tests to abuse and environmental tests.
The magnitude of a cell’s impedance at one fixed frequency, usually 1 kHz, measured in a second with a small alternating signal. It captures mostly the ohmic resistance, so it is quick for production sorting but blind to interfaces and diffusion.
Unit: mΩ Also: 1 kHz impedance
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Aging cells faster than in service — at higher temperature, higher SOC or higher rate — and extrapolating to real conditions with a model such as Arrhenius. The extrapolation only holds if acceleration does not change which mechanism dominates.
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Storing cells or batteries at low air pressure to show they survive unpressurised air freight without leaking, venting or rupturing. UN 38.3 test T1 holds them at 11.6 kPa or less — the pressure at about 15 000 m — for at least six hours at room temperature.
Also: low-pressure test, UN 38.3 T1
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The instrument that charges and discharges cells to a programmed schedule while logging voltage, current and temperature, with one independent channel per cell. Laboratory cyclers resolve microvolts; production formation cyclers handle thousands of cells at once.
Also: battery tester, cycling channel
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Storing cells at a matrix of temperatures and states of charge, typically 25–60 °C and 30–100 % SOC, with periodic reference tests, to fit the calendar-aging model. Months of data at high temperature are extrapolated to years at ambient through the Arrhenius law.
Also: storage test
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A defined capacity test with specified charge, rest, discharge and cutoff conditions, usually a full CC-CV charge, a rest, and a C/3 or lower discharge to the lower cutoff at 25 °C. The delivered ampere-hours are the cell’s measured capacity.
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Measuring a cell’s capacity, resistance, efficiency, rate capability, life and safety under defined conditions. Because every result depends on the conditions, a result without its temperature, current and voltage limits is not a result.
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Stepping an electrode to a fixed potential and recording how the current decays with time. A diffusion-limited current falls with the inverse square root of time, the Cottrell relation, which yields diffusion coefficients; long holds measure leakage currents from electrolyte oxidation or self-discharge, and a staircase of small steps is PITT.
i(t) = n·F·A·c·√(D / (π·t)) Also: potentiostatic hold, potential step
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Applying a constant current and recording the electrode potential over time — the principle behind ordinary galvanostatic cycling and GITT. On lithium metal it measures Sand’s time, when the salt concentration at the surface reaches zero and dendrites begin to grow.
Also: galvanostatic measurement, constant-current measurement
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Repeating a defined charge and discharge cycle at fixed temperature until capacity reaches the end-of-life criterion, with a reference performance test every few hundred cycles. Conditions — rate, depth of discharge, voltage window, temperature — decide the result, so they are always quoted with it.
Also: cycling test, endurance test
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Sweeping an electrode’s potential up and down at a fixed rate and recording the current, so each reaction shows as a peak at its potential. It is a materials-screening tool; in battery work the abbreviation CV more often means constant voltage.
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Keeping a cell, module or pack warm and very humid, steadily or in cycles, to bring out corrosion, seal leaks and condensation that lower insulation resistance. The common cyclic version, IEC 60068-2-30, alternates between about 25 °C and 40 or 55 °C at over 90 % relative humidity in 24-hour cycles for several days.
Also: humidity test, cyclic damp heat, IEC 60068-2-30
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Internal resistance measured from the voltage change during a current pulse of defined length, usually 10 s or 18 s. It is larger than the AC value because it includes charge-transfer and some diffusion, and it depends on SOC, temperature and pulse duration.
Unit: mΩ Also: DC-IR, pulse resistance
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The general name, in test plans, standards and laboratory software, for whatever is being tested — a cell, module, pack or BMS board. A test report should define the DUT exactly, including its state of charge, temperature and fixturing, because results hold only for that configuration.
Also: unit under test, UUT, equipment under test, EUT
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Measuring a cell’s impedance across a range of frequencies, from kilohertz to millihertz, with a small alternating signal. The spectrum separates ohmic, interface and diffusion processes by their time scale and is read on a Nyquist plot.
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Pulling an adhesive tape stuck to a coated electrode away at 90° or 180° while recording the force per unit width, in N/m, to measure how firmly the coating holds to the foil and to itself. It checks binder content, drying and calendering, since weak adhesion leads to flaking during winding and to delamination in service.
Unit: N/m Also: peel test, adhesion test, 90° peel test, 180° peel test
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Deliberately introducing faults — a broken sense wire, a stuck temperature reading, a welded contactor, a lost CAN message — into a BMS or pack to prove each is detected and brought to a safe state in time. Functional-safety standards such as ISO 26262 expect it, and HIL rigs make it safe and repeatable.
Also: fault insertion test, fault injection
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A test cell with both a real positive and a real negative electrode, as in a product. It is the only configuration that shows lithium inventory loss, since the lithium supply is finite.
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A series of short constant-current pulses each followed by a long rest, so that both the equilibrium voltage curve and the solid diffusion coefficient can be extracted at each state of charge. It is slow, often days per cell, and a staple of parameterisation.
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A test cell with the electrode under study against lithium metal, so the measured potential is that electrode’s alone. It is how a new material’s capacity and voltage are first measured, usually in coin-cell format.
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Checking that a cell can, pouch or cooling plate is sealed by detecting, with a mass spectrometer, helium escaping from it into a vacuum chamber. Helium goes in before sealing or is forced in under pressure afterwards; cells are typically screened at around 10⁻⁶ mbar·L/s, tight enough to keep moisture out and electrolyte in for the cell’s life.
Unit: mbar·L/s Also: leak test, helium bombing, tracer-gas leak test
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Sandwiching a thin nickel spiral sensor between two pieces of a sample, heating it briefly and using its own resistance as the thermometer, then fitting the temperature rise to get thermal conductivity and diffusivity. It suits large flat samples such as cell stacks and pads and, for anisotropic materials, separates in-plane from through-plane conductivity.
Also: transient plane source, TPS, hot disk
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A test that applies a short discharge pulse and a short charge pulse at each state of charge, from which resistance and power capability are read as a function of SOC. It is the standard source of equivalent-circuit parameters.
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A cell built or modified with sensors inside — thermocouples in the jelly roll, optical fibres with Bragg gratings for temperature and strain, reference electrodes, pressure sensors — to measure what surface sensors miss. At high current the core can run several degrees hotter than the can, which only such cells show directly.
Also: sensorised cell, embedded sensors, fibre Bragg grating, FBG
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Applying a high DC or AC voltage between the high-voltage circuit and the chassis or housing to verify that insulation holds, with the leakage current below a limit. It is done on every pack at end of line and after abuse tests in R100.
Also: hipot test, dielectric strength test
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Pausing the current for a few seconds every few minutes during a slow constant-current cycle and fitting the voltage response against the square root of time. The instant jump gives internal resistance and the slope a diffusion resistance, mapped across the whole state-of-charge range in a single cycle — a fast alternative to GITT.
Also: current interruption method
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A small device built into a cell during assembly that creates an internal short circuit on demand: a thin wax layer keeps two conductors apart until the cell is heated past the wax’s melting point, roughly 40–60 °C. Developed by NREL with NASA, it reproduces latent field shorts more realistically than nail penetration.
Also: ISC device, NREL/NASA ISC device, implantable short-circuit device
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Holding a cell at constant temperature inside a calorimeter and measuring the heat it gives off, down to microwatts, while it cycles or rests. It separates reversible entropic heat from irreversible losses and reveals the parasitic heat of slow side reactions, a quick indicator of how long a cell will last.
Also: isothermal microcalorimetry, IMC, heat-flow calorimetry
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Firing a brief laser pulse at one face of a thin disc and timing the temperature rise on the far face with an infrared detector, which gives thermal diffusivity. Multiplying by density and specific heat yields thermal conductivity — the through-plane value for electrodes, separators and layered cell samples.
α = 0.1388·L² / t½; k = α·ρ·c_p Also: laser flash method, flash method
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Measuring the open-circuit voltage curve either by stepping through state of charge with long rests, or by a very slow C/25 charge and discharge whose average is taken as pseudo-OCV. The result is the OCV–SOC table a BMS depends on.
Also: pseudo-OCV, C/25 discharge
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Heating a charged cell in an oven, typically at 5 °C/min to a set temperature such as the 130 °C of IEC 62133, and holding it there to check that it survives without fire or explosion. Hot-box variants keep heating until thermal runaway, showing how much margin the separator and chemistry provide.
Also: hot-box test, heating test, thermal abuse test
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An instrument that controls the potential of an electrode against a reference and measures the current, or the reverse as a galvanostat. It is the tool for electrochemical impedance spectroscopy and three-electrode experiments.
Also: galvanostat
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The voltage-step counterpart of GITT: the potential is stepped and the decaying current recorded, giving the diffusion coefficient from the current transient. It needs a potentiostat rather than a cycler.
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The way a random vibration profile is specified: acceleration intensity per unit frequency, in g²/Hz, across a band such as 5–200 Hz. The square root of the area under the curve gives the overall level in g rms. SAE J2380 and ISO 12405 use PSD profiles to stand for road vibration, whereas UN 38.3 uses a sine sweep.
g_rms = √(∫ PSD(f) df) Unit: g²/Hz Also: PSD vibration profile, random vibration, acceleration spectral density, ASD
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Applying a current step of defined size and duration and recording the voltage response. The instant voltage step gives the ohmic resistance, the following curve the slower polarization; HPPC is a standardised sequence of such pulses across state of charge.
Also: current pulse test, DC pulse
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Discharging a cell at a series of rates — C/10, C/3, 1C, 2C, 3C — from a full charge and recording the capacity delivered at each. The result is the rate-capability curve on a datasheet and the first sign of a transport limitation.
Also: C-rate test, discharge rate test
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An electrode of stable, known potential against which another is measured. In lithium-ion work it is a piece of lithium metal, which defines the Li/Li⁺ scale; outside it the standard hydrogen electrode is the primary reference.
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A fixed set of measurements — capacity, resistance by pulse, sometimes impedance — repeated at intervals during an aging test to track state of health under identical conditions. Everything between RPTs is the aging itself.
Also: check-up
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Exposing a pack enclosure, connector or fastener to a fine mist of 5 % sodium chloride solution at 35 °C for hours to weeks to rate its corrosion resistance. Vehicle packs sit under the floor in road salt, so corroded seals and high-voltage connectors are a real failure path; ISO 9227 defines the neutral test.
Also: salt fog test, neutral salt spray, ISO 9227
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The automotive maturity stages of a cell or pack. A-samples are hand-built functional prototypes; B-samples have a near-final design built on prototype tooling; C-samples use series tooling and materials to validate the design; D-samples come off the series line at rate for production approval. Later design or process changes usually require requalification.
Also: A-sample, B-sample, C-sample, D-sample, sample maturity, A to D samples
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Charging a cell to a set state, storing it, and measuring either the OCV drop over days or the capacity lost over weeks. In production it is the K-value check; in the laboratory a potentiostatic hold measures the leakage current directly in hours.
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Measuring how a cell grows during cycling or storage in one of two fixtures: constant pressure, where springs or a pneumatic press hold a set force and the thickness change is logged, or constant volume, where rigid plates fix the gap and the rising force is logged. Module designers need both to size end plates and compression pads.
Also: constant-pressure swelling test, constant-volume swelling test, swelling force test, thickness growth test
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Pulling a welded tab or busbar joint until it breaks, recording the peak force and where the break occurred, to verify weld quality. It is destructive, so samples are taken from each batch or shift; failure through the parent foil rather than at the weld interface indicates a sound joint.
Also: weld pull test, pull test, weld peel test
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Measuring the thermal properties a model needs: specific heat capacity in a calorimeter, thermal conductivity through and along the layers, the entropy coefficient from OCV against temperature, and heat generation under load. Without them a thermal model is a guess.
Also: heat capacity test, entropy test
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Moving a cell or pack rapidly between temperature extremes, typically −40 °C and +60 to +85 °C, for many cycles, to find seals, welds and housings that fail by differential expansion. It is in UN 38.3, R100 and most pack specifications.
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A full cell with an added reference electrode, so the potential of each working electrode can be tracked separately during cycling. It reveals, for instance, when the graphite potential drops below 0 V and plating begins.
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Measuring the charge into and out of a cell with chargers accurate to a few hundredths of a percent, at a temperature held within about ±0.1 °C, so that coulombic efficiency resolves to 0.01 % or better. Side-reaction rates then show within weeks, ranking electrolyte additives and materials long before cycle-life tests would finish.
Also: high-precision coulometry, coulometry, high-precision charger
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Sending ultrasound pulses through a cell and tracking how their travel time and amplitude change. Electrode stiffness and density shift with lithiation, so the signal follows state of charge, while gas pockets and dry regions block sound — making it a way to map electrolyte wetting after filling and to detect gassing and lithium plating.
Also: acoustic testing, acoustic time-of-flight, ultrasound inspection
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Crashing a complete vehicle into a barrier, or striking it with a moving one, then checking that the battery stays in place, spills no electrolyte into the cabin and leaves no electric-shock hazard — voltage below 60 V DC or isolation intact. UN R94 and R95 and the US FMVSS 305 set these post-crash requirements.
Also: crash test, post-crash safety, FMVSS 305
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Shaking a cell or pack on a vibration table to a profile standing for years of road use, and striking it with defined mechanical shocks, then checking for loose connections, leaks and loss of isolation. UN 38.3, R100 and ISO 12405 each specify a profile.
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Extracting diagnostic information from the way a cell’s voltage settles during a rest. After fast charging, a plateau in the relaxing voltage — a peak in dV/dt — reveals plated lithium re-entering the graphite; features of the relaxation curve also track capacity fade, and a rest voltage that keeps drifting down points to self-discharge.
Also: rest-voltage analysis, relaxation voltage, rest voltage diagnostics
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Submerging a pack in water or salt water for a set time to check sealing, insulation and the absence of fire or gas. Chinese GB standards include it, and R100 requires sealing to a water-protection rating or an equivalent test.
Also: salt-water immersion
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The two current-carrying electrodes of an electrochemical test: the working electrode is the one being studied, and the counter electrode completes the circuit. In a lithium half-cell the lithium counter electrode doubles as the reference; adding a separate reference electrode makes a three-electrode cell that isolates the working electrode.
Also: working electrode, counter electrode, auxiliary electrode
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From a single cell to a working battery system, and the electronics that keep it safe.
A pack that integrates two cell chemistries under one BMS — sodium-ion with lithium-ion, say, or LFP with NMC — so that one type covers the other’s weakness, such as poor cold-weather power or low energy density. CATL used the name at its 2021 sodium-ion launch; the BMS must model both voltage curves to estimate SOC.
Also: AB battery pack, mixed-chemistry pack
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Cell balancing that moves charge from fuller cells to emptier ones instead of burning it in resistors. Switched capacitors shuttle charge between neighbours; inductors or transformers carry it further; isolated converters exchange it between one cell and the whole string; bypass switches take a cell out of the string. Currents reach amperes, at the cost of more parts.
Also: capacitive balancing, inductive balancing, switched-capacitor balancing, converter-based balancing, cell bypass
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The small 12 V or 48 V battery in an electric vehicle that powers the controllers, lights and locks and wakes the BMS, kept charged from the high-voltage pack through a DC/DC converter. A flat auxiliary battery immobilises the car however full the main pack is.
Also: 12 V battery, low-voltage battery
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The electronics and software that keep a battery inside its safe window: measuring every cell voltage and many temperatures, estimating SOC and SOH, balancing cells, computing current limits, controlling the contactors and reporting over the vehicle network.
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The complete battery as installed: modules or cells, the BMS, contactors and fuses, busbars, cooling, sensors and an enclosure. Its energy is the sum of its cells’ energies; its mass and volume are a good deal more.
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How a BMS’s electronics are divided across the pack. A centralised BMS wires every cell to one board, suiting small packs; a modular or master–slave design puts a monitoring board on each module reporting to one controller; a distributed design puts electronics on each cell. Stationary systems add tiers: module, rack and system-level BMS.
Also: centralised BMS, centralized BMS, distributed BMS, modular BMS, master–slave BMS, rack BMS
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A busbar connection clamped by a bolt or stud rather than welded, so it can be undone for service. Its resistance depends on keeping the clamping force, which aluminium creep and thermal cycling relax, so designs use conical spring washers, a specified torque and torque marking. A loose joint heats up and is a classic cause of pack hot spots.
Also: bolted joint, screwed busbar connection
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A rigid copper or aluminium conductor that joins cell terminals into series and parallel groups, and modules into the pack. Its cross-section is sized for current and heating, and its joints — welded or bolted — are a classic source of resistance and failure.
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The serial network over which a BMS talks to the vehicle or inverter: a two-wire differential bus, defined in ISO 11898, carrying short prioritised messages at up to 1 Mbit/s, or faster with CAN FD. Every node hears every message, and a dominant bit wins arbitration without any collision.
Also: Controller Area Network, ISO 11898
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An extension of classical CAN that switches to a higher bit rate, up to 5–8 Mbit/s, for the data part of each frame and allows 64 data bytes instead of 8. BMS data-logging and over-the-air updates are its usual battery uses.
Also: CAN with flexible data rate
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The two wires of a CAN bus, a twisted pair driven in opposite directions. Idle, or recessive, both sit near 2.5 V; for a dominant bit CAN_H is pulled up to about 3.5 V and CAN_L down to about 1.5 V, so the receiver reads the 2 V difference. Noise picked up by the pair adds equally to both wires and cancels in the difference.
Unit: V
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A 120 Ω resistor between CAN_H and CAN_L at each end of the bus, matching the cable impedance so signals do not reflect. A healthy bus measures about 60 Ω between the two wires when powered down; 120 Ω means one terminator is missing.
Unit: Ω Also: 120 Ω termination
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The board on each module that measures its cell voltages and temperatures and switches its balancing resistors, reporting to the central BMS controller. It is usually built around a dedicated monitoring chip and linked by isoSPI or CAN.
Also: cell monitoring unit, CMU, slave BMS
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Integrating the cells into the vehicle floor itself, so the battery enclosure is the chassis and the cells help carry its loads. It saves mass and height but binds the battery to the car for life.
Also: cell-to-body, structural battery
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The conventional three-level pack build: cells are assembled into modules with their own frames, sensing and connectors, and modules into the pack. Modules simplify handling, testing and repair — a faulty one can be swapped — but their frames and spacing take mass and volume that cell-to-pack designs reclaim.
Also: cell-to-module, CTM, module-based pack
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Building the pack directly from cells without the intermediate module, using large-format cells that bear load themselves. It raises the cell-to-pack ratio and cuts parts, at the cost of making the pack harder to service.
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A foam sheet between pouch or prismatic cells that keeps a defined pressure on them as they breathe on charge and swell with age. It also provides some thermal separation between neighbours.
Also: foam pad, swelling pad
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The device that measures pack current for coulomb counting and protection: a precision shunt resistor read by an amplifier, or a Hall-effect sensor around the cable. Offset error in this sensor is what makes SOC drift between OCV corrections.
Also: shunt, Hall sensor
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How current divides between strings connected in parallel. A string with lower resistance or a different OCV takes more than its share and ages faster, and connecting strings at different voltages drives a circulating current between them. Systems therefore match voltages before closing a string’s contactors and limit total current to what the weakest string can carry.
Also: cross-string current sharing, string current imbalance, circulating current
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The power electronics that step the high-voltage pack down to 12 V or 48 V for the auxiliary systems, replacing the alternator of a combustion car. Boost converters also appear between an 800 V pack and a 400 V charger.
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Reducing the allowed charge or discharge power as the battery approaches a limit — low temperature, high temperature, high or low SOC, or age. It is how a BMS keeps the cells safe while letting the vehicle do as much as it can.
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The extra resistance where two conductors touch, because current passes only through microscopic contact spots and any oxide film on them. It falls with contact force and good plating and rises with corrosion and fretting. At 300 A a joint of 50 µΩ dissipates 4.5 W, enough to overheat a poorly cooled connection.
P = I²·R_contact Unit: Ω Also: contact resistance, joint resistance, constriction resistance
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A pack concept that skips both the cell can and the module: electrode stacks sealed in thin film are placed directly in the pack enclosure and connected there. 24M, which proposed it, claims electrodes could fill about 80% of pack volume against 30–60% in conventional packs — a step beyond cell-to-pack.
Also: E2P, ETOP
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The sealed case that carries the modules, protects them in a crash, keeps water out to an IP67 rating or better and vents gas in a thermal event. In many cars it is a structural part of the body.
Also: battery housing, battery tray
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The site-level controller of a storage system that decides when to charge and discharge according to prices, grid signals and the battery’s limits, and dispatches those commands to the BMS and inverters.
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The manufacturer-independent CAN data interface of trucks and buses, defined by the major European OEMs, that exposes vehicle data — including, for electric vehicles, battery state of charge, charging status and energy consumption — to fleet-management telematics.
Also: FMS standard, bus FMS
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The single chip in a phone, laptop or power tool that does the BMS’s state-estimation job for one or a few cells: coulomb counting corrected by an OCV model, with impedance tracking in better parts. It reports remaining capacity over SMBus or I²C.
Also: gas gauge
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The power electronics that turn the battery’s DC into AC for a motor or the grid, and back again for charging. In stationary storage it is called the power conversion system and its rating in kW or MW sets the system’s power independently of the battery’s energy.
Also: power conversion system, PCS
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A two-digit code for how well an enclosure keeps out solids and water: the first digit for dust, the second for water. Battery packs are typically IP67, dust-tight and able to survive brief immersion.
Also: ingress protection
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A transformer-isolated, two-wire version of the SPI interface used to chain cell-monitoring chips across modules that sit at different voltages. It carries their measurements to the BMS controller without a separate isolated CAN node per module.
Also: daisy-chain interface
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A cheap single-wire serial bus at up to 20 kbit/s with one master and several slaves, used where CAN is overkill: a smart 12 V battery sensor, a cooling fan or a heater controller reporting to the BMS.
Also: Local Interconnect Network
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A simple industrial register-based protocol, over serial RS-485 or TCP, that stationary storage systems use between battery, inverter and site controller. It is old, open and universally supported, which is why it survives in grid equipment.
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A group of cells connected in series and parallel, mechanically held together with its own voltage and temperature sensing, built as the unit from which a pack is assembled and serviced. Cell-to-pack designs do away with it.
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The nominal voltage of the full series string, about 400 V in most electric cars and 800 V in newer ones. Doubling the voltage halves the current for the same power, so cables, connectors and losses shrink and charging can be faster.
Unit: V Also: 400 V system, 800 V system
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A liquid resin — polyurethane, silicone or epoxy, sometimes foamed — poured around cells or electronics and cured into a solid block. It fixes cells against vibration, insulates them and can slow thermal propagation; some structural packs fill every gap between cylindrical cells with it. The cost is mass and a pack that is hard to repair or recycle.
Also: potting, encapsulant
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A small vent in a sealed pack enclosure, closed by a microporous membrane, often expanded PTFE, that passes air but not water or dust. It equalises internal pressure as temperature and altitude change, protecting the seals without losing the IP rating; some designs add a burst element that opens wide to release gas in thermal runaway.
Also: breather membrane, pack breather, pressure equalization vent, pressure compensation element, ePTFE vent
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The small circuit on a consumer cell or pack that disconnects it on overvoltage, undervoltage, overcurrent or overtemperature, using MOSFETs as switches. It is the minimum BMS; it protects but does not estimate state or balance.
Also: protection board, PCB
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A BMS design that duplicates safety-critical functions so no single failure can hide a hazard: an independent second voltage monitor beside the main measurement chip, two current sensors of different principle, a watchdog or second processor, and two separate paths to open the contactors. It is how BMS hardware reaches ASIL C or D.
Also: redundant BMS, secondary safety monitor
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Cells in series add their voltages; cells in parallel add their capacities and share current. A pack is described as, for example, 96s4p: 96 groups in series, each of 4 cells in parallel. Series strings need balancing; parallel groups self-balance through their shared terminals.
V = n_s·V_cell, Q = n_p·Q_cell Also: xSyP
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The two-wire bus, derived from I²C, over which a laptop or tool battery reports its charge, health and limits to the host and charger. The Smart Battery Data specification defines the register set, so any compliant charger can read it.
Also: System Management Bus, smart battery
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A pack built as two halves that contactors can connect in series or in parallel, so the same battery works at two voltages. GM’s Hummer EV drives at 400 V with its halves in parallel and switches them to series for 800 V fast charging; other designs split an 800 V pack to use 400 V chargers.
Also: switchable pack, reconfigurable pack, 400/800 V switching
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A chain of cells or modules connected in series to reach the system voltage, the basic electrical unit of a large battery. In stationary storage each rack is usually one string of about 1000–1500 V with its own contactors and BMS, and many strings are paralleled on a common DC bus.
Also: battery string, series string
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A load-bearing adhesive, usually epoxy, polyurethane or acrylic, that bonds cells to each other, to the tray or to the lid so the cell block becomes part of the structure. Cell-to-pack and cell-to-chassis designs rely on it, at the price of cells that are hard to replace or to separate for recycling.
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Measuring each series cell group’s voltage through a wire or flexible circuit from its busbar to the monitoring chip. Millivolt accuracy matters because the BMS reads SOC and detects faults from these numbers.
Unit: mV Also: cell tap, sense line
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A pack architecture in which each cell supervision circuit talks to the controller by radio instead of a wiring harness, saving cable, connectors and assembly time. It needs its own redundancy and security design to reach the same safety level.
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The bundle of cables, connectors and fixings that carries power and signals through a pack or vehicle. High-voltage cables outside an enclosure must have an orange covering under UN R100; the low-voltage harness carries cell-sense lines, CAN, HVIL and supply. Chafed wires and fretted connector pins cause many field faults.
Also: cable harness, HV harness, LV harness
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Where batteries are used, and the terms used to buy, size and compare them.
The low-voltage electrical system of trucks, buses and coaches, traditionally fed by two 12 V lead–acid batteries in series. In an electric bus or truck it still powers the controllers, doors and lights, kept charged by a DC/DC converter from the traction pack; its higher voltage than a car’s 12 V halves the current for the same load.
Also: 24 V electrical system, 24-volt system
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A vehicle electrical architecture at 48 V, used for mild hybrids and heavy accessories. It stays below the 60 V threshold at which high-voltage safety rules begin, so it needs no orange cables or interlocks.
Also: mild hybrid
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A business model in which the buyer of an electric vehicle pays for the car without its battery and rents the battery by subscription, lowering the purchase price and moving degradation risk to the provider. Renault leased the batteries of its early electric cars; NIO’s scheme, launched in 2020, pairs the model with battery swapping.
Also: battery leasing, battery subscription
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The manufacturer’s guarantee of capacity retention over time, for electric cars typically 70 % after 8 years or 160 000 km. It is written against state of health as the BMS reports it, which makes the SOH algorithm a contractual matter.
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Where a storage system sits relative to the customer’s electricity meter. Behind-the-meter batteries in homes, shops and factories serve the site first — solar self-consumption, backup, cutting demand charges; front-of-the-meter systems connect directly to the grid and earn from wholesale trading and grid services at utility scale.
Also: behind the meter, front of the meter, utility-scale storage
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Phones, laptops, wearables and tools: the first mass market for lithium-ion and still the one that pays for the highest energy density. It favours pouch cells with LCO or high-nickel positives and silicon-blended negatives.
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The headline price of cells or packs per unit of nominal energy. Pack prices fell by about 90 % between 2010 and the mid-2020s to roughly 100 US dollars per kWh, with LFP cells in China well below that.
Unit: $/kWh
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A battery-electric city or coach bus, with packs of 300–700 kWh on the roof and at the rear, LFP or NMC, charged overnight in the depot or at the terminus by pantograph. Its duty cycle — long hours, deep daily cycles, a twelve-year life — makes battery aging the central engineering question.
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A battery-electric van or pickup of up to 3.5 tonnes gross weight, category N1 in Europe, used for parcel delivery and trades. Packs of about 50–110 kWh suit predictable urban routes and overnight depot charging, but payload is tight: every kilogram of battery is a kilogram less of goods.
Also: electric van, eLCV
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A battery-electric medium- or heavy-duty goods vehicle. A long-haul tractor carries several hundred kilowatt-hours — Mercedes-Benz’s eActros 600 has 621 kWh of LFP in three packs for about 500 km — and needs megawatt charging to refill during a driver’s rest, while the battery’s mass eats into payload.
Also: battery-electric truck, e-truck
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A vehicle driven by an electric motor from a battery charged from the grid. A battery electric vehicle has no engine; it is the largest market for lithium-ion cells and the driver of most pack technology.
Also: BEV, battery electric vehicle
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Charging a battery when electricity is cheap and discharging when it is expensive, the simplest revenue of grid storage. Peak shaving is the same idea applied to a site’s demand charges.
Also: peak shaving, load shifting
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The systems that collect battery state, consumption and fault data from each vehicle in a fleet and bring them to the depot and the operator. For an electric bus fleet they are what turns BMS data into charging plans and warranty cases.
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Rapidly injecting or absorbing power to hold the grid frequency at 50 or 60 Hz, a service batteries do better than any generator because they respond in milliseconds. It cycles the battery shallowly but very often.
Also: ancillary services, frequency response
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A hybrid pairs an engine with a small battery, around 1 kWh, that is cycled hard for power rather than energy; a plug-in hybrid adds a 10–25 kWh pack that can be charged from the grid for electric-only driving. Their cells are designed for power and life rather than energy.
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Two storage technologies combined so each covers the part of the load it suits: typically a battery for energy, with supercapacitors, a flywheel or high-power cells for short peaks. In a bus or tram the supercapacitors absorb braking and acceleration pulses, sparing the battery the high currents that age it fastest.
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Batteries for forklifts, warehouse tugs, automated guided vehicles and mobile robots. Lead–acid forklift batteries are deliberately heavy, doubling as counterweight, and are swapped or recharged over a shift break; LFP replacements allow opportunity charging in short pauses, which suits robots that dock themselves between tasks.
Also: forklift battery, AGV battery, AMR battery, motive power battery
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The total lifetime cost of a storage system divided by the total energy it will discharge, in currency per megawatt-hour. It folds cell price, efficiency, cycle life and degradation into one figure for comparing technologies.
Unit: €/MWh
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Storage that discharges for eight hours or more, filling gaps that lithium-ion’s one-to-four-hour systems leave. Flow, iron–air and thermal technologies compete for it by making energy capacity cheap even when power is not.
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Batteries for ships: all-electric ferries on short crossings, and hybrid propulsion that lets vessels run engines at their best load or sit emission-free in port. Norway’s first all-electric car ferry, in service since 2015, uses about 150–200 kWh per crossing. Classification societies such as DNV set rules for fire safety, ventilation and gas detection in battery rooms.
Also: marine battery, ship battery, electric ferry
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A local network of loads, generators and storage — a campus, an island, a military base — that can run connected to the main grid or on its own. The battery is usually what makes islanded operation possible, forming the voltage and frequency and covering the gap while generators start or solar output dips.
Also: mini-grid
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E-bikes, e-scooters and small motorcycles with packs of 0.3–3 kWh built from cylindrical cells. Their packs are cheap and often charged indoors, which is why they feature disproportionately in fire statistics.
Also: light electric vehicle, LEV, e-bike
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China’s policy category for battery-electric, plug-in hybrid (including range-extended) and fuel-cell vehicles, which receive green licence plates, purchase-tax relief and credits under the dual-credit rules. In the United States the same abbreviation means a neighbourhood electric vehicle, a low-speed car limited to about 25 mph.
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In the battery industry, the vehicle or device maker that buys cells or packs and sells the finished product. Cell makers, pack integrators and OEMs form the three tiers of the supply chain.
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Two design points of the same chemistry: a power cell has thin, porous electrodes and many tabs for high current and fast charging; an energy cell has thick, dense electrodes for maximum watt-hours. A hybrid car wants the first, a long-range car the second.
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How far an electric vehicle travels on a full charge: usable energy divided by consumption per kilometre. Cold weather, speed and heating cut it, and the gap between official and real range is usually consumption, not battery capacity.
Unit: km
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An electric vehicle whose wheels are always driven by the electric motor, with a small combustion engine acting only as a generator to recharge the battery or feed the motor when the battery runs low. Its pack is usually larger than a plug-in hybrid’s, so most daily driving is electric; China counts such vehicles as new energy vehicles.
Also: REEV, range extender, series hybrid
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How fast grid frequency moves after a sudden imbalance such as a large generator tripping. Grids with less rotating inertia see steeper slopes; Great Britain has relaxed its loss-of-mains protection settings from 0.125 Hz/s to 0.5–1 Hz/s. Fast battery response and grid-forming inverters that emulate inertia help keep it within limits.
RoCoF = df/dt Unit: Hz/s
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Supplying or absorbing reactive power to hold local grid voltage within limits. A battery’s inverter can do it at any state of charge, since reactive power circulates rather than draining stored energy, but it shares the inverter’s apparent-power rating with real power: a 1 MVA inverter exporting 0.8 MW has 0.6 Mvar left.
S² = P² + Q² Unit: var Also: reactive power, volt-var control, var support
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The power a vehicle needs at its wheels to overcome aerodynamic drag, rolling resistance, gradient and inertia at a given moment. Drag power rises with the cube of speed, which is why motorway driving drains a battery so much faster than town driving; integrated over a drive cycle it gives energy consumption and range.
P = v·(½·ρ·C_d·A·v² + C_rr·m·g·cos θ + m·g·sin θ + m·a) Unit: W Also: road load, tractive power, traction power demand
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The UITP’s three standardised drive cycles for measuring bus energy consumption: SORT 1 heavy urban, SORT 2 easy mixed, SORT 3 easy suburban. An electric bus’s rated range in a tender is usually quoted per SORT cycle, often with heating or cooling load added as E-SORT.
Also: UITP SORT, Standardised On-Road Test
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Batteries installed in a fixed place — a container at a solar farm, a cabinet in a home — to shift energy in time or support the grid. LFP cells dominate because cost per cycle and safety matter more than mass.
Also: battery energy storage system, ESS
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Capping the energy a battery cycles per day or year so that lifetime throughput stays within the warranty allowance and degradation stays on plan. Grid-storage warranties are often written around one equivalent full cycle per day, so the energy management system weighs every extra megawatt-hour traded against the life it consumes.
Also: cycle limiting, throughput cap
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Purchase price plus energy, maintenance and residual value over a vehicle’s or system’s life. For buses and trucks it is the figure that decides the case for batteries, because fuel and maintenance savings repay the higher purchase price.
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The electric machine that drives a vehicle’s wheels, fed by the inverter from the battery and run as a generator during regenerative braking. Most are permanent-magnet synchronous motors with neodymium magnets; induction and wound-rotor machines avoid rare earths. Its peak power, often 100–300 kW in a car, sets the discharge power the pack must supply.
Also: e-motor, electric machine, drive motor
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A vehicle with no tailpipe emissions in any mode of operation — in practice battery-electric and hydrogen fuel-cell vehicles. The category underpins sales mandates, going back to California’s ZEV programme of 1990, that require a growing share of new sales to qualify; plug-in hybrids count only partly, if at all.
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Where the materials come from, what a battery’s carbon footprint is, and the rules that govern it from mine to market.
The greenhouse gases emitted to make a battery, typically 50–100 kg CO₂-equivalent per kWh, dominated by cathode materials and the electricity used in cell production. The EU regulation requires it to be declared and will later cap it.
Unit: kg CO₂e/kWh
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India’s proposed unique identifier for battery packs, set out in 2026 draft guidelines from the Ministry of Road Transport and Highways: a 21-character code marked on each EV pack, and on industrial batteries above 2 kWh, linked to records of its maker, composition, carbon footprint and service data — a counterpart to the EU battery passport.
Also: Battery Aadhaar
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A digital record for each electric-vehicle and industrial battery, required in the EU from 2027, holding its composition, carbon footprint, due-diligence data, state of health and repair history, accessible by QR code.
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The sequence of industries a battery passes through: mining and refining of lithium, nickel, cobalt, manganese and graphite; active-material and component production; cell manufacturing; module and pack assembly; use in a vehicle or storage system; second life; and recycling back into materials. Refining is where supply is most concentrated, so policy focuses there.
Also: battery supply chain
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The first lifecycle obligation of the EU Battery Regulation for EV, industrial and LMT batteries: a declared carbon footprint per kWh calculated to a harmonised method, followed by performance classes and, later, a maximum threshold above which a battery cannot be sold.
Unit: kg CO₂e/kWh
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The metal that stabilises layered-oxide cathodes, mined largely in the Democratic Republic of Congo under scrutiny for working conditions. Its price and ethics have driven the industry from LCO and NMC111 towards high-nickel and cobalt-free LFP.
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The procedure by which a manufacturer shows a battery meets the EU Battery Regulation — safety, performance, durability and labelling — before affixing the CE mark. For EV and industrial batteries a notified body is involved; the Regulation replaces the Low Voltage Directive route the old rules used.
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The common unit for greenhouse gases: each gas’s mass multiplied by its global warming potential, so that a mix of emissions is expressed as the mass of carbon dioxide with the same warming effect. One kilogram of fossil methane counts as about 30 kg CO₂e; battery carbon footprints are quoted in kg CO₂e per kWh.
CO₂e = Σ mᵢ · GWPᵢ Unit: kg CO₂e Also: carbon dioxide equivalent, CO2e, CO2-equivalent, CO2eq
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Names for the extent of a life-cycle assessment. Cradle-to-gate runs from raw-material extraction to the factory exit, the usual scope of a cell supplier’s data; gate-to-gate covers one production step; cradle-to-grave adds use and disposal; cradle-to-cradle replaces disposal with recycling into new products, the goal of a closed battery loop.
Also: cradle-to-gate, gate-to-gate, cradle-to-cradle
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Materials that an economy depends on and whose supply is concentrated or at risk: for batteries, lithium, cobalt, nickel, natural graphite and manganese. The EU and US both list them and attach sourcing and recycling targets.
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The EU directive requiring electrical and electronic equipment neither to emit electromagnetic disturbance above set limits nor to malfunction when exposed to it. Chargers, inverters and battery management electronics in stationary storage are tested to harmonised standards under it, while road vehicles and their components are approved under UN Regulation No. 10 instead.
Also: EMC Directive, Directive 2014/30/EU
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The earlier European law on batteries, from 2006, that restricted mercury and cadmium, set collection targets for portable batteries and made producers responsible for take-back. It is replaced step by step by the 2023 Battery Regulation.
Also: Directive 2006/66/EC
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The European law, in force since 2023, that governs batteries over their whole life: carbon-footprint declarations, recycled-content minimums, due diligence on raw materials, performance and durability requirements, removability, the battery passport and collection and recycling targets.
Also: Regulation (EU) 2023/1542
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The principle, in the EU Battery Regulation and its predecessor, that whoever first places a battery on the market pays for its collection and recycling at end of life. Producers register nationally, report volumes and fund the collection schemes.
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The quantified service against which a life-cycle assessment reports its results, so that different products can be compared fairly. For EU battery carbon footprints it is one kilowatt-hour of total energy delivered over the battery’s service life, so a longer-lived battery spreads its production emissions over more energy.
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How much heat a greenhouse gas traps over a set horizon, usually 100 years, relative to the same mass of carbon dioxide. On IPCC AR6 values fossil methane scores about 30, nitrous oxide 273 and sulfur hexafluoride about 25 000; multiplying each emission by its GWP gives the CO₂-equivalent totals of a battery’s carbon footprint.
Also: GWP100
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The pair of international standards that define life-cycle assessment: ISO 14040 sets out the principles and framework, ISO 14044 the requirements. They prescribe four phases — goal and scope, inventory, impact assessment and interpretation — and a critical review before comparisons are published; battery footprint methods such as PEF build on them.
Also: ISO 14040, ISO 14044, ISO 14040/44
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The method for totalling a product’s environmental impact from raw material to end of life, standardised in ISO 14040. For a battery it is what turns mining, production, use and recycling data into a carbon footprint.
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Lithium-rich salt water pumped from beneath the salt flats of Chile, Argentina and Bolivia and concentrated in evaporation ponds over a year or more. Direct lithium extraction aims to pull the lithium out chemically in days instead.
Also: salar, DLE
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The commodity form in which most lithium is traded and the lithium source for LFP and mid-nickel cathodes. Lithium carbonate equivalent, LCE, is the unit the industry uses to count lithium supply whatever its chemical form.
Also: LCE, lithium carbonate equivalent
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The lithium chemical required for high-nickel cathodes, which must be fired at temperatures too low for lithium carbonate to react. It is made from spodumene directly or by converting carbonate.
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The EU safety directive for electrical equipment rated 50–1000 V AC or 75–1500 V DC, covering protection against electric shock, overheating and fire. Chargers, wallboxes, inverters and grid-connected storage cabinets carry the CE mark partly on its basis, alongside the Electromagnetic Compatibility Directive.
Also: LVD, Directive 2014/35/EU
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A cheap, abundant metal used in NMC, LMO and LMFP positive electrodes and in alkaline cells. Ore comes mostly from South Africa, Gabon and Australia, but about 95 % of battery-grade high-purity manganese sulfate was refined in China in 2024, which puts manganese on critical-raw-material lists despite plentiful reserves.
Also: manganese sulfate, high-purity manganese sulfate, HPMSM
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The battery-grade nickel chemical fed to precursor plants, made from high-purity class 1 nickel or increasingly from Indonesian laterite ore by high-pressure acid leaching. It is the largest cost in a high-nickel cathode.
Also: class 1 nickel
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The European Commission’s harmonised life-cycle method, which scores a product on 16 environmental impact categories, climate change among them. Category rules, PEFCRs, fix the functional unit, system boundary and data for one product group — rechargeable batteries had one from the pilot phase — and the EU Battery Regulation’s carbon-footprint rules build on the method.
Also: PEFCR, Product Environmental Footprint Category Rules, Environmental Footprint method
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The EU regulation on chemicals: substances made or imported above one tonne a year must be registered, and the most hazardous can be restricted or made subject to authorisation. Suppliers of articles must declare substances of very high concern above 0.1 % by weight, and a restriction in force since 2020 caps worker exposure to NMP, the electrode-coating solvent.
Also: Regulation (EC) No 1907/2006, SVHC, substances of very high concern
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The EU Battery Regulation’s requirement that industrial and EV batteries declare the share of recycled cobalt, lithium, nickel and lead in their active materials, and from 2031 meet minimums of 16 % cobalt, 6 % lithium, 6 % nickel and 85 % lead, rising again in 2036.
Unit: %
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The EU directive restricting ten substances in electrical and electronic equipment — lead, mercury, cadmium, hexavalent chromium, two families of brominated flame retardants and four phthalates — to 0.1 % by weight of each homogeneous material, 0.01 % for cadmium. Batteries themselves fall under battery law instead, but the chargers and devices around them must comply.
Also: Directive 2011/65/EU, Restriction of Hazardous Substances
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The Greenhouse Gas Protocol’s split of a company’s emissions: Scope 1 from sources it owns, such as furnaces and vehicles; Scope 2 from the electricity and heat it buys; Scope 3 from everything else in its value chain. For a carmaker, its cell suppliers’ emissions are Scope 3, as are those of the cars it sells while they are driven.
Also: Scope 1, Scope 2, Scope 3, GHG Protocol scopes
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The hard-rock lithium ore, a lithium aluminium silicate mined mainly in Australia, concentrated to about 6 % Li₂O and shipped to converters, mostly in China, who turn it into carbonate or hydroxide.
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The obligation on battery makers to identify and address human-rights and environmental risks in their raw-material supply chains, following OECD guidance, and now a legal requirement in the EU for cobalt, lithium, nickel and graphite.
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The line in a life-cycle assessment between the processes counted and those left out. The EU’s battery carbon-footprint rules include raw-material extraction, production, distribution and end of life but exclude the use stage, so the footprint describes how the battery is made and recycled, not how clean the electricity that charges it is.
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The control units, chips, protocols and file formats through which a battery is measured, controlled and logged.
The ASAM description of a controller’s internal measurement and calibration variables — names, memory addresses, data types and conversions — that tools need to read or tune them over XCP. It is generated with each firmware build and must match it exactly.
Also: ASAM MCD-2 MC
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The integrated circuit that measures a stack of series cells — typically 6 to 18 per chip — with millivolt accuracy, reads thermistors, switches balancing and talks to the controller over an isolated daisy chain. It is the part of a BMS that touches the cells, and its accuracy limits how well SOC can be known.
Also: cell monitoring IC, battery monitor IC, BMIC
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The circuit that turns a voltage into a number. In a BMS its resolution, offset and drift set the floor for voltage and current accuracy: one millivolt of cell-voltage error is several percent of SOC on a flat LFP curve.
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The XML exchange format of AUTOSAR, describing software components and the communication matrix of a whole vehicle — CAN, LIN, FlexRay and Ethernet — in one model. Carmakers increasingly hand suppliers ARXML instead of DBC files.
Also: AUTOSAR XML
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The plain-text form of a bus log, one frame per line with time, channel, identifier and data bytes. It is larger than BLF but readable in any editor; PEAK’s .trc files are a similar text trace from their interfaces.
Also: Vector ASCII log, TRC, PEAK trace
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Ethernet over a single twisted pair, now the backbone of newer vehicle networks where CAN’s bandwidth runs out. Battery systems still use CAN for control but increasingly send high-rate cell data and software updates over Ethernet.
Also: 100BASE-T1, 1000BASE-T1
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The automotive software architecture standard that splits controller software into a standard basic layer and application components, so BMS functions can be developed and integrated like parts. Classic AUTOSAR runs on microcontrollers, Adaptive on larger processors.
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A programmable power source that behaves like a battery or like each cell of a string, so a BMS or charger can be tested at any voltage, state of charge or fault without real cells. Cell emulators drive every AFE input separately.
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In layered battery systems, the controller between the module-level BMUs and the vehicle or site controller: it aggregates several strings or racks, decides which may connect, and presents one battery to the outside. Stationary storage usually calls the levels cell, module, rack and system.
Also: battery junction controller
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An open, tool-independent format for cell-test time series — time, voltage, current, temperature, cycle and step with agreed names and units — promoted by the Battery Data Alliance so data from different cyclers can be shared and compared without conversion scripts.
Also: Battery Data Alliance
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The master controller of a battery management system: it collects cell voltages and temperatures from the monitoring boards, runs the state estimation and protection logic, drives the contactors and talks to the vehicle. In some architectures the same name is used for a per-module slave, so a datasheet’s block diagram is the safe reference.
Also: BMS master, master BMS
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Vector’s compressed binary format for bus logs: every CAN, CAN FD, LIN or Ethernet frame with its timestamp and channel. It is the usual format of field logs from vehicles and test benches, decoded with the matching DBC file.
Also: Binary Logging Format, Vector BLF
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Protecting a battery’s controllers and data from manipulation through authenticated messages, signed firmware, secure boot and locked diagnostic access; a spoofed limit could overcharge cells. UN R155 has required a certified cybersecurity management system for new EU vehicle types since July 2022, with ISO/SAE 21434 as the engineering standard.
Also: battery cybersecurity, UN R155, ISO/SAE 21434
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The states a BMS moves between to save energy. In active mode it measures, estimates and drives the contactors; asleep it draws microamperes to a few milliamperes from the auxiliary battery and wakes on CAN traffic, ignition, a charger plug or a timer to check cells and balance. Sleep current decides how long a parked vehicle can stand.
Also: sleep mode, active mode, standby mode, wake-up
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Switch-mode circuits that step a DC voltage down (buck) or up (boost) using a fast switch, an inductor and a capacitor, often above 95% efficient. With transistors in place of diodes the same circuit runs both ways, charging a battery from a bus or discharging into it, as in stationary storage and on-board boosters that let 800 V cars use 400 V chargers.
Also: buck converter, boost converter, step-down converter, step-up converter, bidirectional DC/DC converter
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A higher-layer protocol on CAN used in industrial machines, forklifts and light vehicles; device profiles CiA 418 and 419 define how a battery module and a charger exchange status and limits.
Also: CiA 418, CiA 419
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The vehicle-side controller that manages charging: it detects the plug, talks to the charging station over the control pilot or ISO 15118 and DIN 70121, and passes the current and voltage limits the BMS allows. In some bus and truck architectures CCU also names a central or cluster control unit, so the system diagram decides.
Also: charge control unit
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Battery estimation and diagnostics run on servers from data sent by the vehicle or site, alongside the on-board BMS rather than replacing it. With more computing power and a whole fleet to compare against, it can fit aging models, flag cells drifting from their peers and forecast remaining life; safety functions stay on board.
Also: off-board battery analytics, battery analytics, cloud battery management
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The native files of battery testers: Neware .nda and .ndax, Arbin .res, BioLogic EC-Lab .mpr and .mpt, Maccor raw and exported files, and others. Each stores the same time, voltage and current data differently, which is why open readers and the Battery Data Format exist.
Also: .nda, .ndax, .res, .mpr, .mpt, Neware, Arbin, BioLogic, Maccor
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A device on the vehicle or bench that records bus traffic and sensor data to BLF or MDF4 files, often with triggers and remote upload. For field failures it is the black box from which the sequence of events is rebuilt.
Also: CAN logger, telematics logger
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The de-facto text format, from Vector, that describes a CAN network: which messages exist, their identifiers and timing, and how each signal is packed, scaled and named. Without the BMS’s DBC a CAN log is just numbers.
Also: CAN database
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A coded fault a controller stores when a check fails — a cell overvoltage, a sensor out of range, an isolation fault — with a status and often a snapshot of conditions when it occurred. Reading and interpreting DTCs is the first step of any battery root-cause analysis.
Also: fault code
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The ability of electronics to work without disturbing other equipment or being disturbed by it. A BMS must keep its own emissions low and keep measuring cell voltages accurately next to an inverter switching hundreds of amperes; vehicles prove it under UN R10, with filtering, shielding and layout as the tools.
Also: EMC, electromagnetic interference, EMI
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The general name for any controller on a vehicle network — BMU, VCU, CCU and motor controller are all ECUs. Each has its own address, firmware, diagnostic services and calibration data.
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A network of inductors and capacitors, typically common-mode chokes with X and Y capacitors, that stops high-frequency noise travelling along cables. Inverters, chargers and DC/DC converters need them to pass compatibility tests; on high-voltage lines the Y capacitors to chassis also store energy and pass touch current, which safety standards limit.
Also: EMC filter, line filter, noise filter
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Two ways of deciding a control input. Feedback measures the result and corrects an error after it appears; feedforward acts in advance on a known disturbance or setpoint, using a model. A battery cooling loop may feed forward the heat expected from the requested current and use feedback on cell temperature to trim the remaining error.
Also: closed-loop control, open-loop control, feedback control, feedforward control
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A chip whose logic is configured after manufacture, best known from Xilinx, now AMD, and Intel. In battery work it appears where timing must be exact and fast: test-bench and HIL simulators that emulate cells in microseconds, high-speed data acquisition, and some fast protection and power-electronics control.
Also: Xilinx, AMD FPGA
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The software that runs on a BMS or charger controller. Its version decides how SOC, limits and faults behave, so it is tracked like a part number, updated by flashing over CAN or over the air, and recorded in the battery passport.
Also: embedded software, BMS software
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Writing new firmware into a controller’s flash memory, normally through a bootloader that receives the image over CAN with UDS services. Image files come as Intel HEX, Motorola S-record or binary, often signed so the controller refuses unauthorised code.
Also: reprogramming, ECU flashing, bootloader
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Copper traces laminated between thin polyimide or PET films, replacing the round-wire sense harness in many modules. Joined by nickel tabs to each busbar, it carries cell voltages and thermistor signals to the monitoring chip, often comes pre-assembled with the busbar carrier, and saves weight and wiring errors.
Also: flex circuit, flexible PCB
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The set of values a controller saves at the moment a fault is detected — SOC, temperatures, current, the worst cell — attached to the trouble code. It is often the only record of the conditions that caused an intermittent fault.
Also: snapshot data, extended data record
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Reasoning with degrees of truth between 0 and 1, so that a temperature can be partly ‘warm’ and partly ‘hot’, combined through if–then rules. It has been applied to SOC and SOH estimation and to charge control because it encodes expert knowledge without a precise model, though its rules and membership functions still need tuning on test data.
Also: fuzzy inference, fuzzy controller
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Changing a controller’s or estimator’s gains with the operating point, usually by look-up tables indexed by measured variables. Because a cell’s resistance and dynamics change sharply with temperature and SOC, BMS thermal loops and state estimators often switch or interpolate their parameters across those ranges instead of using one fixed tuning.
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Testing a real BMS controller against a real-time simulation of the battery, vehicle and charger, so faults that would be dangerous on real cells can be injected safely. It follows model-in-the-loop and software-in-the-loop, where the same logic is tested as a model or as code on a PC.
Also: SIL, MIL, software-in-the-loop, model-in-the-loop
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General-purpose binary formats for large scientific and tabular data — hierarchical HDF5 and columnar Parquet — used to store battery test and fleet data at scale, where CSV becomes too slow and too large.
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Text formats that carry a firmware or calibration image with its memory addresses and checksums, used to flash controllers: Intel HEX and Motorola S-record (.s19, .srec, .mot). Their content must match the A2L that describes it.
Also: Intel HEX, Motorola S-record, SREC
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Measuring voltage through a separate pair of leads that carry no current, so the drop along current-carrying wires and joints is left out. In a BMS, 100 mA of balancing current through 0.5 Ω of sense wire would add a 50 mV error, so designs either give balancing its own leads or pause balancing while measuring.
Also: four-wire sensing, four-terminal sensing, 4-wire measurement, separate sense and balancing leads
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The standard file that describes a LIN cluster — its nodes, frames, signals and schedule — the LIN counterpart of a DBC file for CAN.
Also: LIN description file
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A reduced-performance state the vehicle or BMS enters after a fault that is not severe enough to shut down, such as a lost temperature sensor or a failed balancing channel. Power and charging are derated so the driver can reach safety or a workshop, and a fault code records why.
Also: limp mode, fallback mode, degraded mode
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Two identical processor cores running the same program slightly offset in time, with hardware comparing their outputs continuously. Any mismatch, from a radiation-flipped bit or a silicon fault, triggers a reset or safe state, giving the high diagnostic coverage a BMS controller needs for ASIL C or D.
Also: dual-core lockstep, DCLS, lockstep processor, lockstep
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The ASAM standard binary format for measurement data, version 4 with the .mf4 extension: it stores decoded signals and raw bus frames side by side with their units, conversions and timestamps, compressed and indexed so large logs open quickly. It is the common exchange format for vehicle and battery test data.
Also: ASAM MDF, Measurement Data Format, MDF
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The processor that runs BMS firmware: state estimation, protection, balancing decisions and communication. Automotive BMS controllers use safety microcontrollers with lockstep cores and hardware self-tests so they can meet ASIL C or D.
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Control that uses a model to predict the system’s behaviour over a short horizon, chooses the input sequence that best meets a goal within constraints, applies the first step and repeats. In batteries it suits fast charging — the most current possible without breaching voltage or temperature limits or risking lithium plating — at a higher computing cost than PID.
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A transistor switched by the voltage on its gate, with an on-resistance of milliohms or less in power parts. Low-voltage packs use back-to-back pairs as charge and discharge switches, since each conducts backwards through its body diode; BMS chips use small ones for balancing, and silicon-carbide MOSFETs switch 800 V inverters.
Also: metal–oxide–semiconductor field-effect transistor, power MOSFET
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The ASAM format that describes a controller’s diagnostics — its UDS services, data identifiers and trouble codes — so a diagnostic tester can talk to it; PDX is the packaged form. Vector’s CDD files play the same role in many supplier projects.
Also: ASAM MCD-2 D, CDD
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Updating a controller’s firmware or calibration remotely over a cellular or Wi-Fi link instead of at a workshop. For a BMS it lets fixes to SOC estimation or charging limits reach a whole fleet, but needs signed images, a fallback copy and a safe vehicle state; UN R156 governs how manufacturers manage such updates.
Also: OTA update, FOTA, SOTA, over the air
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A feedback controller whose output is a weighted sum of the present error, its accumulated integral and its rate of change. It is the workhorse of battery systems — holding coolant temperature with a pump or compressor, regulating charger current and voltage — and often runs as PI only, without the derivative term.
u = K_p·e + K_i·∫e dt + K_d·de/dt Also: proportional–integral–derivative controller, PI controller
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A model of the system being controlled — cells, pack, cooling loop, charger — as distinct from the controller itself. Engineers tune and verify BMS software against it in model-, software- and hardware-in-the-loop tests, so its fidelity, often an equivalent circuit model coupled to a thermal model, limits how much those tests prove.
Also: system model
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The fast closed-loop controller of a grid-connected battery plant that regulates active and reactive power, voltage and frequency response at the point of connection, dispatching setpoints to the inverters. It enforces the grid code, while the energy management system above it decides the schedule.
Also: battery plant controller, plant controller, site controller
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Controlling average power by switching fully on and off at a fixed frequency and varying the fraction of each period spent on, the duty ratio. It drives fans, pumps and contactor coils, sets the output of DC/DC converters and inverters, and signals available current on the 1 kHz control pilot of an AC charger.
V_avg = D·V_supply
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The CAN-based protocol of trucks, buses and off-highway machines, with 29-bit identifiers and standard parameter groups. Commercial-vehicle batteries and chargers often report SOC, limits and faults as J1939 messages, and the bus FMS interface builds on it.
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A small voltage, the Seebeck effect, that appears wherever two different metals meet at different temperatures. Negligible for cell voltages, it matters for shunt current sensing: on a 100 µΩ shunt each microvolt reads as 10 mA, which coulomb counting integrates into SOC drift. Manganin is used for shunts partly because its thermal EMF against copper is under 1 µV/K.
Also: Seebeck error, thermal EMF, thermocouple effect
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The standard diagnostic protocol of vehicle controllers, ISO 14229: services to read data and fault codes, run routines, change sessions and flash firmware. A service tool talks UDS to the BMU over CAN to read cell data, clear faults or update software.
Also: ISO 14229
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A compact record, kept by the BMS, of how long or how much charge the battery has spent in each bin of temperature, SOC, current or C-rate. Instead of storing years of raw data it summarises the load spectrum, which feeds warranty decisions, second-life assessment and aging-model calibration.
Also: load spectrum, load collective, residence-time histogram
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The supervisory controller of an electric vehicle: it interprets the driver’s demand, asks the motor controller for torque and the BMS for the power it may give, and decides when the high-voltage system may switch on. The BMS reports to it, usually over CAN.
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The ASAM protocol for reading internal variables of a running controller and changing its calibration parameters, over CAN, Ethernet or other buses; CCP is its CAN-only predecessor. Engineers use it to watch BMS state estimators in real time and tune thresholds.
Also: Universal Measurement and Calibration Protocol, CCP
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What happens to a battery after its first life: reuse, and the recycling routes that recover its materials, step by step.
Recovering lithium, nickel, cobalt, copper and aluminium from end-of-life cells and production scrap. Scrap is today’s main feedstock; vehicle returns will dominate in the 2030s, and regulation now sets minimum recovery rates.
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Deciding what a returned battery is good for — repair, reuse, repurposing or recycling — from its history, a visual and electrical inspection and a quick state-of-health measurement. Fast, reliable triage is what makes second life economic.
Also: grading for reuse, state-of-health screening
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Leaching metals with acids produced by bacteria or fungi instead of added mineral acid. It uses less energy and chemistry but is slow, and remains at laboratory and pilot scale for batteries.
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The dark powder of mixed electrode materials left after end-of-life cells are discharged, shredded and separated from their casings, foils and separators. It is the traded intermediate that hydrometallurgical refiners buy.
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Keeping materials in use through repair, reuse, remanufacturing and recycling rather than mining and discarding. For batteries it means design for disassembly, second-life use and closed-loop recycling of the metals.
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The EU Battery Regulation’s quotas: portable batteries collected at 63 % by 2027 and 73 % by 2030, light-means-of-transport batteries at 51 % by 2028, with recycling efficiencies of 65 % for lithium-based batteries by 2025 and 70 % by 2030, and material recovery of 50 % of lithium by 2027 rising to 80 % by 2031.
Unit: %
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Evaporating a purified solution until a battery-grade salt crystallises out — nickel sulfate, cobalt sulfate, lithium hydroxide — ready to be sold back to precursor and cathode plants.
Also: evaporative crystallisation, nickel sulfate crystallisation
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The dangerous-goods rules for moving lithium batteries that are damaged, defective or sent for disposal, set in ADR special provisions 376 and 377: specific packagings, and for batteries liable to react dangerously, packaging approved for that risk. A swollen or crashed pack is never shipped as an ordinary battery.
Also: ADR SP 376, SP 377, critical defective battery
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Removing the stored energy before a battery is opened or shredded: electrically through a load, often recovering the energy; by immersion in a salt solution, which is simple but corrodes terminals and makes wastewater; or by cryogenic or thermal treatment. A shredder fed a charged battery is a fire risk.
Also: discharging for recycling, salt-water discharge, electrical discharge
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A mixture of two cheap compounds, such as choline chloride and urea, that melts far below either component and can dissolve metal oxides. It is studied as a milder, recyclable leaching medium for cathode materials.
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Separating materials by density in air or liquid: light separator and plastic film rise or float, heavier copper, aluminium and electrode fragments fall or sink.
Also: air classification, zig-zag sifter, sink-float
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Choosing pack and cell constructions — bolted rather than glued modules, labelled chemistries, no potting — that make end-of-life dismantling fast and safe. It trades a little production convenience for a large saving at the recycler.
Also: design for disassembly
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Recovering cathode material with its crystal structure intact and relithiating it for reuse, instead of breaking it down to metal salts. It promises lower energy and cost but must handle a mix of chemistries and ages.
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Taking a pack apart down to modules or cells to recover the casing, busbars, cables and electronics separately and to send only the cells on. It is still largely manual; robotic disassembly is held back by the variety of designs, glue and potting.
Also: disassembly, pack disassembly
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Ejecting non-ferrous metals such as aluminium from a moving stream with a rapidly rotating magnetic field, which induces currents in conductive pieces and throws them off the belt. It recovers casing and foil aluminium.
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Recovering the organic solvents and lithium salt from spent cells instead of burning them, by evaporation and condensation or by extraction with liquid or supercritical carbon dioxide. Few plants do it yet; most electrolyte is lost to off-gas treatment.
Also: supercritical CO₂ extraction, solvent recovery from cells
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Separating graphite from the oxide particles in black mass by making the water-repellent graphite cling to air bubbles that carry it into a froth. It lets graphite be recovered rather than burned, and leaves cleaner metal oxides for leaching.
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Recovering anode graphite, usually burned or left in leach residue, by flotation or as leach residue, then purifying and re-heating it to restore its structure for battery or other uses. Graphite is an EU critical raw material, which is pushing recyclers to keep it.
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Recycling by dissolving black mass in acid and separating the metals as salts by precipitation and solvent extraction. It recovers lithium and gives battery-grade products, at the cost of chemical consumption and wastewater.
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Removing copper, iron and aluminium from the leach liquor before the valuable metals are separated, typically by cementation and by raising the pH until their hydroxides precipitate. Battery-grade products need impurities in the parts per million.
Also: purification, iron and aluminium removal
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Dissolving the metals in black mass, usually in sulfuric acid with hydrogen peroxide as a reducing agent so cobalt and manganese go into solution as their more soluble lower oxidation state. The leach liquor carries lithium, nickel, cobalt and manganese, plus impurities such as copper and aluminium.
Also: acid leaching, reductive leaching
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Getting the lithium back, which smelting loses to slag and older hydrometallurgical flowsheets left until last at low yield. Newer routes take it out first — by roasting or carbonating black mass and washing out a lithium salt — before the other metals are leached.
Also: early lithium extraction, lithium-first recovery
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Pulling steel — cylindrical-cell cans, screws, brackets — out of the shredded stream with magnets, usually the first separation after shredding.
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The front end of most recycling plants: shredding cells or modules, drying off the electrolyte and separating the stream into casings, copper and aluminium foil, plastics and black mass. How cleanly this is done sets the purity, and the cost, of everything downstream.
Also: mechanical processing
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Recovering a dissolved metal as a solid by adding a reagent that makes it insoluble — nickel and cobalt as hydroxides, lithium as carbonate with sodium carbonate. Co-precipitating nickel, manganese and cobalt together gives a precursor directly.
Also: hydroxide precipitation, carbonate precipitation
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Rejected electrodes, cut-offs and failed cells from gigafactories, today the largest feedstock of battery recyclers. It is clean and of known chemistry, so it can often be processed by simpler routes than end-of-life packs.
Also: manufacturing scrap, electrode scrap
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Heating cells or black mass to a few hundred degrees without oxygen to evaporate the electrolyte and decompose the binder and plastics, so active material detaches from the foils. It makes later separation easier, at the cost of energy and off-gas treatment.
Also: thermal pre-treatment, binder burn-off
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Recycling by smelting whole cells or modules in a furnace, which recovers nickel, cobalt and copper as an alloy but loses lithium, aluminium and graphite to the slag. It is robust to mixed feed and is often the first step before a hydrometallurgical finish.
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The mass of a battery that ends up in useful products, as a share of the battery’s mass, calculated by the method fixed under the EU Battery Regulation; separate material recovery targets apply to lithium, cobalt, nickel and copper. Energy recovery by burning does not count.
Unit: % Also: material recovery rate
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Restoring the lithium a used cathode material has lost, by heating it with a lithium salt in the solid state or in a hot lithium solution, and re-annealing the crystal. It is the core step of direct recycling and works best on a single, known chemistry.
Also: cathode regeneration, hydrothermal relithiation
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Restoring a pack to its original duty by replacing failed or weak modules, cells, electronics or seals, then retesting it. It keeps the most value of any end-of-life route, and depends on packs that can be opened and on cells that can be matched.
Also: refurbishment, module replacement
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Collecting end-of-life and faulty batteries and bringing them to a sorting or recycling site: take-back points, transport as dangerous goods, storage and documentation. For large packs it is often the single biggest cost of recycling.
Also: battery collection, take-back
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Using vehicle packs that have reached their automotive end of life, with 70–80 % capacity left, in less demanding stationary storage before recycling. Grading the used cells and the liability for them are the practical obstacles.
Also: repurposing
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Breaking cells or modules into fragments, under an inert gas, in a liquid or in a vacuum so that the released electrolyte and any remaining charge cannot ignite. Off-gas treatment captures the solvent vapour and the hydrogen fluoride it forms.
Also: crushing, comminution, wet shredding, inert shredding
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Splitting shredded material by particle size: the fine fraction is mostly black mass, the coarse fractions mostly foil, casing and separator. Air classifiers do the same by size and density in a gas stream.
Also: screening, size classification
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Melting battery material in a furnace with fluxes so that cobalt, nickel and copper collect as a metal alloy or matte and the rest — lithium, aluminium, manganese — goes to the slag. The organic parts and graphite serve as fuel and reductant.
Also: alloy, matte, slag
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Separating metals in the leach liquor by contacting it with an organic phase carrying an extractant that picks up one metal at a time, controlled by pH: manganese, then cobalt, then nickel, leaving lithium in the water. It is how recyclers reach battery-grade sulfates.
Also: liquid–liquid extraction, Cyanex 272, D2EHPA
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Turning a recovered cathode material into a more valuable one during relithiation — for example converting old NMC111 to a nickel-richer composition — so that direct recycling keeps up with chemistries that change faster than batteries retire.
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Where and how vehicles are charged: charging strategies, power levels, connectors and the protocols between vehicle and charger.
Charging through the vehicle’s onboard charger from an AC socket or wallbox, at a few kilowatts up to 22 kW. It takes hours, keeps the cells cool and gently loaded, and is how most private cars are charged.
Also: overnight charging, destination charging, Level 2
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Replacing a vehicle’s depleted battery with a charged one at a station in a few minutes, so the battery is charged slowly and separately. It is used for taxis, two-wheelers and some trucks; it requires standardised packs and turns the battery into a shared, leased asset.
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The Japanese DC fast-charging standard, with its own connector and CAN-based communication rather than power-line signalling. It was the first widespread DC system and natively supports bidirectional charging, but in Europe and North America it has given way to CCS.
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The power a vehicle actually accepts against its state of charge during a fast charge: high at low SOC, stepping down as the cells approach voltage and plating limits. The area under it, not the peak kilowatts, decides how long a stop takes.
Unit: kW
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The North American shorthand for charging power: Level 1 is a 120 V household outlet, Level 2 a 240 V AC charger up to about 19 kW, and “Level 3” the informal name for DC fast charging. It maps roughly onto the IEC modes used elsewhere.
Also: Level 1, Level 2, Level 3, SAE charging levels
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The IEC 61851 classes of conductive charging: mode 1 a plain domestic socket, mode 2 a socket with an in-cable control box, mode 3 a dedicated AC charging point with the control pilot, and mode 4 DC charging where the converter is in the station. Most public charging is mode 3 or 4.
Also: IEC 61851, Mode 3, Mode 4
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The signal wire in an AC or CCS charging connector: the charger puts a ±12 V square wave on it whose duty cycle tells the vehicle the maximum current, and the vehicle answers by switching resistors. The proximity pilot beside it tells the vehicle a plug is inserted.
Also: proximity pilot, PP
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Charging from a station that supplies DC straight to the pack, bypassing the car’s onboard charger, at 50 kW to over 350 kW. The BMS, not the charger, sets the current from moment to moment, which is why the charge curve tapers as the pack fills.
Also: rapid charging, HPC
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Changing electricity consumption in answer to a price signal or a grid operator’s request, rather than adding generation. Pausing a fleet’s charging during an evening peak, or letting a home battery carry the house load for an hour, are typical examples; aggregated, such flexible loads can be paid as grid services.
Also: DR, demand-side response, demand-side flexibility
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Charging a fleet of buses or trucks at the depot, usually overnight at 50–150 kW per vehicle, which keeps cell stress low and lets an energy-management system sequence the chargers against the site’s grid connection.
Also: overnight charging
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The German specification for the digital communication between an electric vehicle and a DC charger in the Combined Charging System, the forerunner of ISO 15118. Most DC chargers in Europe still speak it, so vehicles support both.
Also: DIN SPEC 70121
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The charging equipment between the grid and the vehicle: an AC wallbox that only switches and protects the supply, or a DC charger that also converts it. It enforces the current limit, ground-fault protection and communication with the vehicle.
Also: charging station, charge point, wallbox
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The two ends of high-level charging communication: the electric vehicle communication controller in the vehicle and the supply equipment communication controller in the charger. They exchange limits, schedules and authorisation over power-line communication on the control-pilot wire.
Also: electric vehicle communication controller, supply equipment communication controller
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The US Federal Energy Regulatory Commission’s order of September 2020 requiring regional grid operators to let aggregations of distributed energy resources — batteries, electric vehicles and their chargers, rooftop solar, demand response — take part in wholesale electricity markets, with a minimum aggregation size of no more than 100 kW.
Also: Order No. 2222, DER aggregation rule
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China’s national charging standards: GB/T 20234 for the AC and DC connectors and GB/T 27930 for the CAN communication of DC charging. ChaoJi is the successor developed jointly with CHAdeMO for higher power.
Also: GB/T 20234, GB/T 27930, ChaoJi
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Power flowing from the grid into a vehicle’s battery — ordinary charging, named to contrast it with vehicle-to-grid. Managed grid-to-vehicle charging shifts and modulates this one-way flow to suit the grid, offering flexibility without the extra battery cycling or the bidirectional hardware that two-way systems need.
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DC charging at 150 kW and above, up to about 400 kW for cars, usually at 800–1000 V so the current stays within what cable and connector can carry. Liquid-cooled cables make the currents of 500 A and more practical.
Also: ultra-fast charging, ultra-rapid charging
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The power-line communication used by CCS charging: a high-frequency signal superimposed on the control-pilot wire carries the DIN 70121 or ISO 15118 messages, so no extra data wires are needed in the plug.
Also: power-line communication
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Charging without a plug, through coupled coils in the ground and under the vehicle, at about 90 % efficiency when aligned. Static pads suit cars and buses at stops; dynamic charging in the road is in trials.
Also: wireless charging, WPT, SAE J2954
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Part of the network, such as a house with solar and a battery, staying energised while disconnected from the main grid. Intentional islanding, behind a transfer switch with a grid-forming inverter, provides backup power; unintentional islanding endangers line workers, so IEEE 1547 requires inverters to detect it and cease energising the grid within two seconds.
Also: island mode, anti-islanding, intentional islanding
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The communication standard between an electric vehicle and a charging station: identification, authorisation, charge scheduling and, in the −20 edition, bidirectional power transfer. It is what lets a car authenticate itself and start charging with no card or app.
Also: Plug & Charge, V2G communication
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The standard for the safety of a vehicle’s conductive connection to an external electric power supply — charging. It sets the electrical-safety requirements the vehicle side of an AC or DC charging connection must meet.
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The connector and protocol standard for charging heavy trucks and coaches at up to 3.75 MW — up to 3000 A at 1250 V — so a long-haul truck can recharge during a driver’s mandatory break. It uses ISO 15118 communication over Ethernet rather than power-line signalling.
Also: SAE J3271
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The compact AC and DC connector introduced by Tesla and standardised as SAE J3400, now adopted by most carmakers in North America in place of the CCS1 plug. The communication underneath is the same as CCS.
Also: North American Charging Standard, SAE J3400
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The converter inside the vehicle that turns AC from a home or public socket into DC for the pack, typically rated 7–22 kW. DC fast chargers bypass it, which is why they can be so much more powerful.
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The open protocol between a charging station and the back-office system that manages it: authorisation, start and stop, metering, smart-charging limits and remote updates. Depot charging of bus fleets is usually orchestrated through OCPP.
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Topping up a vehicle in short, high-power bursts wherever it stops anyway — a bus at its terminus or at stops, a forklift at breaks — instead of carrying enough energy for the whole day. It allows a smaller, lighter battery, at the price of frequent high-rate cycling and of chargers along the route.
Also: en-route charging, terminus charging
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Fast charging of a bus through an automatic contact on the roof — raised from the vehicle or lowered from a mast — at the terminus or en route, at 150–600 kW for a few minutes. It allows a smaller battery at the price of high-rate cycling and more infrastructure.
Also: OppCharge, SAE J3105
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The standards that define charging connectors: J1772 Type 1 and the IEC 62196 Type 2 plug for AC, and the Combined Charging System that adds two DC pins below them. Europe mandates Type 2 and CCS2; North America is moving to the NACS connector.
Also: Type 1, Type 2, CCS
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Controlling when and how fast vehicles charge to fit grid capacity, electricity prices and departure times, rather than charging at full power on arrival. A depot of buses uses it to stay within its grid connection; homes use it to charge on cheap night tariffs.
Also: managed charging, load management
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A home electrical panel whose circuits software can switch and meter individually. During an outage it lets a home battery or vehicle-to-home system keep essential circuits alive and shed large loads such as an EV charger or heat pump, so a smaller battery and inverter can carry the house for longer.
Also: smart electrical panel, smart breaker panel, load management panel
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The umbrella term for using a vehicle’s battery as a source as well as a load: vehicle-to-load for appliances, vehicle-to-home, vehicle-to-building, vehicle-to-vehicle and vehicle-to-grid. All need bidirectional power electronics and, beyond the simplest, communication such as ISO 15118-20; the abbreviation is also used for vehicle communication networks.
Also: vehicle-to-building, V2B, bidirectional power transfer
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Discharging a vehicle’s battery back into a house or the grid through a bidirectional charger, so parked cars act as storage. Vehicle-to-load and vehicle-to-home are the simpler forms that power appliances or a house directly.
Also: V2L, V2H, bidirectional charging
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Transferring energy from one electric vehicle’s battery to another’s through a bidirectional charger and cable, for example to rescue a car stranded with an empty pack. It is one member of the vehicle-to-everything family; the same abbreviation also names radio communication between vehicles.
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Many small, distributed resources — home batteries, electric vehicles, rooftop solar, heat pumps — aggregated by software and dispatched together as if they were one power station. A few thousand home batteries add up to tens of megawatts of fast, controllable capacity that can trade energy and provide frequency services.
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How heat is made, moved and removed in cells and packs, and the hardware that keeps a battery at the right temperature.
Two idealised thermal boundaries used in testing. Adiabatic means no heat escapes, so every joule raises the sample’s temperature — the principle of accelerating rate calorimetry and the worst case for a pack whose cooling fails. Isothermal means the sample is held at constant temperature while the heat it releases is measured, as in isothermal calorimetry.
Also: adiabatic, isothermal
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Warming a cold battery before charging or use. External methods use electric heaters, a heat pump or warm coolant; internal methods heat the cell through its own resistance with alternating current or rapid charge–discharge pulses. Experimental self-heating cells embed a nickel foil that takes them from −20 °C to 0 °C in about 20 seconds.
Also: battery heater, pulse heating, AC heating, internal heating, self-heating cell
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The ratio of the resistance to heat conduction inside a body to the resistance to convection at its surface. Below about 0.1 the body heats almost uniformly and a lumped thermal model is adequate; large, strongly cooled cells with poor through-plane conductivity exceed it and need a model that resolves the internal gradient.
Bi = h·L / k
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A heat exchanger in which evaporating refrigerant from the air-conditioning circuit cools the battery coolant below ambient temperature. A radiator can only bring coolant close to outside air temperature; the chiller is what lets a pack fast-charge on a 35 °C day. Stationary storage containers use packaged chiller units for the same job.
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The fractional change in length per kelvin of temperature change. Aluminium expands about 23 ppm/K, copper 17, steel 12 and most plastics several times more, so joined parts in a pack — busbars, welds, adhesive bonds, potting — are strained every time it heats and cools.
Unit: K⁻¹ Also: thermal expansion coefficient, thermal expansion
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Keeping liquid water out of a sealed pack that breathes as it heats and cools. Air drawn in through the pressure-equalisation vent can condense on surfaces chilled below its dew point, so designs combine membrane vents that pass air but not water, desiccant cartridges that soak up moisture, and coolant control that avoids over-chilling.
Also: desiccant, desiccant cartridge, breather vent
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The liquid pumped through cooling plates and heat exchangers, usually a roughly 50:50 mix of water and ethylene glycol that stays liquid to about −35 °C. It carries heat better than air or dielectric oils, but it conducts electricity, so a leak inside a pack threatens insulation resistance and can short live parts.
Also: water–glycol, glycol coolant, ethylene glycol
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A flat aluminium channel assembly under or between the cells through which coolant, usually a water–glycol mix, is pumped. Heat crosses from cell to plate through a thermal interface material; the plate also sets the pack’s temperature uniformity.
Also: cold plate
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The temperature at which an amorphous polymer turns from hard and glassy to soft and rubbery, with a sharp fall in stiffness and rise in expansion. Adhesives, potting compounds and circuit boards are chosen with Tg clear of the operating range — standard FR-4 board is about 130–140 °C — so their joints are not loaded differently in service.
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A device that moves heat between two fluids without mixing them, through thin metal walls with as much area as possible. In battery systems the main examples are the chiller, between refrigerant and coolant, and the radiator, between coolant and air; a cooling plate does the same job between cells and coolant.
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The rate of heat flow through a surface per unit area. Dividing a cell’s heat by its cooled area gives the flux the cooling must carry: a 21700 cell shedding 5 W through its roughly 46 cm² side sees about 1 kW/m². Cooling only one face concentrates the flux and steepens the gradient inside.
q″ = Q / A Unit: W/m²
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The heat a cell produces in operation: an irreversible part equal to current times overpotential, and a reversible part from the entropy change, I·T·dE/dT. The Bernardi equation sums them and feeds every thermal model.
q = I(V − E_OCV) + I·T·(dE/dT) Unit: W Also: Bernardi equation
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A sealed tube holding a little working fluid that evaporates at the hot end, condenses at the cold end and returns through a wick. It moves heat with an effective conductivity many times that of copper and little temperature drop. Common in electronics, it has been studied for spreading heat along cells, but packs still rely on cooling plates.
Also: vapour chamber
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A refrigerant circuit run to move heat from a colder place to a warmer one, delivering two to three units of heat per unit of electricity in mild winter conditions. In an electric vehicle it warms the cabin and battery from outside air and the waste heat of the motor and inverter, saving winter range compared with resistive heaters.
Also: coefficient of performance
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A metal body, often extruded aluminium with fins, that draws heat from a component and enlarges the surface it can lose that heat from. Fins multiply the area for convection to air; in batteries heat sinks serve air-cooled cell blocks and, above all, the balancing resistors and power switches of the BMS and DC/DC converter.
Also: fins, cooling fins, finned heat sink
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The heat carried away per unit area per kelvin of difference between a surface and the fluid passing it. Typical values are 5–25 W/(m²·K) for still air, 25–250 for forced air and hundreds to thousands for pumped liquid, which is why fast-charging packs are liquid-cooled. Thermal models use it as their cooling boundary.
Q = h·A·ΔT Unit: W/(m²·K) Also: convection coefficient, film coefficient
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The three ways heat moves: conduction through solids and still fluids, convection carried by a moving fluid, and radiation emitted as infrared by every warm surface. In a pack, conduction takes heat from the cell into the cooling plate and convection carries it away in the coolant; radiation matters mainly at the high temperatures of thermal runaway.
Also: conduction, convection, thermal radiation
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A small region that runs markedly hotter than its surroundings — near a tab, at a high-resistance weld or busbar joint, in the centre of a large cell or around an internal short. Because aging speeds up roughly twofold for every 10 °C, that spot ages fastest, and a temperature sensor a few centimetres away may not see it.
Also: hotspot
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Bathing the cells directly in a non-conducting dielectric fluid that is pumped to a heat exchanger. It cools every surface evenly and slows thermal propagation, at the cost of fluid mass and sealing.
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Heat produced by current flowing through a resistance, equal to the current squared times the resistance. Doubling the current quadruples it: a 1 mΩ cell gives 10 W at 100 A but 40 W at 200 A. It dominates heat generation at high C-rates and also warms busbars, welds and connectors.
P = I²·R Unit: W Also: ohmic heating, resistive heating, I²R loss
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Controlling battery temperature without pumps, fans or compressors. Heat leaves by conduction to the enclosure and natural convection, sometimes helped by fins or phase change material, while insulation slows heat gain in summer and keeps a parked pack warm in winter. It suits small, low-power packs such as phones and e-bikes, not fast-charging vehicles.
Also: passive cooling, thermal insulation
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A material that melts at a chosen temperature, around 30–45 °C for batteries, absorbing a large latent heat — roughly 200 J/g for paraffin wax — with little temperature rise. Packed around cells, often in a graphite matrix to lift its poor conductivity, it caps peaks during short heavy loads, but it must be cooled to reset and adds mass.
Also: paraffin wax, latent heat storage
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Warming or cooling the battery to its preferred temperature before a fast charge or a hard drive, using the vehicle’s own heaters and pumps. Navigating to a charger triggers it in many cars, because a cold pack cannot accept high current safely.
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A finned coolant-to-air heat exchanger, usually behind the vehicle’s front grille, through which a fan draws air. It can only cool the coolant to a few degrees above the outside air, so it handles the battery in mild weather and the chiller takes over when it is hot or the charging load is high.
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A closed vapour-compression circuit: a compressor raises refrigerant pressure and temperature, a condenser rejects that heat to air, an expansion valve drops the pressure, and an evaporator absorbs heat as the refrigerant boils. Batteries draw on it through a chiller or through refrigerant plates that act as evaporators; R1234yf and CO₂ (R744) are the usual refrigerants.
Also: vapour-compression cycle, air-conditioning circuit, evaporator, condenser, compressor, R1234yf, R744
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The water vapour in air as a percentage of the most it could hold at that temperature. The same air reads a different RH when warmed or cooled, so dry rooms are specified by dew point instead. Air at 25 °C and 50 % RH has a dew point of about 14 °C: any surface colder than that collects condensation.
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The heat needed to raise one kilogram of a material by one kelvin; multiplied by mass it gives a body’s heat capacity in J/K. Lithium-ion cells sit near 1,000 J/(kg·K), so a 0.5 kg pouch cell absorbs about 500 J per degree — the figure a thermal model uses to turn heat into temperature rise.
Q = m·cₚ·ΔT Unit: J/(kg·K) Also: heat capacity, specific heat
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Usually a negative-temperature-coefficient thermistor glued to a busbar or cell surface, with a few per module. Because sensors read the surface, the hottest point inside a cell can run several degrees higher than the BMS sees.
Unit: °C Also: thermistor
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How readily a material conducts heat: the heat flux per unit temperature gradient. Cells are strongly anisotropic — around 25–45 W/(m·K) in-plane, along the metal foils, but below 1 W/(m·K) through-plane, across separators and coatings — so the side a cell is cooled from decides how hot its core runs.
q″ = −k·dT/dx Unit: W/(m·K) Also: λ, through-plane conductivity, in-plane conductivity
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How quickly temperature evens out inside a material: thermal conductivity divided by density times specific heat. Heat spreads a distance L in roughly L²/α, so crossing a 10 mm cell at about 0.2 mm²/s through-plane takes several minutes, while aluminium, near 100 mm²/s, equalises almost at once.
α = k / (ρ·cₚ) Unit: m²/s
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A change of temperature with position — within a cell from core to surface, or across a pack from coolant inlet to outlet. Packs are commonly designed to keep cells within about 5 °C of each other, because warmer cells age faster and, in parallel, carry more current, so a gradient grows into an imbalance.
Also: temperature gradient, temperature spread, temperature uniformity
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A soft, thermally conductive paste or pad that fills the gap between cells and the cooling plate so heat does not have to cross air. It is dispensed by the kilogram in a pack and is a surprising share of its cost.
Also: gap filler
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Keeping cells in their comfortable range, roughly 15–35 °C, and within a few degrees of each other: liquid cooling plates, refrigerant plates or immersion for heat removal, and heaters or waste heat for warming before fast charging in the cold.
Also: battery thermal management system, BTMS
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A body’s total heat capacity seen as a buffer against temperature change. A 500 kg pack at about 1 kJ/(kg·K) stores roughly 500 kJ per kelvin, so 10 kW of uncooled heat warms it only about 1.2 K a minute. Together with the thermal resistance to the coolant it sets the pack’s thermal time constant.
τ = m·cₚ·R_th Also: thermal inertia, thermal time constant
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A model of cell temperature: at its simplest one thermal mass with heat generation inside and convection outside, at its most detailed a 3D simulation of the pack. Temperature feeds back into every rate, so electrical and thermal models are usually solved together.
Also: lumped thermal model
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The temperature difference needed to drive one watt of heat along a path, in kelvin per watt. A 1 mm layer of gap filler at 3 W/(m·K) over 100 cm² has about 0.03 K/W, so 30 W through it costs 1 K. Resistances in series add like electrical ones, which is how cell-to-coolant paths are budgeted.
R_th = ΔT / Q = L / (k·A) Unit: K/W
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Mechanical stress caused by a temperature change when a part cannot expand freely or is joined to a material that expands differently. A fully restrained aluminium bar warmed by 50 K would carry about 80 MPa. Repeated cycles fatigue welds, solder joints and adhesive bonds, which is what thermal shock testing sets out to provoke.
σ = E·α·ΔT Unit: Pa
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An adhesive loaded with ceramic filler that both bonds cells to the cooling plate or tray and conducts their heat, typically at 1–3 W/(m·K). Unlike a gap filler it carries load, which suits cell-to-pack designs but makes cells hard to remove for repair or recycling.
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Temperature sensors used alongside the NTC thermistors of a BMS. Thermocouples, junctions of two dissimilar wires such as type K or T, are cheap, small and standard in cell testing, good to about ±1–2 °C; platinum RTDs such as the Pt100 reach a few tenths of a degree; fibre-optic sensors ignore electrical noise and can sit inside a cell.
Also: thermocouple, RTD, Pt100, resistance temperature detector, fibre Bragg grating, FBG
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Solid-state heat pumping by the Peltier effect: current through junctions of semiconductor elements moves heat from one face to the other, and reversing the current reverses the direction. Peltier modules hold small test cells at a set temperature in laboratory fixtures, but their efficiency, usually a coefficient of performance below 1, is too low for vehicle packs.
Also: Peltier cooling, Peltier element, Peltier module
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Imaging surface temperature with an infrared camera, which converts the radiation a surface emits into a temperature map. It reveals hot welds, busbar joints and uneven cell heating at a glance, but bare metal reflects more than it emits, so shiny surfaces are usually coated matt black before measuring.
Also: infrared thermography, thermal imaging, IR camera
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Keeping people safe from the pack’s voltage and keeping its electronics safe when they fail: insulation, switching, fusing and the functional-safety process.
The burst of heat, light and pressure released by a fault arc. The hazard to a worker is rated as incident energy at working distance; 1.2 cal/cm² is the usual onset of second-degree burns. Large battery systems can feed fault currents of many kiloamperes, so arc flash sets protective clothing and approach limits under NFPA 70E.
Unit: cal/cm² Also: DC arc flash, arc-flash hazard, incident energy
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Current continuing through ionised gas across a gap, typically between contacts as they separate. An AC arc goes out by itself at each current zero, a hundred times a second at 50 Hz; a DC arc has no zero and keeps burning until it is stretched and cooled so far that its voltage exceeds the source’s, which makes high-voltage DC far harder to interrupt.
Also: electric arc, DC arc
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The box inside the pack that holds the contactors, pre-charge circuit, main fuse or pyrofuse and current sensor, where the pack’s high-voltage connections are made and broken.
Also: battery junction box
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A short window during which a protection or diagnostic input is deliberately ignored, so that an expected transient — the inrush when contactors close, a load step, switching noise — does not trip it. It spans microseconds in a gate driver’s desaturation protection to tens of milliseconds or more around contactor closure; too long a window delays reaction to a real fault.
Also: blanking time, masking time
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The shortest distance through air between two conductive parts at different potentials. It is sized for the highest transient voltage the insulation must withstand, since air breaks down at roughly 3 kV/mm, and must grow above 2000 m altitude where thinner air breaks down sooner. IEC 60664-1 sets the values for most electronics.
Also: clearance distance, air gap
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The highest voltage at which an insulating material survives 50 drops of a conductive ammonium chloride solution without forming a carbonised track, tested to IEC 60112. Materials fall in groups from I (CTI ≥ 600) to IIIb (100–175); a better group permits shorter creepage distances, which matters for compact 800 V busbar holders and circuit boards.
Unit: V Also: tracking resistance
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A heavy-duty electrically operated switch that connects the pack to the vehicle or inverter and opens it on fault or shutdown. Packs use at least two, one per pole, plus a pre-charge path to avoid welding them on the first connection.
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The means by which a high-voltage DC contactor breaks current under load. Permanent magnets push the arc sideways to stretch and cool it — so many contactors are polarised and break less current in reverse — and hermetically sealed chambers filled with hydrogen or hydrogen–nitrogen gas cool the arc and keep the contacts clean.
Also: magnetic blow-out, arc quenching, arc chute, gas-filled contactor
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A circuit that drives a contactor coil hard to close it, then cuts the power to the much lower level needed to hold it shut, often by pulse-width modulation. A typical 500 A contactor holds on under 2 W at 12 V; the saving matters for heat and for the low-voltage supply when several contactors stay closed for hours.
Also: coil economizer, economiser, PWM coil drive
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A diagnostic that checks a contactor really opened when told to. The BMS compares voltages on each side of each contactor — if the load side still shows pack voltage after opening, the contacts have welded — or reads mirror auxiliary contacts. A welded contactor is latched as a fault, because the pack can no longer be fully disconnected.
Also: welded contactor, stuck contactor diagnostic, contactor diagnostics
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The shortest path between two conductors measured along the surface of the insulation between them. Moisture and dirt on that surface can carry leakage current and tracking, so the required distance grows with working voltage, pollution and a poorer tracking index: at 400 V and pollution degree 2, basic insulation needs about 2 mm on a group I material but 4 mm on group III.
Also: creepage, surface distance
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The fraction of a component’s failure rate that a safety mechanism detects or controls. ISO 26262 treats coverage from about 60% as low, from 90% as medium and from 99% as high; comparing two independent measurements of the same cell voltage typically earns high coverage, while a simple plausibility check earns much less.
coverage = λ_detected / λ_total
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The sudden failure of an insulator to block current once the electric field exceeds its dielectric strength, about 3 kV/mm for air at sea level and far higher for solid films. In 800 V drives, partial discharges in voids, driven by fast inverter switching edges, can erode insulation until it fails at normal voltage.
Also: dielectric breakdown, breakdown voltage, dielectric strength
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A hard-wired path that takes a battery system to a safe state on command, opening contactors and stopping the power converters regardless of what the software is doing. Stationary systems have red push buttons on the enclosure and often remotely; in vehicles the crash signal and the manual service disconnect play the same role.
Also: emergency stop, E-stop
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Connecting every exposed metal part — pack enclosure, motor frame, charger case — firmly to the chassis so that none can sit at a different voltage after an insulation fault. UN R100 requires under 0.1 Ω between exposed conductive parts and the chassis, measured with at least 0.2 A; during conductive charging the chassis is also tied to protective earth.
Also: potential equalisation, earth bonding, chassis bonding, bonding impedance
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Voltage low enough to need reduced shock protection: at most 50 V AC rms or 120 V ripple-free DC under IEC 61140. SELV is separated from higher voltages and from earth; PELV is separated but earthed; FELV is low in value only, without protective separation, so it is protected like the circuit feeding it. Vehicle rules draw their line lower, at 60 V DC.
Also: SELV, PELV, FELV, safety extra-low voltage, protective extra-low voltage
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A structured review that lists every way a component or process could fail, its effect, and how likely it is to happen and be detected, scoring each to prioritise fixes. Battery programmes run it on the cell, the pack design and the production process.
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The two layers that turn safety goals into a design under ISO 26262. The functional safety concept states what must happen — detect a cell above its voltage limit and open the contactors within a set time — without naming parts; the technical safety concept allocates those requirements to hardware and software, such as a specific monitoring chip, diagnostic and contactor driver.
Also: functional safety concept, technical safety concept
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The discipline, standardised for vehicles in ISO 26262, of making sure electronic failures do not cause harm. Battery functions such as overvoltage protection are classified by risk into ASIL levels A to D, which set how redundant and verified their hardware and software must be.
Also: ASIL
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A link that melts and opens the circuit when current exceeds its rating. Packs use a main fuse in the high-voltage path and often a small fuse on each parallel cell connection, so one shorted cell does not drain its neighbours into the fault.
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Choosing the ratings of fuses and breakers in series so that a fault opens only the device nearest to it and the remainder of the system keeps running. For fuses, the downstream fuse’s total clearing I²t must stay below the upstream fuse’s pre-arcing I²t; in a pack, a cell or module fuse should act before the main fuse or pyrofuse.
I²t_clearing(downstream) < I²t_pre-arcing(upstream) Also: selectivity, discrimination, protection coordination
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The ISO 26262 numbers showing that random hardware failures are under control. The single-point and latent fault metrics are the shares of failures that safety mechanisms cover — at least 99% and 90% for ASIL D — and PMHF is the residual rate of violating a safety goal, below 10⁻⁸ per hour (10 FIT) for ASIL D.
Also: single-point fault metric, latent fault metric, probabilistic metric for random hardware failures, hardware architectural metrics
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The ISO 26262 step that lists the hazards a function could cause, rates each in its driving situation for severity (S0–S3), exposure (E0–E4) and controllability (C0–C3), and combines them into an ASIL or QM. Each hazard becomes a safety goal, such as ‘prevent cell overcharge leading to thermal runaway’, that the design must meet.
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A low-voltage signal loop threaded through every high-voltage connector and cover. Opening any of them breaks the loop and the BMS drops the contactors, so a technician cannot reach a live conductor.
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The brief current peak when a circuit is first energised, before its capacitors have charged or its magnetic parts have settled. Connected straight to a pack, an inverter’s empty DC-link capacitors would draw thousands of amperes, so a pre-charge circuit brings them to about 95% of pack voltage before the main contactor closes.
Also: inrush, surge current, switch-on surge
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An unintended low-resistance path between a high-voltage conductor and the chassis, from damaged insulation, coolant leaks or moisture. A vehicle’s high-voltage system floats free of the chassis, so a single fault drives no current; a second on the other pole completes a circuit through the chassis. The insulation monitor therefore flags the first before a second can arise.
Also: ground fault, earth fault, isolation fault, chassis fault
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The resistance between the high-voltage circuit and the vehicle chassis, which must stay above about 100 Ω per volt of pack voltage so a person touching the chassis is safe. An insulation monitoring device measures it continuously.
Unit: Ω/V Also: isolation resistance, IMD
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A resistor and small contactor that charge the inverter’s capacitors slowly before the main contactor closes. Without it the inrush into empty capacitors can reach thousands of amperes and weld the main contactor shut.
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A high-voltage disconnect fired by a small pyrotechnic charge on command, typically from the airbag controller in a crash. It cuts the pack from the vehicle in milliseconds, faster and more reliably than a contactor can open under fault current.
Also: pyrotechnic disconnect
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A structured argument, backed by evidence, that a system is acceptably safe for its intended use: hazard analysis, safety requirements, design analyses such as FMEA, and test and review results, all traced to one another. ISO 26262 requires one for every item with an ASIL, and a functional safety assessment reviews it before release.
Also: safety argument
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The line between circuits that need high-voltage protection and those that do not. UN R100 calls a circuit high voltage above 60 V DC or 30 V AC rms, up to 1500 V DC or 1000 V AC; ISO 6469-3 calls the same band voltage class B and anything lower class A. A 48 V system stays below the line.
Also: voltage class A, voltage class B, high-voltage threshold, HV, LV
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The laboratory techniques that look inside electrodes, interphases and electrolytes to see what a cell is made of and how it aged.
Electron microscopy of samples kept near liquid-nitrogen temperature, which spares beam-sensitive materials from damage. It produced the first atomic-resolution images of lithium-metal dendrites and their SEI in 2017 and is now a standard tool for lithium-metal anodes and other fragile interphases.
Also: cryo-TEM, cryogenic electron microscopy
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Feeding gas from an operating cell straight into a mass spectrometer, so each species is identified and quantified as it forms. It shows ethylene from ethylene carbonate reduction during formation, and the oxygen and carbon dioxide released by layered oxides at high state of charge, tying each gas to the voltage that made it.
Also: OEMS, online electrochemical mass spectrometry
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Heating a milligram sample at a steady rate and recording the heat it releases or absorbs. It gives the decomposition temperatures and heats of electrode materials and electrolyte, inputs to any thermal-runaway assessment.
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Mapping elements inside an electron microscope: the beam excites X-rays whose energies identify the elements present, giving composition maps alongside the image. It shows binder and conductive-carbon distribution, coatings and deposited transition metals, but lithium is effectively invisible to it.
Also: EDX, EDXS, EDS mapping
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A scanning electron microscope paired with an ion beam that mills material away at a chosen spot. It cuts clean cross-sections through particles and coatings, lifts out thin slices for TEM, and by alternately milling and imaging rebuilds an electrode’s microstructure in 3D for porosity and tortuosity.
Also: focused ion beam, FIB, plasma FIB, serial sectioning
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Identifying chemical bonds from the infrared wavelengths a sample absorbs. Battery labs use it to fingerprint electrolyte solvents and their ratios, organic SEI species such as lithium alkyl carbonates, and binders; the attenuated-total-reflectance mode probes electrode surfaces directly, and gas cells analyse vent gas online.
Also: infrared spectroscopy, IR spectroscopy, ATR-FTIR
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Separating the volatile components of a sample in a heated column and identifying each by its mass spectrum. It measures electrolyte composition and aging products such as transesterified solvents and oligomers; with thermal-conductivity detection it also quantifies hydrogen, carbon monoxide, carbon dioxide and hydrocarbons in cell and vent gas.
Also: gas chromatography, GC
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Dissolving a sample in acid, spraying it into an argon plasma of several thousand kelvin and measuring each element by the light it emits (OES) or by ion mass (MS). It is the reference method for cathode stoichiometry, lithium content, black-mass assays and the traces of dissolved transition metals on aged anodes, down to parts per billion.
Also: ICP-OES, ICP-AES, ICP-MS
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Methods using neutrons, which pass easily through steel cans but are strongly scattered or absorbed by lithium and hydrogen. Imaging shows electrolyte filling, gas and lithium distribution in whole cells; diffraction follows graphite staging and cathode phases in commercial cells while they cycle, and can catch lithium plating at low temperature.
Also: neutron radiography, neutron diffraction, neutron tomography
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Probing nuclei such as ⁷Li, ¹⁹F and ¹H in a strong magnetic field, where their resonance frequencies reveal their chemical surroundings. Solid-state ⁷Li NMR separates metallic lithium, shifted by about 250 ppm, from lithium in graphite or the SEI, so it can quantify plating even operando; solution NMR identifies electrolyte decomposition products.
Also: solid-state NMR, ⁷Li NMR, MAS NMR
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Measuring a cell inside its working environment rather than after taking it apart (ex situ): in situ means within the cell or its surroundings, operando means while it is actually charging or discharging. Operando methods catch transient states, such as phases or plated lithium that vanish during rest or disassembly.
Also: operando, in situ, in-situ, ex situ
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Opening an aged or failed cell in an inert glovebox and examining its electrodes by microscopy, diffraction and chemical analysis. It confirms which degradation mechanisms actually occurred rather than inferring them from voltage.
Also: teardown
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Imaging a surface with a focused electron beam at magnifications far beyond light microscopy. In battery work it shows particle cracking, plated lithium and coating morphology; cross-sections show the layer structure of an electrode.
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Recording a sample’s mass while heating it at a controlled rate in air or inert gas. The mass steps give the moisture, binder and carbon content of electrodes and the decomposition of salts, SEI species and residual lithium carbonate; coupled to a mass spectrometer or FTIR it also identifies the gases driven off.
Also: thermogravimetry, TGA-MS
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Sputtering the outermost atomic layers of a sample with a pulsed ion beam and weighing the ejected ions by how long they take to reach the detector. It detects every element, lithium and hydrogen included, at parts-per-million levels, and maps SEI fragments across a surface and, with a second sputter beam, in depth.
Also: SIMS, secondary ion mass spectrometry
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Quantifying metallic lithium in a cycled electrode by reacting it with water and measuring the hydrogen released by gas chromatography. Most SEI lithium compounds give off no hydrogen, so the method separates dead metallic lithium from SEI lithium down to about a microgram; it showed that unreacted metal dominates capacity loss in lithium-metal cells.
2Li + 2H₂O → 2LiOH + H₂ Also: water titration, inactive lithium quantification
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Imaging by passing an electron beam through a specimen thinner than about 100 nm, fine enough to resolve rows of atoms. It reveals the nanometre-thick rock-salt layer that forms on aged nickel-rich particles, the structure of SEI and CEI, and cracks within particles; specimens are usually thinned with a focused ion beam.
Also: STEM, HRTEM
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Taking X-ray images of an object from hundreds of angles and reconstructing them into a 3D volume, without opening it. On whole cells it reveals jelly-roll deformation, electrode overhang, weld defects and foreign particles; at higher resolution it maps electrode porosity, and fast synchrotron CT has filmed thermal runaway as it happens.
Also: X-ray CT, micro-CT, nano-CT, CT scan
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Identifying crystal structures from the angles at which they scatter X-rays. It tracks lithium content and phase changes in electrode materials, and operando XRD follows them while the cell cycles.
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Exciting a sample with X-rays and reading the characteristic X-rays each element re-emits — a fast, largely non-destructive composition measurement. It checks nickel, manganese and cobalt ratios, coating loading and black-mass grades, and finds transition metals deposited on aged anodes, but it cannot detect lithium.
Also: XRF spectroscopy
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Shining X-rays on a surface and measuring the energies of the electrons knocked out, which identify each element and its chemical bonding in the top few nanometres. It is the main tool for SEI and CEI composition — LiF, Li₂CO₃, organic carbonates — and, combined with argon-ion sputtering, for depth profiles.
Also: ESCA, photoelectron spectroscopy
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The regulations and standards a vehicle battery must meet to be approved, and the rules for shipping batteries by road, sea and air.
Title 49 of the US Code of Federal Regulations, whose Hazardous Materials Regulations, issued by PHMSA, govern shipping batteries within and from the United States. Section 173.185 covers lithium cells and batteries: every design must pass UN 38.3, small cells and batteries get lighter rules, and damaged or recalled ones may travel only by road, rail or vessel.
Also: Hazardous Materials Regulations, HMR, PHMSA, 49 CFR 173.185
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The international agreements for carrying dangerous goods by road (ADR, under UNECE), rail (RID, under OTIF) and inland waterway (ADN), revised together every two years in line with the UN Model Regulations. They set how lithium cells and batteries are classified, packed, marked and documented on land; the rules for damaged or defective batteries sit in special provisions 376 and 377.
Also: ADR, RID, ADN
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The approval route for batteries on aircraft. In the US, advisory circular AC 20-184A, reissued in 2026, gives an accepted way to show that installed rechargeable lithium batteries are safe, including thermal-runaway containment demonstrated with every cell in runaway. In Europe, EASA’s Special Condition SC E-19 sets requirements for electric and hybrid propulsion systems, including the propulsion battery and its management system.
Also: EASA SC E-19, SC E-19, AC 20-184A, FAA AC 20-184
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Written permission from a national authority designated under dangerous-goods law to ship what the standard provisions do not allow. By air under the IATA DGR, prototype lithium batteries not yet tested to UN 38.3, or batteries over 35 kg on cargo aircraft, need approval from the State of Origin; by road, an authority can authorise conditions for critically defective batteries.
Also: competent authority, State of Origin approval
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The US Consumer Product Safety Commission’s proposed mandatory rule for lithium-ion batteries in e-bikes, e-scooters and similar products, published in June 2026. It would require e-bikes to meet UL 2849, other personal e-mobility products UL 2272 and standalone replacement packs UL 2271, each with CPSC changes, and adds requirements and warnings for aftermarket chargers.
Also: UL 2849, UL 2272, UL 2271
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The European safety standard for lithium batteries in light electric vehicles — e-bikes, scooters and other LEV — covering cell and pack abuse tests and the protective functions of the pack electronics.
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A notional lithium mass, 0.3 g per ampere-hour of rated capacity, once used to classify lithium-ion batteries for transport; its 8 g battery limit corresponded to about 100 Wh. The rules now rate lithium-ion by watt-hours and lithium-metal batteries by their actual lithium mass, the lightest regime allowing 1 g per cell and 2 g per battery.
ELC = 0.3 g/Ah × rated capacity Unit: g
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The US vehicle safety standard that replaces FMVSS 305 and largely adopts GTR 20. Besides protection against electric shock and electrolyte spillage, it adds requirements for the traction battery itself — overcharge, short-circuit and over-temperature protection, management of vented gases, water exposure — and extends coverage to heavy vehicles. The December 2024 final rule applies from September 2027 for light vehicles and 2028 for heavy ones.
Also: FMVSS No. 305a
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China’s mandatory safety specification for electric bicycles. The 2024 edition, in force since September 2025, caps design speed at 25 km/h, limits plastic parts to 5.5 % of the bike’s mass to reduce fire load, and requires battery and charger to recognise each other before charging. The lithium-ion battery itself must meet the companion standard GB 43854.
Also: GB 43854, e-bike safety standard
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China’s mandatory safety standard for electric vehicles with high-voltage (class B) systems: high-voltage marking, protection against direct and indirect contact, waterproofing, and requirements on the traction battery, collision protection and charging interfaces. The current edition, GB 18384-2025, applies from July 2026 and also covers underbody protection, warnings and event data recording.
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China’s mandatory national safety standard for electric-vehicle traction batteries. Its 2025 revision, mandatory from July 2026, requires that a single-cell thermal runaway produce no fire or explosion in the pack, going beyond the five-minute warning of earlier rules.
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China’s national standard of test methods for the electrical performance of lithium-ion traction battery packs and systems. The 2023 edition merged the former part 1, for high-power packs, and part 2, for high-energy packs; the former safety part, GB/T 31467.3, was superseded by the mandatory GB 38031.
Also: GB/T 31467.1, GB/T 31467.2, GB/T 31467.3
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China’s 2015 safety standard for lithium-ion and nickel–metal hydride traction cells and modules, with abuse tests such as overcharge, over-discharge, short circuit, drop, heating, crush and nail penetration, plus seawater immersion and low pressure for cells. Together with GB/T 31467.3 for packs, it was superseded in 2021 by the mandatory GB 38031.
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China’s technical specification for battery management systems in electric vehicles: requirements, test methods and inspection rules for the BMS of lithium-ion and nickel–metal hydride traction batteries, in force since October 2020. It gives Chinese vehicle makers and BMS suppliers a shared basis for specifying and testing the control electronics.
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The UN Global Technical Regulation on electric vehicle safety, the basis of national rules in Europe, China, Japan and elsewhere. Its thermal propagation clause requires a warning to occupants at least five minutes before a hazardous condition in the cabin.
Also: UN GTR No. 20, EVS-GTR
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The airline industry’s manual for shipping dangerous goods by air, built on the ICAO Technical Instructions and reissued every year. Lithium batteries fall under packing instructions 965–967 for lithium-ion — alone, packed with or inside equipment — and 968–970 for lithium metal. Lithium-ion batteries shipped alone must be at no more than 30 % state of charge; from 2026 so must those packed with equipment above 2.7 Wh.
Also: IATA DGR, packing instruction 965
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The IEC standard setting test methods and requirements that keep primary and rechargeable lithium cells and batteries safe while they are shipped; transport for recycling or disposal is outside its scope. It closely tracks the UN 38.3 test sequence, with an annex listing where the two differ. The current edition is the fourth, of 2019, amended in 2021 and 2023.
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The international standard series for lithium-ion cells in electric vehicles: part 1 performance testing, part 2 reliability and abuse testing, part 3 safety requirements. It fixes test conditions so results from different labs can be compared.
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The IMO’s code for carrying packaged dangerous goods by sea, mandatory under the SOLAS convention since 2004 and amended every two years. It sets how lithium and sodium-ion batteries are classified, packed, stowed and segregated on ships; amendment 42-24, mandatory from 2026, added separate entries for lithium-ion, lithium-metal and sodium-ion battery-powered vehicles.
Also: International Maritime Dangerous Goods Code
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The international standard for testing lithium-ion battery packs and systems in electric vehicles, covering performance, reliability and abuse at pack level. Part 4 is the current performance specification.
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The ISO series defining environmental conditions and tests for electrical and electronic equipment in road vehicles: part 2 electrical loads, part 3 mechanical, part 4 climatic and part 5 chemical. It is the usual basis for qualifying vehicle control units, battery electronics included; high-voltage traction packs are pointed instead to the parallel series ISO 19453, part 6.
Also: ISO 19453
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The ISO series on electric vehicle safety: part 1 the on-board rechargeable energy storage system, part 2 vehicle operational safety, part 3 electrical safety, part 4 post-crash. It is the engineering standard behind the regulatory tests of R100.
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China’s 2006 automotive-industry standard for lithium-ion batteries in electric vehicles, written around 3.6 V cells and modules built from them, with performance tests and abuse tests such as overcharge, short circuit, heating and crush. It is now listed as obsolete; traction batteries in China are tested to national standards such as GB 38031.
Also: QC/T 743-2006
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The part of UN R100 that tests the battery system as a unit: vibration, thermal shock and cycling, mechanical shock and crash impact, fire resistance, external short circuit, overcharge and over-discharge protection, over-temperature protection and, from the 03 series, thermal propagation. Each test ends with a check that there is no fire, explosion, electrolyte leakage or loss of isolation.
Also: REESS tests, R100 Annex 8
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The third series of amendments to UN R100, in force for new vehicle types from 2023. It added the thermal-propagation requirement — a warning to occupants at least five minutes before a hazardous event in the cabin, aligned with GTR 20 — plus documentation of the battery’s safe-state behaviour and a low-energy exemption for small systems.
Also: R100 03 series, R100 series of amendments 03
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The regulatory name, in UN R100 and GTR 20, for the whole traction battery as installed: cells, housing, management electronics, connectors and cooling. Tests apply to the REESS as a unit, which is why a cell approval alone is not a vehicle approval.
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RTCA’s environmental test procedures for airborne equipment — temperature, altitude, humidity, vibration, shock, power input, lightning, electromagnetic emissions and susceptibility, flammability and more — published in Europe as EUROCAE ED-14. Aircraft batteries and their electronics, like any airborne equipment, are qualified against the test categories it defines.
Also: EUROCAE ED-14, DO-160
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RTCA’s minimum operational performance standard for rechargeable lithium batteries and battery systems on aircraft, released in 2017. It sets design requirements and tests, including a thermal-runaway containment test, and is the performance standard behind the FAA’s technical standard order TSO-C179b for such batteries.
Also: DO-311A, TSO-C179b
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SAE’s recommended practice describing common designs of electric-vehicle battery modules — dimensions, terminations, retention, venting and other packaging features. It deliberately sets no performance requirements, which SAE handles in separate documents, and has been stabilised since 2016, meaning SAE does not plan to revise it.
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SAE’s procedure for vibration-durability testing of an electric-vehicle battery module or pack, usually on several samples. For large batteries — typically over 200 kg and part of the vehicle structure — it recommends a profile derived from measurements on the actual vehicle. Crash, pothole and abuse shocks are left to SAE J2464.
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SAE’s abuse-test procedure for vehicle battery systems, J2464, and the safety performance criteria for lithium-ion packs, J2929. They are the North American industry practice behind the regulatory tests, and define the familiar mechanical, thermal and electrical abuse sequences.
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The US safety-science organisation, founded in 1894 as Underwriters Laboratories, whose numbered standards — UL 1642, UL 2580, UL 9540, UL 9540A and others — define much of North American battery safety. Since 2022 it has operated as UL Standards & Engagement, which writes the standards, the commercial UL Solutions, which tests and certifies to them, and UL Research Institutes.
Also: Underwriters Laboratories, UL Solutions, UL Standards & Engagement
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The North American safety standard for electric-vehicle battery packs, covering electrical, mechanical and environmental abuse at pack level together with the protective electronics.
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The United Nations test sequence that every lithium cell and battery must pass before it can be shipped: altitude, thermal cycling, vibration, shock, external short, impact or crush, overcharge and forced discharge. Air shipment of cells also caps state of charge at 30 %.
Also: UN transport test, lithium battery shipping
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The UNECE electromagnetic-compatibility regulation for vehicles and their electronic sub-assemblies. A BMS or charger must show it neither emits interference nor fails under it, including while the vehicle is charging from the grid.
Also: ECE R10, automotive EMC
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The UNECE type-approval regulation for the electric powertrain of cars, buses and trucks, covering protection against electric shock and, in part II, the rechargeable energy storage system itself. A vehicle sold in the EU and most of the world must carry an R100 approval for its battery.
Also: ECE R100, UN ECE R100
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The UNECE regulation that applies the electric-powertrain and battery safety requirements of R100 to motorcycles, scooters and other L-category vehicles. It is the type-approval route for electric two- and three-wheelers in Europe.
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The German association of public-transport operators, whose published recommendations — the VDV-Schriften — have become de-facto specifications for buses across Europe. Several define how electric buses, their batteries and their charging are specified, tested and operated.
Also: Verband Deutscher Verkehrsunternehmen
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The VDV framework recommendation for the procurement of city buses: the technical requirements an operator writes into a tender, from dimensions and accessibility to the drivetrain. Its electric-bus parts reference the battery, charging and safety recommendations in the 26x series.
Also: VDV-Schrift 230
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The VDV recommendation on measuring the energy consumption of buses, including electric ones, by defined drive cycles. Together with the UITP SORT cycles it is how a tender states and checks the consumption, and therefore the range, of an electric bus.
Also: VDV-Schrift 238, SORT cycles
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The VDV recommendation on charging infrastructure for electric buses: depot charging, opportunity charging with pantographs, interfaces and the energy-management interaction with the vehicle. It builds on the OppCharge and SAE J3105 pantograph specifications.
Also: VDV-Schrift 261, e-bus charging
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The VDV recommendation on the IP-based on-board network of a bus, the basis of the European ITxPT architecture. It is how battery state, charging status and energy data from the vehicle reach the operator’s fleet systems in a standard form.
Also: VDV-Schrift 301, ITxPT
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Safety and performance standards for portable, industrial and grid batteries, their electronics and their installation.
The European adoption of IEC 62040-1, the safety standard for uninterruptible power systems with an AC output and an energy storage device — usually a battery behind a DC link — on low-voltage networks up to 1 000 V AC or 1 500 V DC. The battery room or cabinet itself also falls under IEC 62485-2.
Also: IEC 62040-1, UPS safety standard
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China’s national standard for lithium-ion batteries in electrical energy storage, covering cells and modules: electrical performance, environmental adaptability, durability and safety tests such as crush, drop, short circuit, insulation withstand and adiabatic temperature rise. The 2023 edition has applied since July 2024 and adds requirements for liquid-cooled modules.
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Two Chinese national standards for electrochemical storage on the grid: GB/T 36558 sets general technical requirements for storage systems in the power system — power control, efficiency, fault ride-through, frequency response, black start — and GB/T 36545 covers mobile, vehicle-mounted storage systems. Both were revised in 2023 and apply from July 2024.
Also: GB/T 36558, GB/T 36545
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The body that publishes the international standards for electrical technology, including IEC 62133 and IEC 62660 for cells and the IEC 60050 vocabulary, whose part 482 defines battery terms. National bodies adopt its standards with local prefixes.
Also: International Electrotechnical Commission
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Part 5 of the IEC primary-battery series: safety tests and requirements for non-rechargeable batteries with aqueous electrolyte, such as alkaline, zinc–carbon and zinc–air, covering both intended use and reasonably foreseeable misuse. Lithium primary batteries are covered separately, in part 4.
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The IEC test method behind the comparative tracking index (CTI) and proof tracking index (PTI) of solid insulating materials: drops of dilute ammonium chloride fall between two electrodes resting on the material until a conductive track forms. CTI is the highest voltage it survives for 50 drops and sets the material group used to size creepage distances; PTI confirms survival at one stated voltage.
Also: proof tracking index
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The IEC series on automatic electrical controls for household and similar use, whose part 1 covers the safety and functional safety of control electronics. It sorts safety software into classes: B guards against hazards from hardware faults, C must prevent hazards without other protective devices. Battery-management firmware can be assessed to these classes or the equivalent UL 1998, as when a BMS is recognised for UL 1973.
Also: IEC 60730-1, software class B
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The IEC pair for stationary valve-regulated lead–acid batteries in float service — telecoms, UPS, utility switching and emergency power. Part 21 sets the test methods; part 22 sets the requirements and explains the purpose of each test, so that a specifier can choose the ones that matter for an application.
Also: IEC 60896
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The IEC generic EMC standards for industrial environments: 61000-6-2 sets immunity to electrostatic discharge, bursts, surges, radiated and conducted RF and voltage dips, and 61000-6-4 limits emissions. They apply when no product-specific EMC standard exists, and battery-operated apparatus in industrial locations is explicitly within their scope.
Also: EN 61000-6-2, EN 61000-6-4, industrial EMC
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The safety standard for portable sealed cells and batteries, part 2 covering lithium systems. Passing it is a basic requirement for consumer products, and it is often the first safety certification a new cell obtains.
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The hazard-based safety standard for audio/video, information and communication technology equipment — laptops, phones, routers, servers — which replaced IEC 60950-1 and IEC 60065. Its Annex M sets requirements for the batteries and protection circuits inside such equipment, and was substantially revised for lithium batteries in the fourth edition of 2023.
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The general IEC safety standard for power electronic converter systems and equipment rated up to 1 000 V AC or 1 500 V DC. It is the safety basis for many inverters and DC–DC converters that connect batteries to loads and to the grid, and a reference for product standards on bidirectional converters.
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The installation standard for secondary batteries and battery installations: ventilation, protection against electric shock, and the layout of battery rooms. Part 2 covers stationary batteries, part 3 traction batteries for industrial trucks.
Also: EN 50272
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The safety standard for secondary lithium cells and batteries in industrial applications — stationary storage, forklifts, rail and marine — covering cell abuse tests plus battery-system functions such as overcharge and thermal control. It is the industrial counterpart of IEC 62133 for portable and IEC 62660 for vehicles.
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The performance standard for industrial lithium cells and batteries: how to measure and declare capacity, endurance, internal resistance and self-discharge, so that datasheets from different makers can be compared.
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The IEC standard for the in-cable control and protection device of a portable mode 2 charging cable — the box that detects residual current and disconnects the supply, protecting the user when a vehicle is charged from a household socket. The 2024 second edition adds temperature monitoring of the household plug.
Also: in-cable control and protection device
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The IEC safety standard for battery swap stations — systems that exchange an electric vehicle’s swappable battery — whether fed from the grid or from on-site buffer batteries, at up to 1 000 V AC or 1 500 V DC. It is read with part 1, the general system description; a second edition appeared in 2025.
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The IEC series for grid-integrated electrical energy storage systems, written at system level whatever the storage technology: part 2-1 defines unit parameters and test methods, part 5-1 gives general safety considerations, and part 5-2 adds safety requirements for battery-based systems over their whole life, from design to decommissioning.
Also: EES systems, IEC 62933-5-2
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The safety standard for lithium battery systems in electrical energy storage, building on IEC 62619 with system-level requirements for the electronics, enclosure and installation of stationary storage.
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The first part, published in 2022, of an IEC protocol series for managing electric-vehicle charging and discharging infrastructure: definitions, use cases and architecture for energy-transfer management, charger asset management, authentication and payment, and cybersecurity. Like OCPP, it governs the link between chargers and the systems that run them, and its scope includes discharging for vehicle-to-grid.
Also: IEC 63110
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IEEE standards for rechargeable batteries in mobile devices, chosen by pack layout: IEEE 1725 for a single cell or cells only in parallel, as in phones, and IEEE 1625 for packs with cells in series, as in laptops. They treat cell, pack, host device and charger as one system, and underpin CTIA battery certification.
Also: IEEE 1625, IEEE 1725, CTIA battery certification
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IEEE’s recommended practice for characterising and evaluating energy storage technologies in stationary applications, with a companion guide, 1679.1, for lithium-based batteries, revised in 2025. They give a structured way to judge a technology — description, ageing and failure modes, safety, evaluation methods and regulatory issues — before choosing it for a site.
Also: IEEE 1679, IEEE 1679.1
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IEEE’s guide, published in 2019, to the design, operation and maintenance of battery energy storage systems, stationary and mobile, integrated with the electric power system. It spans lead–acid, lithium-ion, flow and sodium–sulfur batteries and covers their grid connection alongside the batteries themselves.
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IEEE’s recommended practice for sizing stationary lead–acid batteries in float service: define the DC load as a duty cycle of currents over time, then choose the cell size and number that will carry it, with allowances for temperature, ageing and design margin. Charger sizing and other chemistries are outside its scope; the current revision dates from 2020.
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The ISO standard for safety-related parts of machine control systems. A risk assessment sets a required performance level from PL a to PL e, met through an architecture category (B, 1 to 4) and a low enough probability of dangerous failure per hour. It applies to cell-production machinery and to battery-powered machines such as automated guided vehicles.
Also: ISO 13849-1, performance level
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The three certifiable management-system standards that cell and pack makers are expected to hold: ISO 9001 for quality, ISO 14001 for environmental management and ISO 45001 for occupational health and safety. Automotive suppliers add IATF 16949, the industry’s quality-system standard built on ISO 9001.
Also: ISO 9001, ISO 14001, ISO 45001, IATF 16949
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The article of the US National Electrical Code for permanently installed energy storage systems above 50 V AC or 60 V DC, introduced in 2017: disconnecting means, ground-fault detection, battery location, ventilation and working space. Alongside it, NFPA 855 calls for detection to NFPA 72 and sprinklers to NFPA 13 at 0.3 gpm/ft², unless large-scale UL 9540A tests justify another density.
Also: NEC Article 706, National Electrical Code, NFPA 13, NFPA 72
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The US fire-protection standard for the installation of stationary energy storage systems: spacing between units, maximum energy per fire area, suppression, explosion control and the UL 9540A data needed to deviate from the defaults.
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The UK specification, published by BSI in 2024, for fire protection of battery storage in homes. It bars batteries from bedrooms, escape routes, lofts and voids, requires interlinked smoke detection where they sit in rarely visited spaces, and caps energy at 20 kWh per enclosure and 40 kWh per dwelling, or 80 kWh outdoors or in a separated garage.
Also: PAS 63100:2024
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The North American safety standard for lithium cells, tested by Underwriters Laboratories through a series of electrical, mechanical and environmental abuse tests. UL 2054 covers the batteries built from them.
Also: UL 2054
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The North American safety standard for inverters, converters, charge controllers and interconnection equipment used with distributed energy resources such as solar and battery storage. Its Supplement SB certifies grid-support functions, such as ride-through and voltage and frequency response, against the tests of IEEE 1547.1-2020, taking over from the earlier Supplement SA.
Also: UL 1741 SB, UL 1741 SA
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The North American safety standard for batteries in stationary storage, vehicle auxiliary power and light electric rail, covering cells, modules and the battery system with its management electronics. It centres on functional safety analysis of hardware and software alongside abuse tests, and a UL 1973 battery is what UL 9540 expects inside a complete energy storage system.
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The North American product safety standard for a complete energy storage system — battery, inverter and controls together — as opposed to UL 9540A, which is the test method for its thermal-runaway behaviour. Listing to UL 9540 is what most US fire codes require for installation.
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A test method, not a pass/fail standard, that characterises thermal runaway and propagation in stationary storage at cell, module, unit and installation level. Fire codes use its data to decide spacing and suppression for a storage site.
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Batteries beyond today’s lithium-ion: lead, nickel and primary cells, flow and metal–air batteries, solid-state and lithium-metal cells, and the multivalent and sodium chemistries in development.
The common 1.5 V single-use cell, with a zinc negative electrode and manganese dioxide positive in potassium hydroxide electrolyte. It is the reference point for most people’s idea of a battery, and is not rechargeable.
Also: zinc–manganese dioxide
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A rechargeable cell with an aluminium-metal negative electrode, usually in a chloroaluminate ionic liquid, in which chloroaluminate anions rather than bare Al³⁺ ions shuttle and intercalate into a graphite or graphene positive. Demonstrations reach about 2 V and thousands of fast cycles, but the positive’s low capacity keeps energy density modest; graphene versions are pursued commercially.
Also: aluminum-ion battery, graphene aluminium-ion battery
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A primary cell that oxidises an aluminium plate with oxygen from the air in an alkaline or saline electrolyte. Aluminium’s theoretical specific energy is about 8 kWh/kg, so practical cells are very energy-dense, but they cannot be recharged electrically: the spent hydroxide must be collected and smelted back into metal, and the plate corrodes while idle.
Also: aluminum-air battery
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An aqueous battery whose charge carrier is the ammonium ion, NH₄⁺, a light, non-metallic cation that hops through host lattices by forming and breaking hydrogen bonds. Hosts include Prussian blue analogues, molybdenum and vanadium oxides and organic polyimides. It is cheap and non-flammable but still at the research stage, held back by low voltage.
Also: NH₄⁺ battery, aqueous ammonium-ion battery
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A lithium-metal cell assembled with bare copper foil as the negative electrode; the first charge plates all its lithium out of the positive material. It maximises energy density but every lost lithium atom is lost capacity.
Also: zero-excess lithium
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Any battery whose electrolyte is water-based, from lead–acid and nickel–metal hydride to aqueous zinc-ion and sodium-ion designs. Water is cheap, non-flammable and highly conductive, but it splits at 1.23 V in theory and around 2 V in practice, which caps cell voltage and energy density.
Also: water-based battery, aqueous electrolyte battery
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A rechargeable cell with a zinc-metal negative and mildly acidic zinc sulfate electrolyte, in which Zn²⁺ ions and protons insert into a manganese oxide or vanadium oxide positive. It is cheap, non-flammable and runs at about 1.3–1.5 V, aimed at stationary storage; dendrites, hydrogen evolution and dissolution of the positive limit cycle life.
Also: zinc-ion battery, Zn-ion, ZIB
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A battery built from bipolar electrodes: one shared current collector carries positive material on one face and negative material on the other, so stacked layers form cells in series inside one housing. Current flows straight through the stack instead of through tabs and busbars, cutting resistance and parts; Toyota’s 2021 Aqua hybrid used a bipolar nickel–metal hydride pack.
Also: bipolar electrode, bipolar stacking
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A battery shuttling divalent Ca²⁺ ions, attractive because calcium is abundant and its metal sits only about 0.17 V above lithium’s potential while carrying two charges per atom. Practical cells remain elusive: calcium metal passivates in most electrolytes, reversible plating at room temperature was first shown in 2018, and Ca²⁺ moves slowly through host lattices.
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The rating of a starter battery: the current it can deliver for 30 seconds at −18 °C while staying above 7.2 V for a 12 V battery. It measures power in the cold, which is what starting an engine needs, not energy.
Unit: A
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A cell in which both ions of the salt do work: on charge, cations enter the negative electrode while anions such as PF₆⁻ intercalate into a graphite positive at about 4.5–5 V. The electrolyte is therefore an active material whose salt content limits capacity, and it must survive very high voltage; the payoff is cheap, cobalt-free electrodes.
Also: dual-graphite battery
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The traditional lead–acid construction with free liquid electrolyte, vents and removable caps for topping up with water. It is cheap and tolerant of overcharge but must stay upright and be maintained.
Also: vented lead–acid, wet cell
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A battery whose energy is stored in liquid electrolytes held in external tanks and pumped through a reaction stack. Energy and power scale independently, which suits long-duration grid storage; vanadium is the most developed chemistry.
Also: vanadium redox flow battery, VRFB
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A battery in which fluoride anions, F⁻, shuttle between metal and metal-fluoride electrodes, such as copper or bismuth fluoride positives, through conversion reactions. Theoretical energy densities exceed lithium-ion, but early cells needed solid electrolytes at about 150 °C; room-temperature cycling with a liquid electrolyte was first reported in 2018, and cycle life remains short.
Also: F-ion battery
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An electrochemical converter that makes electricity from a fuel, usually hydrogen, and oxygen as long as both are supplied, rather than storing energy in its electrodes. Fuel-cell vehicles still carry a battery to buffer power.
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A hybrid flow battery pairing a hydrogen gas electrode, built like a fuel cell’s, with a liquid bromine–bromide electrode, for about 1.1 V. Fast kinetics on both sides give very high power density and hydrobromic acid is cheap; the obstacles are corrosive, toxic bromine attacking the platinum catalyst and membrane, and storing the hydrogen.
Also: HBr flow battery, H2-Br2 flow battery
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A rechargeable alkaline cell that oxidises iron to iron hydroxide — reversible rusting — with oxygen drawn from the air, then reduces it back on charge. Iron is cheap enough that systems built for about 100 hours of discharge make sense for multi-day grid storage, though round-trip efficiency is low and hydrogen evolution on the iron wastes charge.
Also: Fe–air battery, rust battery
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The first modern redox flow battery, developed by NASA in the 1970s, using Fe³⁺/Fe²⁺ and Cr³⁺/Cr²⁺ couples dissolved in hydrochloric acid for about 1.2 V. Both metals are cheap, but ions cross the membrane and the chromium side evolves hydrogen, so cells run warm with catalysts and rebalancing; vanadium chemistry largely displaced it.
Also: Fe–Cr flow battery
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The oldest rechargeable chemistry, lead and lead dioxide electrodes in sulfuric acid, at 2 V per cell. Heavy and short-lived in deep cycling but cheap, recyclable and good at cold cranking, it still starts most cars and backs up most telecom sites.
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A cell of three liquid layers that settle by density: a light liquid metal such as lithium or calcium on top, a molten-salt electrolyte in the middle and a dense metal such as antimony or lead–antimony at the bottom. Operating around 450–500 °C, it has no solid electrodes to crack or wear, promising very long life for grid storage.
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A rechargeable cell whose negative electrode is lithium metal rather than a host material. It promises much higher energy density than lithium-ion, but lithium deposits unevenly on charge, so dendrites and short life have kept it from the mass market.
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A cell in which lithium metal reacts with oxygen at a porous carbon positive, forming lithium peroxide on discharge. Counting the peroxide’s mass, theoretical specific energy is about 3,500 Wh/kg, several times lithium-ion. Insulating peroxide clogs the electrode, charging needs large overpotentials, and moisture and CO₂ in real air poison the reaction.
Also: lithium–oxygen battery, Li–air
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A primary cell whose positive electrode is fluorinated carbon, CFx. Its theoretical specific energy, about 2,180 Wh/kg, is the highest of the commercial primary chemistries, and self-discharge is very low; under load it delivers around 2.5–2.8 V. It powers medical implants, military and space equipment and long-life sensors, but heats noticeably at high rates.
Also: Li/CFx, BR cell, lithium polycarbon monofluoride
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A primary cell with a lithium negative and an iron disulfide positive that gives 1.5 V, so it replaces alkaline AA and AAA cells directly. It is about a third lighter, holds its voltage under high-drain loads such as camera flashes, works down to −40 °C and keeps for many years on the shelf.
Also: lithium iron disulfide, FR6, 1.5 V lithium AA
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The most common lithium primary chemistry: a lithium-metal negative, a heat-treated manganese dioxide positive and an organic electrolyte, giving 3 V. It fills CR-coded coin cells such as the CR2032 and cylindrical CR123A camera cells, and loses only about 1 % of its capacity a year in storage.
Also: CR cell, lithium coin cell, CR123A
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A cell pairing a lithium-metal negative electrode with a sulfur positive electrode, which is cheap, light and converts rather than intercalates. Theoretical specific energy is very high; dissolving polysulfides and short cycle life are the obstacles.
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A 3.6 V primary cell in which liquid thionyl chloride is both the electrolyte solvent and the positive reactant, reduced on a porous carbon electrode. A protective lithium chloride film keeps self-discharge around 1 % a year, so cells run utility meters and trackers for 10–20 years, but it also causes a voltage delay when a load is first applied.
Also: ER cell, lithium thionyl chloride
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A battery with a magnesium-metal negative electrode shuttling divalent Mg²⁺ ions. Magnesium stores about 3,830 mAh per cubic centimetre, nearly twice lithium metal, and plates with less tendency to form dendrites. Progress is slow because the doubly charged ion diffuses sluggishly in most hosts; a 2000 prototype used a Chevrel-phase Mo₆S₈ positive at about 1.1 V.
Also: magnesium battery, rechargeable magnesium battery
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A 1.2 V aqueous cell, rugged and able to deliver very high currents, but containing toxic cadmium and prone to the memory effect. It is now restricted in most consumer uses and survives in aviation and emergency lighting.
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A cell pairing a nickel oxyhydroxide positive with hydrogen gas on a platinum-catalysed electrode, sealed in a pressure vessel whose pressure tracks state of charge. With no negative electrode to wear out it lasts tens of thousands of cycles, powering satellites, the Hubble Space Telescope and, until lithium-ion replaced it, the International Space Station.
Also: Ni–H₂
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A 1.2 V alkaline rechargeable cell with a nickel oxyhydroxide positive and iron negative, developed by Jungner and Edison around 1900. It is nearly indestructible, tolerating overcharge, deep discharge and decades of use, but low energy density, high self-discharge, hydrogen gassing and poor efficiency confined it to railways, mines and off-grid storage.
Also: Edison cell, Edison battery
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A 1.2 V aqueous cell with a nickel hydroxide positive electrode and a hydrogen-absorbing alloy negative. It powered hybrid cars for two decades and is tolerant of abuse, but lithium-ion stores two to three times more energy per kilogram.
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An alkaline rechargeable cell with a nickel oxyhydroxide positive and zinc negative, giving about 1.6 V — more than NiMH — with good power and no flammable electrolyte. Zinc dissolves and redeposits unevenly, changing shape and growing dendrites, which limits cycle life; it is used in AA cells and in high-power backup supplies for data centres.
Also: Ni–Zn
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An active material made of carbon-based molecules or polymers, such as quinones, imides or nitroxide radicals, that store charge by reversible redox of their functional groups. They need no mined metals, work with lithium, sodium, potassium and zinc ions alike, and can be tuned by chemistry; dissolution in the electrolyte, low density and poor conductivity are the obstacles.
Also: organic cathode, organic battery, redox-active polymer
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A positive material built from transition metals and polyanion groups such as PO₄³⁻, SO₄²⁻ or P₂O₇⁴⁻. The strongly bonded groups raise the voltage through the inductive effect and hold oxygen tightly, giving long life and safety at some cost in capacity and conductivity. LFP is the lithium example; Na₃V₂(PO₄)₂F₃ and iron-based Na₄Fe₃(PO₄)₂P₂O₇ serve sodium-ion cells.
Also: polyanion cathode, NVPF, NFPP, phosphate cathode
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A rocking-chair cell shuttling K⁺ ions. Unlike sodium, potassium intercalates into ordinary graphite, forming KC₈ at 279 mAh/g, and its low redox potential allows high cell voltage; potassium is also abundant. The large ion makes graphite swell by about 60 % and strains positives, so Prussian blue analogues with wide channels lead as cathodes.
Also: KIB
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A cell designed to be discharged once and not recharged, such as an alkaline or lithium–manganese dioxide cell. Its reaction is not reversible in practice, unlike the secondary cells this glossary is mostly about.
Also: non-rechargeable battery
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An open-framework compound, AₓM[Fe(CN)₆], in which iron–cyanide units and another metal form a cubic cage with wide channels for large ions. Made at low temperature from cheap elements, its sodium-rich form, Prussian white, is a leading sodium-ion cathode. Water trapped in the lattice degrades cells, and the cyanide groups raise questions in thermal runaway.
Also: Prussian white, hexacyanoferrate
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A starter-battery rating: the minutes a fully charged 12 V battery can deliver 25 A at 27 °C before falling to 10.5 V. It describes how long the vehicle’s electrics run if the alternator fails.
Unit: min
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A battery that uses seawater as its electrolyte or positive reactant. Seawater-activated primaries, such as magnesium–silver chloride cells, sit dry for years and start when immersed, powering sonobuoys and life-jacket lights. Rechargeable versions pull sodium ions from seawater through a NASICON ceramic into a sealed negative electrode, with oxygen reactions on the open seawater side.
Also: seawater-activated battery, rechargeable seawater battery
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A cell whose reaction runs in both directions, so it can be recharged by driving current back into it. Lithium-ion, lead–acid and nickel–metal hydride are all secondary chemistries.
Also: rechargeable battery
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A cell that uses a gel or a solid electrolyte together with a small amount of liquid to keep the interfaces conducting. It is a stepping stone between liquid and all-solid-state cells, and already ships in some vehicles.
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A primary button cell with a silver oxide positive and zinc negative in alkaline electrolyte, giving 1.55 V on an exceptionally flat curve until nearly empty. That stability suits quartz watches and precision instruments; the cells carry SR codes such as SR626SW.
Also: SR cell, silver oxide button cell
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A rechargeable alkaline cell with a silver oxide positive and zinc negative, about 1.5 V, with exceptional energy and power for its era. High cost and a life of tens to hundreds of cycles kept it to missions where performance outweighed both, such as torpedoes, missiles and the Apollo lunar module.
Also: silver oxide–zinc battery
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A cell built like a lithium-ion cell but shuttling sodium ions, usually between a hard-carbon negative electrode and a layered oxide or Prussian-blue positive. It uses no lithium, cobalt or copper, at the cost of lower energy density.
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A high-temperature cell, run at about 270–350 °C, with molten sodium as negative, nickel and nickel chloride in molten sodium tetrachloroaluminate as positive, and a β″-alumina ceramic electrolyte between them, giving 2.58 V. Failed cells fail to low resistance, so a series string keeps working; it has served in buses, telecom backup and grid storage.
Also: Na–NiCl₂, molten-salt battery
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A high-temperature cell of molten sodium and molten sulfur separated by a β″-alumina ceramic electrolyte, operating at about 300–350 °C and giving roughly 2 V. Made commercially by NGK in Japan since the early 2000s, it has supplied hundreds of megawatts of six-hour grid storage; heater losses and fire risk from molten reactants are its drawbacks.
Also: Na–S, sodium sulphur battery
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A cell whose electrolyte is a solid rather than a liquid. It removes the flammable solvent and may allow a lithium-metal anode, but needs intimate solid–solid contact and, for most chemistries, stack pressure to keep it.
Also: all-solid-state battery
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The growth of hard lead sulfate crystals on lead–acid plates when a battery is left discharged, which no longer convert back on charging. It is the usual way a neglected lead–acid battery dies, and has no counterpart in lithium-ion.
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A lead–acid battery whose electrolyte is immobilised in glass-fibre mats (AGM) or a gel, with a pressure valve instead of open vents, so it can be used in any orientation without maintenance. It recombines the gases of overcharge internally.
Also: sealed lead–acid, SLA, AGM, gel battery
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A cell whose positive electrode uses oxygen from the air, so almost all its volume is zinc and its energy density is very high. It powers hearing aids as a primary cell; rechargeable versions are being developed for grid storage.
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A hybrid flow battery: on charge, zinc plates onto the negative electrode while bromine forms at the positive and is captured by a complexing agent into an oily phase stored in a tank. The cell gives about 1.8 V from cheap materials, but zinc dendrites, corrosive bromine and periodic full discharges to strip the zinc complicate operation.
Also: zinc–bromine flow battery, ZBFB
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The original dry cell, descended from Georges Leclanché’s 1866 design: a zinc can as negative, manganese dioxide packed around a carbon rod as positive, and an ammonium chloride or zinc chloride paste. It gives 1.5 V at the lowest cost but holds far less than an alkaline cell and tends to leak as the can is consumed.
Also: Leclanché cell, heavy-duty cell, carbon-zinc battery
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What sits between the electrodes: liquid, gel and solid electrolytes, their salts, solvents and additives, and the separator that keeps the electrodes apart.
An electrolyte based on acetonitrile, CH₃CN, a solvent of very low viscosity and high polarity that gives excellent ionic conductivity. It is standard in supercapacitors, but in lithium-ion cells it is reduced on graphite unless the salt is superconcentrated, an approach shown to allow very fast charging. It is flammable and toxic.
Also: acetonitrile, CH₃CN, nitrile electrolyte
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The organic liquids that dissolve the lithium salt: cyclic ethylene carbonate, which forms a stable SEI, blended with linear carbonates such as DMC or EMC to lower viscosity. All are flammable, which is a root of lithium-ion fire risk.
Also: EC, DMC, EMC, DEC
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In a solid-state cell, the solid electrolyte mixed into the positive electrode so ions can reach every particle, as liquid does in a conventional cell. It can be a different material from the separator layer.
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A polyolefin separator coated with a thin layer of alumina or boehmite particles. The ceramic raises the temperature at which the film shrinks, so the electrodes stay apart longer in a thermal event.
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A linear carbonate solvent with a higher boiling point and viscosity than DMC, used in blends that must tolerate higher temperatures. Typical electrolytes mix EC with one or two of DMC, EMC and DEC.
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A linear carbonate solvent, thin and volatile, blended with EC to cut viscosity and raise ionic conductivity. Its low boiling point, about 90 °C, is part of why cell electrolytes are flammable.
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The two routes to a porous polyolefin film. The dry process extrudes polypropylene or a PP/PE/PP trilayer, anneals it and stretches it lengthwise so slit-like pores open, with no solvent. The wet process mixes polyethylene with paraffin oil, stretches the sheet both ways and extracts the oil, giving thinner, stronger, more uniform films — the usual choice for EV cells.
Also: dry-process separator, wet-process separator, uniaxially stretched separator, biaxially stretched separator
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The ion-conducting medium between the electrodes. In a liquid-electrolyte cell it fills the pores of both electrodes and the separator, so it is not a separate structural layer.
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A compound added to the electrolyte at a few percent to improve one property — vinylene carbonate and fluoroethylene carbonate build a tougher SEI, others suppress gassing or overcharge. Additive packages are among a cell maker’s closest secrets.
Also: VC, FEC
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A linear carbonate solvent, the most common co-solvent in commercial electrolytes, balancing viscosity, boiling point and low-temperature performance between DMC and DEC.
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The cyclic carbonate solvent that every graphite cell needs: it is reduced on the first charge into the stable SEI that lets graphite work at all. It is solid at room temperature, so it is always blended with linear carbonates.
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A cyclic sulfate, 1,3,2-dioxathiolane 2,2-dioxide, added to electrolytes at about 1–2 %, often together with vinylene carbonate. It is reduced on the negative electrode during formation, leaving a sulfur-containing SEI, and keeps cell impedance lower than VC alone would. It is used in both lithium-ion and sodium-ion electrolytes.
Also: 1,3,2-dioxathiolane 2,2-dioxide, DTD additive, glycol sulfate
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An electrolyte whose solvents largely carry fluorine — fluorinated carbonates such as FEC, or fluorinated ethers used as diluents. Fluorine draws electron density from the solvent, raising its oxidation stability towards 5 V, and its reduction leaves a lithium-fluoride-rich SEI. That suits high-voltage cathodes and lithium metal, at higher cost and with PFAS concerns.
Also: fluorinated solvent, all-fluorinated electrolyte
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A fluorinated additive, sometimes a co-solvent, that forms a lithium-fluoride-rich SEI able to survive the large volume changes of silicon and lithium-metal electrodes. It is almost universal in silicon-blend cells.
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A polymer matrix swollen with liquid electrolyte, so the cell behaves like a liquid cell but does not leak. It is what most “lithium polymer” pouch cells actually contain, and what “semi-solid” cells use.
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A newer solid electrolyte family of lithium metal chlorides and bromides, stable at the high voltage of layered oxide cathodes where sulfides decompose, but unstable against lithium metal. Cells often pair a halide catholyte with a sulfide separator.
Also: Li₃YCl₆, Li₃InCl₆
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An electrolyte with so much salt, often 3–5 mol/L instead of the usual 1, that nearly every solvent molecule is bound to a lithium ion. Anions then decompose first and build a robust inorganic interphase, and oxidation stability rises. Viscosity and cost are high, so localised versions dilute it with a non-solvating fluorinated ether that keeps the clustered solvation structure.
Also: superconcentrated electrolyte, localised high-concentration electrolyte, LHCE, water-in-salt electrolyte
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An electrolyte based on a salt that is liquid at room temperature, with negligible vapour pressure and so no flammability. High viscosity, cost and poor graphite compatibility have confined it to niche cells.
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A salt with higher conductivity and far better thermal and moisture stability than LiPF₆, increasingly blended with it or used in fast-charge and lithium-metal electrolytes. Its drawback is corrosion of aluminium at high voltage unless LiPF₆ is also present.
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A borate salt used as an additive at a few percent to stabilise the SEI and the aluminium collector at high voltage and temperature; LiDFOB is its fluorinated relative with better solubility.
Also: LiDFOB
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A very stable imide salt used in polymer and solid-state electrolytes and in research cells. Like LiFSI it attacks aluminium current collectors above about 3.7 V, which keeps it out of mainstream liquid cells.
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A salt-type additive, LiPO₂F₂, used at around 1 % because it dissolves only sparingly in carbonate solvents. It forms thin phosphate-rich films on both electrodes that lower interfacial resistance, improving low-temperature power and high-voltage cycling. Small amounts also form naturally when LiPF₆ meets traces of water.
Also: LiPO₂F₂
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The lithium salt in nearly every commercial electrolyte, chosen for conductivity, aluminium passivation and cost rather than stability: it decomposes above about 60 °C and reacts with water to form HF.
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The dissolved salt that supplies the mobile lithium ions in a liquid electrolyte, almost always lithium hexafluorophosphate, LiPF₆, at about one mole per litre. It reacts with traces of water to form hydrofluoric acid, which is why cells are filled in a dry room.
Also: LiPF₆, LiFSI
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The leading oxide solid electrolyte, a garnet-structured Li₇La₃Zr₂O₁₂ stable against lithium metal. It conducts about 1 mS/cm but is brittle and needs sintering above 1000 °C, which drives its production route.
Also: lithium lanthanum zirconium oxide, garnet electrolyte
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Oxide solid electrolytes with the sodium-superionic-conductor structure, such as lithium aluminium titanium phosphate. They are stable in air and against high-voltage cathodes but are reduced by lithium metal, so they need a protective interlayer.
Also: LATP, LAGP
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The two commodity polyolefins of a cell. Almost every separator is PE, PP or a layered combination: PE melts near 130 °C and closes its pores, while PP keeps its shape to about 165 °C. PP also forms the heat-sealing inner layer of pouch foil, and both appear in packs as insulating films and moulded parts.
Also: polyolefin, polyethylene, polypropylene
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A dry polymer, classically polyethylene oxide with a dissolved lithium salt, that conducts ions through segmental motion of its chains. It is flexible and easy to process but needs 60–80 °C to reach useful conductivity, which has limited it to heated packs.
Also: PEO
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A cyclic carbonate with a wide liquid range and low freezing point, but one that co-intercalates into graphite and exfoliates it unless a good SEI is formed first. It is used in small amounts, in low-temperature blends and with non-graphite anodes.
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A porous, electronically insulating film between the electrodes. Electrons cannot cross it; ions move through the electrolyte in its pores.
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A solid ion conductor that replaces the liquid electrolyte in an all-solid-state cell. Oxide, sulfide, halide and polymer families each need a different production route.
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The solid electrolyte family with the highest conductivity — argyrodites such as Li₆PS₅Cl match liquids, and LGPS exceeds them — and soft enough to be pressed rather than sintered. Their weakness is reaction with moisture, which releases hydrogen sulfide.
Also: LPSCl, argyrodite, LGPS
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A solid in which one ion species moves almost as freely as in a liquid, reaching the order of 1 mS/cm or more, while the rest of the lattice stays rigid. α-silver iodide above 147 °C is the classic case; Li₁₀GeP₂S₁₂ reaches about 12 mS/cm at room temperature. Such materials are the basis of solid electrolytes.
Also: fast-ion conductor, solid ionic conductor
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The most common SEI-forming additive, used at 1–3 %. It is reduced before the solvent on the first charge and polymerises into a thinner, more flexible SEI that lengthens cycle life.
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