Electrochemical stability window

Example

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Connect reaction sites and transport paths.

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Electrolyte decomposition

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.

HOMO–LUMO gap

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.

LNMO

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.

Solid–electrolyte interphase

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.

Voltage window

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.

References & further reading

Technical references

1. Electrolytes and Interphases in Li-Ion Batteries and Beyond

   Kang Xu · Chemical Reviews · 2014

   Technical reference · Electrolyte salts, solvents, additives and electrode interphases.

Further reading on this topic

These sources provide broader context; they are not presented as citations for every statement in this entry.

2. Quantities, Units and Symbols in Physical Chemistry, 3rd edition, 2nd printing

   IUPAC · 2011

   Topic background · Physical-chemistry notation, thermodynamics, electrochemistry and transport quantities.