{ "node": { "id": "term:cell-voltage", "type": "Term", "label": "Cell voltage", "properties": { "id": "cell-voltage", "name": "Cell voltage", "aka": [ "electromotive force", "EMF" ], "section": "topic-electrochemistry", "definition": "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.", "formula": "E = E₊ − E₋ = −ΔG / nF", "unit": "V", "related": [ "electrode-potential", "gibbs-free-energy", "open-circuit-voltage", "nominal-voltage" ], "example": { "title": "Subtract equilibrium electrode potentials", "text": "If two illustrative electrode potentials are 4.0 V and 0.2 V versus the same reference, their equilibrium cell voltage is 3.8 V. Under load, resistance and polarization change the measured terminal voltage." }, "url": "https://lemonergy.com/learn/glossary/cell-voltage/", "mentions": [ "electrode", "negative-electrode", "graphite" ] } }, "edges": [ { "id": "edge:1852", "source": "term:cell-voltage", "target": "topic:topic-electrochemistry", "type": "belongsTo", "properties": { "sourceFile": "terms.json" } }, { "id": "edge:1853", "source": "term:cell-voltage", "target": "term:electrode-potential", "type": "relatedTo", "properties": { "sourceFile": "terms.json", "meaning": "Related context; not a causal claim" } }, { "id": "edge:1854", "source": "term:cell-voltage", "target": "term:gibbs-free-energy", "type": "relatedTo", "properties": { "sourceFile": "terms.json", "meaning": "Related context; not a causal claim" } }, { "id": "edge:1855", "source": "term:cell-voltage", "target": "term:open-circuit-voltage", "type": "relatedTo", "properties": { "sourceFile": "terms.json", "meaning": "Related context; not a causal claim" } }, { "id": "edge:1856", "source": "term:cell-voltage", "target": "term:nominal-voltage", "type": "relatedTo", "properties": { "sourceFile": "terms.json", "meaning": "Related context; not a causal claim" } }, { "id": "edge:mentions/cell-voltage/electrode", "source": "term:cell-voltage", "target": "term:electrode", "type": "mentions", "properties": { "sourceFile": "terms.json", "method": "build_glossary.mention_index + mentions", "field": "definition", "meaning": "Text mention; not a causal claim" } }, { "id": "edge:mentions/cell-voltage/negative-electrode", "source": "term:cell-voltage", "target": "term:negative-electrode", "type": "mentions", "properties": { "sourceFile": "terms.json", "method": "build_glossary.mention_index + mentions", "field": "definition", "meaning": "Text mention; not a causal claim" } }, { "id": "edge:mentions/cell-voltage/graphite", "source": "term:cell-voltage", "target": "term:graphite", "type": "mentions", "properties": { "sourceFile": "terms.json", "method": "build_glossary.mention_index + mentions", "field": "definition", "meaning": "Text mention; not a causal claim" } }, { "id": "edge:1860", "source": "term:cell-voltage", "target": "visual:reaction-energy", "type": "illustratedBy", "properties": { "sourceFile": "visual-pages.json" } }, { "id": "edge:1861", "source": "term:cell-voltage", "target": "reference:iupac-green", "type": "cites", "properties": { "sourceFile": "wiki-references.json", "scope": "direct technical reference" } } ], "neighbors": [ { "id": "topic:topic-electrochemistry", "type": "Topic", "label": "Electrochemistry fundamentals", "properties": { "id": "topic-electrochemistry", "name": "Electrochemistry fundamentals", "lede": "The reactions and potentials that make a cell a battery.", "context": "Connect reaction sites and transport paths.", "example": "A circuit can predict terminal voltage while leaving electrode potentials and reaction kinetics unresolved.", "lesson_url": "https://lemonergy.com/learn/fundamentals/cell-anatomy/", "lesson_label": "Open cell anatomy" } }, { "id": "term:electrode-potential", "type": "Term", "label": "Electrode potential", "properties": { "id": "electrode-potential", "name": "Electrode potential", "section": "topic-electrochemistry", "definition": "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⁺", "related": [ "standard-potential", "cell-voltage", "reference-electrode", "half-reaction" ], "lesson": "labs/battery-materials-lab/#battery-materials-lab", "url": "https://lemonergy.com/learn/glossary/electrode-potential/", "mentions": [ "electrode", "graphite", "electrolyte" ] } }, { "id": "term:gibbs-free-energy", "type": "Term", "label": "Gibbs free energy", "properties": { "id": "gibbs-free-energy", "name": "Gibbs free energy", "abbr": "ΔG", "section": "topic-electrochemistry", "definition": "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.", "formula": "ΔG = −nFE", "unit": "kJ/mol", "related": [ "cell-voltage", "nernst-equation", "faradays-constant", "entropy-coefficient" ], "example": { "title": "Convert voltage to molar free energy", "text": "For a one-electron reaction with equilibrium voltage 3.0 V, ΔG = −nFE is approximately −289 kJ/mol. The sign refers to the reaction direction and the equilibrium electrical work." }, "url": "https://lemonergy.com/learn/glossary/gibbs-free-energy/", "mentions": [] } }, { "id": "term:open-circuit-voltage", "type": "Term", "label": "Open-circuit voltage", "properties": { "id": "open-circuit-voltage", "name": "Open-circuit voltage", "abbr": "OCV", "section": "topic-state", "definition": "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", "related": [ "ocv-soc-curve", "relaxation", "voltage-hysteresis", "k-value", "internal-short-circuit" ], "lesson": "fundamentals/cell-production/#finishing", "url": "https://lemonergy.com/learn/glossary/open-circuit-voltage/", "mentions": [ "state-of-charge" ] } }, { "id": "term:nominal-voltage", "type": "Term", "label": "Nominal voltage", "properties": { "id": "nominal-voltage", "name": "Nominal voltage", "section": "topic-ratings", "definition": "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", "related": [ "nominal-energy", "open-circuit-voltage", "voltage-window", "lfp" ], "lesson": "fundamentals/capacity-and-c-rate/#energy", "url": "https://lemonergy.com/learn/glossary/nominal-voltage/", "mentions": [ "graphite" ] } }, { "id": "term:electrode", "type": "Term", "label": "Electrode", "properties": { "id": "electrode", "name": "Electrode", "section": "topic-components", "definition": "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.", "related": [ "negative-electrode", "positive-electrode", "porous-electrode", "current-collector" ], "lesson": "fundamentals/cell-anatomy/#components", "example": { "title": "Two transport paths", "text": "Electrons need connected solid paths to the collector; ions need electrolyte paths to reaction sites. More of one constituent displaces others at fixed volume." }, "url": "https://lemonergy.com/learn/glossary/electrode/", "mentions": [ "electrolyte", "coating" ] } }, { "id": "term:negative-electrode", "type": "Term", "label": "Negative electrode", "properties": { "id": "negative-electrode", "name": "Negative electrode", "section": "topic-components", "definition": "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.", "related": [ "anode", "graphite", "positive-electrode", "copper-foil" ], "lesson": "fundamentals/cell-anatomy/#anode-cathode", "example": { "title": "Keep the polarity name", "text": "Graphite remains the negative electrode during charge and discharge, while the anode/cathode reaction labels change with operating direction." }, "url": "https://lemonergy.com/learn/glossary/negative-electrode/", "mentions": [ "electrode" ] } }, { "id": "term:graphite", "type": "Term", "label": "Graphite", "properties": { "id": "graphite", "name": "Graphite", "section": "topic-components", "definition": "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.", "related": [ "anode-active-material", "intercalation", "natural-graphite", "synthetic-graphite", "lithium-plating" ], "lesson": "fundamentals/cell-anatomy/#components", "example": { "title": "Compare matching mass bases", "text": "A graphite value per gram of active material cannot be directly compared with a value including binder, additive and foil." }, "url": "https://lemonergy.com/learn/glossary/graphite/", "mentions": [ "milliampere-hour", "active-material" ] } }, { "id": "visual:reaction-energy", "type": "Visual", "label": "Voltage is reaction free energy per charge", "properties": { "title": "Voltage is reaction free energy per charge", "summary": "A spontaneous forward cell reaction has negative Gibbs energy and positive equilibrium voltage under this convention.", "readout": "At 3.7 V, ΔG = -357 kJ/mol reaction for n = 1.", "formula": "ΔG = −nFE", "note": "Equilibrium relation at fixed temperature and pressure. No reaction chemistry, activity model or loaded voltage is calculated.", "software": { "status": "reference", "label": "Reference concept", "body": "This thermodynamic identity explains equilibrium cell voltage. Terminal voltage under load additionally depends on losses and dynamics.", "href": "../chapter-1/" }, "html": "
Reaction free energy
Reaction free energyEquilibrium cell voltage (V) versus ΔG (kJ/mol reaction). Free-energy change. Interpretation follows the graphs.-4820-3621.25-2412.5-1213.7505Equilibrium cell voltage (V)ΔG (kJ/mol reaction)
Free-energy change
" } }, { "id": "reference:iupac-green", "type": "Reference", "label": "Quantities, Units and Symbols in Physical Chemistry, 3rd edition, 2nd printing", "properties": { "title": "Quantities, Units and Symbols in Physical Chemistry, 3rd edition, 2nd printing", "publisher": "IUPAC", "url": "https://media.iupac.org/publications/books/gbook/IUPAC-GB3-2ndPrinting-Online-22apr2011.pdf", "type": "Technical reference", "scope": "Physical-chemistry notation, thermodynamics, electrochemistry and transport quantities.", "year": 2011, "accessed": "2026-10-27" } } ] }