{ "node": { "id": "term:overpotential", "type": "Term", "label": "Overpotential", "properties": { "id": "overpotential", "name": "Overpotential", "abbr": "η", "section": "topic-electrochemistry", "definition": "The extra voltage, beyond the equilibrium potential, needed to drive a reaction at a given rate at one electrode. 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It dominates at high current and low temperature and recovers slowly when current stops.", "related": [ "polarization", "diffusion", "overpotential", "relaxation", "concentration-gradient" ], "url": "https://lemonergy.com/learn/glossary/concentration-polarization/", "mentions": [] } }, { "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. 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Its resistance appears as a semicircle in impedance spectra and grows as films thicken and the cell cools.", "related": [ "butler-volmer", "double-layer", "electrochemical-impedance-spectroscopy", "overpotential", "solvation" ], "url": "https://lemonergy.com/learn/glossary/charge-transfer/", "mentions": [ "impedance", "electrode", "electrolyte" ] } }, { "id": "visual:butler-volmer", "type": "Visual", "label": "Overpotential drives reaction current", "properties": { "title": "Overpotential drives reaction current", "summary": "At equilibrium, forward and reverse reaction currents cancel.", "readout": "At equilibrium net current is zero. At +50 mV, current density is 2.268 A/m².", "formula": "i = 2i₀ sinh(Fη / 2RT)", "note": "Fixed concentrations, symmetric transfer coefficients and no transport limitation.", "software": { "status": "reference", "label": "Reference concept", "body": "This symmetric Butler–Volmer relation assumes one electron, α = 0.5 and 25 °C. It is a reference equation, not an implemented reaction model in battery-core.", "href": "../chapter-1/" }, "html": "
Symmetric reaction kinetics at 25 °C
Symmetric reaction kinetics at 25 °COverpotential (V) versus Current density (A/m²). Net reaction current. Interpretation follows the graphs.-18.5-0.15-9.24-0.075009.240.07518.50.15Overpotential (V)Current density (A/m²)
Net reaction current
" } }, { "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" } } ] }