{ "node": { "id": "term:heat-generation", "type": "Term", "label": "Heat generation", "properties": { "id": "heat-generation", "name": "Heat generation", "aka": [ "Bernardi equation" ], "section": "topic-thermal", "definition": "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.", "formula": "q = I(V − E_OCV) + I·T·(dE/dT)", "unit": "W", "related": [ "entropy-coefficient", "internal-resistance", "thermal-model", "thermal-management", "exothermic" ], "example": { "title": "Keep reversible and irreversible heat separate", "text": "With charging current +5 A and terminal voltage 0.10 V above OCV, the irreversible term is 0.50 W. At 300 K with dE/dT = +0.1 mV/K, the reversible contribution is +0.15 W, giving 0.65 W under this sign convention." }, "url": "https://lemonergy.com/learn/glossary/heat-generation/", "mentions": [ "overpotential" ] } }, "edges": [ { "id": "edge:55", "source": "term:heat-generation", "target": "workflow:loss-accounting", "type": "usedIn", "properties": { "sourceFile": "wiki-blocks.json" } }, { "id": "edge:2183", "source": "term:heat-generation", "target": "topic:topic-thermal", "type": "belongsTo", "properties": { "sourceFile": "terms.json" } }, { "id": "edge:2184", "source": "term:heat-generation", "target": "term:entropy-coefficient", "type": "relatedTo", "properties": { "sourceFile": "terms.json", "meaning": "Related context; not a causal claim" } }, { "id": "edge:2185", "source": "term:heat-generation", "target": "term:internal-resistance", "type": "relatedTo", "properties": { "sourceFile": "terms.json", "meaning": "Related context; not a causal claim" } }, { "id": "edge:2186", "source": "term:heat-generation", "target": "term:thermal-model", "type": "relatedTo", "properties": { "sourceFile": "terms.json", "meaning": "Related context; not a causal claim" } }, { "id": "edge:2187", "source": "term:heat-generation", "target": "term:thermal-management", "type": "relatedTo", "properties": { "sourceFile": "terms.json", "meaning": "Related context; not a causal claim" } }, { "id": "edge:2188", "source": "term:heat-generation", "target": "term:exothermic", "type": "relatedTo", "properties": { "sourceFile": "terms.json", "meaning": "Related context; not a causal claim" } }, { "id": "edge:mentions/heat-generation/overpotential", "source": "term:heat-generation", "target": "term:overpotential", "type": "mentions", "properties": { "sourceFile": "terms.json", "method": "build_glossary.mention_index + mentions", "field": "definition", "meaning": "Text mention; not a causal claim" } }, { "id": "edge:2190", "source": "term:heat-generation", "target": "visual:heat", "type": "illustratedBy", "properties": { "sourceFile": "visual-pages.json" } }, { "id": "edge:2191", "source": "term:heat-generation", "target": "reference:bernardi-energy", "type": "cites", "properties": { "sourceFile": "wiki-references.json", "scope": "direct technical reference" } } ], "neighbors": [ { "id": "workflow:loss-accounting", "type": "Workflow", "label": "Compare grid and battery energy", "properties": { "id": "loss-accounting", "title": "Compare grid and battery energy", "kind": "studio", "summary": "Separate energy and loss signals make efficiency visible.", "steps": [ "Keep battery settings fixed.", "Change converter efficiency." ], "example": "7 kW battery-side power at 95% efficiency requires about 7.37 kW grid power and produces about 0.37 kW converter loss.", "observe": "Battery I²R loss differs from converter loss.", "limits": "A loss signal is not a predicted temperature. This network takes external temperature.", "url": "https://design.lemonergy.com/cosim.html?example=charging-home", "label": "Open the Studio example", "evidence": [ "js/charging-control.js", "js/charging-scenarios.js", "docs/CHARGING_BLOCKS_SPEC.md" ] } }, { "id": "topic:topic-thermal", "type": "Topic", "label": "Thermal management and heat transfer", "properties": { "id": "topic-thermal", "name": "Thermal management and heat transfer", "lede": "How heat is made, moved and removed in cells and packs, and the hardware that keeps a battery at the right temperature.", "context": "Select spatial detail for the question.", "example": "Equal total heat in different layouts can produce different gradients. Average temperature can miss a hot spot.", "lesson_url": "https://lemonergy.com/learn/fundamentals/battery-aging/", "lesson_label": "Open temperature and aging" } }, { "id": "term:entropy-coefficient", "type": "Term", "label": "Entropy coefficient", "properties": { "id": "entropy-coefficient", "name": "Entropy coefficient", "section": "topic-electrochemistry", "definition": "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.", "formula": "q_rev = I·T·(dE/dT)", "unit": "mV/K", "related": [ "heat-generation", "gibbs-free-energy", "open-circuit-voltage" ], "example": { "title": "Track reversible heat with the sign convention", "text": "With positive charging current of 5 A, temperature 300 K and dE/dT = 0.1 mV/K, q_rev = IT(dE/dT) gives +0.15 W. Reversing the current reverses this contribution." }, "notes": [ "The glossary plot takes positive heat as heat released. Other sources may use positive-discharge current and a different written sign." ], "url": "https://lemonergy.com/learn/glossary/entropy-coefficient/", "mentions": [ "state-of-charge" ] } }, { "id": "term:internal-resistance", "type": "Term", "label": "Internal resistance", "properties": { "id": "internal-resistance", "name": "Internal resistance", "abbr": "IR", "aka": [ "DC resistance", "DCIR" ], "section": "topic-units", "definition": "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", "related": [ "ohms-law", "ir-drop", "impedance-rise", "dcir", "area-specific-resistance", "resistance-capacity-product" ], "lesson": "fundamentals/battery-basics/#datasheet", "url": "https://lemonergy.com/learn/glossary/internal-resistance/", "mentions": [ "electrolyte", "cylindrical-cell" ] } }, { "id": "term:thermal-model", "type": "Term", "label": "Thermal model", "properties": { "id": "thermal-model", "name": "Thermal model", "aka": [ "lumped thermal model" ], "section": "topic-thermal", "definition": "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.", "related": [ "heat-generation", "thermal-management", "arrhenius", "newman-model", "thermal-characterisation" ], "url": "https://lemonergy.com/learn/glossary/thermal-model/", "mentions": [ "thermal-mass", "heat-transfer-modes" ] } }, { "id": "term:thermal-management", "type": "Term", "label": "Thermal management", "properties": { "id": "thermal-management", "name": "Thermal management", "abbr": "TMS", "aka": [ "battery thermal management system", "BTMS" ], "section": "topic-thermal", "definition": "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.", "related": [ "cooling-plate", "thermal-interface-material", "operating-temperature", "heat-generation", "preconditioning", "temperature-sensor" ], "url": "https://lemonergy.com/learn/glossary/thermal-management/", "mentions": [ "fast-charging" ] } }, { "id": "term:exothermic", "type": "Term", "label": "Exothermic and endothermic", "properties": { "id": "exothermic", "name": "Exothermic and endothermic", "section": "topic-safety", "definition": "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.", "related": [ "thermal-runaway", "heat-generation", "entropy-coefficient" ], "url": "https://lemonergy.com/learn/glossary/exothermic/", "mentions": [ "graphite", "calcination" ] } }, { "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. Activation overpotential pays for charge transfer, concentration overpotential for depleted reactant, and both appear as polarization at the terminals.", "unit": "V", "related": [ "polarization", "butler-volmer", "exchange-current-density", "concentration-polarization" ], "url": "https://lemonergy.com/learn/glossary/overpotential/", "mentions": [ "electrode", "charge-transfer" ] } }, { "id": "visual:heat", "type": "Visual", "label": "Current and resistive heating", "properties": { "title": "Current and resistive heating", "summary": "Double the current and ohmic heating increases fourfold.", "readout": "At 5 A: 0.5 W. At 10 A: 2 W.", "formula": "P_heat = I²R", "note": "Resistance is constant; reversible entropic heat and other losses are excluded.", "software": { "status": "reference", "label": "Reference concept", "body": "P = I²R is the ohmic contribution. The product Charge session can also use a lumped thermal model; the native Studio battery does not calculate temperature evolution.", "href": "https://design.lemonergy.com/" }, "html": "
Ohmic heating
Ohmic heatingCurrent magnitude (A) versus Heat rate (W). I²R. Interpretation follows the graphs.0025410615820Current magnitude (A)Heat rate (W)
I²R
" } }, { "id": "reference:bernardi-energy", "type": "Reference", "label": "A General Energy Balance for Battery Systems", "properties": { "title": "A General Energy Balance for Battery Systems", "publisher": "Journal of The Electrochemical Society", "url": "https://doi.org/10.1149/1.2113792", "type": "Research article", "scope": "Battery energy balance and irreversible and reversible heat contributions. Reduced thermal models require explicit assumptions and current-sign conventions.", "year": 1985, "authors": [ "Dawn Bernardi", "Ellen Pawlikowski", "John Newman" ], "accessed": "2026-10-27" } } ] }