{ "node": { "id": "term:isothermal-calorimetry", "type": "Term", "label": "Isothermal calorimetry", "properties": { "id": "isothermal-calorimetry", "name": "Isothermal calorimetry", "aka": [ "isothermal microcalorimetry", "IMC", "heat-flow calorimetry" ], "section": "topic-testing", "definition": "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.", "related": [ "heat-generation", "entropy-coefficient", "thermal-characterisation", "accelerating-rate-calorimetry", "ultra-high-precision-coulometry" ], "url": "https://lemonergy.com/learn/glossary/isothermal-calorimetry/", "mentions": [] } }, "edges": [ { "id": "edge:5402", "source": "term:isothermal-calorimetry", "target": "topic:topic-testing", "type": "belongsTo", "properties": { "sourceFile": "terms.json" } }, { "id": "edge:5403", "source": "term:isothermal-calorimetry", "target": "term:heat-generation", "type": "relatedTo", "properties": { "sourceFile": "terms.json", "meaning": "Related context; not a causal claim" } }, { "id": "edge:5404", "source": "term:isothermal-calorimetry", "target": "term:entropy-coefficient", "type": "relatedTo", "properties": { "sourceFile": "terms.json", "meaning": "Related context; not a causal claim" } }, { "id": "edge:5405", "source": "term:isothermal-calorimetry", "target": "term:thermal-characterisation", "type": "relatedTo", "properties": { "sourceFile": "terms.json", "meaning": "Related context; not a causal claim" } }, { "id": "edge:5406", "source": "term:isothermal-calorimetry", "target": "term:accelerating-rate-calorimetry", "type": "relatedTo", "properties": { "sourceFile": "terms.json", "meaning": "Related context; not a causal claim" } }, { "id": "edge:5407", "source": "term:isothermal-calorimetry", "target": "term:ultra-high-precision-coulometry", "type": "relatedTo", "properties": { "sourceFile": "terms.json", "meaning": "Related context; not a causal claim" } }, { "id": "edge:5408", "source": "term:isothermal-calorimetry", "target": "visual:heat", "type": "illustratedBy", "properties": { "sourceFile": "visual-pages.json" } } ], "neighbors": [ { "id": "topic:topic-testing", "type": "Topic", "label": "Testing methods", "properties": { "id": "topic-testing", "name": "Testing methods", "lede": "The measurements and test procedures that characterise a cell or pack, from capacity and pulse tests to abuse and environmental tests.", "context": "Record specimen, state, instrument, temperature and timing.", "example": "Resistance immediately after a current step can differ from a ten-second value because slower polarization contributes.", "lesson_url": "https://lemonergy.com/learn/fundamentals/capacity-and-c-rate/", "lesson_label": "Open capacity measurements" } }, { "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" ] } }, { "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:thermal-characterisation", "type": "Term", "label": "Thermal characterisation", "properties": { "id": "thermal-characterisation", "name": "Thermal characterisation", "aka": [ "heat capacity test", "entropy test" ], "section": "topic-testing", "definition": "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.", "related": [ "heat-generation", "entropy-coefficient", "thermal-model", "accelerating-rate-calorimetry" ], "url": "https://lemonergy.com/learn/glossary/thermal-characterisation/", "mentions": [ "open-circuit-voltage", "thermal-conductivity", "specific-heat-capacity" ] } }, { "id": "term:accelerating-rate-calorimetry", "type": "Term", "label": "Accelerating rate calorimetry", "properties": { "id": "accelerating-rate-calorimetry", "name": "Accelerating rate calorimetry", "abbr": "ARC", "section": "topic-safety", "definition": "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.", "related": [ "onset-temperature", "thermal-runaway", "differential-scanning-calorimetry" ], "url": "https://lemonergy.com/learn/glossary/accelerating-rate-calorimetry/", "mentions": [ "adiabatic-isothermal" ] } }, { "id": "term:ultra-high-precision-coulometry", "type": "Term", "label": "Ultra-high-precision coulometry", "properties": { "id": "ultra-high-precision-coulometry", "name": "Ultra-high-precision coulometry", "abbr": "UHPC", "aka": [ "high-precision coulometry", "coulometry", "high-precision charger" ], "section": "topic-testing", "definition": "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.", "related": [ "coulombic-efficiency", "cycler", "electrolyte-additive", "cycle-life-test", "isothermal-calorimetry" ], "url": "https://lemonergy.com/learn/glossary/ultra-high-precision-coulometry/", "mentions": [ "electrolyte" ] } }, { "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
" } } ] }