{ "node": { "id": "term:laser-flash-analysis", "type": "Term", "label": "Laser flash analysis", "properties": { "id": "laser-flash-analysis", "name": "Laser flash analysis", "abbr": "LFA", "aka": [ "laser flash method", "flash method" ], "section": "topic-testing", "definition": "Firing a brief laser pulse at one face of a thin disc and timing the temperature rise on the far face with an infrared detector, which gives thermal diffusivity. Multiplying by density and specific heat yields thermal conductivity — the through-plane value for electrodes, separators and layered cell samples.", "formula": "α = 0.1388·L² / t½; k = α·ρ·c_p", "related": [ "thermal-characterisation", "hot-disk-method", "thermal-model", "heat-generation" ], "example": { "title": "Convert a half-rise time into diffusivity", "text": "For an ideal 1 mm slab with a rear-surface half-rise time of 0.10 s, α = 0.1388L²/t½ gives 1.388×10⁻⁶ m²/s. Heat loss, finite pulse duration and material anisotropy can require corrections." }, "url": "https://lemonergy.com/learn/glossary/laser-flash-analysis/", "mentions": [ "diffusion-coefficient", "thermal-conductivity", "specific-heat-capacity", "thermal-diffusivity" ] } }, "edges": [ { "id": "edge:5500", "source": "term:laser-flash-analysis", "target": "topic:topic-testing", "type": "belongsTo", "properties": { "sourceFile": "terms.json" } }, { "id": "edge:5501", "source": "term:laser-flash-analysis", "target": "term:thermal-characterisation", "type": "relatedTo", "properties": { "sourceFile": "terms.json", "meaning": "Related context; not a causal claim" } }, { "id": "edge:5502", "source": "term:laser-flash-analysis", "target": "term:hot-disk-method", "type": "relatedTo", "properties": { "sourceFile": "terms.json", "meaning": "Related context; not a causal claim" } }, { "id": "edge:5503", "source": "term:laser-flash-analysis", "target": "term:thermal-model", "type": "relatedTo", "properties": { "sourceFile": "terms.json", "meaning": "Related context; not a causal claim" } }, { "id": "edge:5504", "source": "term:laser-flash-analysis", "target": "term:heat-generation", "type": "relatedTo", "properties": { "sourceFile": "terms.json", "meaning": "Related context; not a causal claim" } }, { "id": "edge:mentions/laser-flash-analysis/diffusion-coefficient", "source": "term:laser-flash-analysis", "target": "term:diffusion-coefficient", "type": "mentions", "properties": { "sourceFile": "terms.json", "method": "build_glossary.mention_index + mentions", "field": "definition", "meaning": "Text mention; not a causal claim" } }, { "id": "edge:mentions/laser-flash-analysis/thermal-conductivity", "source": "term:laser-flash-analysis", "target": "term:thermal-conductivity", "type": "mentions", "properties": { "sourceFile": "terms.json", "method": "build_glossary.mention_index + mentions", "field": "definition", "meaning": "Text mention; not a causal claim" } }, { "id": "edge:mentions/laser-flash-analysis/specific-heat-capacity", "source": "term:laser-flash-analysis", "target": "term:specific-heat-capacity", "type": "mentions", "properties": { "sourceFile": "terms.json", "method": "build_glossary.mention_index + mentions", "field": "definition", "meaning": "Text mention; not a causal claim" } }, { "id": "edge:mentions/laser-flash-analysis/thermal-diffusivity", "source": "term:laser-flash-analysis", "target": "term:thermal-diffusivity", "type": "mentions", "properties": { "sourceFile": "terms.json", "method": "build_glossary.mention_index + mentions", "field": "definition", "meaning": "Text mention; not a causal claim" } }, { "id": "edge:5509", "source": "term:laser-flash-analysis", "target": "visual:thermal-spreading", "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: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:hot-disk-method", "type": "Term", "label": "Hot-disk method", "properties": { "id": "hot-disk-method", "name": "Hot-disk method", "aka": [ "transient plane source", "TPS", "hot disk" ], "section": "topic-testing", "definition": "Sandwiching a thin nickel spiral sensor between two pieces of a sample, heating it briefly and using its own resistance as the thermometer, then fitting the temperature rise to get thermal conductivity and diffusivity. It suits large flat samples such as cell stacks and pads and, for anisotropic materials, separates in-plane from through-plane conductivity.", "related": [ "thermal-characterisation", "laser-flash-analysis", "thermal-model", "thermal-interface-material" ], "url": "https://lemonergy.com/learn/glossary/hot-disk-method/", "mentions": [ "diffusion-coefficient", "thermal-conductivity" ] } }, { "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: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:diffusion-coefficient", "type": "Term", "label": "Diffusion coefficient", "properties": { "id": "diffusion-coefficient", "name": "Diffusion coefficient", "abbr": "D", "aka": [ "diffusivity" ], "section": "topic-transport", "definition": "The proportionality constant D in Fick’s first law, in m²/s. It sets how fast a species spreads for a given concentration gradient.", "unit": "m²/s", "related": [ "ficks-first-law", "solid-state-diffusion", "gitt", "diffusion" ], "lesson": "transport/ficks-first-law/#law", "url": "https://lemonergy.com/learn/glossary/diffusion-coefficient/", "mentions": [ "concentration-gradient" ] } }, { "id": "term:thermal-conductivity", "type": "Term", "label": "Thermal conductivity", "properties": { "id": "thermal-conductivity", "name": "Thermal conductivity", "abbr": "k", "aka": [ "λ", "through-plane conductivity", "in-plane conductivity" ], "section": "topic-thermal", "definition": "How readily a material conducts heat: the heat flux per unit temperature gradient. Cells are strongly anisotropic — around 25–45 W/(m·K) in-plane, along the metal foils, but below 1 W/(m·K) through-plane, across separators and coatings — so the side a cell is cooled from decides how hot its core runs.", "formula": "q″ = −k·dT/dx", "unit": "W/(m·K)", "related": [ "thermal-resistance", "thermal-diffusivity", "thermal-characterisation", "thermal-interface-material", "biot-number", "thermal-model" ], "example": { "title": "Calculate a slab heat flow", "text": "An illustrative 2 mm layer with k = 1 W/(m·K), area 0.01 m² and a 10 K temperature difference transfers 50 W in steady one-dimensional conduction. Contact resistances and edge losses are omitted." }, "url": "https://lemonergy.com/learn/glossary/thermal-conductivity/", "mentions": [ "heat-flux", "thermal-gradient" ] } }, { "id": "term:specific-heat-capacity", "type": "Term", "label": "Specific heat capacity", "properties": { "id": "specific-heat-capacity", "name": "Specific heat capacity", "abbr": "cₚ", "aka": [ "heat capacity", "specific heat" ], "section": "topic-thermal", "definition": "The heat needed to raise one kilogram of a material by one kelvin; multiplied by mass it gives a body’s heat capacity in J/K. Lithium-ion cells sit near 1,000 J/(kg·K), so a 0.5 kg pouch cell absorbs about 500 J per degree — the figure a thermal model uses to turn heat into temperature rise.", "formula": "Q = m·cₚ·ΔT", "unit": "J/(kg·K)", "related": [ "thermal-mass", "thermal-characterisation", "thermal-model", "heat-generation", "thermal-diffusivity" ], "example": { "title": "Estimate a temperature rise", "text": "A 0.5 kg body with cₚ = 900 J/(kg·K) requires 4500 J for a 10 K temperature rise if heat loss and phase change are neglected. The heat capacity of the whole body is 450 J/K." }, "url": "https://lemonergy.com/learn/glossary/specific-heat-capacity/", "mentions": [ "pouch-cell" ] } }, { "id": "term:thermal-diffusivity", "type": "Term", "label": "Thermal diffusivity", "properties": { "id": "thermal-diffusivity", "name": "Thermal diffusivity", "abbr": "α", "section": "topic-thermal", "definition": "How quickly temperature evens out inside a material: thermal conductivity divided by density times specific heat. Heat spreads a distance L in roughly L²/α, so crossing a 10 mm cell at about 0.2 mm²/s through-plane takes several minutes, while aluminium, near 100 mm²/s, equalises almost at once.", "formula": "α = k / (ρ·cₚ)", "unit": "m²/s", "related": [ "thermal-conductivity", "specific-heat-capacity", "thermal-gradient", "biot-number", "thermal-model" ], "example": { "title": "Compare heat-spreading rates", "text": "For an illustrative material with k = 1 W/(m·K), density 2000 kg/m³ and cₚ = 1000 J/(kg·K), α = 5×10⁻⁷ m²/s. A higher α means a temperature disturbance spreads faster for the same geometry." }, "url": "https://lemonergy.com/learn/glossary/thermal-diffusivity/", "mentions": [] } }, { "id": "visual:thermal-spreading", "type": "Visual", "label": "Length sets the diffusion time scale", "properties": { "title": "Length sets the diffusion time scale", "summary": "The characteristic spreading time grows with thickness squared; ideal laser-flash half-rise time has a different coefficient.", "readout": "Thermal diffusivity is 1 mm²/s. At 5 mm, L²/α = 25 s and the ideal half-rise time is 3.47 s.", "formula": "α = k/(ρc_p); t_characteristic = L²/α; t_half = 0.1388 L²/α", "note": "Laser-flash coefficient assumes a homogeneous slab, instantaneous uniform pulse and negligible heat loss. L²/α is a characteristic scale, not an exact equilibration time.", "software": { "status": "reference", "label": "Reference concept", "body": "These analytical relations explain material measurements and thermal time scales. The glossary does not fit a laser-flash experiment or solve a cell temperature field.", "href": "../chapter-1/" }, "html": "
Thickness and response time
Thickness and response timeThickness L (mm) versus Time (s). L²/α characteristic scale; Ideal laser-flash half-rise. Interpretation follows the graphs.00252.5505757.510010Thickness L (mm)Time (s)
L²/α characteristic scaleIdeal laser-flash half-rise (dashed)
" } } ] }