{ "node": { "id": "term:porosity", "type": "Term", "label": "Porosity", "properties": { "id": "porosity", "name": "Porosity", "abbr": "ε", "section": "topic-components", "definition": "The fraction of a layer’s volume that is empty space. In a lithium-ion electrode the pores — roughly 20–35 % of the volume after calendering — are filled with electrolyte, which carries ions to the particles.", "unit": "—", "related": [ "porous-electrode", "tortuosity", "calendering", "bruggeman-relation" ], "lesson": "fundamentals/cell-architecture/#porosity", "example": { "title": "Use the volume basis", "text": "Pore volume of 0.3 cm³ within 1 cm³ total electrode volume means 30% porosity. It does not specify connectivity or tortuosity." }, "url": "https://lemonergy.com/learn/glossary/porosity/", "mentions": [ "electrode", "electrolyte" ] } }, "edges": [ { "id": "edge:571", "source": "term:porosity", "target": "topic:topic-components", "type": "belongsTo", "properties": { "sourceFile": "terms.json" } }, { "id": "edge:572", "source": "term:porosity", "target": "term:porous-electrode", "type": "relatedTo", "properties": { "sourceFile": "terms.json", "meaning": "Related context; not a causal claim" } }, { "id": "edge:573", "source": "term:porosity", "target": "term:tortuosity", "type": "relatedTo", "properties": { "sourceFile": "terms.json", "meaning": "Related context; not a causal claim" } }, { "id": "edge:574", "source": "term:porosity", "target": "term:calendering", "type": "relatedTo", "properties": { "sourceFile": "terms.json", "meaning": "Related context; not a causal claim" } }, { "id": "edge:575", "source": "term:porosity", "target": "term:bruggeman-relation", "type": "relatedTo", "properties": { "sourceFile": "terms.json", "meaning": "Related context; not a causal claim" } }, { "id": "edge:mentions/porosity/electrode", "source": "term:porosity", "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/porosity/electrolyte", "source": "term:porosity", "target": "term:electrolyte", "type": "mentions", "properties": { "sourceFile": "terms.json", "method": "build_glossary.mention_index + mentions", "field": "definition", "meaning": "Text mention; not a causal claim" } }, { "id": "edge:578", "source": "term:porosity", "target": "lesson:fundamentals/cell-architecture/", "type": "explainedIn", "properties": { "sourceFile": "terms.json", "url": "https://lemonergy.com/learn/fundamentals/cell-architecture/#porosity" } }, { "id": "edge:579", "source": "term:porosity", "target": "visual:porous", "type": "illustratedBy", "properties": { "sourceFile": "visual-pages.json" } } ], "neighbors": [ { "id": "topic:topic-components", "type": "Topic", "label": "Cell components and electrode materials", "properties": { "id": "topic-components", "name": "Cell components and electrode materials", "lede": "What a cell is physically made of — active materials, binders, additives, foils and tabs — and how its electrodes are put together.", "context": "Connect each material with its function.", "example": "Electrons travel through additive, foil and tab; ions use electrolyte and separator pathways.", "lesson_url": "https://lemonergy.com/learn/fundamentals/cell-anatomy/", "lesson_label": "Open cell anatomy" } }, { "id": "term:porous-electrode", "type": "Term", "label": "Porous electrode", "properties": { "id": "porous-electrode", "name": "Porous electrode", "section": "topic-components", "definition": "An electrode made of active-material particles, conductive additive and binder with electrolyte-filled pores between them. Its large internal surface is where the reaction happens.", "related": [ "porosity", "tortuosity", "active-material", "porous-electrode-theory", "3d-electrode" ], "lesson": "fundamentals/cell-architecture/#porosity", "url": "https://lemonergy.com/learn/glossary/porous-electrode/", "mentions": [ "electrode", "binder", "conductive-additive" ] } }, { "id": "term:tortuosity", "type": "Term", "label": "Tortuosity", "properties": { "id": "tortuosity", "name": "Tortuosity", "abbr": "τ", "section": "topic-transport", "definition": "How winding the path through a porous layer is, compared with a straight line through it. High tortuosity means ions travel much further than the layer is thick, which limits how fast a thick, dense electrode can be charged or discharged.", "unit": "—", "related": [ "porosity", "bruggeman-relation", "porous-electrode", "rate-capability", "ionic-path" ], "lesson": "fundamentals/cell-architecture/#porosity", "url": "https://lemonergy.com/learn/glossary/tortuosity/", "mentions": [ "electrode", "winding" ] } }, { "id": "term:calendering", "type": "Term", "label": "Calendering", "properties": { "id": "calendering", "name": "Calendering", "section": "topic-manufacturing", "definition": "Compressing a dried electrode coating between rollers to set its thickness, density and porosity. It is one of the electrode-making steps in cell production.", "related": [ "porosity", "electrode-density", "drying", "slitting" ], "lesson": "fundamentals/cell-production/#electrodes", "example": { "title": "Connect thickness and density", "text": "At fixed mass and area, reducing thickness raises bulk density. The pore structure still needs to support wetting and transport." }, "url": "https://lemonergy.com/learn/glossary/calendering/", "mentions": [ "electrode", "cell-production", "coating" ] } }, { "id": "term:bruggeman-relation", "type": "Term", "label": "Bruggeman relation", "properties": { "id": "bruggeman-relation", "name": "Bruggeman relation", "section": "topic-transport", "definition": "The common estimate of effective transport in a porous layer: multiply the bulk conductivity or diffusivity by porosity to the power 1.5. Real electrodes often deviate, so measured tortuosity is preferred when available.", "formula": "D_eff = D · ε^1.5", "related": [ "tortuosity", "porosity", "porous-electrode-theory" ], "example": { "title": "Estimate an effective diffusivity", "text": "Using the illustrative relation D_eff = D ε^1.5 with porosity ε = 0.4 gives D_eff ≈ 0.253D. This empirical geometry approximation does not replace a measured tortuosity." }, "url": "https://lemonergy.com/learn/glossary/bruggeman-relation/", "mentions": [ "diffusion-coefficient" ] } }, { "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:electrolyte", "type": "Term", "label": "Electrolyte", "properties": { "id": "electrolyte", "name": "Electrolyte", "section": "topic-electrolytes", "definition": "The ion-conducting medium between the electrodes. In a liquid-electrolyte cell it fills the pores of both electrodes and the separator, so it is not a separate structural layer.", "related": [ "lithium-salt", "carbonate-solvent", "electrolyte-additive", "ionic-conductivity", "solid-electrolyte", "ionic-liquid-electrolyte" ], "lesson": "fundamentals/cell-architecture/#electrolyte", "example": { "title": "Ions and electrons", "text": "Electrolyte carries ions between electrodes; the external circuit carries electrons. The two paths serve different roles." }, "url": "https://lemonergy.com/learn/glossary/electrolyte/", "mentions": [ "separator" ] } }, { "id": "lesson:fundamentals/cell-architecture/", "type": "Lesson", "label": "Lesson 1B · Cell architecture", "properties": { "url": "https://lemonergy.com/learn/fundamentals/cell-architecture/" } }, { "id": "visual:porous", "type": "Visual", "label": "Porosity reduces effective transport", "properties": { "title": "Porosity reduces effective transport", "summary": "A Bruggeman relation approximates transport through a porous medium.", "readout": "At 40% porosity, D_eff is 25.298% of bulk diffusivity.", "formula": "D_eff = D εᵇ", "note": "An empirical pore-structure assumption; actual tortuosity must be characterized.", "software": { "status": "reference", "label": "Reference concept", "body": "The flux helper accepts a supplied diffusivity. It does not estimate porosity or tortuosity. The shown D_eff = D εᵇ relationship is an explicit teaching assumption.", "href": "../transport/ficks-first-law/" }, "html": "
Effective diffusivity fraction
Effective diffusivity fractionPorosity ε (fraction) versus D_eff / D (fraction). εᵇ; Straight-pore scaling ε. Interpretation follows the graphs.000.250.250.50.50.750.7511Porosity ε (fraction)D_eff / D (fraction)
εᵇStraight-pore scaling ε (dashed)
" } } ] }