{ "node": { "id": "term:knee-point", "type": "Term", "label": "Knee point", "properties": { "id": "knee-point", "name": "Knee point", "aka": [ "rollover", "sudden death" ], "section": "topic-aging", "definition": "The point in a capacity-versus-cycles curve where slow, roughly linear fade turns into rapid loss. It usually marks the onset of lithium plating or electrolyte dry-out, and a cell past its knee is unpredictable and should be retired.", "related": [ "capacity-fade", "lithium-plating", "electrolyte-dry-out", "remaining-useful-life", "end-of-life" ], "url": "https://lemonergy.com/learn/glossary/knee-point/", "mentions": [ "electrolyte" ] } }, "edges": [ { "id": "edge:1576", "source": "term:knee-point", "target": "topic:topic-aging", "type": "belongsTo", "properties": { "sourceFile": "terms.json" } }, { "id": "edge:1577", "source": "term:knee-point", "target": "term:capacity-fade", "type": "relatedTo", "properties": { "sourceFile": "terms.json", "meaning": "Related context; not a causal claim" } }, { "id": "edge:1578", "source": "term:knee-point", "target": "term:lithium-plating", "type": "relatedTo", "properties": { "sourceFile": "terms.json", "meaning": "Related context; not a causal claim" } }, { "id": "edge:1579", "source": "term:knee-point", "target": "term:electrolyte-dry-out", "type": "relatedTo", "properties": { "sourceFile": "terms.json", "meaning": "Related context; not a causal claim" } }, { "id": "edge:1580", "source": "term:knee-point", "target": "term:remaining-useful-life", "type": "relatedTo", "properties": { "sourceFile": "terms.json", "meaning": "Related context; not a causal claim" } }, { "id": "edge:1581", "source": "term:knee-point", "target": "term:end-of-life", "type": "relatedTo", "properties": { "sourceFile": "terms.json", "meaning": "Related context; not a causal claim" } }, { "id": "edge:mentions/knee-point/electrolyte", "source": "term:knee-point", "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:1583", "source": "term:knee-point", "target": "visual:knee", "type": "illustratedBy", "properties": { "sourceFile": "visual-pages.json" } }, { "id": "edge:1584", "source": "term:knee-point", "target": "reference:edge-degradation", "type": "cites", "properties": { "sourceFile": "wiki-references.json", "scope": "direct technical reference" } } ], "neighbors": [ { "id": "topic:topic-aging", "type": "Topic", "label": "Aging and degradation", "properties": { "id": "topic-aging", "name": "Aging and degradation", "lede": "Why a cell loses capacity and gains resistance, and the mechanisms behind it.", "context": "Separate mechanisms, observations and fitted models.", "example": "Capacity loss and resistance rise can have different causes; a film-growth curve cannot identify both.", "lesson_url": "https://lemonergy.com/learn/fundamentals/battery-aging/", "lesson_label": "Open aging" } }, { "id": "term:capacity-fade", "type": "Term", "label": "Capacity fade", "properties": { "id": "capacity-fade", "name": "Capacity fade", "section": "topic-aging", "definition": "The loss of charge a cell can store and deliver, for example through lithium locked into the SEI or active material that has cracked out of service.", "related": [ "loss-of-lithium-inventory", "loss-of-active-material", "state-of-health", "knee-point" ], "lesson": "fundamentals/battery-aging/#chain", "url": "https://lemonergy.com/learn/glossary/capacity-fade/", "mentions": [ "active-material", "sei" ] } }, { "id": "term:lithium-plating", "type": "Term", "label": "Lithium plating", "properties": { "id": "lithium-plating", "name": "Lithium plating", "section": "topic-aging", "definition": "Lithium metal depositing on the negative-electrode surface instead of intercalating into it. It is promoted by charging at low temperature or high current.", "related": [ "dendrite", "fast-charging", "intercalation", "np-ratio", "dead-lithium", "electrodeposition" ], "lesson": "fundamentals/battery-aging/#plating", "url": "https://lemonergy.com/learn/glossary/lithium-plating/", "mentions": [] } }, { "id": "term:electrolyte-dry-out", "type": "Term", "label": "Electrolyte dry-out", "properties": { "id": "electrolyte-dry-out", "name": "Electrolyte dry-out", "aka": [ "electrolyte depletion" ], "section": "topic-aging", "definition": "Loss of liquid electrolyte to decomposition and film growth until parts of the electrode are no longer wetted. It appears late in life as a sudden rise in resistance, and is one cause of the knee in a capacity curve.", "related": [ "electrolyte-decomposition", "knee-point", "wetting", "impedance-rise" ], "url": "https://lemonergy.com/learn/glossary/electrolyte-dry-out/", "mentions": [ "electrode", "electrolyte" ] } }, { "id": "term:remaining-useful-life", "type": "Term", "label": "Remaining useful life", "properties": { "id": "remaining-useful-life", "name": "Remaining useful life", "abbr": "RUL", "section": "topic-state", "definition": "A prediction of how many cycles, or how much time, a battery has left before reaching end of life. It is estimated from the trend of state of health, and is uncertain near a knee point where fade accelerates.", "related": [ "state-of-health", "end-of-life", "knee-point", "cycle-life" ], "url": "https://lemonergy.com/learn/glossary/remaining-useful-life/", "mentions": [] } }, { "id": "term:end-of-life", "type": "Term", "label": "End of life", "properties": { "id": "end-of-life", "name": "End of life", "abbr": "EOL", "section": "topic-state", "definition": "The point at which a cell no longer meets its application’s requirement, conventionally 80 % of initial capacity or a doubling of resistance. It is a definition for warranties and tests, not a point where the cell stops working.", "related": [ "state-of-health", "beginning-of-life", "cycle-life", "second-life", "knee-point" ], "url": "https://lemonergy.com/learn/glossary/end-of-life/", "mentions": [] } }, { "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": "visual:knee", "type": "Visual", "label": "A knee changes the rate of capacity loss", "properties": { "title": "A knee changes the rate of capacity loss", "summary": "A slow early decline can turn into much faster degradation.", "readout": "The chosen knee is at 0.6 relative exposure. Beyond it, the illustrated loss rate accelerates.", "formula": "Illustrative trend: retention = 100 − 10x − 120 max(0, x − knee)²", "note": "A chosen teaching curve, not a prediction of cycles, years or a physical failure mechanism.", "software": { "status": "reference", "label": "Reference concept", "body": "This piecewise curve illustrates a knee without predicting its location. The core aging functions do not forecast knee onset.", "href": "../fundamentals/battery-aging/" }, "html": "
Chosen capacity-fade knee
Chosen capacity-fade kneeRelative life exposure versus Initial capacity retained (%). Capacity retained. Interpretation follows the graphs.Slow declineAccelerated decline200400.25600.5800.751001Relative life exposureInitial capacity retained(%)
Capacity retained
" } }, { "id": "reference:edge-degradation", "type": "Reference", "label": "Lithium ion battery degradation: what you need to know", "properties": { "title": "Lithium ion battery degradation: what you need to know", "publisher": "Physical Chemistry Chemical Physics", "url": "https://doi.org/10.1039/D1CP00359C", "type": "Review article", "scope": "Degradation mechanisms, modes, operational effects and their interactions.", "year": 2021, "accessed": "2026-10-27" } } ] }