{
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    "label": "Early thermal-runaway detection",
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      "id": "early-thermal-runaway-detection",
      "name": "Early thermal-runaway detection",
      "aka": [
        "thermal runaway warning",
        "thermal event detection"
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      "definition": "Spotting a failing cell before it runs away, from the signals that precede heat: a voltage drop or abnormal self-discharge from an internal short, then vent gas, pressure and swelling, then a rising rate of temperature increase. Vehicle rules demand a warning to occupants at least five minutes before a hazard reaches the cabin, so detection cannot wait for heat.",
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        "internal-short-circuit",
        "off-gas",
        "un-r100-03",
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        "bms"
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      "mentions": [
        "self-discharge",
        "swelling"
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      "label": "Safety and abuse",
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        "id": "topic-safety",
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        "lede": "How cells fail dangerously, how that is tested, and what is built in to stop it.",
        "context": "Connect mechanisms with appropriate test evidence.",
        "example": "A low normal-load temperature does not demonstrate thermal-runaway containment.",
        "lesson_url": "https://lemonergy.com/learn/fundamentals/battery-aging/",
        "lesson_label": "Open degradation mechanisms"
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      "id": "term:internal-short-circuit",
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        "name": "Internal short circuit",
        "abbr": "ISC",
        "section": "topic-safety",
        "definition": "An unintended electronic path between the electrodes inside a cell — through a metal particle, a burr, a damaged separator or lithium deposits. It discharges the cell internally and turns its energy into local heat.",
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          "thermal-runaway",
          "dendrite",
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        "mentions": [
          "electronic-path",
          "burr",
          "metal-particle-contamination"
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      "id": "term:off-gas",
      "type": "Term",
      "label": "Off-gas",
      "properties": {
        "id": "off-gas",
        "name": "Off-gas",
        "aka": [
          "vent gas"
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        "section": "topic-safety",
        "definition": "The mixture released when a cell vents: electrolyte vapour, hydrogen, carbon monoxide, carbon dioxide and hydrocarbons, with hydrogen fluoride. It is flammable and toxic, and gas sensors detect it before smoke or heat in a storage container.",
        "related": [
          "venting",
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          "gas-detection",
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        "aka": [
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          "R100 series of amendments 03"
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        "definition": "The third series of amendments to UN R100, in force for new vehicle types from 2023. It added the thermal-propagation requirement — a warning to occupants at least five minutes before a hazardous event in the cabin, aligned with GTR 20 — plus documentation of the battery’s safe-state behaviour and a low-energy exemption for small systems.",
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          "un-r100",
          "un-r100-part-2",
          "gtr-20",
          "thermal-propagation",
          "propagation-test"
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        "mentions": []
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      "id": "term:thermal-runaway",
      "type": "Term",
      "label": "Thermal runaway",
      "properties": {
        "id": "thermal-runaway",
        "name": "Thermal runaway",
        "section": "topic-safety",
        "definition": "Self-accelerating heating in a cell: heat speeds up reactions that release more heat, until the cell vents, catches fire or ruptures. An internal short, overcharge or external heating can trigger it.",
        "related": [
          "onset-temperature",
          "thermal-propagation",
          "venting",
          "separator-shutdown",
          "thermal-runaway-energy",
          "exothermic"
        ],
        "lesson": "fundamentals/cell-anatomy/#short-circuit",
        "url": "https://lemonergy.com/learn/glossary/thermal-runaway/",
        "mentions": [
          "overcharge"
        ]
      }
    },
    {
      "id": "term:bms",
      "type": "Term",
      "label": "Battery management system",
      "properties": {
        "id": "bms",
        "name": "Battery management system",
        "abbr": "BMS",
        "section": "topic-pack",
        "definition": "The electronics and software that keep a battery inside its safe window: measuring every cell voltage and many temperatures, estimating SOC and SOH, balancing cells, computing current limits, controlling the contactors and reporting over the vehicle network.",
        "related": [
          "state-of-charge",
          "cell-balancing",
          "state-of-power",
          "cell-supervision-circuit",
          "contactor",
          "can-bus"
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        "url": "https://lemonergy.com/learn/glossary/bms/",
        "mentions": [
          "state-of-health",
          "cell-voltage"
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      }
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    {
      "id": "term:self-discharge",
      "type": "Term",
      "label": "Self-discharge",
      "properties": {
        "id": "self-discharge",
        "name": "Self-discharge",
        "section": "topic-charging",
        "definition": "The slow loss of stored charge while a cell is not in use. An unexpected rise can signal a leakage path or a soft internal short.",
        "unit": "%/month",
        "related": [
          "internal-short-circuit",
          "calendar-aging",
          "k-value",
          "calendar-life",
          "self-discharge-test"
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        "lesson": "fundamentals/battery-aging/#check-yourself",
        "url": "https://lemonergy.com/learn/glossary/self-discharge/",
        "mentions": []
      }
    },
    {
      "id": "term:swelling",
      "type": "Term",
      "label": "Swelling",
      "properties": {
        "id": "swelling",
        "name": "Swelling",
        "section": "topic-aging",
        "definition": "Growth in a cell’s thickness, reversibly as the electrodes expand on charge and irreversibly as gas and SEI accumulate. Packs allow for it with compression pads, and a sudden swell in service is a warning sign.",
        "related": [
          "gas-generation",
          "pouch-cell",
          "silicon-anode",
          "stack-pressure",
          "compression-pad",
          "swelling-test"
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        "url": "https://lemonergy.com/learn/glossary/swelling/",
        "mentions": [
          "sei"
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}