{
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    "type": "Term",
    "label": "Thermal runaway",
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      "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.",
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        "definition": "The temperature at which a cell begins to generate heat by itself, as the SEI starts to decompose, typically 80–120 °C. Measured in an accelerating rate calorimeter, it marks the start of the path to thermal runaway, not the runaway itself.",
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      "type": "Term",
      "label": "Thermal propagation",
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        "id": "thermal-propagation",
        "name": "Thermal propagation",
        "section": "topic-safety",
        "definition": "Thermal runaway spreading from one cell to its neighbours through conducted heat, hot gas and flame. Pack designs are judged by whether, and how slowly, a single failing cell takes the rest with it.",
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      "type": "Term",
      "label": "Venting",
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        "section": "topic-safety",
        "definition": "The controlled release of gas and vapour from a cell whose internal pressure has risen too far, through a vent designed to open before the case bursts. The vented gas is flammable and toxic, so packs route it away from occupants.",
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      "type": "Term",
      "label": "Separator shutdown",
      "properties": {
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        "name": "Separator shutdown",
        "section": "topic-safety",
        "definition": "A built-in safety feature of polyolefin separators: around 130 °C the polyethylene layer melts and closes its pores, stopping ion flow and the current with it. It helps only if the separator does not also shrink and let the electrodes touch, so shutdown behavior is not universal.",
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        "url": "https://lemonergy.com/learn/glossary/separator-shutdown/",
        "mentions": [
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      "id": "term:thermal-runaway-energy",
      "type": "Term",
      "label": "Thermal-runaway energy",
      "properties": {
        "id": "thermal-runaway-energy",
        "name": "Thermal-runaway energy",
        "aka": [
          "heat release in thermal runaway",
          "total heat release"
        ],
        "section": "topic-safety",
        "definition": "The heat a cell releases when it fails, which exceeds its stored electrical energy because decomposition reactions add heat of their own. Calorimetry on 18650 cells has measured decomposition energy up to about twice the electrical energy, and combustion of the vented contents up to about six times, so a battery fire carries far more energy than its kWh rating.",
        "related": [
          "thermal-runaway",
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        "mentions": [
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      "id": "term:exothermic",
      "type": "Term",
      "label": "Exothermic and endothermic",
      "properties": {
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        "name": "Exothermic and endothermic",
        "section": "topic-safety",
        "definition": "A reaction that releases heat is exothermic; one that absorbs it is endothermic. Thermal runaway is a chain of exothermic reactions; a few cell processes, such as graphite lithiation at some stages, are mildly endothermic and cool the cell.",
        "related": [
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        "mentions": [
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    {
      "id": "term:overcharge",
      "type": "Term",
      "label": "Overcharge",
      "properties": {
        "id": "overcharge",
        "name": "Overcharge",
        "section": "topic-charging",
        "definition": "Charging past the upper cutoff voltage. The positive electrode over-delithiates and releases oxygen, the electrolyte oxidises and lithium plates on the negative, so an unprotected overcharge can end in thermal runaway.",
        "related": [
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        "mentions": [
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      }
    },
    {
      "id": "lesson:fundamentals/cell-anatomy/",
      "type": "Lesson",
      "label": "Lesson 1 · Cell anatomy",
      "properties": {
        "url": "https://lemonergy.com/learn/fundamentals/cell-anatomy/"
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    },
    {
      "id": "reference:feng-runaway",
      "type": "Reference",
      "label": "Thermal runaway mechanism of lithium ion battery for electric vehicles: A review",
      "properties": {
        "title": "Thermal runaway mechanism of lithium ion battery for electric vehicles: A review",
        "publisher": "Energy Storage Materials",
        "url": "https://doi.org/10.1016/j.ensm.2017.05.013",
        "type": "Review article",
        "scope": "Electrical, mechanical and thermal abuse; thermal-runaway mechanisms and propagation.",
        "year": 2018,
        "authors": [
          "Xuning Feng et al."
        ],
        "accessed": "2026-10-27"
      }
    }
  ]
}