{
  "node": {
    "id": "term:phase-change-material",
    "type": "Term",
    "label": "Phase change material",
    "properties": {
      "id": "phase-change-material",
      "name": "Phase change material",
      "abbr": "PCM",
      "aka": [
        "paraffin wax",
        "latent heat storage"
      ],
      "section": "topic-thermal",
      "definition": "A material that melts at a chosen temperature, around 30–45 °C for batteries, absorbing a large latent heat — roughly 200 J/g for paraffin wax — with little temperature rise. Packed around cells, often in a graphite matrix to lift its poor conductivity, it caps peaks during short heavy loads, but it must be cooled to reset and adds mass.",
      "related": [
        "passive-thermal-management",
        "thermal-mass",
        "thermal-management",
        "thermal-conductivity"
      ],
      "url": "https://lemonergy.com/learn/glossary/phase-change-material/",
      "mentions": [
        "graphite"
      ]
    }
  },
  "edges": [
    {
      "id": "edge:4694",
      "source": "term:phase-change-material",
      "target": "topic:topic-thermal",
      "type": "belongsTo",
      "properties": {
        "sourceFile": "terms.json"
      }
    },
    {
      "id": "edge:4695",
      "source": "term:phase-change-material",
      "target": "term:passive-thermal-management",
      "type": "relatedTo",
      "properties": {
        "sourceFile": "terms.json",
        "meaning": "Related context; not a causal claim"
      }
    },
    {
      "id": "edge:4696",
      "source": "term:phase-change-material",
      "target": "term:thermal-mass",
      "type": "relatedTo",
      "properties": {
        "sourceFile": "terms.json",
        "meaning": "Related context; not a causal claim"
      }
    },
    {
      "id": "edge:4697",
      "source": "term:phase-change-material",
      "target": "term:thermal-management",
      "type": "relatedTo",
      "properties": {
        "sourceFile": "terms.json",
        "meaning": "Related context; not a causal claim"
      }
    },
    {
      "id": "edge:4698",
      "source": "term:phase-change-material",
      "target": "term:thermal-conductivity",
      "type": "relatedTo",
      "properties": {
        "sourceFile": "terms.json",
        "meaning": "Related context; not a causal claim"
      }
    },
    {
      "id": "edge:mentions/phase-change-material/graphite",
      "source": "term:phase-change-material",
      "target": "term:graphite",
      "type": "mentions",
      "properties": {
        "sourceFile": "terms.json",
        "method": "build_glossary.mention_index + mentions",
        "field": "definition",
        "meaning": "Text mention; not a causal claim"
      }
    }
  ],
  "neighbors": [
    {
      "id": "topic:topic-thermal",
      "type": "Topic",
      "label": "Thermal management and heat transfer",
      "properties": {
        "id": "topic-thermal",
        "name": "Thermal management and heat transfer",
        "lede": "How heat is made, moved and removed in cells and packs, and the hardware that keeps a battery at the right temperature.",
        "context": "Select spatial detail for the question.",
        "example": "Equal total heat in different layouts can produce different gradients. Average temperature can miss a hot spot.",
        "lesson_url": "https://lemonergy.com/learn/fundamentals/battery-aging/",
        "lesson_label": "Open temperature and aging"
      }
    },
    {
      "id": "term:passive-thermal-management",
      "type": "Term",
      "label": "Passive thermal management",
      "properties": {
        "id": "passive-thermal-management",
        "name": "Passive thermal management",
        "aka": [
          "passive cooling",
          "thermal insulation"
        ],
        "section": "topic-thermal",
        "definition": "Controlling battery temperature without pumps, fans or compressors. Heat leaves by conduction to the enclosure and natural convection, sometimes helped by fins or phase change material, while insulation slows heat gain in summer and keeps a parked pack warm in winter. It suits small, low-power packs such as phones and e-bikes, not fast-charging vehicles.",
        "related": [
          "phase-change-material",
          "heat-sink",
          "thermal-management",
          "enclosure",
          "thermal-mass"
        ],
        "url": "https://lemonergy.com/learn/glossary/passive-thermal-management/",
        "mentions": [
          "heat-transfer-modes"
        ]
      }
    },
    {
      "id": "term:thermal-mass",
      "type": "Term",
      "label": "Thermal mass",
      "properties": {
        "id": "thermal-mass",
        "name": "Thermal mass",
        "aka": [
          "thermal inertia",
          "thermal time constant"
        ],
        "section": "topic-thermal",
        "definition": "A body’s total heat capacity seen as a buffer against temperature change. A 500 kg pack at about 1 kJ/(kg·K) stores roughly 500 kJ per kelvin, so 10 kW of uncooled heat warms it only about 1.2 K a minute. Together with the thermal resistance to the coolant it sets the pack’s thermal time constant.",
        "formula": "τ = m·cₚ·R_th",
        "related": [
          "specific-heat-capacity",
          "thermal-resistance",
          "thermal-model",
          "phase-change-material",
          "thermal-management"
        ],
        "example": {
          "title": "Calculate a thermal time constant",
          "text": "With mass 0.5 kg, cₚ = 900 J/(kg·K) and R_th = 2 K/W, the lumped thermal time constant is 900 s, or 15 min. The calculation assumes a nearly uniform internal temperature."
        },
        "url": "https://lemonergy.com/learn/glossary/thermal-mass/",
        "mentions": []
      }
    },
    {
      "id": "term:thermal-management",
      "type": "Term",
      "label": "Thermal management",
      "properties": {
        "id": "thermal-management",
        "name": "Thermal management",
        "abbr": "TMS",
        "aka": [
          "battery thermal management system",
          "BTMS"
        ],
        "section": "topic-thermal",
        "definition": "Keeping cells in their comfortable range, roughly 15–35 °C, and within a few degrees of each other: liquid cooling plates, refrigerant plates or immersion for heat removal, and heaters or waste heat for warming before fast charging in the cold.",
        "related": [
          "cooling-plate",
          "thermal-interface-material",
          "operating-temperature",
          "heat-generation",
          "preconditioning",
          "temperature-sensor"
        ],
        "url": "https://lemonergy.com/learn/glossary/thermal-management/",
        "mentions": [
          "fast-charging"
        ]
      }
    },
    {
      "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:graphite",
      "type": "Term",
      "label": "Graphite",
      "properties": {
        "id": "graphite",
        "name": "Graphite",
        "section": "topic-components",
        "definition": "Layered carbon, the negative active material of nearly all lithium-ion cells. Lithium intercalates between its layers up to LiC₆, a theoretical 372 mAh/g, at a potential about 0.1 V above lithium metal.",
        "related": [
          "anode-active-material",
          "intercalation",
          "natural-graphite",
          "synthetic-graphite",
          "lithium-plating"
        ],
        "lesson": "fundamentals/cell-anatomy/#components",
        "example": {
          "title": "Compare matching mass bases",
          "text": "A graphite value per gram of active material cannot be directly compared with a value including binder, additive and foil."
        },
        "url": "https://lemonergy.com/learn/glossary/graphite/",
        "mentions": [
          "milliampere-hour",
          "active-material"
        ]
      }
    }
  ]
}