{
  "node": {
    "id": "term:electrolyte-decomposition",
    "type": "Term",
    "label": "Electrolyte decomposition",
    "properties": {
      "id": "electrolyte-decomposition",
      "name": "Electrolyte decomposition",
      "section": "topic-aging",
      "definition": "Reduction of the electrolyte at the negative electrode and oxidation at the positive, outside its stability window. A little is useful — it builds the SEI — but continued decomposition consumes lithium, dries the cell and makes gas.",
      "related": [
        "sei",
        "cei",
        "electrochemical-stability-window",
        "gas-generation",
        "electrolyte-dry-out"
      ],
      "url": "https://lemonergy.com/learn/glossary/electrolyte-decomposition/",
      "mentions": [
        "electrode",
        "negative-electrode",
        "electrolyte",
        "oxidation",
        "reduction"
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      "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:sei",
      "type": "Term",
      "label": "Solid–electrolyte interphase",
      "properties": {
        "id": "sei",
        "name": "Solid–electrolyte interphase",
        "abbr": "SEI",
        "section": "topic-aging",
        "definition": "A film of electrolyte reaction products on the negative-electrode particles — graphite, and also silicon or lithium metal. It protects the electrode from further reaction but grows slowly for the whole life of the cell, consuming cyclable lithium.",
        "related": [
          "passivation",
          "formation",
          "calendar-aging",
          "loss-of-lithium-inventory",
          "cei"
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        "url": "https://lemonergy.com/learn/glossary/sei/",
        "mentions": [
          "electrode",
          "graphite",
          "electrolyte"
        ]
      }
    },
    {
      "id": "term:cei",
      "type": "Term",
      "label": "Cathode–electrolyte interphase",
      "properties": {
        "id": "cei",
        "name": "Cathode–electrolyte interphase",
        "abbr": "CEI",
        "section": "topic-aging",
        "definition": "The counterpart of the SEI on the positive electrode: a thin layer of electrolyte oxidation products on the oxide surface. It is thinner and less stable than the SEI, and its growth contributes to impedance rise, especially at high voltage.",
        "related": [
          "sei",
          "electrolyte-decomposition",
          "impedance-rise",
          "high-nickel"
        ],
        "url": "https://lemonergy.com/learn/glossary/cei/",
        "mentions": [
          "impedance",
          "electrode",
          "positive-electrode",
          "electrolyte",
          "oxidation"
        ]
      }
    },
    {
      "id": "term:electrochemical-stability-window",
      "type": "Term",
      "label": "Electrochemical stability window",
      "properties": {
        "id": "electrochemical-stability-window",
        "name": "Electrochemical stability window",
        "section": "topic-electrochemistry",
        "definition": "The potential range within which an electrolyte is neither reduced nor oxidised. Carbonate electrolytes are only stable from about 1 V to 4.3 V vs Li/Li⁺; graphite operates below that, which is why the SEI, not thermodynamics, keeps the cell alive.",
        "unit": "V",
        "related": [
          "electrolyte-decomposition",
          "sei",
          "voltage-window",
          "lnmo",
          "homo-lumo"
        ],
        "url": "https://lemonergy.com/learn/glossary/electrochemical-stability-window/",
        "mentions": [
          "graphite",
          "electrolyte"
        ]
      }
    },
    {
      "id": "term:gas-generation",
      "type": "Term",
      "label": "Gas generation",
      "properties": {
        "id": "gas-generation",
        "name": "Gas generation",
        "aka": [
          "gassing"
        ],
        "section": "topic-aging",
        "definition": "Formation of gases — ethylene, hydrogen, carbon monoxide and carbon dioxide — by electrolyte decomposition, mostly during formation and later under high voltage or temperature. In a pouch cell it shows as swelling; in a can it raises pressure until the vent opens.",
        "related": [
          "swelling",
          "degassing",
          "electrolyte-decomposition",
          "vent",
          "formation"
        ],
        "lesson": "fundamentals/battery-aging/#gas",
        "url": "https://lemonergy.com/learn/glossary/gas-generation/",
        "mentions": [
          "electrolyte",
          "pouch-cell"
        ]
      }
    },
    {
      "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: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:negative-electrode",
      "type": "Term",
      "label": "Negative electrode",
      "properties": {
        "id": "negative-electrode",
        "name": "Negative electrode",
        "section": "topic-components",
        "definition": "The electrode at the lower potential, usually graphite on copper foil in a lithium-ion cell. It holds the lithium when the cell is charged and releases it on discharge, and industry calls it the anode.",
        "related": [
          "anode",
          "graphite",
          "positive-electrode",
          "copper-foil"
        ],
        "lesson": "fundamentals/cell-anatomy/#anode-cathode",
        "example": {
          "title": "Keep the polarity name",
          "text": "Graphite remains the negative electrode during charge and discharge, while the anode/cathode reaction labels change with operating direction."
        },
        "url": "https://lemonergy.com/learn/glossary/negative-electrode/",
        "mentions": [
          "electrode"
        ]
      }
    },
    {
      "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": "term:oxidation",
      "type": "Term",
      "label": "Oxidation",
      "properties": {
        "id": "oxidation",
        "name": "Oxidation",
        "section": "topic-electrochemistry",
        "definition": "Loss of electrons by a species. On discharge the negative electrode is oxidised as lithium leaves it as Li⁺, which is why that electrode is called the anode.",
        "related": [
          "reduction",
          "anode",
          "redox-reaction"
        ],
        "url": "https://lemonergy.com/learn/glossary/oxidation/",
        "mentions": [
          "electrode",
          "negative-electrode"
        ]
      }
    },
    {
      "id": "term:reduction",
      "type": "Term",
      "label": "Reduction",
      "properties": {
        "id": "reduction",
        "name": "Reduction",
        "section": "topic-electrochemistry",
        "definition": "Gain of electrons by a species. On discharge the positive electrode is reduced as it takes up lithium ions and electrons, which is why it is called the cathode.",
        "related": [
          "oxidation",
          "cathode",
          "redox-reaction"
        ],
        "url": "https://lemonergy.com/learn/glossary/reduction/",
        "mentions": [
          "electrode",
          "positive-electrode"
        ]
      }
    },
    {
      "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"
      }
    }
  ]
}