Mica covers a group of silicate minerals used in a thin sheet form as a thermal barrier in battery pack designs to contain thermal runaway.
Tesla Cybertruck Battery
This image shows the foam and mica sheet that is used in the pack to inhibit thermal propagation.
Material properties
Mica is a sheet silicate (phyllosilicate) mineral group. Two types are used in battery pack thermal barriers: muscovite, which resists continuous temperatures up to roughly 500–600°C, and phlogopite, which is more thermally stable and can withstand 800°C or higher — making it the more common choice for thermal runaway barriers. Both forms are also strong electrical insulators as well as thermal barriers, which is useful where a material needs to block heat and prevent short circuits between cells or modules. Mica is manufactured into thin, flexible sheets, sometimes reinforced with a glass-cloth backing, that can be cut and formed around cells, modules, or pack walls.
Advantages
- Does not burn and does not release significant toxic gas when heated, unlike some polymer-based barrier materials
- Mechanically robust — can be cut, formed, and handled repeatedly during pack assembly without degrading
- Dual role as both a thermal and electrical insulator, which can reduce the number of separate materials needed in a pack design
Disadvantages
- Denser and heavier than alternatives such as aerogel, adding more mass for a given thickness
- Achieving a given level of thermal blocking can require more material volume than higher-performance barriers, affecting pack packaging and weight budgets
- Sourcing and material cost can be a consideration, as mica supply is concentrated in a small number of regions
How mica compares to other thermal barrier materials
Mica is one of several thermal barrier materials used in battery packs, alongside aerogel and intumescent coatings, each with different trade-offs between weight, cost, thickness, and temperature performance. See Thermal Barrier Materials for how these options compare.
See also: Aerogel, Thermal Barrier Materials