Thermal Runaway Protection for Power Batteries: How Mica Creates a Reliable Internal Safety Barrier

Under abnormal operating conditions such as extrusion, penetration, overcharging and aging, lithium‑ion batteries undergo chained chemical reactions internally and release massive heat in a short period. This phenomenon is known as thermal runaway.

Once thermal runaway occurs in a single cell, high temperatures of thousands of degrees Celsius, high‑temperature molten slag and flammable gas will be released instantly. Without effective barriers, heat will rapidly transfer to adjacent cells and trigger cascading thermal propagation, which may lead to risks of battery pack fire and deflagration.

The core goal of thermal runaway protection is not to eliminate single‑cell failures entirely, but to block the spread of heat and flame, slow down thermal propagation, and gain precious escape time for vehicle occupants.

A complete protection solution includes active early warning via the BMS (Battery Management System) and heat dissipation through liquid thermal management systems. Passive thermal and dielectric insulation materials deployed at cell‑module‑pack levels are also indispensable. Mica serves as a key component within this passive protection system.

Mica is a layered silicate mineral. Through processes such as pulping, compounding and pressing, it can be processed into various forms including mica paper, mica plates, mica tapes and special‑shaped finished parts, suited for the complex assembly environment inside battery packs.

Different from organic polymer flame‑retardant materials, mica is an inorganic mineral material with core characteristics well‑suited for power‑battery applications:

• Structural stability under high‑temperature conditions When exposed to transient high temperatures generated by thermal runaway, mica resists melting and dripping. It retains its barrier structure to block high‑temperature molten slag and flame propagation toward surrounding components, delivering physical fire and heat insulation and lowering the possibility of cascading activation of adjacent cells.
• Combined high‑temperature resistance and high‑voltage dielectric performance In the high‑voltage system of power batteries, risks of high‑voltage arcing and short‑circuits exist alongside thermal hazards. With favorable dielectric properties, mica blocks heat and isolates live components. It helps prevent secondary short‑circuits caused by burnt‑out busbars and wiring harnesses during thermal runaway and stops faults from escalating.
• Low‑smoke and low‑toxicity for environmental compliance At elevated temperatures, mica produces little smoke and releases limited toxic and harmful gases. It satisfies environmental‑protection requirements for new‑energy interior trims and battery‑pack auxiliary materials and reduces secondary injuries induced by smoke in incident scenarios.
• Processability for lightweight‑design demands Mica can be manufactured into thin sheets, flexible tapes and rigid plates, and supports die‑cutting and stamping. It fits diverse application positions such as cell gaps, module partitions, high‑voltage busbars and harness wrapping. Compared with bulky metallic thermal‑insulation parts, it features controllable overall weight and aligns with battery‑pack design trends toward lightweighting and high space‑utilization efficiency.

Mica‑based protection does not rely on a single component. Instead, it is deployed at multiple critical positions within the battery pack to create multi‑layered safeguarding.

• Thermal isolation between cells and modules Placed in gaps between cells and modules, it slows lateral heat transfer when thermal runaway occurs in one unit and reduces risks of cascading thermal propagation.
• Protection for high‑voltage busbars and wiring harnesses Mica tapes and mica sleeves wrap high‑voltage busbars and sampling harnesses. Under extreme high‑temperature conditions, they safeguard electrical connections, prevent BMS monitoring failure caused by harness burnout, and mitigate risks of high‑voltage short circuits.
• Fire‑resistant barrier for battery pack top cover and compartment Serving as inner‑layer protection for the battery pack top cover, it separates the battery compartment from the passenger cabin. It blocks high heat and flue gas from penetrating into the cockpit and meets relevant flue‑gas isolation requirements specified in the new national standards.
• Protection for large‑scale energy‑storage battery systems Within large‑format energy‑storage cell systems, mica is also applied for module separation and high‑voltage cabinet insulation to accommodate safety‑design requirements of high‑capacity energy‑storage equipment.

With the implementation of new national standards and the popularization of CTB and CTC integrated battery structures, large‑format cells and high‑energy‑density products keep iterating. Battery safety protection has gradually expanded from former module‑level protection to cell‑level protection, driving sustained market demand growth for high‑temperature‑resistant thermal‑insulation and dielectric materials.

Beyond conventional mica, synthetic mica featuring higher purity and favorable temperature‑resistance performance is seeing gradually rising adoption in high‑end power battery and energy‑storage projects. The industry is also exploring composites of mica and other thermal‑insulation materials to further optimize overall protection performance.

There is no single solution for power battery safety. Iterations across material R&D, cell design, thermal‑management algorithms and passive‑protection auxiliary materials collectively lift the baseline for battery safety.

Technological progress ultimately aims to safeguard end‑user safety. While we focus on range, fast‑charging and intelligent parameters, the unseen safety designs behind batteries also deserve attention.