Thermal runaway barriers between cells
Mica and aerogel sheets are placed between battery cells as thermal barriers, helping prevent or slow fire propagation when a cell goes into thermal runaway and giving users additional time to reach safety.
Thermal runaway is a scenario every battery engineer must plan for. When a cell overheats, its internal temperature can exceed 600 °C within seconds. Without a barrier, the neighboring cell will be heated and a chain reaction will spread through the entire module.
How fire propagates in a battery module
Heat from a failed cell transfers to adjacent cells through three paths: conduction through contact surfaces, thermal radiation, and hot gases vented from the safety valve. A propagation barrier material needs to block all three paths while remaining thin and light so it does not reduce the energy density of the pack.
Mica vs. aerogel
| Criterion | Mica sheet | Aerogel sheet |
|---|---|---|
| Thermal conductivity | Approx. 0.2 – 0.5 W/m·K | Approx. 0.015 – 0.025 W/m·K |
| Temperature resistance | Above 800 °C | Above 650 °C |
| Typical thickness | 0.2 – 1.0 mm | 1.0 – 3.0 mm |
| Mechanical properties | Rigid, withstands the impact of hot gases | Soft, compressible to absorb tolerances |
| Suitable location | Module lid, above the vent valves | Between pouch cells and prismatic cells |
In many designs, the two materials are used together: aerogel between cells for thermal insulation, and mica on top to withstand hot gas jets and ejected metal particles.
Production requirements
Barrier sheets must be precisely cut to cell dimensions and can be laminated with a single-sided tape for quick positioning on the line. Aerogel requires a PET or PI film wrap to prevent silica dust from falling into the module during assembly.
- Check compression recovery, as cells swell slightly over charge and discharge cycles.
- Confirm dielectric strength if the barrier is in direct contact with the cell casing.
- Conduct module-level thermal propagation tests using heater triggering or nail penetration.
Converting to customer drawings
AMS converts mica and aerogel sheets to customer drawings, laminates tape and packs parts in trays ready to go straight to the production line.
For projects still in development, AMS engineers can propose several different layered structures for customers to test in parallel, balancing thickness, weight and propagation delay time. The options are summarized together with manufacturer data so the design team can make decisions faster.
Contact AMS Vietnam for advice on the right propagation barrier structure for your pack design.
