Where Should Thermal Barriers Be Placed Inside an EV Battery Pack?

Using excellent insulation in the wrong location can still allow heat, flame or vent gases to bypass the barrier and propagate through the battery pack.

Battery insulation should be placed according to the expected propagation path. Cell-to-cell barriers target the nearest neighboring cell, module-to-module barriers create a second level of separation, while pack-level materials protect covers, enclosures and sensitive electrical zones.

A robust thermal propagation prevention strategy therefore uses material location as carefully as material performance. The objective is not to fill the battery with insulation, but to interrupt the most important thermal and electrical pathways.

Where Should Cell-to-Cell Barriers Be Installed?

If adjacent cells have a direct thermal path, one failed cell can rapidly transfer energy into its neighbor.

Place cell-to-cell barriers at the interfaces where neighboring cells can exchange the most damaging heat. For prismatic and pouch architectures, the barrier may also need to accommodate cell swelling and compression throughout battery life.

Aspen Aerogels describes its PyroThin products specifically as cell-to-cell thermal barriers for pouch and prismatic batteries, combining thermal protection with mechanical behavior under battery compression.^[1]

Where Should Module-to-Module Barriers Go?

Stopping direct cell-to-cell conduction does not guarantee that a thermal event cannot reach another module through structural parts, vent gases or flames.

Use module-level separation to interrupt the next propagation path. Barrier geometry should consider module walls, gaps, structural interfaces and likely vent direction rather than simply placing a sheet between two module housings.

Saint-Gobain identifies thermal-runaway pads for both cell cushioning and locations between modules, illustrating how barrier strategy can extend beyond individual cells.^[2]

Does the Battery Pack Lid Need Thermal Insulation?

A barrier strategy focused only between cells can leave the pack cover exposed to jet flames, hot gases and ejected particles.

Evaluate the pack lid and enclosure as separate thermal-runaway protection zones. UL Solutions notes that battery thermal runaway can produce jet-like flame, pressure and particles capable of eroding protective enclosure material.^[3]

This is why cell-to-cell insulation and enclosure protection should not be treated as interchangeable. The thermal and mechanical exposure can be very different.

How Should Engineers Decide Barrier Placement?

Adding insulation everywhere can increase weight, cost and compression without controlling the dominant propagation mechanism.

Map the thermal event before defining the die-cut parts. Identify the initiating cell, neighboring cells, vent direction, module boundaries, busbars, cooling structures, pack cover and potential flame or gas pathways.

Barrier thickness and material can then be optimized for each location rather than forcing one insulation sheet to perform every function.

Need Help Turning a Battery Layout Into Die-Cut Insulation Parts?

Send Fuqiang your cell arrangement, module drawing, available gaps, vent direction and insulation requirements. Our engineering team can review cell-to-cell, module-level and pack-level barrier locations and prepare samples for validation.

FAQ

Where should insulation go between battery cells?

It should be positioned at the cell interfaces where it can reduce heat transfer to adjacent cells while accommodating the required compression and cell movement.

What is a cell-to-cell thermal barrier?

It is a material placed between neighboring cells to reduce heat transfer and help prevent a thermal event in one cell from triggering the next.

What is a module-to-module barrier?

It is thermal or fire protection positioned between battery modules to help limit propagation beyond the affected module.

Should EV battery insulation cover the entire pack?

Not necessarily. Barrier location should follow thermal, flame, electrical and venting risks. Adding material where it provides little protection can unnecessarily increase mass and cost.

Is cell-to-cell insulation enough to stop thermal propagation?

Not always. Pack design must also consider vent gases, flames, structural conduction, module boundaries and enclosure protection.

A 15-Year Automotive Wire Harness and EV Battery Perspective

After 15 years working with automotive electrical systems, I approach battery insulation much like harness protection: put the protection where the failure energy actually travels. Correct placement can be as important as the thermal conductivity or temperature capability printed on the material datasheet.

Authoritative References

[1] Aspen Aerogels — Cell-to-Cell Thermal Barriers for EV Batteries

[2] Saint-Gobain — TRP Series Cell and Module Thermal Runaway Pads

[3] UL Solutions — Battery Enclosure Thermal Runaway Evaluation