Thermal materials for batteries: which one is right for you?
Battery thermal management is the deciding factor in the lifespan and safety of the entire system. This article compares three common material groups, thermally conductive silicone pads, two-part thermal gap fillers and phase change materials, to help engineers choose the right solution for each battery design.
Lithium-ion cells perform best between 20°C and 40°C. When the temperature difference between cells exceeds 5°C, the battery ages unevenly and the capacity of the whole pack drops quickly. The thermal interface material placed between cells, modules and the cooling plate is the bridge that carries heat out efficiently.
Thermally conductive silicone pads
Gap pads are very soft, easy to handle and can compensate for assembly tolerances from 0.5 mm up to several millimeters. Typical thermal conductivity ranges from 1.5 to 6 W/m.K. The drawbacks are that they are difficult to automate on high-speed lines and costs rise sharply for high-conductivity pads.
Two-part thermal gap fillers
Liquid gap fillers are applied with metering-dispensing equipment, fill every gap and cure in place. They are the choice of many EV battery manufacturers because they suit high-volume production and can be removed for repair. Attention should be paid to viscosity, dispensing speed and the abrasiveness of the filler on the mixing head.
Phase change materials
Phase change materials are solid during assembly and soften once they reach about 50–60°C, forming a very thin contact layer with low thermal resistance. They suit flat surfaces and small gaps, such as between a power control module and its heat sink, and are rarely used for large gaps.
| Criterion | Silicone pad | Two-part gap filler | Phase change material |
|---|---|---|---|
| Thermal conductivity (W/m.K) | 1.5–6 | 2–4 | 3–8 |
| Suitable gap | 0.5–5 mm | 0.3–3 mm | Below 0.2 mm |
| Automation | Moderate | Excellent | Good |
| Reworkability | Easy | Moderate | Easy |
When selecting a material, engineers should also consider the following criteria:
- UL94 V-0 flame rating for materials placed near cells.
- Dielectric breakdown voltage appropriate to the system voltage.
- Compressive force exerted on the cells during assembly.
- Density, which affects the total weight of the pack.
In practice, many battery designs combine two material groups: a two-part gap filler at the bottom of the module in contact with the cooling plate, and silicone pads at the sides where large tolerances must be absorbed or parts must be removed for maintenance. Before finalizing the design, thermal cycling and vibration tests should be run to check whether the material delaminates or hardens over time.
To receive samples and technical data sheets for battery thermal management materials, contact AMS Vietnam.
