Thermal interface materials for extended EV battery lifespan

25 September 2020

Heat dissipation and thermal management are growing issues in the design of electric vehicles (EVs) and their components. Within the battery pack, heat is generated during the operation of the battery. However, batteries operate more efficiently and retain their capacity longer if their environment is maintained within a narrow range of temperature.

Maintaining the temperature of the pack is essential and will increasingly be scrutinized as manufacturers and drivers try to get the most from a battery pack. Thankfully, dissipating heat from electrical parts and electronics is a well-studied issue. Energy transfer between battery components and cooling devices is most optimally accomplished by using thermal interface materials (TIMs).

There are different ways in which TIMs are used in battery modules. They are placed on the bottom plate of the battery or as heat spreaders between the array of cells and the cooling plate, thereby conducting heat and providing a thermal path for heat to flow away from the battery. The functionality of a TIM comes from thermally conductive material(s) that are laden in a dispersion or solid matrix. Since these TIMs are used in close contact with electrical components like batteries, they must have high dielectric strength.

Figure 1: TIMs ensure waste heat is safely exhausted from sensitive electronics, despite inherent surface area challenges. Source: Saint-Gobain Tape SolutionsFigure 1: TIMs ensure waste heat is safely exhausted from sensitive electronics, despite inherent surface area challenges. Source: Saint-Gobain Tape Solutions

Gap fillers (also commonly referred to as thermal pads) are a specific type of TIM ideal for conforming to rough, curved, uneven or dynamic surfaces. This provides a thermally conductive pathway to exhaust excess heat and keep components within operating specifications, even if the component surfaces present challenges. The thermal pad is intended to maintain maximum surface area contact between the battery and the heat sink, minimizing potential thermal impedance and providing the shortest pathway to conduct the heat away.

It is very common to specify a TIM product based on their characteristics (“product specifications”) like thermal conductivity, impedance and electrical resistance. But, in an actual application there are other features that need to be taken into consideration to effectively utilize a product.

In many instances, these application specific features are conformability, surface characteristics like tack level and the ability to re-work during the assembly process. These features are closely tied to a specific assembly/disassembly process. A tailored approach to considering these aspects is needed so as not to compromise the main qualities of the product like the thermal impedance and electrical isolation.

The 3 attributes of the TIM that play very important role are:

  • Hardness or CFD – this is the ability of the material to conform without exerting excessive pressure on cells
  • Surface tack – this would help the cells or modules to be held in position with minimal movement during the assembly process
  • Liner options – to aid in ease of assembly and to automate placement of pads

The Saint Gobain ThermaCool product range, including TC2006, TC2005, TC2008 and TC3007, is specifically developed with these customizations in focus. Thermal conductivity and electrical isolation properties are maintained mostly constant, while the other characteristics as indicated above are tailored to different levels to suit any specific assembly process.

Another example, ThermaCool R-10404 is a closed-cell type of silicone sponge rubber. This material provides the conformability needed to maintain contact between the EV battery and the heat sink. It adapts to the dimensional changes of the EV battery due to its highly stable compression set resistance. This also helps protect against the shocks and vibration, and the related noise or rattle, that are common in automobiles. This sturdy characteristic combined with thermal conductivity and dielectric strength, ensures that battery packs serve an extended lifespan. Options here include type of adhesive or substrate, dimensions and shape.

Often, a custom solution can pay for itself many times over thanks to process improvements that these customizations can provide. Saint-Gobain engineers work with customers to determine the most efficient way to integrate and scale the use of TIMs in manufacturing. Gaining a clear understanding of these various considerations vastly simplifies TIM selection.

To learn more about how Saint-Gobain Tape Solutions innovates materials and solutions for today’s manufacturing challenges, visit their webpage.

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