Thermal interface materials (TIMs) play a critical role in battery thermal management systems by improving heat transfer between cells and cooling plates. Efficient heat dissipation is essential for maintaining optimal operating temperatures, preventing thermal runaway, and extending battery lifespan. TIMs fill microscopic air gaps between surfaces, reducing thermal resistance and enhancing conductive heat transfer. The selection of TIMs depends on material properties, application requirements, and performance metrics such as thermal conductivity, thickness, and mechanical compliance.

Several types of TIMs are commonly used in battery systems, including silicone-based materials, thermal greases, gap fillers, and phase change materials. Silicone-based TIMs are widely adopted due to their flexibility, chemical stability, and resistance to degradation under thermal cycling. These materials often incorporate ceramic or metal fillers, such as aluminum oxide or boron nitride, to enhance thermal conductivity. Typical silicone-based TIMs exhibit thermal conductivities ranging from 1 to 5 W/mK, with softer formulations ensuring better conformity to surface irregularities.

Thermal greases, also known as thermal pastes, offer higher thermal conductivity, often between 3 and 10 W/mK, due to their high filler content. These materials are viscous and can be applied in thin layers, minimizing thermal resistance. However, greases may suffer from pump-out effects under prolonged thermal cycling, where material migrates away from the interface, reducing effectiveness over time. To mitigate this, some formulations include cross-linking agents to improve stability.

Gap fillers are elastomeric pads designed to accommodate larger gaps between cells and cooling plates, typically ranging from 0.5 to 5 mm in thickness. These materials provide both thermal conduction and mechanical cushioning, protecting cells from vibrations and mechanical stress. Gap fillers often feature thermal conductivities between 1 and 6 W/mK, with higher-performance variants incorporating advanced fillers like graphite or carbon fibers. Their compressibility ensures uniform pressure distribution, improving contact and heat transfer efficiency.

Phase change materials (PCMs) represent another category of TIMs that transition from solid to liquid at specific temperatures, conforming closely to surface imperfections. In their liquid state, PCMs achieve low thermal resistance, with conductivities typically between 1 and 3 W/mK. These materials are particularly useful in applications where temperature fluctuations are frequent, as they can adapt to changing interface conditions. However, containment measures are necessary to prevent leakage after phase transition.

Performance metrics for TIMs include thermal conductivity, thermal impedance, thickness, and mechanical properties. Thermal conductivity, measured in W/mK, indicates the material’s inherent ability to conduct heat. However, the actual performance in an application is better represented by thermal impedance, which accounts for the material’s thickness and contact resistance. Lower impedance values signify more efficient heat transfer. The optimal thickness of a TIM depends on the gap size and pressure applied during assembly; thinner layers generally reduce thermal resistance but require smoother surfaces.

Mechanical properties such as hardness, compressibility, and adhesion strength are equally important. Softer materials conform better to rough surfaces, reducing interfacial resistance, while higher adhesion prevents delamination under mechanical stress. Durability under thermal cycling is another critical factor, as repeated expansion and contraction can degrade TIM performance over time. Accelerated aging tests are often conducted to evaluate long-term reliability.

In battery systems, TIMs must also address electrical insulation requirements to prevent short circuits between cells or conductive cooling plates. Most polymer-based TIMs are inherently insulating, but filler selection must avoid electrically conductive particles unless isolation layers are incorporated. Dielectric strength is a key parameter, with values typically exceeding 10 kV/mm for reliable operation in high-voltage battery packs.

The application method of TIMs influences their effectiveness. Dispensing techniques such as screen printing, stenciling, or automated dispensing ensure uniform coverage and minimize air entrapment. Pre-formed pads offer ease of installation and consistent thickness but may lack adaptability to complex geometries. The choice between these methods depends on production volume, precision requirements, and cost considerations.

Recent advancements in TIM formulations focus on improving thermal conductivity while maintaining mechanical compliance. Hybrid materials combining silicone matrices with high-conductivity fillers like boron nitride nanosheets or aluminum nitride particles have demonstrated conductivities exceeding 10 W/mK in experimental studies. However, trade-offs exist between conductivity and mechanical properties, as higher filler loading can reduce elasticity and increase hardness.

Environmental factors also influence TIM selection. Automotive and aerospace applications demand materials that withstand wide temperature ranges, humidity, and exposure to chemicals such as electrolytes or coolants. Silicone-based TIMs generally perform well in harsh environments, whereas other polymers may degrade under similar conditions. Outgassing is another consideration, particularly in enclosed battery systems where volatile organic compounds could affect other components.

In summary, TIMs are indispensable for efficient thermal management in battery systems, bridging the gap between cells and cooling plates to enhance heat dissipation. Material selection involves balancing thermal performance, mechanical properties, and environmental resilience. Ongoing research aims to develop TIMs with higher conductivity, better durability, and easier manufacturability, supporting the advancement of safer and more efficient energy storage solutions.