Polymer-BN Composites as Thermal Interface Materials for Lithium-Ion Battery Modules: Experimental and Simulation Insights

Efficient thermal management is critical for the safety and performance of lithium-ion battery (LIB) systems, particularly under high C-rate charge–discharge cycling. Here, we investigate two classes of polymer composite thermal interface materials (TIMs): graphene-PLA (GPLA) fabricated via 3D printing and boron nitride nanoplatelets (BN)-loaded thermoplastic polyurethane (TPU) composites with 20 and 40 wt.% BN content. To understand cooling dynamics, we developed a simple analytical model based on Newtonian heat conduction, predicting an inverse relationship between the cooling rate and the TIM thermal diffusivity. We validated this model experimentally using a six-cell LIB module equipped with active liquid cooling, and complemented it with finite-element simulations in COMSOL Multiphysics incorporating experimentally derived parameters. Across all approaches, analytical, numerical, and experimental, we observed excellent agreement in predicting the temperature decay profiles and inter-cell temperature differentials ($\Delta T$). Charge–discharge cycling studies at varying C-rates demonstrated that high-diffusivity TIMs enable faster cooling but require careful design to minimize lateral thermal gradients. Our results establish that an ideal TIM must simultaneously support rapid vertical heat sinking and effective lateral thermal diffusion to ensure thermal uniformity. Among the studied materials, the 40% BN–60% TPU composite achieved the best overall performance, highlighting the potential of BN filler-engineered polymer composites for scalable thermal management in next-generation battery systems.