Effective thermal conductivity and cooling performance of battery pack modules as a function of porosity introduced during thermal interface material application

Abstract Thermal interface materials serve as critical components for facilitating heat transfer between cells and the cooling system in electric vehicle battery packs. However, internal porosity introduced during manufacturing can substantially reduce their thermal conductivity. In this study, the internal pore structure of actual thermal interface material samples was characterized using X-ray computed tomography, and porosity was quantitatively determined through a regression-based thresholding method implemented in MATLAB. The resulting pore distributions were incorporated into finite volume-based thermal simulations in Ansys Fluent, enabling the calculation of effective thermal conductivity as a function of porosity ratio. The simulated effective thermal conductivity values closely matched those predicted by the Effective Medium Theory, particularly at low porosity levels. In contrast, conjugate thermal-fluid analyses of electric vehicle battery packs revealed that local temperature increases of up to 1.3°C can occur depending on pore location and distribution. These findings indicate that Effective Medium Theory-based average conductivity models are inadequate for capturing localized thermal hotspots. Consequently, thermal interface material application processes and design strategies should address not only the allowable porosity threshold but also the spatial distribution of pores to ensure robust thermal management in electric vehicle battery systems.