Thermal Interface Material Selection for Prismatic Battery Modules
Matching material compliance to prismatic swell while controlling bond line thickness dictates thermal impedance, voltage isolation, and pack yield.
Thermal Pads
Meaning
Gap filling interface materials facilitate the transfer of heat from battery cells to a cooling plate or heat sink. Usage of thermal pads compensates for mechanical tolerances and surface irregularities that would otherwise create insulating air pockets. These components are usually made from a silicone or acrylic base filled with thermally conductive ceramic particles.
Material Composition
Ceramic fillers like aluminum oxide or boron nitride provide the necessary thermal pathways while maintaining electrical insulation. Depending on the specific formulation, thermal pads can achieve conductivities ranging from 1 to 10 Watts per meter Kelvin. The choice of binder determines the softness and tackiness of the finished sheet.
Compression Requirement
Effective heat transfer depends on the pad being squeezed between the two mating surfaces to ensure intimate contact. Standard designs for thermal pads specify a target deflection, often between ten and forty percent of the original thickness. Over-compression can damage the cells or lead to oil bleeding, while under-compression leaves air gaps that reduce efficiency.
Efficiency Measure
Measurement of thermal resistance is the primary value used to compare the performance of different gap fillers. Because thermal pads are thicker than thermal grease, they are better suited for large assemblies where the distance between components varies.