A method for evaluating the cooling performance of a battery system assembly considering the mechanical behavior of the thermal interface material

Lithium-ion batteries, the power source of electric vehicles (EVs), can undergo thermal runaway when overheated, leading to fire or explosion; effective thermal management of the battery system assembly (BSA) is therefore essential. To improve BSA cooling performance, thermal interface materials (TIMs) are applied as heat-dissipating media in battery packs. A TIM typically comprises a polymer matrix (e.g., silicone) filled with highly conductive particles and exhibits time-dependent viscoelastic behavior. Consequently, mechanical attributes of the TIM, such as interfacial contact pressure, evolve over time and can affect heat-transfer performance. This study evaluates BSA cooling performance while accounting for the viscoelastic behavior of a pad-type TIM implemented in an EV battery pack. The thermal contact resistance (TCR) at the TIM interface was obtained as a function of contact pressure, and comparison between heat-transfer tests using a newly devised TIM specimen model and thermal analyses incorporating the TCR verified that time-dependent changes in heat-transfer performance can be predicted with fidelity. Computational fluid dynamics (CFD) simulations of an indirect liquid-cooled battery pack with TCR reflecting viscoelasticity showed the battery temperature rising to 42.94 °C, outside the optimal operating window. Neglecting the viscoelastic character of the TIM can thus lead to overestimation of the BSA's cooling capability. The findings provide a methodology for more accurate and reliable assessment of BSA cooling performance and will inform precise battery thermal management system (BTMS) design to enhance EV performance and safety. • Proposed a new BSA cooling evaluation method considering TIM viscoelasticity. • Quantified time-dependent TCR by viscoelastic behavior of TIM. • Proposed a method and apparatus to evaluate heat transfer performance of TIM. • Performed CFD with TCR at TIM interfaces to assess BSA cooling more precisely. • TIM viscoelasticity increased battery temperature beyond optimal range due to TCR.