Compressive mechanical behavior and constitutive modeling of power lithium-ion battery separators under strain rate-temperature coupling

As a crucial component to ensure the safety and reliability of lithium-ion batteries (LIBs), the polymer separator plays a significant role in ensuring the mechanical abuse safety of the battery, and its mechanical properties have become an important indicator of battery safety performance. This study focuses on the compressive mechanical behavior of separators in prismatic power batteries under coupled strain rate and temperature conditions. Quasi-static and dynamic compression experiments were conducted under a wide range of strain rates and temperatures. These tests assessed the mechanical behavior and damage mechanism of separator at elevated temperatures and different strain rates. The strain rate-dependent and temperature-dependent mechanical properties of the separator was meticulously explored. The results indicated that the mechanical behavior of separator is highly sensitive to both the strain rate and the temperature. As the strain rate increases, the yield point of the separator decreases. Additionally, both the elastic modulus and the yield stress of the separator decrease as the temperature. At low strain rates, the yield point shifts forward, whereas at high strain rates, the yield strain increases with the temperature. Additionally, the coupled effects of temperature and strain rate were found to alter the damage failure modes, subsequently affecting the separator’s mechanical properties and structural integrity. At low strain rates, the failure of the separator is primarily characterized by plastic deformation and local buckling, whereas complex dynamic failure modes may occur at high strain rates. Based on experimental data, a nonlinear viscoelastic constitutive model was developed, incorporating the effects of temperature-strain rate coupling. This model offers essential insights for the safe and optimized design of lithium-ion batteries. The comprehensive experimental analysis and model developed in this study provide critical references for advancing the design, manufacturing, and practical application of LIB separators, enhancing their reliability and safety across a diverse range of operational conditions.