Investigating the strength of heat-sealed cast polypropylene film for lithium-ion pouch cells considering thermo-mechanical coupling effects

This study investigates the failure mechanism of the heat-sealed cast polypropylene (CPP) film of lithium-ion pouch cells (LIPC) under varying loads and temperatures. Firstly, an in-situ tensile test was conducted on strips cut from the sealing edge adhesive area (SEAA) to measure the maximum strength and peel displacement. Subsequently, an accelerated degradation test (ADT) under different constant loads and temperatures was performed to simulate strength degradation process of the SEAA. The stress-normalized displacement curves were measured, and residual strengths were obtained for each condition. Results of data analysis showed that the strength of the adhesive area decreased slowly over time for a given load and temperature. Moreover, the strength degradation rate was positively related to the level of load and temperature. A modified cohesive zone model (CZM) was established to describe the failure behavior and strength degradation of the SEAA. Finally, the proposed model is validated by experimental data.