Analysis of mechanical failure at the interface between graphite particles and polyvinylidene fluoride binder in lithium-ion batteries

摘要

The capacity fade corresponding to the mechanical failure of active materials is one of hurdles to overcome in the widespread of echo-friendly vehicles. However, the mechanisms of the mechanical failure at the electrode are not fully understood. In this study, the initiation and propagation of debonding at the interface between an active particle and a binder are investigated using a coupled electrochemical-mechanical and cohesive-zone finite-element model. The effects of particle sizes and lithiation kinetics on the progressive growth of interfacial debonding are studied, and critical states of charges are determined. The normal and shear tractions at the interface are systematically analyzed to understand their role in debonding behavior. The simulation results show that the interfacial debonding is less likely to happen as the particle size and C-rate increase, which is opposite to the inner-particle fracture behavior. The numerical study indicates that there is a trade-off between the inter-particle failure and inner-particle fracture. This study suggests that the binder effect needs to be included in the theoretical model for better understanding of the mechanical failure at the electrode. The debonding failure maps provided from the study can assist in engineering design of active materials and safe operation of batteries.