Impact of grain boundaries on the fracture behavior of polycrystalline electrode materials: a chemo-mechanical phase field model

Abstract

Grain boundaries play a dominant role in Li⁺ transport and mechanical deformation of polycrystalline electrode materials. Herein, a chemo-mechanical phase field model is developed to investigate the effects of grain boundary on chemo-mechanical responses in lithium batteries. It is demonstrated that grain boundaries with high diffusion coefficients provide a fast pathway for the Li⁺ transport, which alleviates the nucleation of inter- and intra-granular fracture while accelerates crack propagation through the particle center. Grain boundaries with low diffusion coefficients hinder the Li⁺ transport between grains, which leads to crack mainly initiated in the outer layer of electrode particles. Improving grain boundary fracture toughness is efficient for alleviating inter-granular fracture. Interestingly, high grain boundary fracture toughness even hinders crack propagation along grain boundaries but has no effect on the total damage of the particle. For high rate operation of batteries, increasing grain boundary fracture toughness is more significant to mitigate inter-granular fracture. This fundamental study provides insights into the multi-physical behavior of polycrystalline electrodes with various chemical and mechanical properties of grain boundaries.