Phase field modeling of lithium diffusion, finite deformation, stress evolution and crack propagation in lithium ion battery

Mechanical degradation under cyclic charging and discharging has been the one of the most important bottlenecks for the developments of lithium ion batteries. Understanding of stress evolution process of anode during cycling is a way to deeply understand the mechanical degradation. In this paper, a phase field model (PFM) coupling lithium diffusion, finite deformation, stress evolution with crack propagation is established. Then the model is applied to spherical silicon particle to explore the stress evolution with taking account of finite deformation, elastic softening and plastic flow. The numerical results show that small deformation model and finite deformation model provide different stress states especially when the anode undergoes a large volumetric expansion. Elastic softening has not a significant effect on stress evolution in spherical particle. Plastic flow decreases the magnitude of stress, and deeply changes the stress evolution, making the hoop stress near the particle surface to become positive during charge process, indicating the particle surface is subjected to tensile hoop stress.