Phase Field Modeling of Lithium-Ion Diffusion and Crack Formation in the Solid Electrolyte Interphase of Silicon-Based Lithium-Ion Battery

Lithium-ion batteries (LIBs) play a key role in portable equipment, electric vehicles, and other energy storage modules. Solid electrolyte interface (SEI) layer cause a significant degradation for lithium-ion batteries’ electrochemical performance. Recently, silicon or Si-based anodes becomes an attractive candidate for the electrode of LIBs due to the low cost and high theoretical specific capacity. However, the mechanism of lithium-ion transport through the SEI layer is not fully understood as well as the crack formation of SEI layer due to silicon severe volume change. A phase field model is employed and developed to simulate the SEI structure and lithium-ion diffusion inside SEI layer including the thermodynamic chemical potential and elastic energy. SEI layer is believed to have multilayered structure; And SEI formation can be regarded as a solidification process. The phase field model is a powerful tool to investigate solidification problems without explicitly tracking the interfaces between the SEI species and electrolyte solution. Two sets of phase field variables are used to describe the microstructure of SEI layer and Lithium-ion transport in SEI layer. One is associated with the volume fraction of the interface. And the other is associated with the concentrations of SEI species. Lithium-ion transport will cause the elastic energy change. Therefore, elastic field needs to be considered in the developed model. And the elastic energy can be applied to investigate the crack initiation and propagation. Most importantly, the present developed model has great potential to be extended to three dimensional spaces for SEI layer spatial growth investigation.