Mechanical and Li Diffusion Properties of Interface Systems in the Solid Electrolyte Interphase

Lithium (Li) metal has emerged as one of the most promising electrode materials with great potential to fulfill the demands of high-energy-density batteries. The solid electrolyte interphase (SEI) on the Li metal anode plays a critical role in electrochemical processes and undergoes large deformation. SEI failure could promote the growth of Li dendrites, leading to performance degradation and security hazards in Li metal batteries. The native SEI exhibits poor mechanical properties, which can be attributed to the presence of heterogeneous interfaces between various components. In this work, we construct the heterogeneous interface by two SEI inorganic components of LiF and Li₂O. Using density functional theory calculations, we investigate the mechanical properties of the LiF/Li₂O interface system and explore the diffusion mechanisms of Li ions through the strained LiF/Li₂O interface. The results indicate that the heterogeneous interface system has relatively low Young's modulus and tensile strength. In addition, tensile strain increases the energy barriers of interface diffusion, thereby reducing the rate of electrochemical reactions. This study could contribute to the analysis of SEI failure, providing theoretical understanding for Li interface diffusion in the SEI.