Understanding and Regulating the Mechanical Stability of Solid Electrolyte Interphase in Batteries

Abstract The unstable interface between reactive anodes and electrolytes in batteries has been identified as a critical factor in limiting the long‐cycle stability of batteries. An effective solution is to build a solid electrolyte interphase (SEI) that acts as a passivation layer to mitigate the side reactions between reactive anodes and electrolytes. The mechanical stability of SEI is important because SEI with poor mechanical stability cannot survive the volume and topography fluctuation of the anode upon cycling. The stress built‐up would cause mechanical failure of SEI, resulting in exposure of the fresh anode surface to the electrolyte, consuming the limited active materials and electrolytes, and inducing rapid battery decay. Therefore, understanding and regulating the mechanical stability of SEI is imperative for improving battery cycle life. In this review, the mechanical properties of SEI are discussed. Then, advanced characterization tools to measure the mechanical properties of SEI are introduced. Additionally, recent progress on improving the mechanical stability of SEI is presented in terms of in situ and ex situ modifications of SEI. Finally, an insightful outlook is provided to further understand and regulate the mechanical stability of SEI for improving battery performance.