Uncovering the critical impact of the solid electrolyte interphase structure on the interfacial stability

Abstract Solid electrolyte interphase (SEI) plays a critical role in determining the interfacial stability, which in turn impacts the plating/stripping process of the lithium metal anode. Substantial research has been focused on the composition of SEI and its contribution to the interfacial stability. Herein, we illustrate the significance of SEI structure, in a comprehensive comparison of a diluted electrolyte (1 M LiTFSI‐PC) and a super‐concentrated electrolyte (8 M LiTFSI‐PC). Illustrated by in situ optical and atomic force microscope observation, homogeneous plating on lithium anode is achieved in the concentrated electrolyte. However, x‐ray photoelectron spectroscopy and molecular dynamics simulations reveal that, contrary to the general understanding, the components of SEI is nearly identical for lithium anode cycled in both two electrolytes. Detailed characterizations demonstrate the structure of SEI is quite different. In concentrated electrolyte, a compact structure of SEI layer can be obtained, mainly due to the reduced solubility and outstanding formation kinetics of the interfacial layer. This work provided a new understanding to the excellent performance of super‐concentrated electrolyte in lithium metal battery.