In Situ Construction of a LiF‐Enriched Interface for Stable All‐Solid‐State Batteries and its Origin Revealed by Cryo‐TEM

Abstract The application of solid polymer electrolytes (SPEs) is still inherently limited by the unstable lithium (Li)/electrolyte interface, despite the advantages of security, flexibility, and workability of SPEs. Herein, the Li/electrolyte interface is modified by introducing Li 2 S additive to harvest stable all‐solid‐state lithium metal batteries (LMBs). Cryo‐transmission electron microscopy (cryo‐TEM) results demonstrate a mosaic interface between poly(ethylene oxide) (PEO) electrolytes and Li metal anodes, in which abundant crystalline grains of Li, Li 2 O, LiOH, and Li 2 CO 3 are randomly distributed. Besides, cryo‐TEM visualization, combined with molecular dynamics simulations, reveals that the introduction of Li 2 S accelerates the decomposition of N(CF 3 SO 2 ) 2 − and consequently promotes the formation of abundant LiF nanocrystals in the Li/PEO interface. The generated LiF is further verified to inhibit the breakage of CO bonds in the polymer chains and prevents the continuous interface reaction between Li and PEO. Therefore, the all‐solid‐state LMBs with the LiF‐enriched interface exhibit improved cycling capability and stability in a cell configuration with an ultralong lifespan over 1800 h. This work is believed to open up a new avenue for rational design of high‐performance all‐solid‐state LMBs.