Solid-state Li metal battery technology is attractive, owing to the high energy density, long lifespans, and better safety. A key obstacle in this technology is the unstable Li/solid-state electrolyte (SSE) interface involving electrolyte reduction by Li. Herein we report a novel approach based on the use of a nanocomposite consisting of organic elastomeric salts (LiO-(CH2O)n-Li) and inorganic nanoparticle salts (LiF, -NSO2-Li, Li2O), which serve as an interphase to protect Li10GeP2S12 (LGPS), a highly conductive but reducible SSE. The nanocomposite is formed in situ on Li via the electrochemical decomposition of a liquid electrolyte, thus having excellent chemical and electrochemical stability, affinity for Li and LGPS, and limited interfacial resistance. XPS depth profiling and SEM show that the nanocomposite effectively restrained the reduction of LGPS. Stable Li electrodeposition over 3000 h and a 200 cycle life for a full cell were achieved.
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