Advanced High‐Voltage All‐Solid‐State Li‐Ion Batteries Enabled by a Dual‐Halogen Solid Electrolyte

Abstract Solid‐state electrolytes (SEs) with high anodic (oxidation) stability are essential for achieving all‐solid‐state Li‐ion batteries (ASSLIBs) operating at high voltages. Until now, halide‐based SEs have been one of the most promising candidates due to their compatibility with cathodes and high ionic conductivity. However, the developed chloride and bromide SEs still show limited electrochemical stability that is inadequate for ultrahigh voltage operations. Herein, this challenge is addressed by designing a dual‐halogen Li‐ion conductor: Li 3 InCl 4.8 F 1.2 . F is demonstrated to selectively occupy a specific lattice site in a solid superionic conductor (Li 3 InCl 6 ) to form a new dual‐halogen solid electrolyte (DHSE). With the incorporation of F, the Li 3 InCl 4.8 F 1.2 DHSE becomes dense and maintains a room‐temperature ionic conductivity over 10 −4 S cm −1 . Moreover, the Li 3 InCl 4.8 F 1.2 DHSE exhibits a practical anodic limit over 6 V (vs Li/Li + ), which can enable high‐voltage ASSLIBs with decent cycling. Spectroscopic, computational, and electrochemical characterizations are combined to identify a rich F‐containing passivating cathode‐electrolyte interface (CEI) generated in situ, thus expanding the electrochemical window of Li 3 InCl 4.8 F 1.2 DHSE and preventing the detrimental interfacial reactions at the cathode. This work provides a new design strategy for the fast Li‐ion conductors with high oxidation stability and shows great potential to high‐voltage ASSLIBs.