A Li‐Rich Fluorinated Lithium Zirconium Chloride Solid Electrolyte for 4.8 V‐Class All‐Solid‐State Batteries

Abstract Chloride solid‐state electrolytes (SEs) represent an important advance for applications in all‐solid‐state batteries (ASSBs). Among various chloride SEs, lithium zirconium chloride (Li 2 ZrCl 6 ) is an attractive candidate considering the high natural abundance of Zr. However, Li 2 ZrCl 6 meets the challenge in practical ASSBs because of its limited ionic conductivity and instability when paired with high‐voltage cathodes. This is a major drawback, which can result in a high internal resistance, a low capacity utilization of cathode, and poor cycle stability, especially at high voltage. Existing methods cannot achieve simultaneous enhancement on both ionic conductivity and high‐voltage stability due to a trade‐off between lithium‐ion migration and structural stability. Here a two‐pronged strategy based on partial fluorination and incorporation of lithium ions in excess of stoichiometric ratios is introduced that enables high‐voltage stability while increasing ionic conductivity concurrently. The Li‐rich fluorinated halide SE (Li 2.3 ZrCl 6.1 F 0.2 ) exhibits a significant advancement in performance, with an ionic conductivity that is double that of the pristine Li 2 ZrCl 6 and much better high‐voltage stability. By leveraging Li 2.3 ZrCl 6.1 F 0.2 with the LiCoO 2 cathode and the Li–In anode, the all‐solid‐state cell exhibits a remarkable initial specific capacity (198.0 mAh g −1 at 0.1 C) and a high capacity retention (78.5% after 150 cycles) within 3.0–4.8 V.