Recovering the Ionic Conductivity of Oxygen‐Doped Li3.25InCl5.75O0.25 Electrolyte through Heat Treatment: Reconstructing the Structure Damaged by Moisture

Metal halide solid‐state electrolytes (MHSEs), especially oxyhalides, possess a broad electrochemical stability window, optimized interfacial compatibility and suitability for high‐voltage cathode materials, making them promising candidates for next‐generation all‐solid‐state lithium metal batteries (ASSBs). However, their commercialization is still hindered by several critical technical challenges, especially the significant moisture sensitivity. In this study, the damage to the structure and electrochemical performance of Li3.25InCl5.75O0.25 electrolyte caused by humid air exposure is evaluated, and a heat treatment is proposed and proven effective in recovering the damage. A series of spectroscopic experiments reveal that humid air exposure triggers hydrolysis and hydration reactions in Li3.25InCl5.75O0.25, leading to lattice contraction, that significantly hindering lithium‐ion transport. After thermal processing at 400 °C, the lattice is reconstructed, and the ionic conductivity reaches an 83.5% recovery (7.6×10‐4 S·cm‐1 vs. pristine 9.1×10‐4 S·cm‐1). ASSBs based on the repaired electrolyte demonstrate excellent cycling and rate performance, retaining 76.1% capacity after 1000 cycles at 2C. The ASSBs also retains substantial capacity output under extreme temperatures (60 °C/ ‐20 °C), further verifying the comprehensive enhancement of the heat treatment strategy on electrochemical performance and its engineering application potential.