High‐Humidity‐Tolerant Chloride Solid‐State Electrolyte for All‐Solid‐State Lithium Batteries

Halide solid-state electrolytes (SSEs) hold promise for the commercialization of all-solid-state lithium batteries (ASSLBs); however, the currently cost-effective zirconium-based chloride SSEs suffer from hygroscopic irreversibility, low ionic conductivity, and inadequate thermal stability. Herein, a novel indium-doped zirconium-based chloride is fabricated to satisfy the abovementioned requirements, achieving outstanding-performance ASSLBs at room temperature. Compared to the conventional Li₂ZrCl₆ and Li₃InCl₆ SSEs, the hc-Li_2+xZr_1-xIn_xCl₆ (0.3 ≤ x ≤ 1) possesses higher ionic conductivity (up to 1.4 mS cm^-1), and thermal stability (350 °C). At the same time, the hc-Li_2.8Zr_0.2In_0.8Cl₆ also shows obvious hygroscopic reversibility, where its recovery rate of the ionic conductivity is up to 82.5% after 24-h exposure in the 5% relative humidity followed by heat treatment. Theoretical calculation and experimental results reveal that those advantages are derived from the lattice expansion and the formation of Li₃InCl₆ ·2H₂O hydrates, which can effectively reduce the migration energy barrier of Li ions and offer reversible hydration/dehydration pathway. Finally, an ASSLB, assembled with reheated-Li_2.8Zr_0.2In_0.8Cl₆ after humidity exposure, single-crystal LiNi_0.8Mn_0.1Co_0.1O₂ and Li-In alloy, exhibits capacity retention of 71% after 500 cycles under 1 C at 25 °C. This novel high-humidity-tolerant chloride electrolyte is expected to greatly carry forward the ASSLBs industrialization.