UCl₃-Type Crystalline Oxychloride Electrolytes for All-Solid-State Lithium-Ion Batteries

Halide solid-state electrolytes are promising for next-generation all-solid-state lithium-ion batteries due to their high ionic conductivity and wide electrochemical windows. While most research focuses on close-packed crystal structures, nonclose-packed frameworks─exemplified by UCl₃-type structures─offer unique advantages in enhancing lithium-ion transport via reduced diffusion barriers. Here, we report a new family of UCl₃-type crystalline oxychloride electrolytes, Li_{0.388+<i>x</i>}La_0.475Ta_0.238Cl_3-<i>x</i>O_<i>x</i> (0 ≤ <i>x</i> ≤ 0.388, LLTCO), synthesized via rapid high-energy shake milling. The material with an optimized composition (<i>x</i> = 0.15) exhibits high ionic conductivity above 2 mS cm^-1 at 30 °C, oxidative stability exceeding 5 V vs Li/Li⁺, and excellent mechanical compressibility. Moreover, the LLTCO-based Li-Li symmetric cells show a long cycle life, indicating their strong capacity to suppress lithium dendrite formation. Spectroscopy analyses reveal the successful incorporation of oxygen, which preferentially substitutes Cl^- around Ta⁵⁺ sites without compromising crystallinity, even at a high oxygen content. The oxygen incorporation further promotes the formation of Li environments with fast dynamics, accounting for the enhanced conductivity. All-solid-state batteries utilizing the optimized oxychloride electrolyte in conjunction with Ni-rich cathodes demonstrate enhanced reversible capacities compared to their undoped counterparts. This work highlights the benefits of nonclose-packed UCl₃-type oxychloride electrolytes, offering new design strategies for high-performance all-solid-state batteries.