Tailoring the Work Function of Oxyhalide Solid Electrolytes via Sulfur Doping to Boost High‐Performance All‐Solid‐State Lithium Batteries

ABSTRACT Achieving high ionic conductivity alongside interfacial stability is essential yet challenging for solid‐state electrolytes. Here, we report a sulfur‐doped oxohalide solid‐state electrolyte, LiTaO _0.5 S _0.5 Cl ₄ , synthesized via a facile high‐energy ball milling method. Confirmed by the experimental and theoretical simulation results, sulfur incorporation significantly elevates the work function and ionization energy to 4.54 and 8.0 eV, respectively, reducing electron availability for interfacial charge transfer and enhancing oxidative stability against high‐voltage cathodes. In addition, the coexistence of S ²⁻ and O ²⁻ promotes in‐situ formation of a Ta ₂ O/TaS ₂ composite protective layer, featuring high electronic insulation and low Li ⁺ migration barrier. Consequently, the all‐solid‐state Li battery delivers a high‐capacity retention of 75.5% after 500 cycles at 0.5 C using LiNi _0.8 Co _0.1 Mn _0.1 O ₂ cathodes. This work demonstrates that anion doping is an effective strategy for concurrently improving ionic conductivity and cathode interfacial stability.