Universal Oxychlorination Strategy in Halide Solid Electrolytes for All‐Solid‐State Batteries

ABSTRACT Research into halide solid electrolytes has intensified due to their high ionic conductivity, oxidation stability and ductility, yet their close‐packed anion frameworks offer limited structural tunability, hindering further enhancement of bulk Li + conduction. Here, we demonstrate a universal bulk oxygen incorporation strategy for halide solid electrolytes, using WO 2 Cl 2 to enable controlled introduction of oxygen into diverse Li x MCl 6 (M = Zr, Y, Er, and In) lattices, effectively enhancing Li + conduction. Complementary structural, spatial, and vibrational analyses, including synchrotron X‐ray techniques, depth‐resolved spectroscopy, and Raman measurements, confirm oxygen incorporation via the [WO 2 Cl 4 ] 2− polyhedral unit, validating the structural integrity of the modified halides. First‐principles calculations reveal that the anchored oxygen flattens the Li + migration energy landscape by diversifying Li sites and weakening Li–Cl interactions, accounting for the observed conductivity enhancement. In addition, the alleviation of the thermodynamic driving force for hydrolysis improves air and moisture stability, and the enhancement in ionic conductivity leads to improved electrochemical performance. These oxygen‐anchored oxychlorides offer lattice‐level regulation principles that underpin conventional halide design, ensuring both practicality and broad applicability.