Li and Vacancy Co‐Enriched Halide Electrolytes via Non‐Equimolar Substitution for Stable All‐Solid‐State Lithium Batteries

Abstract Halide solid electrolytes (SEs) have emerged as promising candidates for all‐solid‐state batteries (ASSBs) owing to their considerable ionic conductivity, mechanical deformability, and compatibility with high‐voltage cathodes. However, the conventional equimolar substitution strategy for developing halide SEs has limitations, as it fails to simultaneously ensure the presence of abundant vacancies and mobile Li‐ions, which are two critical factors governing ionic conductivity. Herein, a non‐equimolar substitution strategy is adopted to design a Li and vacancy co‐enriched Li₂Zr_0.75Ta_0.2Cl₆ with high ionic conductivity (1.74 mS cm⁻¹) and compatibility with high‐voltage Ni‐rich cathode. Specifically, more Zr⁴⁺ is substituted with less Ta⁵⁺ to generate Zr‐vacancies without depleting Li‐ion content while maintaining charge neutrality. Under the Li‐rich state, abundant Zr‐vacancies provide additional Li‐ion migration pathways within the non‐Li‐centered octahedral framework and promote uniform and efficient Li‐ion transport. ASSBs assembled with single‐crystalline LiNi_0.8Co_0.1Mn_0.1O₂ (scNCM811) cathode demonstrate exceptional cycling stability with high‐capacity retention (80.0% over 7800 cycles) and maintain stable cycling over 12 000 cycles at a high rate of 5 C. Notably, even under high loading conditions (20.62 mg cm⁻² scNCM811), the ASSBs maintained a capacity retention of 80.8% over 800 cycles and 70.1% over 2300 cycles at a high rate of 1 C.