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

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 Li 2 Zr 0.75 Ta 0.2 Cl 6 with high ionic conductivity (1.74 mS cm −1 ) and compatibility with high-voltage Ni-rich cathode. Specifically, more Zr 4+ is substituted with less Ta 5+ 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 0.8 Co 0.1 Mn 0.1 O 2 (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.