Lithium‐Deficient Halide Solid‐State Electrolytes with Enhanced Electrochemical Performance for All‐Solid‐State Batteries

Abstract The halide solid‐state electrolyte (SSE) Li 2 ZrCl 6 has emerged as a promising candidate for all‐solid‐state batteries (ASSBs) due to the abundance of Zr in the Earth's crust and its low cost. However, its relatively low ionic conductivity prevents it from meeting the essential performance threshold (> 1 mS cm −1 ) required for application in ASSBs. In this work, a novel strategy is presented to enhance ionic conductivity by incorporating high‐valence Ta 5+ into the Li 2 ZrCl 6 framework, resulting in a series of Li‐deficient Li 2– x Ta x Zr 1– x Cl 6 (LTZC, 0 ≤ x ≤ 0.4) SSEs. Remarkably, the LTZC ( x = 0.275) achieves a high ionic conductivity of 1.43 mS cm −1 at 30 °C, surpassing that of Li‐rich Li 2 ZrCl 6 ‐based SSEs (e.g., Li 2+2 x Zr 1– x Mg x Cl 6 ). Neutron powder diffraction reveals a pronounced rearrangement of Li + ions upon Ta 5+ doping, and bond‐valence site energy calculations indicate that this rearrangement enhances Li + transport within the lattice. Furthermore, ASSBs incorporating LTZC SSE with LiCoO 2 or LiNi 0.8 Co 0.1 Mn 0.1 O 2 cathode and Li‐In anode exhibit excellent cycling performance. This work underscores the effectiveness of structural regulation in developing Li‐deficient halide SSEs as a viable strategy for enhancing their electrochemical performance.