Promoting Ion Conduction and Li Metal Compatibility Through Nb ⁵⁺ ‐Substituted Zirconium‐Based Chlorides for All‐Solid‐State Batteries

ABSTRACT Zirconium‐based halide electrolytes were created as prospective candidates for all‐solid‐state lithium batteries (ASSLBs) because of their low cost, wide electrochemical window, and superior compatibility with oxide cathodes. However, practical implementation is hindered by limitations such as suboptimal room‐temperature (RT) ionic conductivity (< 1 mS cm −1 ) and poor interfacial compatibility with lithium metal. Herein, we report a new class of zirconium‐based chlorides, Li 2− x Zr 1− x Nb x Cl 6 , synthesized by a high‐valent Nb 5+ doping method. The introduction of Nb 5+ induces local lattice decrease, which simultaneously weakens the binding intensity of Li─Zr and optimizes ion migration pathways and defect concentrations. Therefore, the optimal composition, Li 1.75 Zr 0.75 Nb 0.25 Cl 6 (denoted as LZC‐Nb), achieves a high RT ionic conductivity of 1.82 mS cm −1 and exceptional moisture resistance. Furthermore, the dynamic interfacial modulation of LZC‐Nb forms a low‐impedance passivation layer, enhancing Li + transport kinetics. This improvement in interfacial stability enables symmetric batteries to exceed a critical current density of 1.3 mA cm −2 . Combined with a LiNi 0.8 Mn 0.1 Co 0.1 O 2 cathode, the resultant ASSLB retains 81.8% of its initial capacity (157.5 mAh g −1 ) after 600 cycles at 0.3 C. This study provides a proven strategy for developing inorganic ionic conductors with superior ionic transport and interfacial compatibility, offering a viable pathway toward high‐performance ASSLBs.