Liquid‐Phase Synthesis of Halide Solid Electrolytes for All‐Solid‐State Batteries Using Organic Solvents

Halide solid electrolytes (SEs) show high ionic conductivity and good compatibility with cathode active materials, providing long‐life all‐solid‐state lithium‐ion batteries (ASSLIBs). Liquid‐phase synthesis technology is a feasible option for the large‐scale manufacturing of halide SEs. However, no leading liquid‐phase synthesis method for halide SEs has been developed because of a limited understanding of the solvent effect on the formation of halide SEs. Herein, a scalable and universal liquid‐phase synthesis method for halide SEs using organic solvents is reported. The Li 3− x YCl 6− x SEs synthesized via pyridine transform trigonal structure to metastable orthorhombic structure as the Li concentration decreases, forming a highly pure orthorhombic phase with an ionic conductivity of 1.3 × 10 −4 S cm −1 at 25 °C in the composition of x = 1. Spectroscopic analysis indicates that pyridine acts as a reducing ligand, stabilizing the orthorhombic Li 2 YCl 5 by modulating the valence state of yttrium ions. Additionally, the developed synthesis method is extended to the synthesis of bromide SEs with high ionic conductivity. ASSLIBs using LiNi 0.8 Co 0.1 Mn 0.1 O 2 ‐Li 2 YCl 5 cathode composites demonstrate good cycling stability for 100 cycles. The liquid‐phase synthesis technology reported here opens opportunities for the practical manufacturing of halide‐based ASSLIBs.