Liquid-Phase Synthesis of Lithium Argyrodite Sulfide Electrolytes Using Tetrahydrofuran and Water

Li₆PS₅Cl argyrodite sulfide electrolytes exhibit high ionic conductivity, making them promising candidate electrolyte materials for all-solid-state batteries. Although water is an environmentally friendly and attractive solvent, its use in the synthesis of Li₆PS₅Cl has been limited due to the low moisture stability of Li₆PS₅Cl. In this study, Li₆PS₅Cl argyrodite sulfide electrolytes were synthesized via liquid-phase synthesis using water as the main solvent through optimization of both the synthesis conditions and the composition of the Li₃PS₄·Li₂S·LiCl precursor. In this process, the precursor is formed via the aqueous phase, followed by heat treatment that drives the crystallization of Li₆PS₅Cl and improves its crystallinity. A series of electrolyte samples derived from precursors with varying Li₃PS₄ contents, xLi₃PS₄·Li₂S·LiCl (x = 1.0-1.4), were systematically prepared and characterized, revealing their structural and electrochemical properties. The electrolyte derived from the optimal precursor composition (x = 1.2) exhibited a high ionic conductivity of 1.2 × 10^-3 S cm^-1 at 25 °C in a green compact, and the all-solid-state cells assembled using this electrolyte demonstrated reversible charge-discharge behavior over 100 cycles at room temperature. These results demonstrate that water can be successfully used as the main solvent to synthesize argyrodite-type sulfide electrolytes and provide a versatile strategy for sustainable production of high-performance sulfide solid electrolytes suitable for practical use.