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

Abstract 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.