Liquid-phase synthesis of Li₂S and Li₃PS₄ with lithium-based organic solutions

Sulfide solid electrolytes are widely regarded as one of the most promising technical routes to realize all-solid-state batteries (ASSBs) due to their high ionic conductivity and favorable deformability. However, the relatively high price of the crucial starting material, Li 2 S, results in high costs of sulfide solid electrolytes, limiting their practical application in ASSBs. To solve this problem, we develop a new synthesis route of Li 2 S via liquid-phase synthesis method, employing lithium and biphenyl in 1, 2-dimethoxyethane (DME) ether solvent to form a lithium solution as the lithium precursor. Because of the comparatively strong reducibility of the lithium solution, its reaction with sulfur proceeds effectively even at room temperature. This new synthesis route of Li 2 S starts with cheap precursors of lithium, sulfur, biphenyl and DME solvent, and the only remaining byproduct (DME solution of biphenyl) after the collection of Li 2 S product can be recycled and reused. Besides, the reaction can proceed effectively at room temperature with mild condition, reducing energy cost to a great extent. The as-synthesized Li 2 S owns uniform and extremely small particle size, proved to be feasible in synthesizing sulfide solid electrolytes (such as the solid-state synthesis of Li 6 PS 5 Cl). Spontaneously, this lithium solution can be directly employed in the synthesis of Li 3 PS 4 solid electrolytes via liquid-phase synthesis method, in which the centrifugation and heat treatment processes of Li 2 S are not necessary, providing simplified production process. The as-synthesized Li 3 PS 4 exhibits typical Li + conductivity of 1.85×10 −4 S⋅cm −1 at 30 °C.