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

Abstract

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, Li2S, 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 Li2S 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 Li2S starts with cheap precursors of lithium, sulfur, biphenyl and DME solvent, and the only remaining byproduct (DME solution of biphenyl) after the collection of Li2S 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 Li2S owns uniform and extremely small particle size, proved to be feasible in synthesizing sulfide solid electrolytes (such as the solid-state synthesis of Li6PS5Cl). Spontaneously, this lithium solution can be directly employed in the synthesis of Li3PS4 solid electrolytes via liquid-phase synthesis method, in which the centrifugation and heat treatment processes of Li2S are not necessary, providing simplified production process. The as-synthesized Li3PS4 exhibits typical Li+ conductivity of 1.85×10−4 S⋅cm−1 at 30 °C.