Investigation of Complex Intermediates in Solvent-Mediated Synthesis of Thiophosphate Solid-State Electrolytes

Lithium thiophosphates represent a promising class of solid Li+ conductors for all-solid-state batteries. Scalable solvent-mediated synthesis routes for several Li-P-S ternary compounds have been reported, but little is known regarding the reaction mechanism of such pathways. This work demonstrates that solvent-mediated synthesis of lithium thiophosphate solid electrolytes from mixtures of Li2S and P2S5 proceeds through a highly soluble P2S62- intermediate. This intermediate exhibits virtually the same Raman spectra in several solvents including acetonitrile, methyl acetate, ethyl acetate, ethyl propionate, dimethoxyethane, tetraethylene glycol dimethyl ether, and tetrahydrofuran. Based on this universal intermediate, a general reaction mechanism is proposed for the solvent-mediated synthesis of several lithium thiophosphates including (LiPS3)(n), Li2P2S6, Li7P3S11, and Li3PS4.