Unveiling Insights in the Formation Mechanism of Li₃PS₄·2THF Solvato-Complex: H₂S Release and Solvent-Phase Interaction

Liquid phase synthesis of solid sulfide electrolytes has become a hot topic in recent years, as it is faster, less energy-demanding, and easier to industrialize than solid-state methods. Li₃PS₄ is one of the most studied solid electrolytes and can be relatively simple to synthesize in tetrahydrofuran (THF), with a high ionic conductivity (10^-4 S·cm^-1 at 25 °C). In this study, the formation mechanism of the intermediate Li₃PS₄·2THF solvato-complex was investigated with liquid and solid-state NMR characterization techniques. We also highlight, for the first time, the formation of hydrogen sulfide (H₂S) as a byproduct during the reaction of Li₂S and P₂S₅ in THF despite the dry synthetic conditions. This finding is of great significance with regards to scaling-up, since H₂S is harmful and corrosive. We demonstrate that H₂S production is the result of an interaction between the solvent and precursors during the formation of two intermediates: Li₂P₂S₆ and Li₃PS₄·2THF.