Investigation of the Carbothermic Reduction of Lithium Sulfate for the Production of Lithium Sulfide

Abstract Although lithium sulfide (Li 2 S) is a key raw material for solid electrolytes in all-solid-state batteries, its production is costly. To develop an effective production method for high-purity Li 2 S, carbothermic reduction of lithium sulfate (Li 2 SO 4 ) was investigated. In this study, the principle of the carbothermic reduction was elucidated using thermodynamic analysis using a chemical potential diagram and experimental results. The reduction of Li 2 SO 4 using carbon (C) was performed at 1000–1100 K for 1–10 h under an argon (Ar) gas atmosphere. When the carbothermic reduction was performed at 1100 K for 10 h, a mixture of Li 2 S and C was obtained. To produce high-purity Li 2 S powder, the residues obtained after the reduction were leached using anhydrous ethanol (EtOH) at 298 K, followed by filtration and heat treatment. The results of this study show the mechanism and feasibility of the production of high-purity of Li 2 S from Li 2 SO 4 by utilizing carbothermic reduction. Graphical Abstract