A Novel H2S Reduction Process of Li2SO4 for High-Purity Li2S Production Toward Next-Generation Batteries

For the efficient production of high-purity lithium sulfide (Li 2 S), a crucial raw material for sulfide-based solid electrolytes in all-solid-state batteries, the reduction of lithium sulfate (Li 2 SO 4 ) with hydrogen sulfide (H 2 S) gas was investigated. In this study, H 2 S ( g ) was generated by dissolving iron sulfide (FeS) in a sulfuric acid (H 2 SO 4 ) solution at 293 K, and then reacted with Li 2 SO 4 at 873–1073 K. When the reduction of Li 2 SO 4 with H 2 S ( g ) was conducted at 1073 K for 6 h, high-purity Li 2 S was produced. In these experiments, a deposit of excess elemental sulfur (S) was observed. The excess S was produced by the decomposition of H 2 S ( g ) and the reaction between H 2 S ( g ) and sulfur dioxide (SO 2 ) gas generated by the reaction of Li 2 SO 4 with H 2 S ( g ). In addition, the mechanism for the reduction of Li 2 SO 4 with H 2 S ( g ) was elucidated using a chemical potential diagram considering the chemical potentials of the species involved in the reaction. These findings demonstrate the feasibility of producing high-purity Li 2 S by reducing Li 2 SO 4 with H 2 S ( g ) generated by dissolving FeS in a H 2 SO 4 solution.