[Abstract]

For the efficient production of high-purity lithium sulfide (Li₂S), a crucial raw material for sulfide-based solid electrolytes in all-solid-state batteries, the reduction of lithium sulfate (Li₂SO₄) with hydrogen sulfide (H₂S) gas was investigated. In this study, H₂S (g) was generated by dissolving iron sulfide (FeS) in a sulfuric acid (H₂SO₄) solution at 293 K, and then reacted with Li₂SO₄ at 873–1073 K. When the reduction of Li₂SO₄ with H₂S (g) was conducted at 1073 K for 6 h, high-purity Li₂S was produced. In these experiments, a deposit of excess elemental sulfur (S) was observed. The excess S was produced by the decomposition of H₂S (g) and the reaction between H₂S (g) and sulfur dioxide (SO₂) gas generated by the reaction of Li₂SO₄ with H₂S (g). In addition, the mechanism for the reduction of Li₂SO₄ with H₂S (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 Li₂S by reducing Li₂SO₄ with H₂S (g) generated by dissolving FeS in a H₂SO₄ solution.