Facile Synthesis of High Purity Li2S by Titanothermic Reduction

Lithium sulfide (Li2S) is indispensable for lithium–sulfur batteries and sulfide solid-state batteries. However, its high preparation cost and strict process conditions represent core bottlenecks restricting large-scale commercial application. To address this issue, a novel process featuring a low-cost, high-safety, and controllable reaction is proposed in this work. Compared with the commercial H2S-based route for Li2S production, the developed process presents distinct advantages, including accessible raw materials, high safety, low overall cost, and low environmental load. Using Li2SO4·H2O as the raw material and Ti as the reducing agent, high-purity T-Li2S (>99.9%) is successfully synthesized via solid-state sintering and purification, yielding a higher purity level than that of commercial C-Li2S (>99.7%). Furthermore, sulfide all-solid-state electrolytes T-Li5.3PS4.3ClBr0.7 and C-Li5.3PS4.3ClBr0.7 are prepared using the as-obtained T-Li2S and commercial C-Li2S as precursors, respectively. The room-temperature Li-ion conductivities are determined to be 14.5 mS/cm and 11.0 mS/cm, revealing faster ion migration and efficient ion transport in T-Li5.3PS4.3ClBr0.7 without high-temperature assistance, which fully validates the feasibility of the proposed strategy. Overall, this work provides a new technical route for the preparation of high-purity Li2S, showing promising application prospects.