Low-cost preparation and purification of Li₂S for sulfide solid electrolytes

Lithium sulfide (Li₂S) is a key raw material for synthesizing sulfide solid electrolytes (SSEs), which has been considered as one of the most promising solid electrolytes for all-solid-state lithium batteries (ASSLBs). However, the high cost of Li₂S limits the development of SSEs. Herein, a novel approach for the preparation of Li₂S through carbothermal reduction of lithium sulfate (Li₂SO₄) is designed and optimized. Two novel strategies for purifying rough Li₂S materials are proposed in this work. A low raw material cost of $148 kg⁻¹ and a high yield of 88.50 % are achieved. Subsequently, Li₆PS₅Cl and Li_9.54Si_1.74P_1.44S_11.7Cl_0.3 solid electrolytes are synthesized with the self-made Li₂S and the corresponding electrochemical performances are evaluated. In NCMA|Li₆PS₅Cl|Li/In system, a high discharge capacity of 135 mAh g⁻¹ is maintained after 500 cycles at 1C. In NCMA|Li_9.54Si_1.74P_1.44S_11.7Cl_0.3|Li/In system, a high discharge capacity of 132 mAh g⁻¹ is maintained after 350 cycles at 1C. The high capacity and long cycle life demonstrate the effectiveness of Li₂S preparation and purification strategy proposed in this work.