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

Lithium sulfide (Li 2 S) 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 Li 2 S limits the development of SSEs. Herein, a novel approach for the preparation of Li 2 S through carbothermal reduction of lithium sulfate (Li 2 SO 4 ) is designed and optimized. Two novel strategies for purifying rough Li 2 S 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, Li 6 PS 5 Cl and Li 9.54 Si 1.74 P 1.44 S 11.7 Cl 0.3 solid electrolytes are synthesized with the self-made Li 2 S and the corresponding electrochemical performances are evaluated. In NCMA|Li 6 PS 5 Cl|Li/In system, a high discharge capacity of 135 mAh g −1 is maintained after 500 cycles at 1C. In NCMA|Li 9.54 Si 1.74 P 1.44 S 11.7 Cl 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 Li 2 S preparation and purification strategy proposed in this work.