Preparation of high-quality lithium sulfide by reducing lithium sulfate with hydrogen: a green and cost-effective method

Lithium sulfide (Li2S) is the critical raw material used for the synthesis of sulfide solid-state electrolytes, but its high cost and pollution restrict the commercialization of sulfide solid-state electrolytes and sulfide-based all-solid-state batteries. A new green and cost-effective method for the synthesis of high-quality Li2S is designed and proposed in this work. The method of reducing Li2SO4 with H2 circumvents the disadvantages of many side reactions, complicated purification processes, impure products and emission of greenhouse gases (CO and CO2) associated with traditional carbothermal reduction methods, and high-purity Li2S (H-Li2S) is obtained. Subsequently, H-Li5.6PS4.6Cl1.4 solid electrolyte was synthesized and compared with the C-Li5.6PS4.6Cl1.4 electrolyte synthesized from commercial Li2S (C-Li2S). The ionic conductivity (8.06 mS cm−1) and chemical/electrochemical stability as cathode/anode material were better than those of C-Li5.6PS4.6Cl1.4. Besides, the rate performance and long cycling stability of an all-solid-state lithium battery NCM//Li5.6PS4.6Cl1.4//Li–In assembled with H-Li5.6PS4.6Cl1.4 are better than those of batteries assembled with C-Li5.6PS4.6Cl1.4. It can maintain a discharge capacity of 133.23 mA h g−1 after 300 cycles at 1C (95% of the initial discharge capacity), and has a high discharge capacity of 127.9 mA h g−1 at 3C. The high electrochemical performance of the all-solid-state battery confirms the superiority of high-purity H-Li2S and the advantages of the hydrogen reduction method.