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

Abstract

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-Li_5.6PS_4.6Cl_1.4 solid electrolyte was synthesized and compared with the C-Li_5.6PS_4.6Cl_1.4 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-Li_5.6PS_4.6Cl_1.4. Besides, the rate performance and long cycling stability of an all-solid-state lithium battery NCM//Li_5.6PS_4.6Cl_1.4//Li–In assembled with H-Li_5.6PS_4.6Cl_1.4 are better than those of batteries assembled with C-Li_5.6PS_4.6Cl_1.4. 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.