Low-cost And Scalable Synthesis Of Li₂S With High-purity For Sulfide Solid Electrolyte

All-solid-state lithium batteries using non-flammable solid electrolytes can effectively improve battery safety.Among those developed solid electrolytes,sulfide solid electrolyte has the highest ionic conductivity,and attracted great attention from research institutions at home and abroad.The key raw material for the synthesis of sulfide electrolyte is Li₂S.At present,the high cost of Li₂S leads to the high price of sulfide electrolyte.Therefore,low-cost and large-scale synthesis of Li₂S is the key to promote the practical use of sulfide electrolytes and sulfide solid-state batteries.This article focuses on the low-cost synthesis technology of Li₂S,and explores the low-cost preparation method of high-purity Li₂S,Furthermore,the feasibility of this method is verified by the synthesized sulfide solid electrolyte Li₆PS₅Cl.The main research contents are as follows:（1）The feasibility of preparing high-purity Li₂S using low-cost lithium sulfate carbothermic reduction method is explored.Lithium sulfide prepared with the traditional carbothermic reduction method is tightly compounded with carbon,resulting in low purity and cannot be used for the synthesis of sulfide solid electrolytes.Optimizing the mixing method can improve the mixing efficiency and uniformity,and make it more suitable for scale-up preparation.In virtue of XRD,SEM and other characterization comparisons,it is found that the improved method can increase the conversion rate of Li₂S in the reaction.Carbothermal reaction products are analyzed,and purification steps are designed according to the difference in physical and chemical properties of Li₂S and impurities.With the help of recyclable solvents,the purification cost is reduced,and the purification effect is explored.（2）In order to verify the quality and purity,the self-made Li₂S and the expensive commercial Li₂S are simultaneously used to prepare sulfide electrolyte Li₆PS₅Cl for comparison.It is found that the parameters of the electrolyte from self-made Li₂S are equivalent to that from commercial Li₂S.All-solid-state lithium battery assembled using Li-In alloy anode and single crystal NCM622@AlO cathode displays outstanding electrochemical performance.The average coulombic efficiency is 99.89%during 700cycles at 1 C,and the cycle performance is better than that from commercial Li₂S.The excellent electrochemical performance proves the feasibility of this Li₂S preparation method,then the influence of different carbon sources and the amount of carbon on the reaction is further explored.The reaction conditions are optimized by combining cost and other factors,and the yield and cost is analyzed.