Synthesis of Deliquescent Lithium Sulfide in Air

Inthe field of lithium-sulfur batteries (LSBs) and all-solid-statebatteries, lithium sulfide (Li2S) is a critical raw material.However, its practical application is greatly hindered by its highprice due to its deliquescent property and production at high temperatures(above 700 & DEG;C) with carbon emission. Hereby, we report a newmethod of preparing Li2S, in air and at low temperatures(& SIM;200 & DEG;C), which presents enriched and surprising chemistry.The synthesis relies on the solid-state reaction between inexpensiveand air-stable raw materials of lithium hydroxide (LiOH) and sulfur(S), where lithium sulfite (Li2SO3), lithiumthiosulfate (Li2S2O3), and waterare three major byproducts. About 57% of lithium from LiOH is convertedinto Li2S, corresponding to a material cost of & SIM;$64.9/kg_Li2S, less than 10% of the commercial price. The success of conductingthis water-producing reaction in air lies in three-fold: (1) Li2S is stable with oxygen below 220 & DEG;C; (2) the use ofexcess S can prevent Li2S from water attack, by forminglithium polysulfides (Li2S n ); and (3) the byproduct water can be expelled out of the reactionsystem by the carrier gas and also absorbed by LiOH to form LiOH & BULL;H2O. Two interesting and beneficial phenomena, i.e., the anti-hydrolysisof Li2S n and the decompositionof Li2S2O3 to recover Li2S, are explained with density functional theory computations. Furthermore,our homemade Li2S (h-Li2S) is at least comparablewith the commercial Li2S (c-Li2S), when beingtested as cathode materials for LSBs.