Synthesis of Deliquescent Lithium Sulfide in Air.

In the field of lithium-sulfur batteries (LSBs) and all-solid-state batteries, lithium sulfide (LiS) is a critical raw material. However, its practical application is greatly hindered by its high price due to its deliquescent property and production at high temperatures (above 700 °C) with carbon emission. Hereby, we report a new method of preparing LiS, in air and at low temperatures (∼200 °C), which presents enriched and surprising chemistry. The synthesis relies on the solid-state reaction between inexpensive and air-stable raw materials of lithium hydroxide (LiOH) and sulfur (S), where lithium sulfite (LiSO), lithium thiosulfate (LiSO), and water are three major byproducts. About 57% of lithium from LiOH is converted into LiS, corresponding to a material cost of ∼$64.9/kg_LiS, less than 10% of the commercial price. The success of conducting this water-producing reaction in air lies in three-fold: (1) LiS is stable with oxygen below 220 °C; (2) the use of excess S can prevent LiS from water attack, by forming lithium polysulfides (LiS); and (3) the byproduct water can be expelled out of the reaction system by the carrier gas and also absorbed by LiOH to form LiOH·HO. Two interesting and beneficial phenomena, i.e., the anti-hydrolysis of LiS and the decomposition of LiSO to recover LiS, are explained with density functional theory computations. Furthermore, our homemade LiS (h-LiS) is at least comparable with the commercial LiS (c-LiS), when being tested as cathode materials for LSBs.