Lithium sulfide powder is a high-purity, inorganic compound that appears as a white to yellowish crystalline powder. It has a molecular weight of 45.95 g/mol and a density of 1.82 g/cm³. Lithium sulfide is a strong nucleophile and has the chemical formula Li₂S. It readily reacts with water to produce lithium hydroxide and hydrogen sulfide gas. It is also soluble in some organic solvents, such as pyridine and dimethyl sulfoxide.

High-purity lithium sulfide is primarily used as a precursor in the synthesis of other lithium compounds such as lithium thioacetate, lithium tetrafluoroborate, and thio-LISICONs, which are used in lithium-ion batteries among other applications. High-purity lithium sulfide can also be used directly in battery applications as a cathode material in lithium-sulfur batteries. With a theoretical capacity of up to 1166 mAh/g, almost four times that of lithium cobalt oxide, lithium sulfide has gained attention as next-generation cathode material. Additionally, lithium sulfide is used as a precursor in the semiconductor industry for the production of thin-film transistors (TFTs) and other electronic devices, especially lithium sulfide-phosphorus oxide (Li2S-P2O5) TFTs. It is also used in the chemical manufacturing industry as a precursor for lithium hydride, lithium borohydride, and lithium amide, among many other applications.