Lithium sulfide ($\mathrm{L}{\mathrm{i}}_2\mathrm{S}$)

Lithium sulfide is $\mathrm{L}{\mathrm{i}}_2\mathrm{S}$, with lithium cations and sulfide anions. Sulfur has the formal oxidation state −2 in this composition.

Oxidation of sulfide toward elemental sulfur connects lithium sulfide with the chemistry of lithium-sulfur batteries. The transformation changes both oxidation state and solid-phase composition, so charge transport and material redistribution affect practical behaviour.