Structural, thermal and electrical properties of lithium-manganese spinel with a sulphur-substituted oxygen sublattice

Sulphur substituted LiMn2O4-ySy spinels were obtained using the sol-gel method followed by calcination at 300 °C. The crystallinity of the samples was improved by further calcination at 800 °C. The monophase system was formed up to y = 0.20. At higher sulphur concentrations an additional phase (Mn2O3) appeared. The sulphided spinels were thermally stable in air up to about 900 °C. They decomposed above this temperature, with the oxidation of sulphur to SO2. The decomposition products, LiMnO2 and Mn3O4, reacted during slow cooling and formed stoichiometric LiMn2O4. Sulphur substitution retarded the phase transition at room temperature, although a new one appeared at higher temperatures (540-580 °C). Such an effect does not exist in sulphur-free spinels.