SOL-GEL SYNTHESIS OF MANGANESE OXIDES

Transparent and stable manganese dioxide gels are obtained upon reduction of permanganate aqueous solutions AMnO4 [A = Li, Na, K, NH4, N(CH3)4] by fumaric acid. All xerogels are amorphous when dried at room temperature. Their thermal behavior however depends on the nature of the counter cation A+. Ammonium permanganates lead to the formation of α- or γ-Mn2O3 while AMnO2 mixed oxides are obtained at high temperature when A = Li, Na, K. Other crystalline phases such as LiMn2O4 or Na0.7MnO2 are also formed at lower temperature around 500°C. Oxidation of these mixed oxides into sulfuric acid lead to the formation of λ- or δ-MnO2 while A+ and Mn2+ ions are released into the solution. Such manganese dioxides could be good candidates for making reversible cathodes in nonaqueous lithium batteries. © 1990.