Formation of spinel structured compounds in the lithium permanganate thermal decomposition

Products of thermal decomposition of lithium permanganate LiMnO4·3H2O, which are formed in temperature range 160–900 °C, have been characterized by powder XRD and chemical analysis. It has been found that the decomposition of the permanganate results in the formation of an equimolar mixture of manganate(IV) Li2MnO3 and stoichiometric spinel LiMn2O4 at the temperatures above 700 °C. Intermediate products with spinel structure are formed at lower temperatures with oxidation number of manganese being between +4 and +3.5. These compounds can be related to overstoichiometric spinel phases with general formula Lia[Mn(1 + 0.5a)Li(1 − 0.5a)]O4, where a > 1. Electrochemical properties of these intermediates with regard to the reaction of Li extraction were investigated. The data are of interest for the development of synthesis methods for mixed oxides containing lithium and manganese with lithium permanganate as the lithiating reagent.