MECHANISM OF LI+ INSERTION IN SPINEL-TYPE MANGANESE OXIDE - REDOX AND ION-EXCHANGE REACTIONS

Three kinds of spinel-type manganese oxide were prepared by heating a mixture of MnOOH and Li2CO3 at different conditions (varying the starting Li/Mn ratio and temperature) followed by an acid treatment with a HCl solution. The insertion reactions of lithium ions in these samples were investigated by chemical, X-ray, DTA-TG analyses, and pH titration. The insertion sites could be classified into three groups, e.g. a redox-type site, a Li+-specific ion-exchange site, and a nonspecific ion-exchange site. The proportion of each group varied depending on the preparation conditions of manganese oxide. The pH titration study showed that the Li+-specific ion-exchange site had a stronger acidity than the redox-type site. The origin of these sites is discussed in terms of the physicochemical properties of the heat treated precusors. The variation of the oxidation state of manganese in the precursor relates to the formation of different kinds of site.