Electrochemical lithium intercalation in disordered manganese oxides

Four highly disordered manganese oxides were prepared by reduction of sodium permanganate by chloride, iodide, hydrogen peroxide or oxalate in aqueous medium containing a large excess of Li+ ions, yielding hydrated oxides with Mn valence in the range 3.80–3.92. Thermogravimetric studies showed that the iodide-reduced oxide can be dehydrated to 92% at 240°C, while the other three ones retain water at temperatures up to ca. 400°C, where crystallization is significant. The electrochemical behaviour was studied potentiostatically and galvanostatically in lithium cells on samples dried at 240°C. All samples give a unique, broad, reversible oxidation–reduction peak in the range of 2.0–3.6 V. Cycling capacities vary in decreasing order iodide>hydrogen peroxide>chloride>oxalate. The best compound, Li0.60Na0.16MnO2.33I≈0.05, has an initial capacity of >170 Ah/kg, slowly decreasing on cycling to reach 140 Ah/kg after 70 cycles. These performances, which are far superior to those of manganese spinels, are compared to those of recently reported amorphous manganese oxi-iodides prepared in anhydrous conditions.