Electrode Properties of Todorokite-type Tunnel-structured Manganese Oxide for Calcium Secondary Batteries

The electrode properties of todorokite-type tunnel-structured manganese oxides (TodMO) were examined for their potential use as cathode materials in calcium batteries. TodMO with a chemical composition of Mg0.19Na0.07MnO2·0.37H2O was prepared through hydrothermal treatment of layer-structured manganese oxide using magnesium ions as interlayer guest ions. The TodMO exhibited a dis-charge and charge capacity of 100 and 80 mAh g−1, respectively, at a relatively large current density of 100 mA g−1. The reaction mecha-nism was studied in detail using X-ray absorption spectroscopy measurements. Consequently, it became clear that the newly formed Mn3+-compound converted from TodMO is responsible for the reversible capacity.