Insertion of Calcium Ion into Prussian Blue Analogue in Nonaqueous Solutions and Its Application to a Rechargeable Battery with Dual Carriers

We observed the first electrochemical insertion of Ca2+ into Prussian blue analogue, MnFe­(CN)6, in nonaqueous solutions of Ca­(CF3SO3)2 and various solvents including ionic liquid at 60 °C. The kinetics for the Ca2+ insertion reaction were studied by cyclic voltammetry, and were compared to those of Na+ intercalation. By coupling this phenomenon with metallic anodes, two energy storage devices were made. Ca anode produced a primary cell that operated at a voltage of around 2.0 V. When Mg plate was used as an anode, the negative active material associated with CF3SO3 –, which we have already reported was newly formed at the surface of Mg plate. By combining the negative active material, we have fabricated a novel rechargeable battery using dual ion transport species of Ca2+ for the cathode and CF3SO3 – for the anode, and demonstrated that the battery showed repeated discharge/charge performance.