The Effect of the Synthesis Method of the Layered Manganese Dioxide on the Properties of Cathode Materials for Aqueous Zinc-Ion Batteries

The dependence of physico-chemical, structural, and electrochemical properties of cathode materials for aqueous zinc-ion batteries based on the manganese dioxide with birnessite-type structure on the conditions of the MnO2 hydrothermal synthesis are analyzed. The manganese oxides obtained are capable of the reversible zinc ion intercalation into their crystal lattice because of large interlayer distances. Two approaches to the synthesis are considered: a reaction between manganese sulfate and potassium permanganate at 160°С (MnO2-I) and hydrothermal treatment of potassium permanganate solution at 220°С (MnO2-II). From the structural analysis, both methods are shown to allow obtaining the birnessite-type manganese dioxide. At the same time, the electrochemical properties of the cathodes obtained differ in the prototypes of aqueous zinc-ion batteries. The MnO2-II-based material demonstrated higher initial specific capacity (180 mA h g–1 at the current density of 0.3 A g–1), while its cyclic stability is by 40% lower than that for the MnO2-I-based material. This can be explained by higher surface area and lower crystallinity of the active material.