Preparation and characterization of manganese dioxides with nano-sized tunnel structures for zinc ion storage

α-, β-, γ-, and δ-types manganese dioxide (MnO2) with different tunnel structures and morphologies have been successfully synthesized by a common liquid co-precipitation method based on the redox reactions of Mn4+ and Mn2+. The crystalline tunnel structure, particle size, and morphology of the manganese dioxides have been characterized by X-ray diffraction and scanning electron microscopy. It is found that the morphology of as-prepared MnO2 changes with the concentration of raw materials. Depending on the procedure of preparation, spherical particles about 20 nm in diameter, nanorods of 40–100 nm in length and about 20 nm in diameter, or interlocked nanosheet of 10–20 nm in thickness are formed. The effect of crystallographic forms of MnO2 on Zn2+ ion storage properties has been revealed. The electrochemical performances of the α-, β-, γ-, and δ-MnO2 were characterized by the galvanostatic charge–discharge and cyclic voltammetry tests. The δ-MnO2 shows the highest specific capacity (269 mAh g−1) in the new zinc battery system Zn|ZnSO4(aq)|MnO2.