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

alpha-, beta-, gamma-, and delta-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 alpha-, beta-, gamma-, and delta-MnO2 were characterized by the galvanostatic charge-discharge and cyclic voltammetry tests. The delta-MnO2 shows the highest specific capacity (269 mAh g(-1)) in the new zinc battery system Zn[ZnSO4(aq)]MnO2. Crown Copyright (C) 2012 Published by Elsevier Ltd. All rights reserved.