Synthesis and electrochemical properties of polycrystalline nano manganese dioxide

Abstract

Different crystal forms of manganese dioxide （MnO2） are synthesized using KMnO4， MnSO4·H2O， （NH4）2S2O8， and hydrochloric acid as raw materials by precisely controlling the temperature and duration of a hydrothermal reaction. The structure and morphology of the materials are characterized using XRD， SEM， and TEM. The results show that the synthesized MnO2 nanoparticles display different microscopic morphologies depending on their crystal forms. A comparison of their electrochemical performances indicates that δ-MnO2， due to its unique flower-like structure， provides many reaction sites， leading to superior performance compared to other crystal forms of manganese dioxide. At a current density of 2 A/g， δ-MnO2 achieves a capacity of 623.48 mAh/g after 1400 cycles. The kinetic properties of the MnO2 electrode are investigated using cyclic voltammetry， electrochemical impedance spectroscopy， and constant current intermittent titration techniques. It reveals that δ-MnO2 exhibits a higher Li+ diffusion rate.