Preparation And Properties Of Manganese Dioxides And Their Composites For Supercapacitors

In this thesis, the hydrothermal synthesis method was used to prepare manganese dioxide and its composites, including MnO2 nanocomposites, MnO2/NixCo1-xOy core-shell nanocomposites and GO/MnO2/PANI nanocomposites. We study the improvement of active area and electrical conductivity and try to enhance its capacity and cycle life. The main researches are showed as follows:1.The hydrothermal synthesis method and heat treatment was used to prepare MnO2 with different structure and morphology successfully. It was found that the wormlike MnO2 nanospheres evolved toward nanowires along with the increasing of reactants, and the growth evolution was explained by the Ostwald ripening mechanism and directional growth mechanism. Electrochemical performance measurements illustrate that the specific capacitance of MnO2 nanowires is highest, and Such MnO2 nanowire showed a high specific capacitance of 223.4 F g-1 at 0.5 A g-1 and an attractive cycling stability of 99.5% retention after 1000 cycles. Nanowire is obviously superior to other forms when it is used as supercapacitor electrode material.2. The simple hydrothermal synthesis method and heat treatment was used to prepare a-MnO2/NixCo1-xOy core-shell nanostructures.a-MnO2/NixCo1-xOy nanostructures with different load degrees were synthesized by regulating the ratio of reactants. In electrochemical tests, ?-MnO2/NixCo1-xOy core-shell nanocomposite shows excellent performance of capacitance of 476.8 F g-1at 0.5 A g-1.When the current density reaches4times, it can maintain 81.7% of specific capacitance. ?-MnO2/NixCo1-xOy nanostructure can remained 94.3% of specific capacitance after 1000 cycle. It has a good application prospect in terms of high performance supercapacitor.3.The simple hydrothermal synthesis method was used to prepare GO/Mn2/PANI composites in situ polymerization. We study the effect of changing the load of polyaniline to nanocomposites. The result shows that PANI in the surface of MnO2did not change the original composite structure because of the formation of aniline in situ polymerization process. The specific capacitance of GO/MnO2/PANI electrode material reached 364.1 F g-1 at 0.5 A g-1. It also shows excellent electrical conductivity in the analysis of ac impedance. However, specific capacitance will decrease after charging and discharging repeatedly.