The Syntheses And Electrochemical Performance Of MnO₂ Supercapacitor

Supercapacitor is a kind of power-type energy storage device that can provide a high power density.It is characterized by environmental friendliness,high safety,and good efficiency and can be operated in a wide temperature range with a long cycle life.Manganese oxides were excellent electrode material for supercapacitor with good electrochemical properties,wide potential window,low cost and high energy density.In this paper,MnO2 materials have been synthesized by hydrothermal method and chemical deposition.The microstructure and morphology of the samples were characterized by X-ray diffraction(XRD),scanning electron microscope(SEM).The electrochemical performances of the MnO2 as the electrode materials for supercapacitors were evaluated by cyclic voltammetry,impedance,cycle life and galvanostatic charge-discharge measuremance.The effects microstructures and morphology of electrode materials on the electrochemical performances were investigated.The MnI2 prepared by low-temperature hydrothermal method indicated that it was a ?-MnI2 phases.The MnO2 microspheres showed different diameter disterbution,bad crystallinity.The crystallinity of MnO2 became more and more perfection with the increase of reaction temperature.The XRD test showed that through the change of the temperature the material transform from ?-MnO2 to hausmannite Mn3O4.In 1.0M Na2SO4 electrolyte,the S-80 MnO2 show a big specific capacitance,and it can be achieved about 198Fg-1 at 0.25Ag-1.Mesoporous manganese oxides microspheres were synthesized by the chemical deposition of manganese carbonate precursors at room temperature and followed by the low-temperature calcinations under 300,350 and 400?.The obtained MnO2 materials exhibit the Akhtenskite type MnO2 crystalline microstructure and the microspherical morphologies with the diameter of about 1?m.The as synthesized MnO2 microspheres under 300? exhibit the largest specific area(240.5m2g-1)and the optimal mesopore volume(0.231cm3 g-1),which contribution to the optimal electrochemical performances for supercapacitors.An asymmetric supercapacitor AC//MnO2 is assembled and tested successfully in this paper.The aa-assembled activated carbon AC//MnO2 hybird capacitor exhibits a wide working voltage(1.8V),high power and energy densities(2197W kg-1 and 12.8Wh kg-1 at 4 Ag-1),excellent cycling behavior(94.3%capacitance retention after 5000 cycles at 1 Ag-1).