| Supercapacitors are new energy storage equipment and component between traditional capacitors with high power output, high charge-discharge efficiency, long cycle life characteristics in mobile communications, electric vehicles, and so have broad application prospects. It can be used as electronic components, small appliances and DC power conversion. Supercapacitors have become a hotspot in research because of their wide potential application.According to the principle energy storage, supercapacitors are divided into two types:double-layer capacitance and faraday pseudocapacitance. Electrode material mainly contains carbon material, metal oxide and conducting polymer. Studies on supercapacitor are mainly focused on the preparation of high performance electrode material. Recently, the natural abundance, low cost of manganese (Mn) oxide, accompanied by its satisfactory capacitive behavior in mild electrolytes and environmental compatibility, have made it one of the most promising electrode materials of supercapacitor.This paper discussed the relations of manganese dioxide preparation, chemical modification and electrochemical properties. In this study, Nanoα-MnO2 was synthesized with solid-phase reaction through heat treatment and acid treatment at room temperature by using KMnO4 and Mn(CH3COO)2·4H2O as raw materials. The sample was characterized by XRD and SEM. The electrochemical characteristics of the sample were characterized by CV and constant current charge-discharge tests. The effect about different electrolytes on electrical properties of nanoα-MnO2 has been researched systematically, and determined the optimal electrolyte by experiments. The thesis has investigated electrochemical properties of MnO2-Cr composite material with different doping ratio, and determined the best formula additive. The main results were as follows:The average diameter of nanoα-MnO2 was 3-5 nm. The specific capacitance was 222.73 F/g in 1.0 mol/L Na2SO4 electrolyte at the scan rate of 3 mV/s, the current density of 300 mA/g, in the window of-0.1～0.8V (vs.SCE). After 1000 times cycle, the capacity is maintain of 85%, a good circulation performance and capacitance stability. Electrochemical properties of the sample were investigated by testing the charge/discharge curves and cyclic voltammetrys in different electrolytes. The results were as follows:nanoα-MnO2 had highest discharge- specific capacitance in 1.5 mol/L (NH4)2SO4 solution compared with different concentration (NH4)2SO4 solution, reaching 196.77 F/g; the lowest discharge-specific capacitance was 3.92 F/g in 1.0 mol/L K2SO4 solution and the highest discharge-specific capacitance was 220.86 F/g in 1.0 mol/L Na2SO4 compared with other neutral solutions; the maximum discharge- specific capacitance arrived at 185.06 F/g in 7 mol/L KOH compared with different KOH solution concentration.Nanoα-MnO2 modificated by dopping Cr with different molar ratio. XRD tests showed that Cr doping did not change the crystal structure ofα-MnO2, but peak broadening. Composite materials was still composited of nano particles. Cr doping could improve the dispersion of composite particles and the electrical conductivity. When the ratio of Cr is 1%, composite material had best electrochemical performance compared with other moler ratio, and the maximum discharge-specific capacitance could reach 318.27 F/g, higher than 40% pure manganese dioxide. After 1000 cycles, the capacity retention rate is more than 80%, better cycle life. |
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