Preparation Of Manganese Oxide By The Method Of Molten Salt And Hydrothermal And Investigation On The Performance Of Supercapacitor

Supercapacitor, a new energy storage device between batteries and electrostatic capacitors, has the advantage of high power density, excellent reversibility and long cycle life. Manganese oxide as pseudocapacitance electrode material has attracted much interest of electrochemists due to its typical faraday pseudocapacitance behavior and low price.Manganese oxides were prepared using different reactants in different molten salt systems. It was found that different salt systems can produce samples with different structure,λ-MnO₂ was obtained in the system of NaCl-LiCl. Different reactants have a great effect on the electrochemical characteristics of the resulting MnO₂. The sample prepared with KMnO₄ show the best performance. The specific discharge capacitance in KCl-LiCl-AlCl₃, KCl-AlCl₃, and NaCl-LiCl at 1mA·cm^-2 of the sample prepared in different salt system are 290.12F·g^-1, 290.72F·g^-1 306.92F·g^-1.Manganese oxides were synthesized by hydrothermal method in alkaline solution. The influences of different conditions were studied. It was found that different conditions have different effects on the structure and property of the sample. When the ratio of solid to liquid, concentration of KOH, time, temperature and reactant are 1:5, 12%, 5h, 100℃and MnCO₃ respectively, the resulting manganese oxide has a specific discharge capacitance of 216.04F·g^-1 at 1mA·m^-2. When the ratio of solid to liquid, concentration of NaOH, time, temperature and reactant are 1:3, 10%, 20h, 100℃and MnSO₄ respectively, the resulting manganese oxide has a specific discharge capacitance is 163.50F·g^-1 at 1mA·m^-2. When the ratio of solid to liquid, concentration of NH₃·H₂O, time, temperature and reactant are 1:9, 10%, 5h, 100℃and Mn(CH₃COO)₂ respectively, the resulting manganese oxide has a specific discharge capacitance is 197.81F·g^-1 at 1mA·cm^-2.Mini-type capacitor was assembled. The positive electrode was the sample with optimal property prepared by molten salt method and hydrothermal method respectively. The negative electrode was active carbon. The constant current charge/discharge test showed that the capacitor can be charged/discharged at large currents. By keeping the potential at constant for 5min between charge and discharge, the specific capacitance of the capacitor assembled with the sample prepared by molten salt method and hydrothermal method was increased by 69.92% and 32.21% respectively. The electrochemical measurement indicated the leakage current were 0.40mA·cm^-2 and 0.25mA·cm^-2 respectively. Long cycle life and high coulombic efficiency were also demonstrated after charge/discharge cycles.