Preparation And Electrochemical Performance Of Cobalt Manganese Oxides Composites

Manganese oxides have high theoretical capacitance, but the practical capacitance is far from theoretical capacitance because of the bad electrical conductivity. Likewise,cobalt oxides also possess high theoretical capacitance and high conductivity. However,the weak points, such as higher price than other inexpensive transition metal oxides and environmental pollution, affect its extensive application.In this paper, for improving the electrical conductivity, promote the ion diffusion and reduce the cost, manganese oxides and cobalt oxides are composited and modified by doping, replacing and coating. Then we illustrate these compounds, investigate their electrochemical properties and analyze the results.After Mn₃O₄ is doped by trace amounts of cobalt, the diameter of hexagonal nanosheets become small, the conductivity is enhanced and the diffusion impedance decreased. When the ratio of doping is 1.0%, Mn₃O₄ exhibit the maximum specific capacitance of 307.9 Fg^-1 at 0.5 Ag^-1 which is higher than the undoped of 242.5 Fg^-1,201.2 Fg^-1 at 10 Ag^-1 and the retention ratio is 65.28%. The capacitance does not minish after 1000 cycles.Cobalt-manganese binary metal oxides(Co_1.5Mn_1.5O₄) nanosheets have been successfully synthetized via a simple liquid phase precipitation method. The cobalt oxides are partly replaced by manganese oxides. We determine that the best mole ratio of Co Cl2 and MnCl2 is 1:1. The nanosheet structure, high surface area, right pore size and good conductivity make Co_1.5Mn_1.5O₄ show outstanding electrochemical performances, such as a high specific capacitance of 472.5 Fg^-1 at 0.5 Ag^-1, long term cyclability of almost100% capacity after 1000 cycles and excellent rate capability of 338.5 Fg^-1 at 10 Ag^-1.The ultrthin MnO2 nanosheets have high surface area but poor conductivity and instable structure, and the Co3O4 nanowires have high electrical conductivity and stable structure. Thus through Co3O4 nanowires coated with ultrthin MnO2 nanosheets,Co₃O₄@MnO₂ core-shell array composite electrode materials are synthesized on nickel foam. This electrode show high specific capacitance of 533.9 Fg^-1 at 0.5 Ag^-1,long termcyclability of almost 100% capacity after 2000 cycles and excellent retention ratio of63.9% in rate capability.