Production Of Nickel-cobalt Hydroxide Electrode Materials And Study Of Their Electrochemical Properties

Among numerous active electrode materials, nickel hydroxide is a promising electrode in electrochemical capacitors. Nickel hydroxide research has thus far focused on the crystalline rather than the amorphous phase or the weak one.In this thesis,we synthesized amorphous nickel hydroxide, amorphous nickel-cobalt hydroxide, nickel hydroxide and hybrid Cox Ni1-x(OH)2 nanosheets with weak crystallinity via different methods. The materials’ microstructures and morphologies were characterized through SEM、TEM 、XRD and XPS measurements. The performance of electrochemical has been evaluated by cyclic voltammetry(CV), galvanostatic charge-discharge and electrochemical impedance spectra(EIS).In our study, we synthesize amorphous nickel hydroxide nanospheres and Co doping amorphous nickel hydroxide nanospheres using a simple, low-cost, green-technology electrochemistry technique. With the Co doping, the performance of the amorphous nickel hydroxide was well improved. First, the conductivity and the utilization were improved at the same time; Second, as the addition of cobalt, the original material stability was well improved,and the formation of γ-Ni OOH was controlled. The third factor, the change of redox potential charge and discharge efficiency was improved. With the addition of cobalt, the specific capacitance of the material improved from 1692 F g-1 to 1769 F g-1. And the circulation loss decreased from 27% to 17%.We synthesized a nickel hydroxide material with weak crystallinity through hydrothermal method and their composites at different ratio of Co doping. We found that the material has the most excellent performance at a reaction condition of 90℃ for 6h, all the materials were nanosheets with wrinkle surface. The thickness of the materials were changed with the different content of cobalt.The most final thin nanotheet was 2 nm. Explain that the addition of cobalt on the material was of certain influence to the structure of the distribution.When the current density was 1 A g-1 with the content of Co was 7%, the specific capacitance of the materials improved from 1145 F g-1 to 1852 F g-1. The capacitance rentation vary from 52.7% to 91% after 1000 cycles.In addition, we also have successfully assembled an asymmetric supercapacitor using amorphous Ni(OH)2 and amorphous nickel-cobalt hydroxide as positive electrode and AC as negative electrode, respectively. The asymmetric supercapacitor was investigated in 3 M KOH electrolyte between the potential window of 0~1.3 V. Showed good specific capacitance and cycle performance. The highest specific capacitance was 106 F g-1, the highest energy density was 25 Wh kg-1. When the power density was 1.56 k W kg-1, the energy density was still at 19.1 Wh kg-1. Which is significantly higher than those of the previously reported Ni(OH)2 based asymmetric supercapacitors. The Co doping material has a good cycle performance than the original material, after 3000 cycles, the specific capacitance rentation was still 81%.