Research On Supercapacitor Electrodes Of Hierarchically Structured Metal Oxides

Supercapacitor is a new type energy storage device. Transition metal oxides have been widely investigated by researchers at home and abroad, which is due to their excellent electrochemical properties, abundant resource, environmentally friendly and low price. In this paper, with hierarchically structured cobalt and nickel metal oxides as research objects, the effects of the synthesis conditions and materials compounds on the formations, structures and electrochemical properties were investigated. The main contents as follows:1. Hierarchically structured sphere Co3O4 nanocrystal material was prepared by hydrothermal method. The electrochemical properties were investigated. The results show that:Co3O4 material which the diameter of hierarchically structured microsphere was 1-6μm, was consisted by 5-10nm nanoparcitles. The Co3O4 material kept great activity and excellent electrochemical properties by the hierarchical structure. The specific capacitance was 576.6 F/g at the discharge current of 4 mA/cm2.The CoC2O4·2H2O with prismatical structure was synthesized by hydrothermal method, which used PEG as surfactant and template. The precursor of the CoC2O4·2H2O was heated treatment. The lamella-like hierarchically structured Co3O4 material can be obtained when the precursor was calcined at 400℃for 3h, while the ordinal microsphere hierarchically structured Co3O4 material can be obtained when the the precursor was calcined at 35O℃for 1h and then 750℃for 2h.2. The nanoflakes microsphereα-Ni(OH)2 material was prepared by hydrothermal method using SDS as surfactant, and urea as precipitant. The as-preparedα-Ni(OH)2 material which the diameter of hierarchically structured microsphere was 2-10μm, was self-assembled by the nanoflakes of 5nm in thickness. The specific area of theα-Ni(OH)2 material reached to as high as 182.9m2/g, and the specific capacitance of theα-Ni(OH)2 material was 1772F/g. The phase and morphology of theα-Ni(OH)2 material can be kept by the heat treatment for nanoflakesα-Ni(OH)2 microsphere at lower than 250℃. Theα-Ni(OH)2 material had good specific capacitance and discharging at heavy current, by which the hierarchically structure and the opened interlayer was formed with the heat treatment. The specific capacitance of theα-Ni(OH)2 electrode reached to 2398F/g by 200℃at discharge current of 4mA/cm2. The specific capacitance of the NiO material which was obtained by heat treatment for theα-Ni(OH)2 material at 300℃, was 826.4F/g. 3. The hierarchically structured composites of Co3O4/Ni(OH)2, CNT/Ni(OH)2 and mesoporous carbon/Ni(OH)2 materials were synthesized by hydrothermal method. The structures and electrochemical properties of the composites were investigated. The results show that:all morphologies maintained hierarchically structured microsphere. The high specific capacitance of electrode can be obtained by optimal proportion. The specific capacitance of Co:Ni=1:1 was 899.3 F/g, the specific capacitance of the 20% percentage composition with CNT was 2144 F/g, and the specific capacitance of the 5% percentage composition with mesoporous carbon was 2191F/g.4. The nanoflakes Co(OH)2 hierarchically structured films were synthesized by electrochemical deposition. The efflects of the deposit voltage, deposit temperature, proportion of water and ethanol and different substrates on the electrochemical properties for the Co(OH)2 films were discussed. The great active Co(OH)2 films can be obtained by the optimization parameters. The specific capacitance of the Co(OH)2 films was 2610 F/g at current density of 4A/g, which the films were prepared at-0.7V deposit voltage on nickel foam substrate in water-ethanol(1:1 volume ratio), and followed by heat treatment at 100℃.