Preparation And Electrochemical Performance Of Cobalt-based Metal Oxides And Heterogeneous Metal Oxides

Compared to batteries, supercapacitor exsits a lot of advantages, such as high power,long cycle life and wide operating temperature range. Thus, supercapacitor becomes an important energy storage device of new generation. Yet, supercapacitor’s wide applications are hindered by its relatively low energy density. As the typical faradaic pseudocapacitance materials, metal oxides have attracted significant attention, which can produce highly desirable capacitance. But, the electrical conductivity of metal oxides is poor, to address this drawback, recent studies have been concentrated on controlling morphology and designing structure of metal oxides.Cobalt oxide (Co3O4) nanomaterials with different morphologies have been synthesized on nickel foam via a simple solvothermal process. The influence of different solvents(Ethanol, ethylene glycol and glycerol) on crystal structure and morphology has been investigated in detail. The formation mechanisms have been speculated, and proposing that the viscosity and dielectric constants of solvents are the principal elements to determine the morphology of Co3O4 crystal. By contrast, it it found that Co3O4 nanomateriais synthesized in glycerin solvent exhibits highest specific capacitances of 1063 F/g at 10 mA/cm2, and remarkable cycling stability (after 1000 cycling of a capacity retention of 90.8%),which is due to the mesh structure is favourable to the electron transfer along the direction of one dimensional. Thus, solvents play a key role in the self-assembly process of different Co3O4 nanostructures.The hierarchical porous mixed metal oxides have been built on nickel foam via a rapid and controllable hydrothermal method. In the process, the Co3O4 nanowires support for deposition of the MnO2 crystal, then the Co3O4/MnO2 core/shell structure forms. When it is applied to supercapacitor electrode,the Co3O4/MnO2 core/shell nanowire composite has a great capacity (in the discharge current density of 5 mA/cm2, the specific capacitance of 1280F/g), excellent rate performance and cycling stability (after 1000 cycles of capacitance ratio is 93.8%).Hierarchical NiCo2O4@NiO core/shell nanowire are designed and fabricated via a simple hydrothermal method. Due to the synergetic effect of the two nanomaterials, the assembled capacitor shows wonderful pseudocapacitive performance. Specifically,the final composite achieves a very high specific capacitance of 1792 F/g at 5 mA/cm2,and good rate capability and cycle performance (after 5000 cycles of capacitance ratio is 87.5%). Besides,the wide working voltage can provides high energy density for its practical applications.