Electrochemical Performance Of Actived Carbon Modified By Nickel And Cobalt Oxides

Active carbon(AC) has the disadvantages of the low conductivity and low double-layer specific capacitance, which could limit the actual application of AC as the electrode material for supercapacitors. Compared to the pure carbon-based materials, it’s theoretical that the specific capacitance of AC composite can be significantly improved after doped with nickel or cobalt. With a low electrical resistivity and good chemical stability, the inorganic conductive oxide is expected to become a promising material for improving the conductivity of the carbon-based electrode materials. In the AC composite, the AC structure not only serves as the physical support but also provides the channels for charge transport. The conductive oxide plays a beneficial conductive role. The metal oxides produce a high pseudocapacitance. A synergistic effect of all the components of the AC composite could be expected to produce high specific capacitance, conductivity, energy density and cycle stability.In this thesis, the active carbon for supercapacitors is mainly doped with nickel oxide or cobalt oxide to produce AC composite. The morphology and microstructure of the composites obtained in different experimental conditions are investigated via scanning electron microscopy(SEM), X-ray diffraction(XRD), and high-resolution transmission electron microscopy(HRTEM). Cyclic voltammetry(CV), galvanostatic charge/discharge test(GCD), and electrochemical impedance spectroscopy(EIS) are performed to characterize electrochemical performance.1. The research of the AC@LNO/NiO composite as the electrode materials.(1) Active carbon@LNO/NiO hybrid coatings are synthesized using different molar ratios of La/Ni to improve the electrochemical performance of active carbon materials. At a molar ratio of La/Ni 1:2, the electrochemical electrode shows that the resistance of the composite is 2.97 ?, which is half of that in pure active carbon. The highest energy density and the highest power density are 70.37 Wh kg–1 and 32.4 kW kg–1. The CV results present a high specific capacitance of 710.48 F g–1 at a scan rate of 1mV s–1.(2) LNO is used as the conductive material. With the deposition and pyrolyzation cycles, the different nanostructures of AC@NiO composites are investigated to achieve high specific capacitance and low resistance. After two-time repeated deposition and pyrolyzation, S2 shows the highest crystallization of the metal oxides, which arrange closely on the AC surface to form a better porous structure. The highest specific capacitance of the AC@NiO composite with La2NiO4 is 652.19 F g-1 at the scan rate of 1 mV s-1. The conductivity of S2 is better than those of S1 and S3. With the synergistic effect of AC, La2NiO4 and NiO, the electrochemical performance of S2 is much better than pure AC.2. The research of the AC@LCNO/Co3O4 composite as the electrode materials.LCNO is a good inorganic conductive oxide, with the similar structure as LNO. LCNO/Co3O4 is deposited in the surface of AC to synthesized AC@LCNO/Co3O4 composite at the different mass ratios of Ni/Co. At the mass percent of Ni 15%, the film of the metal oxides on the surface of AC is more consistent to produce largest specific surface area. At the scan rate of 1 mV s–1, the specific capacitance is 739.42 F g–1. A 6.21% capacitance loss of the composite up to 5000 cycles shows an excellent cycling performance, at the mass percent of Ni 15%.