Studies On Synthesis And Electrochemical Properties Of High Capacity Electrode Materials For Supercapacitor Applications

A supercapacitor is an efficient energy-storage device that lies between batteries and electrostatic capacitors. For a supercapacitor system, electrode materials are the key components that directly determine the overall performance of the supercapacitor. The performance of electrode materials is determined by microstructure, surface morphology, conductivity, and specific surface area, among others. With regard to the shortcomings of several kinds of electrode materials, this thesis aims not only to optimize electrode materials’ surface states, structure and morphology, specific surface area, etc., but also to discuss the influence and mechanism of these factors on the electrode materials’ capacitive properties. Explicity studies involved in this thesis are as follows.1. The studies have been performed on the preparation of ordered mesoporous carbon（CMK-3） by hard template method, and the influence of nitric acid activation on pore structure, morphology, surface states and capacitive performances of CMK-3. The results showed that ultrasound-assisted activation sharply improved the activation rate and efficiency. Meanwhile, it also introduced huge numbers of carbonyl and carboxyl oxygen containing functional groups which improved the hydrophilicity of CMK-3 in electrolytes and reduced the internal resistance of the electrode materials. The CMK-3 activated with ultrasound-assistance showed best specific capacitances of 178.8F/g and 233.4F/g, respectively, in neutral and alkaline electrolytes, with good power capability and excellent cycling stability. Additionally, symmetric supercapacitors prepared utilizing the activated CMK-3 samples had obvious higher energy density and power density than those of CMK-3 without activation.2. The influence of heat treatment temperature and external magnetic field on the crystal microstructure, morphology and electrochemical performance of MnO₂ has been studied. The results showed that the increase of heat-treatment temperature dramatically affected the crystal structure, microscopic morphology, and specific surface area, and greatly improved the electrochemical performance of MnO₂. When an external magnetic field was applied, with the increasing intensity of magnetic field, the nucleation rate of birnessite-MnO₂ increased, resulting in decreasing diameter and increasing specific surface areas of the MnO₂ nanospheres. The optimal MnO₂ electrode synthesized under 3.2m T magnetic fields had a specific capacitance of 493.0F/g and a retention ratio of 95.6% over 1000 charge/discharge cycles.3. The influence of surfactants（SDS, PEG, CTAB） and magnetic fields on the microstructure, morphology and electrochemical performance of Co₃O₄ have been studied. The results showed that surfactants had a great influence on the surface morphology, and the optimal Co₃O₄ electrodes were obtained with the CTAB surfactant. When synthesized in a magnetic field with increasing intensity, Co₃O₄ nanoneedles were obtained with a decreasing degree of self-aggregation. The optimal Co₃O₄ electrode, synthesized under 9.5m T magnetic fields, had a specific capacitance of 970.8F/g and a retention ratio of 93.7% over charge/discharge 1000 cycles.4. The influence of ordered mesoporous carbon（CMK-3） addition and magnetic fields on the microstructure, surface morphology and electrochemical performance of Co₃O₄/CMK-3 composite materials has been studied. The results showed that the CMK-3, embedded in the compact layer of Co₃O₄ films, effectively restrained the agglomeration of the Co₃O₄ nanoneedles. Moreover, the introduction of the magnetic fields significantly improved the capacitive properties of Co₃O₄/CMK-3 composite materials. The Co₃O₄/CMK-3 composite electrode with 0.005 g CMK-3 achieved the best specific capacitances of 1496.9F/g, as well as good power capability and a retention ratio of 96.7% over 1000 charge/discharge cycles.