Preparation And Characterization Of Mo_X -based Electrode Materials For Supercapacitor

Supercapacitor is a new type of electrochemical energy storage devices. Compared with traditional capacitor, it can provide high energy density, long cycle life, low equivalent series resistance and good environmental compatibility, and so on. It can play an important role in the fields such as electric vehicles, space flight technology, portable computer and military field, etc.. Therefore, it becomes a hot topic to study supercapacitor. Transition metal oxides with various oxidation states have received much interest. In this thesis, MO_x-based electrode materials were prepared. The microstructural characterizations and morphological of as-prepared materials were investigated by X-ray diffraction and scanning electron microscopy, respectively. Cyclic voltammetry, chronopotentiometry and electrochemical impedance spectroscopy were used to evaluate the electrochemical properties.The main contributions and innovations of this thesis are as follows: (1) Redox reaction and sol-gel method were used to prepare MnO₂ and SnO₂, respectively. According to different weight ratio, MnO₂ and SnO₂ were mixed as electrode materials. The electrochemical properties for SnO₂-modified MnO₂ composite electrode were evaluated in KCl solution. It was shown that the composite electrode had excellent properties in capacitance, and the specific capacitance of single electrode with 10 wt% SnO₂ was up to 302.1 F g-1. Furthermore, SnO₂-modified MnO₂ composite electrode exhibited a very stable capacitance after repeating cycles compared to that of the separate MnO₂ or SnO₂ electrode.(2) Co₂SnO₄ was synthesized by co-precipitation method. The spherical beads with three-dimensional nanostructure were depicted by scanning electron microscopy. The electrochemical performance of Co₂SnO₄/AC composite electrode was investigated in KCl solution. It was shown that the composite materials with 25 wt% Co₂SnO₄ had excellent specific capacitance up to 285.3 F/g, and decrease 4.2% of initial capacitance after 1000 cycles. Compared with activated carbon electrode, capacitance performances and cyclic stability of the composite electrode had been noticeably improved.(3) Co₂O₃-doped MnO₂ was prepared by solid state reaction at low temperature. The electrochemical performance was evaluated for Co₂O₃-doped MnO₂ composite electrode. It was found that composite electrode with 2.3 wt% Co had excellent properties in specific capacitance up to 340.1 F/g in 1.0 mol/L KCl aqueous solution. Furthermore, the specific capacitance could keep 291.1 F/g event after 1000 cycles, presenting high operation stability in a continuous charge/discharge process. The stability of electrode materials was studied by electrochemical impedance spectroscopy. It was demonstrated that electrochemical test did not induce significant structural or microstructure changes of electrode active materials, which could be attributed to the co-effect of cobalt doping.