Study On The Electrochemical Performance And The Influenced Factors Of Metal Oxide/activated Carbon Asymmetric Supercapacitor

Supercapacitors, also called electrochemical capacitors, are divided into symmetric and asymmetric supercapacitors. At present, the latter become to research hotspot. In this thesis, we successfully synthesized electrode materials and assembled asymmetric supercapacitors. Then, the microstructures and compositions of these materials were investigated by X-ray diffraction measurements (XRD),scanning electron microscope (SEM) and energy dispersive spectrum measurements (EDS). The electrochemical performance has been evaluated by cyclic voltammetry (CV), galvanostatic charge-discharge and electrochemical impedance spectra (EIS). And the factors that influence the performance of asymmetric supercapacitor were discussed. The main content is the following:1. Cobalt-manganese oxides for electrode materials of supercapacitor , which exhibited excellent electrochemical performance, are successfully synthesized by a facile chemical coprecipitation method. By controlling the Co-Mn content ratio, Co_0.9Mn_0.1 oxide was obtained, which consists of interconnected nanoflakes. The loosely packed nano-flakes play a basic role in the morphology requirement for electrochemical accessibility of electrolyte OH? to active material and a fast diffusion rate within the redox phase. The specific capacitance of Co_0.9Mn_0.1 oxide single electrode in 2 M KOH aqueous solution within a potential window of 0 to 0.4 V is 814 F/g, which is the highest report of cobalt-manganese oxides for electrochemical capacitors. To enhance the energy density and the work voltage of the supercapacitor devices, we proposed a new asymmetric supercapacitor assembly based on this cobalt-manganese oxide as a positive electrode in combination with AC as a negative electrode in 2 M KOH aqueous solution. Within a potential window of 0 and 1.6 V, values of the maximum specific capacitance and specific energy of this device are 80.2 F/g and 28.5 Wh/kg, respectively. The correlations of the structure and their electrochemical performance of the prepared materials have also been investigated.2. We successfully synthesized NiO electrode material by a facile chemical coprecipitation method. The specific capacitance of it is 454 F/g. In this work, a asymmetric supercapacitor was assembled based on this NiO as a positive electrode in combination with AC as a negative electrode and PP as diaphragm material. Then the electrochemical performances of the asymmetric supercapacitor and the factors that influence them were investigated. The results show that the highest specific capacitance of the asymmetric supercapacitor is 67.32 F/g when each electrode contained about 8 mg of active material. It can effectively improve the capacity by adding a small amount of LiOH to the 2 M KOH aqueous solution. Especially in 1.6 M KOH + 0.4 M LiOH aqueous solution, the specific capacitance of 82.15F/g can be obtained, which increased by 22.03% than that in 2 M KOH aqueous solution. And a better electrochemical performance can be obtained by using PVDF binder. Moreover, the work voltage increased to 2.4 V by using organic electrolyte solutions, while with low specific capacitance.