Preparation Of Transition Metal Oxides ?MnO₂?MoO₃? And Their Applications In Supercapacitors

Supercapacitor is a kind of new-style power storage device, the energy density and power density of which are between battery and traditional capacitor. The advantages of high power density, rapid charge/discharge rate and long recycling life make supercapacitor have potential applications in a lot of fields, such as electric vehicle, mobile electronic products, storage backup system, and so on. Nowadays, the electrode materials of commercial supercapacitors are porous carbon. Although the supercapacitors have high power density, energy density is not enough?vs. battery?, which limits their applications. In the future, supercapacitors should have not only high power density, but also high energy density. According to the energy formula of capacitor: E=CV2/2, to improve the energy density of supercapacitor by means of improving the specific capacitance of materials or improving the working voltage window. Therefore, the research contents of this thesis mainly concentrate on improving the specific capacitance of electrode materials and the working voltage window of device.This paper prepares porous carbon through high-temperature carbonization of organic metal salt.Organic metal salt resolves into carbon with metal and metal oxides in it, and the metal and metal oxides will be removed by acid, porous carbon being prepared. For improving the specific capacitance of carbon based supercapacitor, a layer of MnO₂ is cladded onto carbon through water bath. Potassium permanganate can be reduced to MnO₂ on the surface of carbon, and cladding onto carbon, forming MnO₂@carbon composite. To improve the working voltage window of device further, a asymmetric device is designed with MnO₂@carbon for positive electrode, carbon for negative electrode, 1 M Na2SO4 aqueous solution for electrolyte, GF for membrane, assembling in a button cell. Taking electrochemical tests, the asymmetric device's power density and energy density are 2.2 k W/kg, 10.7 Wh/kg respectively with the voltage window of 0-1.8 V.MoO₃ nanostructure materials are obtained by hydrothermal process in this paper, and the influences of different solvents, acid concentration, surfactants, reaction time on the microstructure of prepared MoO₃ are investigated. Two kinds of typical MoO₃ materials are selected to be taken electrochemical tests. The rate capability and specific capacitance of the prism-MoO₃ are poorer than those of the belt-MoO₃. In three-electrode test, the specific capacitances of the belt-MoO₃ are 586.01 F/g,457.10 F/g,424.50 F/g,250.64 F/g respectively with the current density of 1 A/g,2 A/g,5 A/g,10 A/g?in 1 M H2SO4 aqueous solution?. To improve the specific energy of MoO₃ based supercapacitor further, a asymmetric supercapacitor with belt-MoO₃ for positive electrode and carbon for negative electrode is assembled, the energy density and power density of which are 25.69 Wh/kg and 1482.25 W/kg respectively.