Preparation And Studies On Capacitance Performance Of MnO₂and Its Composites

Supercapacitors are new energy storage components between batteries and electrostatic capacitors. They have excellent properties, such as higher power density compared with rechargeable batteries, larger specific capacitor compared with conventional capacitors, and broad operating temperature range and long cycle life. Supercapacitors have become a hotspot in the study of new energy resouces, because of their wide potential application.Studies on supercapaitors mainly focus on the preparation of high performance electrode materials now. In this dissertation we used two methods to prepare manganese dioxide materials used for supercapacitors. Polyaniline(PANI) was prepared either by chemical oxidation polymerization under low temperature or by using manganese dioxide as oxidizing agent under normal temperature. We also prepared the composite materials composed of manganese dioxide, functionalization carbon nanotubes and PANI. The capacitive property of the composite materials was investigated using cyclic voltammetric (CV) and constant current charge/discharge techniques. Scanning electron microscope(SEM) and fourier-transform infrared spectrometer were used to analyze the structure of electrode materials. The main results are as follows:(1)MnO2/PANI composites with different proportions were prepared using excess MnO2as an oxidation agent to polymerize aniline, Mn15/PANI1has the best electrochemical activity and its specific capacitance reaches67.5F·g-1. The composite Mn15/PANI1/ST prepared from the combination of Mn15/PANI1with MWCNT showed better supercapacitor activity and electrochemical activity than others, its current density and specific capacitance reache1.82A·g-1and127.6F·g-1respectively.(2)MnO2/SMWCNT composites with different proportions were prepared by chemical precipitation method from the functionalized carbon nanotubes, potassium permanganate and manganese chloride. The highest current density and specific capacitance among the materials reaches2.83A·g-1and145.2F·g-1respectively.Corresponding c-Mn/ST13was then combined with PANI with different proportions to obtain the c-Mn/ST13-104PANI electrode, which presents excellent capacitance activity, its current density and specific capacitance reache4.17A·g-1and308.1F·g-1respectively. The capacitance property of the composite electrodes dipped PANI is better than that of the electrode with no PANI, Results show that c-Mn/ST13-104PANI was an ideal material used for the capacitor.(3)MnO2/SMWCNT composites with different proportions are prepared by chemical precipitation method from functionalized carbon nanotubes, potassium permanganate and manganese sulfate as raw materials in aqueous solution. The highest specific capacitance among the materials reaches174.2F·g-1. The corresponding Mn/ST—Mn/ST11was then combined with prepared PANI with different proportions. Oxidation current density of Mn/ST11-PANI66reaches6.02A·g-1and its specific capacitance reaches318.6F·g-1. It presents the best activity as a supercapacitor and long-term cycle life.