Preparation Of Metal Oxide/Activated Carbon Asymmetric Supercapacitor And Its Electrochemical Studies

As a new type of energy storage system, electrochemical capacitors have become oneof the focuses in the field of energy storage home and abroad. The faraday capacitanceof metal oxide is far greater than that of the carbon material with double layercapacitance. Meanwhile, the transition metal oxide such as anadium pentoxide （V₂O₅）and manganese dioxide （MnO₂） are rich in resources, cheap and easy to obtain.Therefore, we choose V₂O₅and MnO₂as electrode materials to assemble metaloxide/activated carbon （AC） asymmetric capacitors.The physichemical properties of the prepared samples were analyzed using x-raydiffraction （XRD）, differential thermal analysis （TG-DTG）, scanning electronmicroscope （SEM）, and the infrared absorption spectroscop （FTIR）. Theelectrochemical performances of the capacitors with the metal oxide as electrodematerials were measuered by cyclic voltammogram （CV）, galvanostaticcharge-discharge （GC） and elecrochemical impedance spectra （EIS）. The thesis wasdivided into three parts.Part I: In order to increase the ionic conductivity of V₂O₅,the nanoporous vanadiumpentoxide particles were prepared by sol–gel method using PMMA as template reagentvia a phase transformation process. We have studied the cycling performance of theV₂O₅/AC capacitors with different electrolytes, such as1.0mol/L LiPF6/（EC+DEC+DMC）,2mol/L NaCl, KCl, LiCl and1mol/L KCl. The results suggest thatthe2mol/L KCl was the best electrolyte，in which the asymmetric capacitor possessesthe highest specific capacitance up to184F/g at5mV/s. Moreover, the greaterconcentration of KCl is the higher specific capacitance within a certain range ofconcentration.Part II: In order to increase the electronic conductivity of V₂O₅, manganese-dopedV₂O₅materials had been prepared. The circling performance and discharge-chargecharacteristics of the doped V₂O₅with different doping molar were tested in the2mol/L KCl electrolyte. The results proved that the specific capacitance of themanganese-doped V₂O₅with a10%doping molar was higher than that of with a15%doping molar. Their specific capacitance could reach233F/g,210F/g respectively.Part III: MnO₂nanospheres were prepared by chemical precipitation. We havestudied its electrochemical properties in the electrolytes containing univalent and polyvalent cations. In the electrolyte solutions of0.1mol/L Al（NO₃）3, Mg（NO₃）₂,Ca（NO₃）₂, Ba（NO₃）₂and0.2mol/L NaNO₃, the specific capacitance of the V₂O₅/ACcapacitors were37,301,290,240and154F/g respectively. The results suggest that theMnO₂electrode have the better electrochemical properties in the electrolytes containingpolyvalent cations than that containing univalent cations.Our study proved that V₂O₅and MnO₂possess high faraday capacitances of, andexhibit good electrochemical performances in neutral aqueous electrolytes.