Research On Graphene(Oxide)/Polypyrrole Composite Electrode Material In Asymmetric Supercapacitors

Supercapacitor, with a large capacity, high power density and long cycle life, is anew type of energy storage device between electrostatic capacitors and rechargeablebatteries, which has a wide value and great market potential in electric vehicles,electromagnetism weapons, national defense, military and new energy and manyother areas of high and new technology. However, the energy density of supecapacitoris still low compared with rechargeable batteries. According to the capacitorcalculation equation of energy: E=1/2CV2, it can be found that working voltage (V)and electrode specific capacitance (C) is the key determinant of energy density.Therefore, enhancing working voltage and the capacitance of electrode materials caneffectively improve the energy density of supercapacitor. The former can achievethrough composing asymmetric supercapacitors. The latter can obtain by preparingcomposite electrode materials with nano-sized or special structure. This work startingfrom the electrode material was prepared nanocomposites with high specific surfacearea and structural stability, which was based on asymmetric supercapacitors toimprove the power density, energy density and cycle performance of supercapacitorsas the fundamental purpose. The experiment content and results are as follows:1. Graphene oxide/polypyrrole nanowire composites was obtained via chemicalpolymerization way using low temperature for structural characterization andelectrochemical properties of the test. The research results showed that polypyrrolenanowires either sandwiched between GO sheets or growed on the GO surfaces witha flat and layered structuer; with the increase of graphite oxide, the electrochemicalperformance of supercapacitor has greatly improved. When the mass ratio of GO toPy is15:100, the GO/PPy composite electrode shows the highest capacitance of290.6F/g. Asymmetric supercapacitor has been successfully assembled using grapheneoxide/polypyrrole (15%) composite (positive electrode) and activated carbon(negative) in a neutral aqueous sodium sulfate electrolyte, which its electrochemicalperformance was tested. The asymmetric supercapacitor can be cycled reversibly in the voltage range of0–1.6V, and shows the maximum energy density of20.0Wh/kgat a power density of333.9W/kg.2. By changing experimental conditions, graphene oxide/polypyrrolecomposites were prepared by a chemical polymerization at low temperature. Then,the composite structure and electrochemical properties were characterized. Theresults showed that polypyrrole nanoparticles adhered closely on the graphene oxidesheets; by the optimization of the composite ratio, it could be found that when themass ratio of GO to Py is10:100, the composite material has the highest capacitanceof332.6F/g. Asymmetric supercapacitor has been successfully developed usinggraphene oxide/polypyrrole (10%) composite as positive electrode and activatedcarbon as negative electrode in a neutral aqueous sodium sulfate electrolyte in thevoltage range of0-1.6V. The asymmetric supercapacitor displays the maximumenergy density of21.4Wh/kg at a power density of453.9W/kg.3. Graphene was prepared using redox method, and graphene were compoundedwith polypyrrole nanoparticles, which obtained graphene/polypyrrole compositesthrough the low-temperature chemical polymerization approach. Meanwhile, thestructure and electrochemical properties of the composites were studied. It is turnedout that polypyrrole nanoparticles coated closely on the graphene sheet withoutspecial morphology; by adjusting the ratio of compounds, it was obtained that therGO/PPy composite electrode shows the highest capacitance of332.6F/g, when themass ratio of rGO to Py is10:100. The rGO/PPy composite (positive electrode) andactivated carbon (negative) were assembled into an asymmetric supercapacitor usingsodium sulfate electrolyte, the electrochemical performance was measured.Asymmetric supercapacitor has the specific capacitance of478.1F/g, the energydensity of19.7Wh/kg.