Supercapacitors With High-performance Carbon-based Composite Materials

Supercapacitor is a new kind of energy storage device between traditional electrostatic capacitor and second battery. As supercapacitors have the advantages of high power density, high energy density, long cycle life and fast charge and discharge, they have been widely applied in civilian and military areas. The electrode material is an important component influencing the performance of supercapacitors. Therefore, the research on electrode materials has been a hot topic in this filed. Carbon-based electrode materials have attracted great attention, because of their abundant raw materials, low price, simple preparation and excellent performance. This dissertation has investigated the preparation of carbon-based composites and their performance. The main results are as follows:(1) The research of high-performance activated carbon electrode materialsPetroleum coke was chosen as the raw material because of its rich source, low price, high fixed carbon and low ash content. The result indicated that activated carbon material has larger specific surface area based on BET test when petroleum coke grain was 200 orders, the radio of KOH and petroleum coke was 3 and the time of microwave activation was 15 minutes. The specific surface area went to 2683m²/g, the average pore volume was 1.5973cm³/g and the average adsorption pore diameter was 2.59nm. Through the test of cyclic voltammetry, constant current charge-discharge and alternating current impedance the activated carbon capacitance got better, capacitor resistance was about 0.75? and specific capacitance reached 361F/g.(2) The research of AC (activated carbon) / MnO₂ composite electrode materialsIn order to enhance the specific capacitance characteristics of activated carbon materials, this paper used MnO₂ which has Faraday quasi-capacitance characteristics to be the composite component because of its cheap price. The AC/MnO₂ composite electrode materials were made through a "carbon oxide conversion route" so that activated carbon occurrs reaction under the conditions KMnO₄ through a novel in situ synthesis idea. The prepared composite electrode materials were assembled as simulated supercapacitor and some electrochemical performance testing were did. The research on the influence of different ratio of activated carbon and KMnO₄ (the ratio of carbon manganese) to the composite electrode material properties were studied. The experimental results indicated that when the ratio of carbon manganese went to 2.259 the prepared AC/MnO₂ composite electrodes performance were improved greatly compared with the pure activated carbon as electrode materials. The capacitor resistance declined. Compare with the activated carbon the capacitance of composites increased about 13% which went to 386 F/g.(3) The research of a new type graphene electrode materialThrough the "re-oxidation reduction" method, NaNO₃, concentrated H2SO₄ and KMnO₄ were used to oxidate the graphite flake. Then a new type graphene electrode material was prepared by reduction graphite oxide with hydrazine. Graphene which were prepared to assemble a simulated capacitor were tested the electrochemical performance. The results compared with graphite and graphite oxide materials showed that the impedance properties of graphene was poorer than graphite'but better than graphite oxide', and the specific capacitance was greatly improved, about 20 times for the graphite, reaching 66.8 F/g.