Study On Preparation And Electrochemical Performance Of Core-Shell Nanostructure Composites

At present, supercapacitor and lithium ion battery, they play a very important role in all kinds of energy storage system. Compared with conventional capacitors, the supercapacitor is a new type of energy storage device and has great potential prospect. It has high power density, fast charging and discharging speed, long cycle life, low equivalent series resistance and environmental friendliness, widely concerned by scientists around the world. The key factors affecting the performance of supercapacitor is the type of the properties of electrode materials and electrolyte, the focus of research is improving the capacitance and energy density. The supercapacitor plays an important role in electric cars, portable notebook computer, mobile communication and national defense, etc. Lithium ion batteries has also attracted much attention due to its high working voltage, high energy density, low self-discharge rate and green environmental protection. Moreover, it has been widely applied in small appliances, space technology, national defence industry, electric vehicles, UPS and other fields of development. The key technology of lithium ion battery is embedded electrode material, further improving the manufacturing process, its main direction is how to reduce the cost and improve the electrochemical performance. In addition, the supercapacitor can also be combined with lithium ion batteries as the power supply system of electric vehicle. At present, the nanomaterial electrode show great advantage, because of its high specific surface area, especially the nanocomposite material, is considered the most promising electrode materials, because they have shortly path of the electron and ion transmission. As a new type of core-shell structure, it can realize the function of the core and shell of composite and complementary. Recently, the design concept has also been applied to supercapacitor and lithium ion battery materials. Herein, we report on the preparation and electrochemical performance of the core-shell nanocomposite materials, the formation mechanism, morphology and electrochemical properties were studied in detail. The main work includes the following aspects:(1) The first time using the liquid phase method of core-shell worm-like graphene/PANI nanocomposites synthesis. The characterization of XRD, SEM, TEM, Raman, BET and XPS respectively for graphene, PANI and graphene/PANI nanocomposites crystal structure, particle morphology, surface area and chemical component analysis. Unlike previous preparation methods on the preparation of graphene/PANI nanocomposites that here is through the surface of the worm-like PANI coated graphene nanocomposites thin, wormlike a core-shell structure was obtained. Finally, by cyclic voltammetry, respectively for graphene PANI and graphene/PANI composite electrode (CV), galvanostatic charge-discharge and AC impedance (EIS) testing, results show that the worm-like graphene/PANI nanocomposites than the other two kinds of single component materials have higher capacitance, namely in the0.5A g-1current density the specific capacitance of up to488.2F g-1, and also can effectively improve the electrochemical cycling stability and rate capability.(2) At first, the uniform TiO2nanobelts arrays on the pure Ti substrate are synthetised by hydrothermal method, and then through the sacrifice layer template method with ultrathin MnO2nanosheets coated with a layer of dense in the TiO2NBs, TiO2/MnO2NBAs band array consists of a composite material with core-shell structure. Using XRD, SEM, TEM, Raman and XPS respectively for TiO2NBs and TiO2/MnO2NBAs of the crystal structure, morphology and chemical composition were characterized. Finally, under the same test conditions respectively, the electrochemical properties of TiO2NBs and TiO2/MnO2NBAs electrode was tested, the results showed that TiO2/MnO2NBAs electrode with good rate capability and excellent cycle performance, due to its reasonable design of nanostructure. In1M Na2SO4aqueous solution as electrolyte, the current density of200mV s-1to obtain a high capacitance is557.6F g-1, after3000cycles at the same current densities the capacity remains at454.2F g-1. In addition, in2A g-1when its energy density and power density of7.5Wh kg-1and1kW kg-1. To sum up the core-shell TiO2/MnO2nanobelts array composite material has high quantity of unit capacitors, excellent cycle stability and great application prospect.(3) At first, Co3O4nanostructure arrays with different morphologies at different temperatures were synthesized by hydrothermal method. Through the analysis and comparison, we selected Co3O4nanometer needle array structure growth at120℃hydrothermal reaction time for the next step of experiment. Then, through the ZnO template method at the expense of Co3O4nanometer needle coated to form a layer of dense lamellar α-Fe2O3, got a nanometer composites of "core-shell" type. Using XRD, SEM, TEM and Raman measurements separately on the Co3O4NNs and Co3O4/a-Fe2O3NNs crystal structure, morphology and chemical composition were characterized.