Flexible Electrodes Material Based On Polypyrrole Composites And Capacitance Properties For Supercapacitor

Supercapacitors, also known as electrochemical capacitors, are new kind energy storage device that interposed between the secondary battery and the conventional capacitor. It has been widely used in many fields due to its high power density, extremely large capacitance, long cycle life, high charge-discharge efficiency, wide temperate range and environmental-friendly. With electronic products become increasingly common in our daily life, developing of the electrochemical capacitor with the flexible, lightweight and efficient properties has become one of the focuses. The electrode material is the key element for the development of capacitors because it determines the main performance indicators. When preparing the supercapacitor electrode materials, the substrates that earried the electro-active materials also play the important role. In this thesis, polypyrrole, carbon nanotubes and graphene are chosen as the electro-active materials and loaded on different flexible substrates by using the methods of dip-dry, chemical reduction and polymerization in vapor phase. Conductive composites prepared in this thesis possess inherent flexibility and the characteristics of capacitor electrodes, then the capacitance properties of the composite materials have been investigated further.(1) The carbon nanotubes (CNTs) have been loaded on the melamine foam (MF) to form the composite (CNTs/MF) by dip-dry process, then polypyrrole (PPy) is coated on CNTs/MF (PPy/CNTs/MF) through chemical oxidation polymerization by using FeCl3· 6H2O adsorbed on CNTs/MF as oxidant to polymerize the pyrrole vapor. Finally, CNTs are coated on the surface of PPy/CNTs/MF to increase the conductivity of the composite (CNTs/PPy/CNTs/MF) by dip-dry process again. The morphology of the composite is examined by scanning electron microscope (SEM), the composition of the composite is examined by XRD, and the properties of the capacitor cells assembled are investigated by cyclic voltammetry (CV), galvanostatic charge/discharge and electrochemical impedance spectroscopy (EIS) measurements. The results show that the optimum CNTs/PPy/CNTs/MF exhibits the specific capacitance of about 184 F g-1 based on the total mass of the composite and 262 F g-1 based on the mass of PPy.(2) The reduced graphene oxide/nonwoven fabric (rGO/NWF) composites have been fabricated through dipping the NWF in the mixture of GO and HONH2·HCl and heating at 130℃, during which the GO is chemically reduced to rGO. Then PPy deposited on rGO/NWF (PPy/rGO/NWF) has been prepared through chemically polymerizing pyrrole vapor by using the FeCl3·6H2O adsorbed on rGO/NWF substrate as oxidant. Finally, the CNTs are used as conductivity enhancer to modify PPy/rGO/NWF through dip-dry process to obtain CNTs/PPy/rGO/NWF. The morphology of the composite is examined by SEM, the element content of the composite is examined by X-ray photoelectron spectroscopy (XPS), and the properties of the capacitor cells assembled are investigated by CV, CD, and EIS measurements. The results show that the optimum composite CNTs/PPy/rGO/NWF has highest capacitance of about 319 F g-1 and is more suitable for the electrode materials of the flexible electrochemical capacitor. The optimum composites also show better cycling stability, for example, the initial specific capacitance only falls 5.5% after cyclic testing of 1000 times at scanning rate of 80 mV s-1.