Synthesis And Electrochemical Properties Of The Co-Based Composites For Supercapacitors

ABSTRACT:Supercapacitors have the merits of very high power density, extremely stable cycle life, long shelf life, high efficiency, wide range of operating temperatures, safety, environmental friendliness and therefore can be used as an energy storage devices for the supplementary power sources for EVs and HEVs. While the electrode materials play the most important role in the performance of the suprecapacitors. Because of low cost, natural abundance, environmental safety and excellent electrochemical properties, cobalt oxide is found to be one of most promising electrode materials of supercapacitors. However, the charge transfer on interface is limited due to the poor electronic conductivity of CO3O4and the difficulty in the penetration of electrolyte into the microstructure of electrode. Therefore, the incorporation with carbon materials such as graphene which are high electronically conductive, or the synthesis of nanostructure、porous honeycomb mesh structure, which facilitates the transfer of ion, are both the method which improve the electrochemical performance of Co3O4electrode. The specific works are as follows:(1) Firstly, a promising nickel cobaltite oxide (NiCo2O4) composite electrode material are successfully synthesized by a sol-gel method and followed by a simple sintering process. The microstructure and surface morphology of NiCo2O4modified by hexadecyltrimethylammonium bromide (CTAB) are physically characterized by power X-ray diffraction diffraction and scanning electron microscopy. The optimized experiment get a composite of three-dimensional honeycomb netlike structure. The NiCo2O4composite with pore structure has good electrical conductivity, and enlarge the reactive sites, thereby improving the capacity and rate performance.(2) Co-Al layered double hydroxides (LDHs) are prepared through a fast nucleation and a subsequent hydrothermal treatment. The samples consist of hexagonal platelets with a lateral size as large as about200nm, which is of high quality in terms of size, uniformity, and crystallinity. The Co-Al LDHs(2:1) symple has a specific capacitance of450F g-1at current density of0.5A g-1.(3) Co3O4/moCNTs/rmGO is synthesized in ethanol/H2O solution by a general two-step method. In the first step, CO3O4nanoparticles were grown on mildly oxidized GO sheets (mGO) and mildly oxidized CNTs freely suspended in solution by hydrolysis and oxidation of cobalt acetate (Co(OAc)2) at80℃. Subsequent hydrothermal reaction at180℃led to crystallization of CO3O4and reduction of mGO to form the Co3O4moCNTs/rmGO hybrid. The hybrid shows excellent electrochemical performance, and has a specific capacitance of502F g-1at current density of0.5A g-1. The cycling performance is also increasing apparently compared with pure Co3O4.