Study On The Synthesis And Properties Of NiO-based Electrode Materials For Supercapacitors

Supercapacitors with high power capability, long cycle lifetime and fast charge and discharge rate have received great interests in recent years. Electrode materials are the core of supercapacitor, which directly affects its performances. Many materials have been considered as the electrode materials for supercapacitors. Among them, NiO exhibits many attractive advantages, such as low cost, easy availability, and high theoretical specific capacitance (2584 F/g within 0.5 V). So it has been extensively investigated.In order to obtain the NiO-based edectrode materials with superior performance and discuss the influence mechanisms of its electrochemical performance, the main researches and conclusions of this thesis are summarized as following:(1) Three kinds of nano NiO electrode material with various morphologies were synthesized via different synthesis process. Comparing the electrochemical performances of the as-synthesized NiO nanostructures, it is different due to the changes of the specific surface area, the crystal particle size and surface condition. The results show that the larger specific surface area, the smaller the particle size and abundant surface defects are conducive to the electrochemical performances of NiO electrode materials for supercapacitors.(2) NiO-based composites (such as NiO/carbon sphere, NiO/carbon nanotube and NiO/reduced graphene oxide) were parpared via various synthetic processes. The morphologyies of these NiO-based composites were influenced by the morphologies of the adding carbon materials. Carbon materials hindered the aggregation of nano-NiO particles during the synthesis process. The composites with the increasing specific capacitance values originate from the conductive carbon materials, the special morphologies, abundant surface defects and larger specific surface area. In addition, the cycle performances of these NiO-based composites were obviously improved by the introduction of carbon materials to Nano-NiO.(3) A series of NiO/RGO composites were proposed by the same hydrothermal method combined with different calcination temperatures. The composites calcined at 250℃ exhibits higher capacitance and better stability than that calcined at higher temperature due to the smaller particle size, the more surface defects, larger specific surface area and more content of RGO. Which results verify the explanations of the influence mechanism of NiO-based electrode materials.(4)The electronic structure, the surface energy, the influence of vacancy in crystal or surface and the adsorption of OH onto NiO (001) surface were investigated by DFT theory. As a wide band gap semiconductor, the conductivity of NiO crystal can be improved by the vacancy defects. NiO (001) with the minimum energy in the low-index surfaces is the promising stably outer surface. The work function of NiO (001) will be decreased with the presence of surface vacancy, thus enhancing its surface chemical activity. The surface active site for the adsorption of OH group is the top site of Ni atom in the cleaning NiO (001), and that adsorption will bring disturbance to the surface, which significantly affects the cycle performance of NiO-based electrode materials.The researches of this thesis can provide some useful reference for the synthesis electrode materials with excellent electrochemical performance and the development of the theory about the influence mechanism of the electrochemical performance of similar electrode materials.