Preparation Of Functionalized Carbon Materials And Its Application In Supercapacitors

As a new type of energy storage device, supercapacitor is a kind of green energy with high energy density, high power density and long service life, which shows great application potential in the future. Thus, it has very large practical significance and social benefit to carry out research work about supercapacitors. Here, we are intended to study the electrode materials which are the key component of supercapacitors. We choose carbon material as electrode’s base material. In order to increase the capacitance of the carbon electrode materials, we improved its composition and microstructure through different approaches. Various kinds of functionalized carbon electrode materials with high capacitance were obtained. Morphology and structure of the materials were characterized by variety methods. Electrochemical performances were tested by cyclic voltammetry, galvanostatic charge-discharge and electrochemical impedance spectroscopy. The synthetic mechanism and results were discussed aimed to generate carbon electrode material with excellent electrochemical performance. The main researches are as follows:1. The new nitrogen-doped hierarchical porous carbon material was obtained by using nano-Ca CO3 as hard template, melamine formaldehyde resin(MF) as carbon and nitrogen precursors. Both the morphology and nitrogen content of the resulting carbons can be easily controlled by simply varying the template amount and carbonized temperature. The nitrogen content is up to 20.9 wt% with abundant porous structure and high specific surface area(834 m2 g-1). Electrochemical test results reaveled that the carbon material carbonized at 900 ℃with high template proportion had the highest capacitance value of 283 F g-1(1 A g-1). In addition, the electrode also showed excellent rate capability and long charge-discharge cycle stability. The method is simple, low cost, which could provide a new approach for the synthesis of porous carbon materials.2. Graphene/Ni(OH)2 composite electrode material was prepared by simple hydrothermal process. Ni(OH)2 with α and β crystalline phase appeared two kinds of morphologies: nanowire and nanosheet, which loaded on graphene uniformly. Compared with graphene or pure Ni(OH)2, the composite has higher specific capacitance value(970 F g-1), excellent rate capability and good stability. The reasons are summarized as follows: Firstly, Ni(OH)2 has excellent pseudocapacitive property which could greatly improve the overall capacitance value of the graphene/Ni(OH)2 composite; secondly, as structural support, graphene could prevent Ni(OH)2 from aggregation, which increased the contact area between electrolyte ion and active sites, and improved the conductivity of the material; Thirdly, the presence of graphene effectively improved the rate capability and stability of the material.3. Functionalized three-dimensional(3D) hierarchical porous graphene was synthesized through low temperature hydrothermal process using Si O2 spheres as spacer, ionic liquid(IL) as structure-directing agent. The material has abundant macroporous and mesoporous with a specific surface area up to 341 m2 g-1. The introduction of Si O2 spheres gave rise to large number of open macroporous structure. IL attached to the graphene sheet can prevent it from stacking in subsequent processing, and improve its conductivity. The unique 3D hierarchical porous structure facilitates the ions diffusion and charge transfer, and improves the utilization efficiency of the material. The reserved numerous oxygen-containing functionalities after low temperature treatment not only improve the accessibility of the material, but also contribute pseudocapacitance during the charge-discharge process. Experimental results show the material has high specific capacitance value, good rate capability and excellent cycle stability. Besides, assembled symmetrical two-electrode capacitor with high power density of 13.3 k W kg-1, which exhibits the great application potential. Furthermore, the 3D functionalized porous graphene material is expected to be applied to other areas. The method we used could also play a guiding role for the design of other novel materials.