Synthesis, Electrochemical Performance And Mechanical Stability Of Electrode Material Based On Graphene

Supercapacitor is a kind of new energy storage device between traditional capacitor and battery. It can be widely used in electric vehicles, aerospace, defense technology, information transportation, military industry and other fields due to be many advantages such as high power density, high energy density, fast charging speed, long cycle life and little pollution to the environment. However, the electrode material play key role for the electrochemical performance of supercapacitors. Therefore, the design and synthesis of the electrode material with high performance is very important for the supercapacitor with high performance.In this paper, the design of supercapacitor, the synthesis, electrochemical performance and mechanical stability of electrode materials were studied in detail. The results and innovations are as follows:(1) A supercapacitor with superlayer structure was designed, and the electrode material in the supercapacitor was used as the object. The magnetron sputtering method was used to prepare graphene film on nickel foam. The technology was used to synthesis of the graphene/nickel foam, graphene/cobalt tetroxide/nickel foam and graphene/nickel hydroxide /nickel foam electrode materials were studied respectively. Furthermore, the effect of structure on properties of electrode materials was investigated in detail.(2) 3D-G/NF electrode material was fabricated by the magnetron sputtering graphene film on Ni Foam (NF) collector. The effects of sputtering temperature and time on the structure and electrochemical properties of 3D-G/NF electrode were investigated. The results showed that:(A) The RF magnetron sputtering method was a new process for the preparation of graphene film on NF, which could be directly deposited on NF without adding any conductive agent and polymer binder. Compared with the traditional CVD method, the preparation temperature was relatively low. (B) The 3D-G/NF electrode material has the advantages of simple preparation process, good adhesion between the graphene and the nickel foam. When the current density was 1.0mA/cm2, the specific capacitance of the electrode material was about 2.45F/cm2. The results indicated that the electrode material was high specific capacity, good rate performance and cycle stability characteristics.(3) Co3O4/Ni Foam (Co3O4/NF) was prepared by hydrothermal and calcination methods, and then Co3O4/NF electrode material was used as the substrate, and then the graphene/cobalt tetroxide/NF (G/Co3O4/NF) electrode materials were further synthesized by the RF magnetron sputtering method. The results showed that:(A) The morphology of Co3O4 grown on nickel foam was affected by the reaction time, which further determined by the electrochemical performance of Co3O4/NF. The Co3O4/NF electrode material prepared at 10h had a high specific capacitance (specific capacitance:0.45F/cm2 at a current density of 1.0mA/cm2) and good electrochemical stability (95.6% at 1000mA/cm2 after 1000 cycles). (B) Electrochemical performance of G/Co3O4/NF was better than that of Co3O4/NF electrode material, in which it was a specific capacitance of 0.67F/cm2 at a current density of 1.0mA/cm2. Compared with Co3O4/NF, the specific capacitance was improved to be 49%.(4) Ni(OH)2/NF and graphene/nickel hydroxide/nickel foams (G/Ni(OH)2/NF) were prepared by hydrothermal method and magnetron sputtering method. The effects of hydrothermal reaction time and magnetron sputtering process on the microstructure and electrochemical properties of the electrode materials were studied. The results showed that: (A) The Ni(OH)2/NF had a specific capacitance of 1.2F/cm2 at a current density of 1.0 mA/cm2 when the hydrothermal temperature was 180? and the hydrothermal time was 24h. (B) The properties of G/Ni(OH)2/NF electrode materials were further improved by magnetron sputtering deposition of graphene, For example, the G/Ni(OH)2/NF8h had a good specific capacitance and cycle life, in which the specific capacitance of G/Ni(OH)2/NF8h was improved to be 16 times comparing with Ni(OH)2/NF8h electrode material. These results further indicated that the deposition of graphene on the traditional electrode material could effectively improve the electrochemical performance of the electrode material.(5) Based on the theory of laminates and the finite element modal analysis theory, the mechanical stability of graphene film/nickel foam (G/NF) electrode materials was investigated. The stress, strain, displacement and mode of G/NF electrode material with different thickness of graphene film were analyzed by finite element method. The results showed that:(A) When the graphene film thickness was 100nm and the force was 0.1N, the stress was 171MPa, which was much larger than the adhesion strength between graphene film and Ni foam. So, the force was lower than 0.03N to ensure that the electrode material was not damaged. (B) The G/NF electrode materials with three different thickness graphene films had high natural frequency, and the thickness of the film had little effect on the natural frequency of the electrode material.