Preparation And Characterization Of High Specific Energy Density Self-supporting Composite Electrode And Their Electrochemical Performance

Supercapacitors, also called electrochemical capacitor, is a kind of electrode materials of energy storing device based on carbon material with high specific surface area, conducting polymer, transition metal oxide and sulphide. Different from the traditional capacitor, Supercapacitors make a storage charge though electrostatic adsorption on the interface between the electrode and the electrolyte and reversible oxygen reduction reaction on the surface or inside of the electrode. Supercapacitors with desirable performance of high power density, decent reversibility, long cycle life, high efficiency of charging and discharging and low maintenance cost, have a extensive application in military and civilian, especially in the use of new energy vehicles with an important strategic position. We make an application on water system hybrid supercapacitors, which provides a theoretical and scientific basis for high energy density, high power density supercapacitors. The details are as follows:(1) Homogeneous ZnCo2O4 nanoflowers have been synthesized on a 3D layered structure of carbon nanotubes/nitrogen-doped graphene( NGN/CNTs) film by a hydrothermal process and subsequent calcination method. The ZnCo2O4 nanoflowers have an average diameter of 4 μm, and are composed by petals less than 100 nanometers. The as-synthetic ZnCo2O4/NGN/CNTs film can be directly used as a flexible electrode with a high specific capacitance of 1802 F/g at 1 A/g and excellent cycling stability(almost 0% fade after 4000 sustaining charge/discharge at 10 A/g). Carbon nanotubes/nitrogen-doped graphene with a 3D structure and larger specific surface area can supply a large number of reactive sites. The thin film based on carbon nanotubes/nitrogen-doped graphene can attain a high conductivity and great rate performance. In addition, a binder-free asymmetric supercapacitor has been synthesized with ZnCo2O4/NGN/CNTs film as the positive electrode and NGN/CNTs film as the negative electrode. This demonstrates superior energy density( ≈ 37.19 Wh/kg at 750 W/kg) and power density( ≈ 15 kw/kg at 14.16 Wh/kg)(2) Based on light and flexible carbon cloth, we make a Zn0.76Co0.24S/carbon cloth composite though hydrothermal preparation of zinc cobalt precursors and subsequent vulcanization, which simplify electrode manufacture processing. Carbon cloth not only support active materials but also serve as current collector, which proved an expressway for charge transfer and eliminated the use of ancillary conducting material and binder. Nano electrode material directly loading on carbon-based material can improve effective contact area and enhance the transfer efficiency of electronics and electrolyte ions in device, showing a lower diffusion impedance and better ratio performance.the Zn0.76Co0.24S/carbon cloth presents a higher specific capacity of 1634 F/g at 5 A/g and excellent cycling stability( almost 0 % fade after 5000 sustaining charge/discharge at 10 A/g). Moreover, an assembling asymmetric supercapacitor with Zn0.76Co0.24S/carbon cloth as the positive electrode and NGN/CNTs film as the negative electrode is also fabricated. Which exhibits a prominent energy density of 39.83Wh/kg at 776.72W/kg.(3) Here, a unique controlled synthesis of zinc cobalt sulfide crosslinking nanosheet supported on a 3D layered structure of carbon nanotubes/nitrogen-doped graphene( NGN/CNTs) film is obtained by a hydrothermal process, subsequent calcination stage and final sulfidation process. Benefiting from the less electronegativity of sulfur compared with oxygen, the new electrode material has a faster electronic migration and can prevent structure collapse by stretching in the process of charging and discharging, which lead a better cycle life. Benefiting from the characteristic features and 3D electrode architectures, the ZnxCo1-xS exhibits a higher specific capacity of 2484 F/g at 2 A/g and excellent cycling stability( almost 0 % fade after 4000 sustaining charge/discharge at 10 A/g). Moreover, an assembling asymmetric supercapacitor with Zn0.76Co0.24S/NGN/CNTs film as the positive electrode and NGN/CNTs film as the negative electrode is also fabricated. Which exhibits a prominent energy density of 50.16 Wh/kg at 387.49 W/kg.