Fabrication And Electrochemical Properties Of Porous Textile-based Energy Storage Materials

Energy provides the firm matrial foundation for the development of human society. With the continuous growth of energy consumption, the exhaustion of fossil energy,the environmental pollution and ecological damage caused by the utilization of fossil energy, we have to develop new and efficient energy storage materials and devices. As a kind of novel energy storage devices, electrochemical capacitors exhibit some promising properties. Their energy density and power density are higher than the traditional capacitors and the batteries, respectively. Recently, fexible and wearable electronic devices that are suitable for arbitrary installation and applications have attracted great attention. All these electronic applications require cheap,fexibility, light-weight, wearable power conversion and storage devices. However, the conventional electrochemical capacitors cannot effectively meet the requirements.Therefor it is necessary to develop flexible electrochemical capacitors.In this thesis, textile-based flexible electrode materials were fabricated by using cotton fabrics, graphene sheets and pseudocapacitor materials. The morphologies,material structures and electrochemical properties of thes electrode materials were studied in detail.(1) Graphene/cotton composite fabrics were synthesized by using a facile“dipping and drying” process followed by Na BH4 chemical reduction method and thermal reduction method.The graphene/cotton composite electrode prepared by Na BH4 chemical reductionmethod exhibits a good conductivity. The sheet resistance was 560 ? /sq. The gaphene/cotton composite electrode showed a good specific capacitance and cycle stability. The specific capacitance was determined to be 40F/g within 0.0-1.0 voltage window. During 1000 cycles of charge-discharge process, the specific capacitance had a slight decrease and retained 90% of its initial capacitance.The graphene/cotton composite electrodes prepared by the thermal reduction method showed excellent cycle stability. The reduction atmosphere, reaction temperature and reaction time have effect on the material structures and electrochemical properties. The lowest sheet resistance was 3000?/sq when reducting in H2. The electrode material prepared in H2 exhibited a specific capacitance of17F/g。After 1000 cycle of charge-discharge process the specific capacitance retained95%.(2) Co-Ni LDH/graphene/cotton composite electrode(Co-Ni LDH/G/CF) was synthesized by the chemical deposition of Co-Ni LDH on graphene/cotton composite fabrics(G/CF).The Co-Ni LDH/graphene/cotton composite electrode with a Co/Ni molar ratio of 2/3 showed the highest specific capacitance of 578F/g. The asymmetric supercapacitor device assembled by using Co-Ni LDH/G/CF as the positive electrode and G/CF as the negative electrode exhibited a specific capacitance of 238F/g and energy density of 18Wh/kg.(3) Mn O2/graphene/cotton composite electrode was synthesized by electrochemical deposition of Mn O2 on gaphene/cotton composite fabrics.The specific capacitance of the Mn O2/graphene/cotton composite electrode was693F/g. In order to improve the electrochemical performance of Mn O2/graphene/cotton composite electrode, polypyrrole was deposited on Mn O2/graphene/cotton composite fabrics. After the deposition of polypyrrole, the cycle stability of Mn O2/graphene/cotton composite electrode was enhanced. During3000 cycle charge-discharge process, the specific capacitance of polypyrrole/Mn O2/graphene/cotton composite electrode retained 97%.