Preparation And Supercapacitive Properties Of Graphene/Layered Double Hydroxides Composites

With unique structure, simple preparation and low cost, layered double hydroxides (LDHs) have attracted wide attention as electrode materials for supercapacitor in which electrical double layer capacitance and faradaic pseudocapacitance can be simultaneously acquired. However, the low electronic conductivity and rapid capacity decay under high current density during charge/discharge process limit their futher advancements in promising applications. The combination of LDHs and graphene sheets (GNS) with good conducting property, high specific surface area and exceptional mechanical strength has been proposed as perfect electrode materials with good electrochemical properties for supercapacitors due to synergistic effect of GNS and LDHs. Focusing on LDHs, this dissertation aims at the preparation and characterization of the GNS-based LDHs composites and their applications in supercapacitors in order to obtain electrode materials with large specific energy density, power density and good cycle stability. The details are as follows:1. A simple refluxing method is used to synthesize a series of GNS/CoAl-LDH composites. A maximum specific capacitance of711.5F/g at low current density of1A/g, and516.8F/g at10A/g can be obtained for the composite with a GNS content of9.3%. Furthermore, the capacitance keeps at least about519.8F/g after2000cycles at10A/g.2. GNS/CoAl-LDH composite has been fabricated by gas-liquid interfacial synthesis method and it is compared with pure CoAl-LDH and GNS/CoAl-LDH composite prepared with traditional hrdrothermal method. Electrochemical data analysis demonstrates that the obtained composite synthesized by gas-liquid interfacial method has a specific capacitance of479.2F/g and339.2F/g at the current densities of1A/g and10A/g, respectively, and the cycle life has been also improved.3. A series of GNS/NiAl-LDH composites have been prepared though a liquid phase deposition method, and the influence of different synthesis conditions have been discussed on the structures and the properties. The best properties can be obtained for the composite in which30mg GO is added into the system to allow reaction at50℃for48h. The as-obtained composite get high-capacitance performance with specific capacitance of1255.8F/g at the current density of1A/g and755.6F/g at6A/g, respectively. Moreover, the composite exhibites excellent cycling performance with an increase of6%capacitance compared with the initial capacitance after1500cycle tests.