Preparation And Electrochemical Properties Of The Graphene-Based Composites

The electrode materials for supercapacitors and lithium ion batteries have always been the hot topic focused on by researchers. Since graphene was found in2004, it has become the hot research issue in various fields. Graphene, with a unique two-dimensional sp2-hybridized single layer carbon structure, possesses many excellent properties such as high mechanical strength, superb chemical stability, extraordinarily high electrical conductivity and large theoretical specific surface area, exhibiting much greater potential for applications in supercapacitors and lithium ion batteries as compared with traditional porous carbon materials. In recent years, the researches on the compounds of graphene coupled with transition metal oxides as the supercapacitor and lithium ion battery electrod materials have received much attention. It has been proved that the addition of graphene can improve electrochemical properties and cycle life of transition metal oxides due to its good conductivity and stability. The main researches carried out in this dissertation are presented as follows:(1) Graphite oxide (GO) was synthetized by the modified Hummers’ method, followed by a hydrothermal route to form reduced graphene oxide (RGO)-Cu2O with ethylene glycol and glucose as the reducing agents, respectively. The composition and morphology of RGO-Cu2O were characterized by X-ray diffraction (XRD) and transmission electron microscope (TEM). As the supercapacitor electrod materials, RGO-CU2O shows discharge specific capacitances of53.18and43.58F g-1at0.2A g-1reduced with ethylene glycol and glucose, respectively, while the Cu2O is25.62F g-1. After200cycles, the capacitance retention rates of RGO-CU2O reduced with ethylene glycol and glucose, and Cu2O are99%,94%and74%, respectively. With the RGO-Cu2O composite reduced by ethylene glycol as the lithium ion battery anode material, it shows the first discharge and charge specific capacities of731.9and419.3mAh g-1, while430.4and351.1mAh g-1for bare Cu2O electrode. Evidently, the introduction of RGO can greatly improve the electrochemical performances and stability of Cu2O electrod materials.(2) RGO-InVO4nanocomposite was prepared by a hydrothermal route, of which composition and morphology were characterized by XRD and TEM. The charge-discharge properties and cyclic stability of RGO-InVO4and InV04as anode materials for lithium ion batteries were tested under different current densities. The results show that the first discharge and charge specific capacities of the RGO-InVO4electrode were1047.5and599mAh g-1while994.2and482mAh g-1for the InVO4electrode, respectively. After50cycles under different current densities, the discharge and charge specific capacities of the RGO-InVO4electrode were472.4and456.7mAh g-1, while138.4and132.9mAh g’1for the InVO4electrode, respectively. The introduction of RGO can pronouncedly improve the electrochemical properties of InVO4, especially for cyclic stability.(3) RGO-Cu2O-TiO2ternary nanocomposite was successfully fabricated via a one-step solution-phase hydrothermal method. The synthesized RGO-Cu2O-TiO2nanocomposite was characterized by XRD, TEM, atomic force microscopy (AFM) and Raman spectroscopy, and its electrochemical properties as an active electrode material for supercapacitors were investigated through cyclic voltammetry (CV) and galvanostatic charge/discharge measurements. The results show that the specific capacitance of RGO-Cu2O-TiO2electrode were80.0F g-1at0.2A g-1, while41.4and32.7F g-1for the RGO-Cu2O and RGO-TiO2electrodes, respectively. Furthermore, after1000cycles, the specific capacitance of RGO-Cu2O-TiO2increases from80to91.5F g-1, while the specific capacitances of RGO-Cu2O and RGO-TiO2decrease from41.4to34.5F g"1and from32.7to25.2F g-1, respectively. The excellent cycle stability is required for supercapacitors.