Synthesis And Lithium Storage Investgation Of Graphene-Based Nanocomposites

Lithium-ion batteries (LIBs) have important applications in portable devices, device miniaturization and environmental-friendly energy, due to the advantages of high energy density, high capacity, high single-battery potential, no memory effect and environmental-friendship. Graphene has been a research hot topic in physics, chemistry and materials science in recent years because of its unique properties. Graphene-based nanocomposites (GBNCs) have combined the merits of each component together, and have wide applications in LIBs, supercapacitors, solar cells, photocatalysis, among others. This thesis mainly concentrates on the synthesis and application in LIBs of GBNCs. Through the construction of mesoporous GBNCs, the conductivity and stability of the electrodes are enhanced, strengthening the rate capability and cycle performance of LIBs. The investigation of GBNCs preparation and properties not only has great academic value but is also essential for obtaining enhanced performances and the practical applications. The main listed as follows:1. A general strategy for synthesizing GBNCs is developed, using oil-phase dispersible nanocrystals as building blocks. This method contained two assembly steps:(1) hydrophobic nanoparticles were assembled to water-dispersible colloidal spheres with positive charge via an emulsion-based bottom-up self-assembly (EBS) method by choosing proper surfactant;(2) the colloidal spheres were assembled with negative charged graphene oxide (GO), obtaining nanocrystal spheres/graphene composites. With a heat treatment,3D mesospheres/graphene composites (MGCs) were achieved. TiO2, Cu2S and CeO2MGCs were successfully prepared using this method, which laid solid basis for the construction of multicomponent GBNCs. Using TiO2MGCs as electrodes of LIBs, they exhibit enhanced rate capabilities and cycle performances compared to the corresponding TiO2mesospheres.2. Inspired by the idea for preparing GBNCs with electrostatic assembly, VO2(B) nanobelts (NBs)/graphene composites were successfully fabricated with VO2(B) NBs and graphene nanosheets (NSs) as the building blocks and the control of the surface properties. Negatively charged VO2(B) NBs were synthesized via a hydrothermal process; APTMS is then applied to modify the surface of VO2(B) NBs; VO2(B) NBs/graphene composites were finally obtained with the assembly of modified VO2(B) NBs and GO. Using the composite films as cathode of LIBs, they exhibit enhanced lithium storage performance compared to VO2(B) NBs films. With higher graphene content in the composites, the performance improved. Electrostatic assembly is a feasible strategy to fabricate GBNCs by making full use of the surface properties of GO.