Synthesis And Electrochemical Property Of Graphene-based Composite Materials

To develop lithium-ion batteries (LIBs) with high performance, it requires higher energydensity, higher power density, longer cycle life and lower cost. Anode material is one of thekey factors to improving battery performance. Graphene is a novel2D nano-sized cabonmaterials with high electrical conductivity, which has great potential application in energystorage field. To improve the reversible specific capacities of anode materials forlithium-ion batteries, the graphene, Fe2O3-graphene nanocomposite, SnO2-graphenenanocomposite, and Fe2O3-SnO2-graphene nanocomposite were prepared. The XRD andSEM were adopted to characterize the microstructure and morphology of the as-preparedmaterials. The electrochemical performance of as-prepared composites were investigatedby galvanostatically discharged and charged test and impedance measurements in detail.The main research content is as follows:Firstly, garaphene was prepared by redox method, which had uniform size distribution,fewer layers, and flat microstructure. The results of XRD and SEM show that the randomgraphene sheets possess a curled and wrinkled paper-like morphology. Electrochemicaltests show that the reversible capacity of graphene was kept at614mAhg-1after30cycles.It was indicated that the graphene possess more excellent electrochemical performance thanthe graphite for lithium storage performance.Secondly, Fe2O3-graphene nanocomposite was prepared by hydrothermal method toimprove the lithium storage capacity of graphene and to prevent the volumn expansion ofFe2O3nanoparticles. The results of XRD and SEM show that Fe2O3nanoparticles weresuccessfully deposited onto the surfaces of graphene sheets, and Fe2O3nanoparticles whichhad a uniformly cubical or spherical morphology. Both graphene and Fe2O3nanoparticlesformed a microporous structure for lithium storage. Electrochemical tests show thatFe2O3-graphene nanocomposite possesses higher reversible capacity than graphene orFe2O3nanoparticles. The reversible capacity of Fe2O3-graphene nanocomposite still was 1252mAhg-1after30cycles. In addition, Fe2O3-graphene nanocomposite has an excellentcycle performance and rate performance. The more increase of grephene, the higherreversible capacity of Fe2O3-graphene nanocomposite.Thirdly, SnO2-graphene nanocomposite was prepared by hydrothermal method. Theresults of XRD and SEM show that SnO2nanoparticles prevent effectively theagglomeration of graphene, graphene sheets inhibit the volumn expansion of SnO2nanoparticles at the same time, and SnO2-graphene nanocomposite has a plenty ofmicroporous structure for lithium storage. Electrochemical tests show that SnO2-graphenenanocomposite with a good cycle performance was much higher reversible capacity thangraphene or SnO2nanoparticles. The reversible capacity of SnO2-graphene nanocompositewas1252mAhg-1after30cycles, but SnO2-graphene nanocomposite had a bad rateperformance. Furthermore, the more increase of grephene, the higher reversible capacity ofSnO2-graphene nanocomposite.Finally, in order to further enhance the reversible capacity and rate performance ofgraphene-based composites. Fe2O3-SnO2-graphene nanocomposite was synthesized throughhydrothermal method. The results of XRD and SEM show that Fe2O3-SnO2-graphenenanocomposite had a wrinkled paper-like and spherical morphology and large numbers ofmicroporous structures between graphene, Fe2O3nanoparticles and SnO2nanoparticles.Electrochemical tests show that the reversible capacity and rate performance were muchsuperior to Fe2O3-graphene nanocomposite or SnO2-graphene nanocomposite.Fe2O3-SnO2-graphene nanocomposite was as high as1378mAhg-1after30cycles.Furthermore, the more increase of grephene, the higher reversible capacity ofFe2O3-SnO2-graphene nanocomposite.