Synthesis And Electrochemical Property Ofgraphene-based Composite Materials

Development of lithium-ion battery will move towards high specific capacity,good cycle rate and long life direction in the future,in which the anode material will be an key factor in determining the performance of lithium-ion batteries.Since its discovery,graphene has been used in energy storage because of its excellent performance in many aspects.In this thesis,to improve of the reversible capacity of the negative electrode material of lithium ion battery,the Fe₂O₃-graphene,Fe₂O₃-SnO₂-graphene and Li₄Ti₅O₁₂-graphene nanocomposites were prepared by hydrothermal method.The structure and morphology of the composites were characterized by XRD,SEM and other techniques.Thespecificsurfaceareaandporevolumewerestudiedby adsorption-desorption test.Its electrochemical performance was tested by galvanostatic charge-discharge test,cyclic voltammetry and AC impedance.The main research contents are as follows:First,PVP-assisted hydrothermal method was used to prepare Fe₂O₃-graphene nanocomposites,and the effect of the addition amount of PVP on the composite material was also studied.XRD analysis showed that the product obtained by hydrothermal method was mainly composed of Fe₂O₃.SEM analysis showed that the distribution of Fe₂O₃ is very uniform,mostly polyhedron particles.The distribution of Fe₂O₃ and graphene are staggered,and Fe₂O₃ is better dispersed on the surface of graphene.The specific surface area and pore size of the nanocomposites were obtained by nitrogen adsorption-desorption test.The results of electrochemical tests show that the composites material in the lithium storage performance is very prominent,its lithium capacity up to 1050mAh/g.After adding PVP to improve the overall capacity.Even at 1.5C,the capacity still reaches 510mAh/g.Secondly,in order to further increase the capacity of lithium-doped Fe₂O₃-graphene nanocomposites and their cycling multiplicities,a Fe₂O₃-SnO₂-graphene nanocomposite was prepared by hydrothermal method with the aid of PVP.XRD analysis shows that the hydrothermal method successfully composite graphene,Fe₂O₃ and SnO₂.SEM analysis shows that Fe₂O₃ and SnO₂ are both granular and the shape of graphene is curly and wrinkled.Adsorption and desorption tests show that the composite has a large specific surface area and pore size distribution.The staggered deposition of graphene,Fe₂O₃ and SnO₂ provides many micropores for lithium ion storage.Electrochemical tests show that the composite has higher capacity than Fe₂O₃-graphene nanocomposites and has a capacity of 1250mAh/g.After adding PVP to improve the overall capacity.Even at 1.5C,still can reach 760mAh/g.Finally,Li₄Ti₅O₁₂-graphene nanocomposites were prepared by hydrothermal method.XRD analysis showed that there was Li₄Ti₅O₁₂2 in the product.SEM analysis showed that most Li₄Ti₅O₁₂2 particles were spheroidal and evenly distributed.The surface of graphene has a large number of Li₄Ti₅O₁₂2 attached,both sides of the reunion was significantly alleviated.Adsorption and desorption test obtained the composite surface area and pore size,confirmed that the composite material has a large number of micropores,the formation of micropores is conducive to the storage of lithium ions.Electrochemical tests show that the composite has good lithium intercalation performance and its capacity is 220mAh/g.In the 1.5C high current,still up to 130mAh/g,magnification performance is excellent.