Synthesis And Electrochemical Property Of Graphene-based Composite Materials

There are more and more high requirements to battery on varies portable electronic devices including power car system,energy storage device in today's society.Due to its excellent performance on the electricity,optics,mechanics,calorifics,and so on,graphene has a good application prospect in the field of energy storage as the thinnest material of the world.Graphene-transition metal oxide composite materials have been studied as their advantages such as rich in reserves,non-toxic harmless,low cost and high theoretical specific capacity of transition metal oxide.To simplify tichnique process and improve the reversible specific capacities of anode materials for lithium-ion batteries,Fe₂O₃-graphene nanocomposite,CoO-graphene nanocomposite,and Fe₂O₃·Co O-graphene nanocomposite were prepared by improving the experimental method.The XRD,SEM,TEM,FT-IR were adopted to characterize the microstructure and morphology of the as-prepared materials,and chemical composition analysis.Adsorption stripping test was adopted to study the specific surface area,pore size distribution and pore volume.The electrochemical performance of nanocomposites was investigated by constant current charge and discharge test and impedance measurements.The main research content as follows:Graphite oxide prepared by modified Hummers method.Firstly,Fe₂O₃-graphene nanocomposite was prepared by puffing calcination method.X-ray diffraction was used to study the phase structure of the composite,and discussed the influence of different reduction temperature time on the result.The results of SEM and TEM show that Fe₂O₃ nanoparticles were successfully deposited onto the surfaces of graphene sheets.Electrochemical tests show that the discharge specific capacity of nanocomposite at the mass ratio of 1:3 can be 927mAh/g under the current density of 100mA/g,and it can still be 580mAh/g under the current density of 1000mA/g.Next,CoO-graphene nanocomposite was prepared by puffing calcination method.The results of XRD show that the CoO was successfully prepared,and there was also some Co2O3 mixing in it.The results of SEM show that the CoO particles loaded to the graphene surface uniformly,and coated phenomenon was more and more obvious as the ratio increased.The results of TEM show that it was mesoporous structure,and there was also a small amount of reunion particles and pore volume also decreased accordingly.Electrochemical test shows that the discharge specific capacity of nanocomposite at the mass ratio of 1:3 can reach 937mAh/g under the current density of 100mA/g.In the process of charging and discharging,capacity had obvious change,but remained above 800mAh/g.Finally,puffed calcination method is used to prepared Fe₂O₃·CoO-graphene nanocomposite and put forward a new method of preparation of anode composite material.The results of XRD and SEM show that Fe₂O₃·CoO particles successfully loaded to the surface of graphene.Adsorption stripping test shows the specific surface area,pore size and pore volume of Fe₂O₃·CoO-graphene nanocomposite.Electrochemical tests show that the reversible capacity of nanocomposite can be 870mAh/g,lower than the former two.It can still be 560mAh/g under the current density of 1000mA/g.Fe₂O₃-graphene nanocomposites showed the best electrochemical performance through the relative analysis of three kinds of composite materials.