| Graphene refers to the single-layer graphite layer that peels off the graphite.It is by far the thinnest two-dimensional nano-carbon materialsis with only one atomic thickness,and its basic repeat cycle unit is benzene ring which is the most stable structure in organic chemistry.Graphene has many excellent properties,such as the thinnest and lightest properties,high electric and thermal conductivity,high charge mobility,free electron moving space,high strength and hardness etc,so it has received increasing attention and became a new star in the fields of physics,nano-electronic devices,catalysts,batteries,capacitors,optoelectronic devices,new composite materials and so on.In this paper,graphene with few layers was successfully prepared by Hummers and liquid-phase exfoliation respectively.The prepared samples were characterized by Fourier transform infrared spectroscopy(FT-IR),scanning electron microscope(SEM),Raman spectra,X-ray diffraction(XRD)and atomic force microscopy(AFM).Characterizations show that the prepared redox graphene sample is few layers,and its layer number is below 4.After the graphene oxide is reduced by ammonia,the C=C bond is repaired and the defect degree of graphene is reduced.In the same time,liquid-phase exfoliation graphene with higher electrical conductivity is used as control group to evaluate the application of redox graphene as conductive agent.The surface of liquid-phase exfoliation graphene is smooth and flat.Its number of layers is less,and it contains fewer functional groups,few defects as well as high quality.But the liquid-phase exfoliation of graphene layers are not uniform in the practical application,it is difficult to meet the requirements of industrialization.In this paper,graphene prepared by two kinds of methods was used as the conductive agent of the cathode material in the lithium-ion battery,and its effects on the lithium-ion battery performance were studied.In the study,the binder.s of the positive electrode paste for making lithium-ion battery is PVDF;the positive active material is lithium iron phosphate;and the conductive agents consist of the mixtures of conductive black carbon and graphene with differentproportions.Finally,the assembled button batteries were tested in LAND battery test system.By comparing the charge and discharge capacities,efficiency,charge and discharge medium potential and discharge final potential performance,it can be seen that the charge and discharge capacity of the battery shows a tendency to increase first and then decrease.The difference between the charge medium potential and discharge medium potential shows a tendency to decrease first and then increase.So it can be concluded that with the increase of the graphene amount in the conductive agent,the performance of the lithium-ion battery shows a order of first increase and then decrease.In addition,in the case of the same addition amount of the redox graphene and the liquid phase exfoliation graphene in the conductive agent,the performance of lithium ion battery with liquid phase exfoliation graphene is superior to ones which has redox graphene.Finally,the charge and discharge cycle of IV battery with the highest charge and discharge capacity,highest efficiency and best other performances is tested.The result shows that the IV battery cycle performance is stable.In summary,we can conclude that graphene can greatly improve the performance of lithium-ion battery,when it is applied to the lithium-ion battery as a conductive agent.Therefore,the research in this paper that graphene is used as a conductive agent to improve the performance of lithium batteries has a certain reference significance. |
