Study On The Modification And Electrochemical Performances Of Anode Materials For Lithium Ion Batteries

Lithium ion batteries(LIBs)is environment-friendly energy storage devices,which play an increasingly important role in modern society.The anode material,as a key component,directly determines the energy storage performance of LIBs.Graphite is one of the most used anode materials due to its advantages such as low charge-discharge potential and abundant resources.However,its structure is unstable under the large current charge-discharge processes,and the compatibility of graphite with some electrolytes is very poor.These problems will badly impact the cycle stability and the rate performance of LIBs.Graphene materials,with excellent flexibility and conductivity,can be used to enhance the electrochemical performances of graphite anode materials by modifying the interfacial nature and improving the electrochemical reaction conditions.In this paper,graphene is used as a conductive additive to compare the electrochemical performance with the that of traditional conducting agent.The effect of graphene addtion on the performance of graphite electrode was studied.At the same time,graphite anode materials with "core-shell" structure can be prepared by modifying graphite anode materials with graphene oxide.The structure of the composites is revealed by scanning electron microscope(SEM)and X-ray diffraction(XRD).The electrochemical performance of the composites was investigated by a variety of electrochemical testing techniques.Compared with the traditional conductive agent,graphene can effectively improve the cycling stability of graphite electrode,which is mainly attributed to the formation of a good conductive network.Graphite anode materials with "core-shell" structure can be prepared by modifying graphite anode materials with graphene.The cyclic performance of the material exhibits the best performance with the added graphene amount of 0.5%.The capacity retentions of both artificial graphite and natural graphite are 98.4% and 97.0% after 50 cycles at the current density of 0.2C,respectively.It ishigher than those of pure artificial graphite and natural graphite electrode(86.0% and 81.4%,respectively),indicating a good cycle performance with graphene modification.When the current density increase to 1.0 C,the capacity retentions of artificial graphite and natural graphite are 96.2% and 84.9% after 300 cycles,respectively,which are higher than those of pure artificial graphite and natural graphite electrode(62.1% and 64.7%,respectively),showing better performances at large rate.This is mainly attributed to the graphene materials coated on the surface of graphite,which can limit the volume expansion of graphite during the charging-discharging process,prevent the reduction reaction of electrolyte on the surface of the graphite and improve the electrolyte invasive.The kinetic analysis shows that,the nanoporous channels on graphene surface can shorten the diffusion distance of lithium ions,which is beneficial to reduce the charge transfer resistance and facilitate the insertion/desertion process of lithium ions.The graphene-modified graphite anode also keep a good energy storage performance in the full battery using 18650 LIBs during large current charge-discharge,showing a good practical application value.At the current density of 0.5C/1.0C,the retention rate of the graphene modified artificial graphite battery was 70.5% after 300 times,which was higher than that of the pure artificial graphite.At the same test current condition,the retention rate of graphene modified natural graphite battery was 70.0% after 200 times,which was higher than that of pure natural graphite.Graphene coating process improves the compatibility of graphite materials with electrolyte.It can also inhibit the expansion of the graphite in the charge-discharge process,thus improving the electrochemical properties of graphite anode.