Research On Preparation And Properties Of Graphene Modified Silicon Based Anode Materials For Lithium Ion Batteries

The theoretical capacity of commercial cathode materials is only 372mAh·g-1,which is far from meeting the requirements of high energy density and high power density lithium ion batteries.In the anode materials of lithium ion batteries,silicon materials have high theoretical capacity(up to 4200mAh·g-1),and are rich in resources,which have great potential in the development of high capacity and high power battery.However,the serious volume effect of silicon materials will lead to the rapid degradation of its electrochemical properties,and the low efficiency of Kulun is always the main problem to hinder its commercialization.Graphene is a new type of carbon material made up of monolayer carbon atoms.Because of its excellent properties,it can be used to modify tin based,silicon based and transition metal electrode materials and prepare graphene composites with excellent electrochemical performance.In this paper,we studied the preparation of graphene,and the dispersion and coating modification of silicon materials by graphene and polyaniline,to improve the volume effect of silicon materials and the low efficiency of the first time.The main contents include the following aspects:1.Using natural flake graphite as raw material,graphite oxide was prepared by the improved Hummers method.The graphene oxide was obtained by ultrasound,centrifugation,dialysis and freeze drying.The removal of oxygen containing functional groups on the surface of graphene oxide was prepared by high temperature thermal reduction.Using high resolution scanning electron microscopy(SEM),transmission electron microscopy(TEM),atomic force microscopy(AFM),Raman spectroscopy(Raman),X-ray diffraction(XRD)on the graphene morphology and structure characterization.The prepared graphene has a thickness of about 1.5 nm,a number of layers of about 2-4 layers,and a width of 3-5 mu m.2.Silicon/graphene(Si-G)composite anode material was prepared by ultrasonic dispersion method and vacuum thermal reduction method using nano silicon and graphene oxide as raw materials.The morphology and structure of Si-G composite anode material were characterized by SEM and XRD.Then the button cell was assembled with Si-G composite anode material as electrode material,and the electrochemical performance of Si-G composite anode materials were analyzed by using electrochemical workstation and other equipment.Compared with silicon nano negative electrode material,silicon/graphene composite anode material has obvious increase in specific capacity.The specific capacity retention rate increases from 40%to 67.3%.3.Using aniline monomer as raw material and ammonium sulfate as oxidant,silicon/polyaniline composites were synthesized by low temperature chemical oxidation method.Preparation of silicon/polyaniline/graphene(Si-PANI-G)composite anode materials by ultrasonic dispersion and freeze drying method.The morphology and structure of Si-PANI-G composite anode materials were characterized by SEM and XRD.Then the button cell was assembled with Si-PANI-G composite anode materials as electrode material,and the electrochemical performance of Si-PANI-G composite anode materials were analyzed by using electrochemical workstation and other equipment.Compared with the silicon nano negative electrode material and the silicon/graphene composite negative electrode material,the specific capacity has obviously improved and the specific capacity of 497mAh·g-1 is maintained after 30 cycles.