Preparation And Electrochemical Properties Of Graphene Hollow Spheres

Graphene is a honeycomb two-dimensional planar material composed of a single carbon atom in a sp~2 hybrid manner and adjacent carbon atoms to form a six-membered annular space structure,which has a thickness of only one atom,about 0.34nm.Since the discovery of graphene,it has been a research hotspot for researchers.Because graphene has many outstanding properties,such as electrical,optical,thermal and mechanical properties,it is used in electronic devices,energy storage materials,catalysis,medicine and composite materials.Many fields have great application prospects.Graphene hollow spheres have many electrochemical properties such as large specific surface area,large pore volume,excellent electrode conductivity and chemical stability,and have been extensively studied in recent years.In general,the pore size,pore length and structure of graphene hollow spheres are important factors directly affecting their application.For example,a large specific surface area can provide many lithium ion insertion sites and reactive active sites in a lithium ion battery;a rich interconnect channel facilitates the rapid transport of lithium ions;these factors can affect the electrochemical performance of the material.Graphene hollow spheres are synthesized by selecting different carbon sources or different preparation methods.At present,there are mainly template method,chemical meteorological deposition method and hydrothermal method for preparing graphene hollow spheres,but these methods have their own advantages and disadvantages.Therefore,it is urgent to find a simple,fast,efficient,controllable,low-cost and large-scale preparation method of graphene hollow spheres,or to improve the original methods.The main research contents of this paper are as follows:(1)In this paper,a silica sol template was prepared by St?ber method.The carbonized coating method was used to test the self-made acrylonitrile oligomer(LPAN)as a carbon source.The low temperature pretreatment at 220°C was performed at a sintering temperature of 800°C.,heat preservation for 2h,and then remove the silica template by 10%HF to obtain carbon hollow spheres(HCS).By controlling the single variable method,the effects of different LPAN additions on the structure of carbon hollow spheres were investigated in detail.Scanning electron microscopy(SEM),transmission electron microscopy(TEM),fully automated surface area and void analyzer(BET),X-ray photoelectron spectroscopy(XPS),X-ray powder analysis(XRD),etc.Characterization analysis.Then the effects of different LPAN additions on the electrochemical properties of carbon hollow spheres(HCS)were investigated.The results show that the morphology of carbon hollow spheres(HCS)prepared by adding LPAN is 30%,and the electrochemical performance is also optimal.At 0.1C and 1C current density,the discharge ratio after 100 cycles The capacities are 550 mAh/g and 510 mAh/g,respectively.(2)The carbon hollow spheres(HCS)prepared under the above optimal conditions are used as raw materials,and then subjected to high-temperature sintering treatment to obtain graphene hollow spheres(HGS).By controlling the single variable method,the effects of secondary sintering temperature and holding time on the structure of graphene hollow spheres were investigated.Scanning electron microscopy(SEM),transmission electron microscopy(TEM),fully automatic surface area and void analyzer(BET),X were performed on the graphene hollow spheres(HGS)prepared at the optimum sintering temperature and optimum incubation time.Characterization and analysis of graphene hollow spheres by ray photoelectron spectroscopy(XPS),X-ray powder analysis(XRD),Raman spectroscopy,etc.Then the electrochemical properties of the graphene hollow spheres were studied.The results show that the quality of the prepared graphene hollow spheres is the best at the final calcination temperature of 2800°C for 6 h,and the electrochemical performance is also optimal.At 0.1 C and 1 C current density,100 cycles The specific discharge capacity after the cycle reached 725mAh/g and 620 mAh/g,respectively.(3)Carbon hollow spheres(HCS)and graphene hollow spheres(HGS)prepared under optimal conditions were directly used as anode active materials for lithium ion batteries,and assembled button cells were used for electrochemical performance testing,cyclic voltammetry and AC impedance test.The experimental results show that compared with carbon hollow sphere(HCS)materials,graphene hollow spheres(HGS)have higher specific capacity and first coulombic efficiency,that is,graphene hollow spheres(HCS)have better electrochemical performance.