The Research On Controllable Synthesis And Lithium Storage Performance Of The Three-dimensional Graphene/Active Anodes

As the most common anode material for lithium-ion batteries（LIBs）,graphite has achieved great success in commercial application of LIBs.However,the theoretical capacity of graphite anode is as low as 372mAh·g^-1.It is difficult to meet the requirements of high-performance energy storage devices for the rapid development of the"information society".Therefore,the development of new high-capacity LIBs anode materials is of great significance.Meanwhile,as a new high-capacity anode material should meet abundant,low development costs and high efficiency requirements.Among non-metallic materials,silicon,germanium,phosphorus,and metal tin and antimony with high theoretical specific capacities have received extensive attention from scientific researchers.Among them,the research on silicon-based anodes is more extensive.Silicon-based anodes generally include silicon（Si）and silicon oxide compounds（SiO _x）.The theoretical specific capacity of pure silicon anode with abundant reserve is as high as 4200mAh·g^-1.However,the shortcomings of Si itself,such as poor conductivi ty and huge volume expansion（400%）,severely limit the further commercial application of Si anode materials.The theoretical specific capacities of silicon-oxygen compounds（SiO_x）are between1200-2700mAh·g^-1（the specific capacities are related to the value of x in SiO_x）.Besides,SiO_xwith simpler preparation process,lower cost,and smaller volume expansion（160-220%）is more suitable as a new high-capacity anode for LIBs.The conductivity of the non-metallic electrode is poor,while metal-based anodes can avoid this shortcoming.The antimony metal electrode with excellent conductivity displays high theoretical capacity(660mAh·g^-1)about twice that of the graphite electrode.These two kinds of alloy electrode materials have great application prospects in the field of storage of large amount of electric energy and efficient conversion and transmission of electric energy.This thesis focuses on the synthesis and electrochemical performance of silicon-based and antimony-based anode materials.The specific inquiry is as follows:1.In this chapter,a three-dimensional holey graphene framework（3D-HGF）and silicon monoxide were used as precursors to prepare composting electrode（3D-HGF/SiO）as conductive agent-free,binder-free and free-standing anode for lithium-ion battery.The preparation steps of the composite electrode include preparation of porous graphene oxide or graphene oxide,graphene/silicon monoxide precursor,and three-dimensional holey graphene/silicon monoxide composite electrode.Graphene oxide has an excellent processability.Generally,the diameter of GO is about 2μm.In this chapter,a modified Hummers method is used to prepare large-scale graphene oxide（the diameter is about 30μm）.Large-scale GO with outstanding structural integrity and mechanical properties can effectively inhibit the volume expansion of SiO during charge and discharge processes.At the same time,the three-dimensional graphene framework with hierarchically porous structure highly promotes the ion transportation;further improve the lithium storage capacity of LIBs.The impedance theory and complex capacitance theory of porous electrodes were used to characterize the prepared three-dimensional electrode to verify the good internal charge transfer performance.Through a series of electrochemical characterizations,the 3D-HGF/SiO electrode can provide high areal capacity of up to 13mAh·cm^-2 at a current density of 2.2mA·cm^-2,and excellent rate performance.Additionally,the3D-HGF/SiO electrode presents high capacity retention rate up to 74%after continuous 220 cycles.Various physical characterizations and electrochemical performance analysis suggest that the 3D-HGF/SiO composite electrode with high areal capacity and ideal cycle stability shows great application prospects in the field of high-performance energy storage devices.2.In this chapter,a three-dimensional porous graphene/antimony electrode（3D-HGF/Sb）was obtained by the composite of porous graphene oxide and metallic antimony-based precursor.In addition,it is proved by impedance theory that the three-dimensional porous frame structure can highly promote the conduction of charge（electron and ion）.Then,SEM,XRD,EDS Mapping were used to characterize internal structure and composition of the composite electrode.Electrochemical test results showed that the areal capacity of the electrode was about two times that of the conventional commercial graphite electrode.Meanwhile,the 3D-HGF/Sb displayed a high areal capacity of 2.7mAh·cm^-2 at a current density of 2000mA·g^-1.When the current density is 2.0mA·cm^-2,the 3D-HGF/Sb presented outstanding cycle stability and high reversible capacity of 6.7mAh·cm^-2.These results show that the 3D-HGF/Sb electrode has great potential for practical applications.