Growth Of Three-dimentional Garhene On Carbon Black And Flake Graphite And Their Performances For Electrical Conduction And Lithium Storage

In recent years,the development of lithium-ion power batteries is in full swing,especially in the field of new energy vehicles.However,for the commercial lithium-ion batteries,many problems still exist in the currently used cathode material?mainly LiFePO₄?and anode material?graphite?.The conductivity of LiFePO₄ is poor,limiting its capability of charging and discharging at high current density.Graphite possesses low gravimetric specific capacity and poor rate performance.These issues make the present power batteries difficult to meet the ever-growing demand of the market.Therefore,improving the structure and performance of cathode and anode electrode materials is important for enhancing the electrochemical performance of the battery.Graphene is widely used in new energy field due to its high electrical conductivity,high specific surface,and high mechanical strength.However,the van der Waals force between graphene sheets results in serious agglomeration,which greatly diminishes the advantages of high specific surface and numerous active sites.The development of a vertically oriented three-dimensional graphene structure is favorable for opening the edges of graphene sheets and forming a cross-linked porous network.This porous structure not only enhances the conductive network of the material,but also provides a channel for the rapid diffusion of lithium ions.Therefore,in this thesis,three-dimensional graphene/carbon black and three-dimensional graphene/graphite composite materials were prepared by thermal CVD method.They were used as the conductive agent of LiFePO₄ electrode and the anode active material respectively,which not only enhances the electrochemical performance of the cathode and anode electrodes,but also expands the application of three-dimensional graphene in the field of electrochemistry.In the preparation process of 3D graphene/carbon black?CB-3DGNs?composite materials,the effects of growth temperature,time,and concentration on graphene structure were studied.The prepared CB-3DGNs composites were used as the conductive agents of LiFePO₄ electrodes,and the electrochemical performance was tested.The results show that the LiFePO₄ electrode using CB-3DGNs composite conductive agent shows excellent electrochemical performance.Galvanostatic charge-discharge tests were carried out on the LiFePO₄ electrodes with different amounts of CB-3DGNs conductive agents?10%,7%,5%,and 3%?.When the 3DGN was grown at 1100°C for 4 hours and the addition amount was 5%,the LiFePO₄electrode shows high gravimetric specific capacity?165.3 mAh/g?,high rate performance?80.2 mAh/g,20 C,1 C=172 mAh/g?,high mass loading?5.2 mg/cm²?,and good stability?1100 cycles,1 C,85%?.The study of three-dimensional graphene/graphite?3DGN@G?composite anode materials also includes the effects of growth temperature,time,and concentration on the structure of three-dimensional graphene.The prepared 3DGN@G composite materials were used as the negative electrode materials for lithium-ion batteries,and the lithium storage performance was tested.The results show that the 3DGN@G composite anode materials exhibit excellent electrochemical performance.The galvanostatic charge-discharge tests show that the sample prepared at 1100°C for 12 hours possesses high gravimetric specific capacity?702 mAh/g?,high rate performance?327 mAh/g,5 C,1 C=372 mAh/g?,high mass loading?⁹ mg/cm²?,and good stability?1500 cycles,2 C,85%?.