Preparation Of Doped Graphene Three-dimensional Current Collector And Research On Its Stabilization Of Lithium Metal Anode

So far,the growing demand for electric vehicles has further stimulated the development of rechargeable batteries towards high energy density and high power density energy storage devices.Among all types of commercial rechargeable batteries,lithium-ion batteries（LIBs）have become the"superstars"of battery field due to their high energy density and long cycle life.However,the latest LIB can only reach a specific energy density of≈250 Wh kg^-1,which has become a bottleneck for LIB composed of a graphite-based anode and a cobalt-rich transition metal oxide-based cathode.Lithium metal provides a high theoretical capacity of 3860 m Ah g^-1,a very low reduction potential,and a low volume density,making it possible to recharge lithium batteries.The energy density is higher than commercial lithium-ion batteries based on intercalation anodes,such as graphite.Benefiting from the above advantages,metal lithium has become the most ideal negative electrode material for the next generation of high-energy density lithium batteries.However,it has not been practically used for many years,mainly because there are some safety problems in the metal lithium negative electrode that have not been resolved.Including the growth of dendrites due to uneven nucleation of metallic lithium,which causes some short circuit problems;Lithium metal and organic solvents have extremely high chemical reaction activity resulting in low coulombic efficiency;uncontrollable infinite volume changes during the deposition/dissolution of lithium metal.In response to the above problems,this paper designed graphene oxide（GO）as the base material,and added hydrofluoric acid in the hydrothermal process to obtain a three-dimensional frame structure and use it as a lithium metal anode current collector.The Li F-rich artificial SEI（solid electrolyte interface）film is formed between the metal lithium and the electrolyte during the deposition and dissolution process,and the deposition and dissolution of Li can be realized at a given current density,and the fluorinated graphene still maintains the good conductivity of the graphene oxide.The high specific surface area can effectively reduce the actual current density,so as to achieve uniform deposition,thereby inhibiting the growth of lithium dendrites.And by doping graphene oxide polyatomic atoms to further improve the cycle stability and rate performance of the lithium anode,the specific research content is as follows:（1）A self-assembled cross-linked 3D porous fluorine graphene was synthesized by a hydrothermal method as a current collector,and metal lithium was induced to deposit uniformly on it,and a lithium-free dendritic lithium metal negative electrode was prepared.The cross-linked 3D frame structure has a large specific surface area and good electrical conductivity.As the current collector of the lithium metal negative electrode,it can effectively reduce the actual current density and buffer the volume change caused by the deposition and dissolution of Li metal.In addition,the fluorinated graphene current collector maintains a very high Coulombic efficiency even at a current density of 1m Ah cm^-2 for 230 cycles,and even at a higher current density(6 m Ah cm^-2),it can stably cycle for 50cycles.The assembled symmetrical battery has been stably cycled for more than 600 hours at a current density of 0.5 m Ah cm^-2,and the overpotential is only 15 m V.Compared with the unfluorinated reduced graphene oxide composite negative electrode,it shows better cycle stability and long cycle life.（2）Based on the research results of single-atom doping,the lithium-philicity of polyatomic doped substrates and the influence on the deposition behavior of metallic lithium are deeply explored.On the one hand,the introduction of pyridine nitrogen functional group by hydrothermal method improves the lithium-philicity of the base material,and the introduction of semi-ionic C-F bond by fluorine doping makes the base surface of the material highly wrinkled and the disorder is enhanced.It is used as a current collector to prepare a composite lithium negative electrode with high stability and excellent rate performance.On the basis of the previous work,the deposition/extraction behavior of lithium metal was further stabilized,the coulombic efficiency of the first lap was significantly improved,and the stability was maintained during long cycles.The voltage fluctuations of the prepared NF-HGH@Cu electrode at current densities of 1 m A cm^-2,2 m A cm^-2,4 m A cm^-2 and 8 m A cm^-2 are very small,indicating that the metal lithium is in the current collector during rapid insertion/extraction,the entire 3D nanosheet frame structure still maintains good stability,is not damaged by irreversible reactions,and has good rate performance.In summary,we believe that GO as a base material can be used to uniformly deposit lithium metal,and a synergistic strategy is used to inhibit the growth of lithium dendrites,promote the stability of solid electrolyte phases,and thus improve the performance of lithium metal anodes.If further polyatomic doping is modified to improve the lithium-philicity,the synergistic effect of the system’s conductivity and lithium-philicity can be used to improve the utilization efficiency of lithium,and a more efficient and stable metal lithium negative electrode can be prepared.