Study On Graphene Based Composite Lithium (Sodium) Metal Anode

With the popularization of mobile electronic devices and electric vehicles,the energy density and safety of battery system have become the significant obstacle to meet the practical demand.Lithium metal,with the theoretical specific capacity of3,860 mAh g^-1 and the electrode potential of-3.04 V,is deemed as the"Holy Grail"of the negative electrode materials.However,the instinct characteristics of Li,such as high reactivity,large volume expansion and dendrites growth,have led to the low Coulomb efficiency,short cycle life and serious safety hazards of lithium metal batteries.Besides the above problems,the resource reserve of lithium is scarce to satisfy the huge demand for lithium based energy storage systems.Furthermore,the uneven distribution and high costs of industrial production lithium metal both deteriorate the situation.In contrast,the metallic sodium,which is abundant,has a high specific capacity of 1166mAh g^-1 and an electrode potential of-2.71 V.However,due to its similar or even more active chemical properties,metal sodium is faced with the same or even more serious problems as metal lithium.Moreover,there is difficulty in processing and moduling of the soft metallic sodium.To solve the above problems,the graphene-based composite metal lithium?sodium?anode was prepared by incorporating molten metal into the graphene scaffold.Guided by designing the composite electrode structure and controlling Li⁺distribution,a serious of experiments were carried out to inhibite or guide dendrite growth,relieve the electrode volume expansion,improve electrochemical performance and make the electrode processable and moldable.This research mainly includes the following three aspects:?1?Aiming at the problem that bending can promote the dendrite growth,graphene/lithium composite lithium anode?r-GO/Li?was prepared by combining r-GO with molten lithium.The viewpoint that bending tolerant lithium metal anode was proposed.Under the bending state,the symmetrical battery and full cells?Li-S and Li-O₂?assembled with the r-GO/Li electrode exibite lower overpotential and better cycling performance.Mechanism analysis shows that r-GO layer can promote deposition/dissolution of lithium uniformly.The assembled r-GO skeleton can reduce the loss of metal lithium.Meanwhile,flexible r-GO can help dissipate bending stress and delay the proliferation of defects in the lectrode,and inhibitating the generation of bending cracks.In the bending state,the composite anode can significantly prevent the growth of lithium dendrites,thus improve the cycling performance of the flexible metal batteries.?2?The patterned composite lithium anode was prepared to control the growth direction of lithium dendrite.The electronic field around the voids area is much stronger than the flat area.Li⁺can deposite at the surface of metal lithium in the voids,which was separated by the r-GO sheets,with lower nucleation barrier.As a result,Li prefers to nucleate at the void edges and grows horizontal centripetally to fill the voids.Symmetrical batteries can cycle for more than 2000 h at 0.5 mA cm^-2 and maintain a stable cycling performance at 10 mA cm^-2.This strategy fundamentally controls the growth of lithium and alleviates the expansion of electrode volume.This work can provide reference for the development of safe and efficient dendritic-free lithium metal anode.Also,this methode can be extended to other alkali metal systems.?3?The composite sodium anode?Na@r-GO?was developed to settle the problems of sodium metal in processing and molding.Planar 2D film with controllable thickness,dimensions and shapes,1D fiber and 3D macroform electrode can be fabricated.The mechanical strength and chemical/electrochemical stability of the composite electrode were improved.It provides a reference for changing the way in processing,moduling,storage,transportation and utilization of sodium metal anode.