Preparation And Electrochemical Performance Of Graphene-Coated Lithium Metal Anode

Lithium metal anode is considered as an ideal anode material for high specific energy battery system due to its high theoretical specific capacity(3860 m Ah g^-1),low electrochemical potential（-3.04 V）and low density(0.534 g cm^-3).However,the problems of unstable solid electrolyte interphases（SEI）,dendrite growth and volume expansion of lithium metal anodes lead to shortened cycle life and reduced coulombic efficiency.At the same time,during the charging process of lithium metal anode,the dendrites formed by the uneven deposition of lithium are easy to pierce the separator,causing short circuit and serious safety hazards.These problems limited the commercial application of lithium metal batteries.The uneven deposition of lithium is the root of many problems.Promoting the uniform deposition of lithium and improving the stability of SEI are important ways to realize the practical application of lithium metal anodes.Graphene materials have excellent physical and chemical properties such as high conductivity,good structural stability and large specific surface area.They have great application prospects in many research fields such as electronic devices and energy storage devices,and have also been widely studied in lithium metal batteries.In this paper,starting from the innovation of the composite method of graphene and lithium metal anode,a graphene layer with three-dimensional structure was constructed on the surface of lithium metal by slurry coating.The excellent conductivity and high specific surface area of graphene were used to disperse the current density to induce the uniform deposition of lithium metal.At the same time,the influence of the arrangement and structure of graphene sheets in the three-dimensional graphene layer on the electrochemical performance was investigated.It is proved that the three-dimensional porous graphene structure is beneficial to the transport of lithium ions and significantly prolongs the cycle life.The specific research work is as follows:Firstly,a graphene coating modified lithium metal anode（G@Li）was designed and prepared by a simple slurry coating method.Different from the traditional three-dimensional graphene as a current collector,the large surface area consumes too much electrolyte and causes the electrolyte to dry up.The three-dimensional graphene layer on the surface of the metal lithium anode induces the uniform deposition of lithium metal,reduces dendrite growth and dead lithium accumulation,and can provide lithium ion transmission channels for the irreversible lithium loss during the lithium source replenishment cycle.The average coulombic efficiency is as high as 99.87%after 470cycles at a current density of 0.1C and 0.3C discharge,which significantly prolongs the cycle life and has a good practical application prospect.Secondly,Li F was further introduced into the graphene coating to obtain Li F-G@Li composite anode.After Li F modified graphene,a more stable Li F-rich SEI is formed,which improves the cycle stability of the lithium metal anode,and the three-dimensional porous graphene layer can still provide a channel for the irreversible loss of the lower lithium source during the cycle.In the lithium-free anode without additional lithium source,the coulombic efficiency remains at 98.70%after 200 cycles at a current density of 1 m A cm^-2,which greatly improves its deposition reversibility.In symmetrical batteries,it can work stably for more than 1000 h at a current density of 0.5 m A cm^-2-1 m Ah cm^-2and a deposition capacity cycle.