Structural Design And Preparation Of Metallic Lithium Anode And The Study Of Its Electrochemical Performances

With the rapid development of portable intelligent electronic devices and the electric vehicle market,there is an urgent need for a new generation of energy storage devices with high energy density and high power density,which greatly promotes the development of high performance electrode materials for lithium batteries.Among them,metallic lithium has a very high theoretical specific capacity(3860 mAh/g or2061 mAh/cm~3)and a very low electrochemical potential(-3.04 V vs.standard hydrogen electrode),which is considered to be the final choice for the development of lithium battery anode.However,problems such as the formation of lithium dendrites and the volume expansion of the electrodes during charging and discharging seriously impede their practical application.At present,the structural design of metallic lithium anode is considered to be one of the effective methods for solving the above problems.That is,by introducing a porous metal such as copper foam and nickel foam or a porous carbon material such as graphene,it is composited with lithium metal to prepare a three-dimensional structured composite metallic lithium anode.The porous conductive skeleton can disperse the current density,stabilize the electric field distribution and inhibit the formation of lithium dendrites.At the same time,the pore structure of the substrate can provide sufficient space for lithium metal deposition and accommodate the Li/SEI phase formed during the cycle,so as to maintain electrochemical activity and relieve the volume expansion of the electrode.Therefore,how to design a three-dimensional matrix with a suitable pore structure and the preparation of large-area three-dimensional structured composite metallic lithium anodes with controllable mass loads by simple and easy operation are still the focus of future research.Based on this,this paper focuses on the design and controllability of structural metallic lithium anodes.The specific research contents are as follows:(1)In order to solve the problem that the conventional porous metallic foam matrix has a large pore size which can't effectively limit the size of lithium metal,we propose the idea of pore-channel regulation by nesting cross-linked graphene networks in pores of copper foam.A suitable three-dimensional copper foam/graphene porous matrix(CuFG)is designed,and then lithium metal is supported on the substrate by means of heat-melting immersion to prepare a copper foam/graphene supported three-dimensional structural composite metallic lithium anode(CuFG@Li).The results show that the CuFG@Li composite anode can be stably circulated for more than 180 h in a symmetrical battery at a high current density of 5 mA/cm~2,and has a low polarization voltage(~120 mV).At the same time,due to no lithium dendrites and"dead lithium"formed,the coulombic efficiency remained above 98%after more than 200 cycles.Electrochemical test are carried out after matching it with the lithium iron phosphate(LFP)cathode to form a full battery.It is found that the full cell with CuFG@Li as the anode has better rate performance,lower interface resistance and lower voltage polarization than the conventional metallic lithium foil.(2)In order to further realize the goal of preparing a large-area three-dimensional structural composite metallic lithium anodes with controllable mass loads by simple and easy operation,we directly use micron-sized lithium metal powder as a lithium source to mix with graphene,prepare a composite electrode(G@Li-P)by slurry coating method.And then heating and melting activation are carried out to obtain a three-dimensional graphene/lithium metal composite anode(G@Li).The results show that the G@Li composite anode can stably cycle for more than 90 h at a current density of3 mA/cm~2 in a symmetric battery,and has a lower polarization voltage(~200 mV).After the cycle,the morphology of the electrode is stable,no dendrites and"dead lithium"are formed,and the thickness of electrode is substantially unchanged.Electrochemical test are carried out after matching it with lithium-rich cathode to form a full battery.It is found that the full battery with G@Li as the anode has a good long-cycle performance,and the capacity is~220 mAh/g after 120 cycles at 1 C.The capacity retention rate is 98%,and it also has a good rate performance.The charge/discharge cycle test are carried out with G@Li anode and lithium-rich cathode assembled into a pouch cell.It is found that the first coulombic efficiency of the battery is maintained at about 92%,and the cycle stability has improved,but the capacity attenuation problem still exists.