Preparation And Structure-Property Relationship Of Copper-based Structural Lithium Metal Anode

Lithium(Li)metal has been considered as the "Holy Grail" of negative electrode material for the next generation of high specific energy batteries due to its high theoretical capacity and low potential.However,the problems of dendritic growth,infinite volume expansion and serious side effects,cause the sharp decline of battery performance and serious safety hazards,which seriously restrict the development and application of Li metal batteries(LMBs).In recent years,the structured design of Li anode had been widely applied to effectively alleviate the bottleneck problem,and is expected to realize the practical application of high safety and long-life LMBs.However,some problems,such as high cost of skeleton raw materials,complex processing process,unclear Li deposition behavior and poor compatibility with solid electrolyte,are also limited the development of structured Li metal anode.Based on these scientific problems,a 3D composite Li metal anode with high coulombic efficiency,long life and dendrite-free growth was prepared by electrodeposition and melting method with commercial copper-based materials as the current collector.By studying the evolution process of Li deposition/stripping on the surface and inside the current collector to clarify the mechanism of inhibiting Li dendrite growth.At the same time,combined with the preparation of liquid/solid LMBs and the evaluation of electrochemical performance,revealing the structureproperty relationship of 3D composite Li metal anode,and finally the electrochemical performance of LMBs is greatly improved.Relevant studies have fully verified and provided a demonstration for the construction of advanced structured Li metal anode.The detail research contents are as follows:Choosing the commercial brass mesh(Copper-zinc alloy)as the skeleton,a square meter 3D lithiophilic modified current collector(ZnO-CuZn)is achieved by the redox reaction during the heat treatment at 300? on brass mesh.Brass mesh can not only provide 3D structure,but also provide zinc source to promote the formation of ZnO.Relevant physical characterization and electrochemical performance analysis show that this 3D structure and lithiophilic layer can significantly reduce the nucleation overpotential of Li for the uniform nucleation and growth of Li on the surface of brass mesh,which can inhibit the generation of Li dendrites.Thus,the half-cell based on ZnO-CuZn current collector can cycle stably over 100 cycles at a current density of 1 mA cm-2.To further meet the serious volume change of Li metal anode,A vertical graphene array structure(a thickness of 500 nm)is constructed on the surface of copper mesh by chemical vapor deposition(CVD),to achieve a 3D micro/nano composite copper-based current collector(VGCM).The results show that the VGCM can be used as a Li storage carrier to alleviate the volume expansion of Li metal anode.At the same time,the surface functional groups of vertical graphene can promote the uniform deposition/growth of Li in the VGCM.The half-cell of VGCM/Li can cycle stably for more than 250 and 150 cycles at a current density of 2 and 5 mA cm-2,respectively.Further,when paired with LLZTO/PVDF solid-state electrolyte,the solid-state LMBs also shows excellent electrochemical performance.However,this limited Li storage space of vertical graphene is still unable to face with the serious volume change problems with continues Li deposition/stripping cycle of LMBs under a large deposition capacity.Thus,the insulating/conductive/lithiophilic gradient structure(PVDF/Cu/Cu2Se,PCS)is prepared,to realize the "bottom-up" deposition of Li in the 3D skeleton.The experimental results show that the maximum Li loading in the gradient skeleton can be reached to 20 mAh cm-2 with no dendritic growth.Meanwhile,Cu2Se nanoparticles as lithiophilic can not only reduce the Li nucleation overpotential,but also can in situ generate artificial SEI layer of Li2Se during the Li deposition process,which is conducive to the realization of dendrite-free Li deposition.The full cell of PCS/Li?LFP also shows an ultra-stable cycle performance over 400 cycles at 1C.Finally,we further carry a modified melting method to optimize and explore the feasibility in the practical process of 3D composite Li metal anode.A porous oxide layer is formed on the surface of copper mesh by heat treatment.Then,the structural evolution of oxide layer during Li melting was studied,and a selfpropagating mechanism was proposed to prepare 3D network composite Li metal anode(Cu/Li)with low loading and high Li utilization of Li.The composite anode owns good conductivity and specific surface area,which is benefit to realize the uniform deposition of Li.Even at a deposition capacity of 6 mAh cm-2(the utilization rate of Li is 75%),the symmetrical battery can also cycle stably for more than 600 h.In addition,when the 3D composite Cu/Li anode paired with solid electrolyte,the solid-state LMBs also has a stable interface and an excellent electrochemical performance.