Optimization Of The Interface Between Anode And Current Collector For Lithium Metal Batteries

Lithium metal anodes(LMAs)have been considered as attractive candidates for the next generation of high-energy secondary battery anode materials due to their extremely low density(0.534 g cm^-3),ultrahigh theoretical capacity(3861 m Ah g^-1),and extraordinary negative redox potential(-3.04 V vs.standard hydrogen electrode(SHE)).However,LMAs suffer from dendrites and chalking during repeated charging and discharging process,resulting in capacity degradation and reduced cycling performance.More seriously,the resulting safety hazards such as fire even explosion have greatly restricted the commercial application of LMAs.Current researchers have proposed various modulation strategies such as electrolyte additives and artificial SEI,however,they still face the problem of failure at high current densities and large charge/discharge depths during practical use.The current collector is an important component of the battery system and is generally considered to play a role in transferring electrons from the external circuit.In recent years,researchers have found that modulating the composition and structure of the current collector has a significant impact on the battery performance.For example,the crystallographic orientation and three-dimensional structure of copper collectors play an important role in the deposition behaviors of lithium metal anodes.However,the current mechanism on the lattice defects of copper collectors is unclear,and the surface lithiophilic properties of copper and carbon collectors are poor,so efficient and low-cost regulation methods are required.To address the above problems,this thesis investigates influences of the lattice defects and the lithiophilic layers on lithium deposition/dissolution behaviors and electrochemical performance.Based on the above research,a high-performance collector-free lithium anode with recycled lithium metal as a self-template was developed.The details of the research are as follows:(1)Effects of lattice defects(dislocations)in copper collectors on lithium nucleation(the deposition state under the capacity of 0.1 m Ah cm^-2)and growth behaviors.The effect of controlled tensile strain(?=0,1,5,10%)on the nucleation and growth behavior of lithium was investigated by generating dislocation defects with different densities within commercial copper foils.The results show that the dislocation line density increases continuously with increasing?,reaching a peak at 5%,and at?=10%,the copper foil fractures with decreasing dislocation line density and increasing dislocation rings.The electrochemical deposition results with the amount Li of 0.1 m Ah cm^-2 show that the nucleation size of lithium was 2.14,2.78,3.27,and 2.49?m with increasing?,showing a positive relationship dependent on the dislocation density.The subsequent lithium nucleation growth shows different growth patterns,when?=0%,the deposited lithium grows in radial dendrite morphology.As?increasing to 5%,the deposited lithium gradually shows a lateral growth-dominated pattern and then forms a homogeneous and complete lithium layer.Increasing?to 10%,the radial growth rate of the deposited lithium increases and dendrites appear again.Combining the homogeneous nucleation equation and density functional theory(DFT)calculations confirm that dislocations facilitate the reduction of the nucleation potential,thus promoting the homogeneous nucleation of Li.The electrochemical performance results show that the samples with?=5%(S-5%)all exhibit low overpotential,excellent cycling stability and multiplicative performance.(2)Modulating the interfacial properties of copper foam collectors with zinc oxide(Zn O).The lithiophilic properties of the copper foam skeleton were modulated through the fabrication of the Zn O interfacial layer,and the composite anode(LCZ)was prepared through thermal infusion of molten Li.The reduction products between Zn O and Li modulated the lithium deposition behaviors and electrochemical tests showed that the prepared LCZ composite anode exhibits extremely low overpotentials at high current densities(15,33 and 50 m V after 100 cycles at current densities of 3,5 and 8 m A cm^-2,respectively)in symmetrical cells.When LCZ is paired with Li₄Ti₅O₁₂(LTO),the full cell is cycled 1000 times at a current density of 10C,the capacity retention can reach 80.8%.Through investigating the morphological evolution of the LCZ during cycling,we found that the three-dimensional structure can effectively regulate the Li deposition/dissolution behaviors via reducing the local current density and promoting the smooth electrochemical reaction at the electrode interface.In addition,the 3D skeleton also provides space for Li deposition/dissolution,greatly relieving the volume expansion during cycling.(3)Modulating the interfacial properties of carbon felt(CF)with nickel oxide.Using three-dimensional carbon felt as the backbone,a nickel oxide lithiophilic layer was prepared on the surface of the CF by electrodeposition and heat treatment.Then the 3D composite anode(CFt/Ni-Li)was prepared through thermal infusion of molten lithium.Benefiting from the large specific surface area and low density of the 3D CF,the Li metal loading in the composite anode is up to 80%and the theoretical mass specific capacity reaches 3320 m Ah g^-1.The electrochemical tests show that the CFt/Ni-Li composite anode in the symmetric cell can maintain a low overpotential(?40 m V)at a high current density of 10 m A cm^-2 for 200 cycles without the formation of dendrites and"dead Li".When paired with Li Fe PO₄(LFP)cathode in the full cell,it also exhibits superior long-term cycling performance with high-capacity retention of 83.3%even after 600 cycles at the current density of 1C.Comparing to Cu foam,the CF is flexible which can greatly relieve the stress during the Li plating/stripping process.(4)Modulating Li plating/stripping behaviors through mechanical compression on dendritic Li.The role of the applied load(p=1,4,7,10 MPa)on lithium deposition and dissolution behavior was investigated by controlling the surface morphology of the dendritic lithium and generating the non-uniform residual stress field.The results show that the extent of the surface deformation of dendritic lithium gradually increases with increasing pressure.At 7 MPa,the surface becomes flat and distributed with micron-sized pores.When the load increases to 10 MPa,the dendritic lithium surface becomes dense and a large number of micron-sized pores disappear.The morphological evolution during cycling indicate that Li is preferentially deposited and dissolved in the pores.The finite element simulation(FEM)calculations reveal a non-uniform residual stress field around the dendrite deformation.The FEM simulation combined with the Monroe-Newman model reveal that the residual stress affects the electrochemical potential at different locations within the dendrite resulting in the preferential deposition of Li at the pores.The synergistic effects of the unique three-dimensional structure after compression and the residual stress field modulate the deposition/dissolution behavior of Li.The electrochemical performance show that the samples(PC-Li7)under 7 MPa exhibit low overpotential,excellent cycling stability and rate capability.In addition,the method also sheds lights on the recycling of lithium metal.