Research On The Highly Reversible Cycling Mechanism Of Metallic Lithium Based On Interfacial Modification Of Lithiophilic Metal And Oxide Composite Films

In recent years,with the rapid development of wearable devices and electric vehicles,it is particularly important to develop lithium batteries with high specific energy,long cycle stability,and high safety performance.The energy density of Li-ion batteries based on transition metal oxide cathodes and intercalated graphite anodes has approached its theoretical value(?300 Wh/kg),it is still difficult to meet people's growing energy demands.Lithium metal batteries are often considered the ultimate solution for high energy density batteries because of their ability to deliver high mass and volumetric energy densities.However,from a theoretical point of view,using lithium-containing transition metal oxides,etc.as the positive electrode,and using the positive electrode as the lithium source,the battery structure that omits metallic lithium on the negative electrode side can provide higher energy density.To this end,researchers have proposed the concept of a anode-free lithium battery.However,the development of anode-free lithium batteries still faces many difficulties,the biggest of which is the irreversible loss of lithium metal during cycling.Most studies have focused on two key aspects of stabilizing lithium deposition and maintaining lithium capacity.Based on the above considerations,from the perspective of optimizing the nucleation kinetics,this thesis uses a magnetron sputtering process to modify the surface of the current collector,which significantly improves the stability of metal lithium deposition and the reversibility of cycling.The main research contents are divided into the following two points:(1)First,the technical principle of the modification layer to improve the deposition of metallic lithium is verified.The modified current collector(Cu-AS)was prepared by depositing a nanoscale composite modification layer of lithiophilic metal(Au)and oxide(Si O2)on the surface of copper foil by magnetron co-sputtering.The Au in the modified layer can improve the lithiophilic properties of the copper foil surface,and the formed Au nanoparticles can provide sites for the deposition of metallic lithium and induce the nucleation of metallic lithium.Si O₂ has a high specific capacity,so it has a good carrying capacity for lithium deposition.In addition,the volume expansion problem of Si O₂ during cycling is very small at the nanoscale.When the current collector is used as the working electrode to form a half-cell with lithium foil,the battery exhibits a lower polarization voltage,and the lithium nucleation overpotential is significantly reduced.After 800 cycles,it still exhibits excellent electrochemical performance with an average Coulombic efficiency of 98.4%.At the same time,the deposition behavior of metallic lithium on the Cu-AS current collector was also explored.The uniform distribution of Au clusters can make the nucleation of metallic lithium uniform,and the metallic lithium can be uniformly deposited and exfoliated during the cycle.Inhibit the growth of lithium dendrites.(2)Secondly,the lithiophilic properties of Cu-AS were regulated by adjusting the magnetron sputtering power to control the content ratio of the lithiophilic metal Au in the modified layer,and the effects of different proportions of lithiophilic metals in the Cu-AS current collector on the lithium deposition performance were explored.Influence.Experiments show that the addition of Au can reduce the lithium nucleation overpotential of the current collector,and only the appropriate binding energy strength can achieve uniform nucleation and deposition of lithium.Finally,when the Au content in the Cu-AS current collector is 45.4%,it has more excellent electrochemical performance.The analysis found that at this content,the SEI could be formed on the surface of the current collector faster during cycling and remained stable over long cycles.After 160 cycles at0.5 C in the full cell with LFP,it still has a reversible specific capacity of 137.8 m Ah/g with a capacity retention rate of 93.5%.The above experimental results demonstrate the promising prospects of Cu-AS current collectors in practical applications.