Study On Surface Modification And Structure Modification Of Lithium Anodes Based On Carbonate Electrolyte System

Limited by the theoretical capacity of the electrode materials themselves,the lithium-ion batteries?LIBs?which are commonly used in the market cannot meet the demand of new energy vehicles for energy storage equipments with high-energy density.Therefore,developing new electrode materials to improve batteries energy density has become a research hotspot in the industry of LIBs.Lithium metal is a very promising anode for developing high-energy density batteries because of its high theoretical specific capacity(3860 mAh g^-1)and extremely low reduction potential?-3.04 V vs.standard hydrogen electrode?.However,the uncontrollable side reactions between lithium and electrolytes,and the dendritic lithium formation during electrochemical cycling expose lithium metal batteries?LMBs?to poor stability and poor safety.Based on this background,this paper proposes two methods for the modification of lithium anodes,including surface modification and structural modification.The specific contents are as follows:In the study of surface modification of lithium anodes,MgCl₂ was introduced into a conventional carbonate electrolyte to serve as an additive.MgCl₂ was reduced on the surface of the lithium anode,and the reduction products including metallic magnesium and inorganic LiCl participated in the construction of the lithium anode^'s surface film.The coexistence of inorganic LiCl and metallic Mg species in the interface could effectively decrease the surface side reactions,lower interphase resistance,promote Li ions diffusion,and result in uniform lithium deposition.The electrochemical tests show that the reversible utilization rate of lithium for Li/Cu asymmetrical cells increased by 10%and the polarization of Li/Li symmetrical cells was reduced noteworthily with such surface modification.Furthermore,this surface modification of lithium anode was also successfully used in Li/Li₄T₅O₁₂ and Li/LiFePO₄ full cells.In aspect of structural modification of lithium anodes,Zn nanoparticles which is lithiophilic was introduced into molten lithium to prepare the Li-Zn composite anode.A Li/Zn mass ratio of 1/0.3 was found to be the best filling condition in the screening experiments.The growth of lithium dendrites was suppressed,the cycling stability and rate performance of the composite anode were significantly improved under this filling condition.In the process of identifying the morphology and phase of the composite anode under different discharge depths,we found that Zn nanoparticles were changed into LiZn alloy which with micro-rod morphology in the composite anode.The lithium present alone was preferentially dissolved,while the LiZn alloy retained its micro-rod morphology during the process of lithium dissolution.Based on this,we speculated the mechanism of the introduction of zinc particles to improve the stability of lithium anodes may be based on the following:a much easier nucleation,which facilitates uniform nucleation;the increased nucleation sites,which facilitates the dispersion of lithium ions and currents;the skeleton structure provided by micro-rods helps to suppress the huge volume expansion during the repeated charging/discharging process.