Surface Modification And Electrochemical Performance Of Copper Host For Lithium Metal Anode

Li metal anode has attracted much attention due to its lowest potential（-3.04 V vs.standard hydrogen electrodes）and high specific capacity(3860 m Ah g^-1 or 2061Wh cm^-3).However,the uneven and infinite volume-varying Li deposition lowers the stability of the solid-electrolyte interface（SEI）,or even rupture,where the new SEI re-formed,consuming the active Li metal and electrolyte,and reducing the Li reversibility.Moreover,the protuberance present on the SEI rupture possesses a higher local electric field,favoring further Li deposition,which eventually evolves into Li dendrites.Moreover,the dendrites can be easily broken during the Li stripping（isolated Li）,forming"dead"Li and"dead"SEI,further reducing the Li reversibility.In long-term vicious circles,the active Li metal and electrolyte are depleted,eventually leading to battery failure.Among the numerous modifications,the modified host is considered to be the basis for regulating the Li deposition/stripping.Therefore,designing a host capable of inducing uniform Li deposition/stripping and limiting volume change becomes focus of current research.This paper focuses on the electrochemical behavior on the Li metal anode.Cu host is commonly used in the anode,a lithiophilic modified Cu host is constructed to inhibit Li dendrites.The preparation process,structure and electrochemical performance of the modified Cu host are optimized.The relationship between Li deposition and SEI formation is studied,and the mechanism of the influence of electrochemical behavior on SEI is analyzed.The 3D modified Cu host is designed to induce the lateral deposition of Li deposition,limit the volume change.Cu host is modified by CuO layer with ammonia water as complexing agent in constant temperature water bath.It is found that uniform Li deposition（no Li dendrites）can be achieved between micronano CuO lamellar,and larger CuO lamellar has more Li storage space.By optimizing the concentration of ammonia water,micronano CuO lamellar modified layer is constructed on the optimal Cu foam to reduce the effective current density of the anode and restrict infinite volume change.The adsorption energy of Li atom with CuO and Cu are calculated by density functional theory（DFT）,and it is found that CuO has stronger adsorption ability with Li atom.Moreover,the lithiophilic advantage of CuO（strong adsorption of CuO with Li atom,interfacial reaction of CuO with Li metal）can reduce Li nucleation overpotential and induce uniform Li deposition/stripping.Electrochemical performance tests show that half-cell has an average Coulombic efficiency of 98.5%after 450 cycles at 1 m A cm^-2/1 m Ah cm^-2,and the full-cell ISG-CuO|NCM has a capacity retention rate of 72.3%after 200 cycles at 1 C（～200 m A/g）.However,the long-term interfacial reaction of Li metal with CuO also reduces the stability of SEI.The Ag nano layer modified Cu host is prepared by displacement plating method.Aqueous solution of Ag NO₃ and ethylenediamine is used as plating solution and additive-vanillin is introduced to optimize the morphology of Ag plating.The adsorption energy of vanillin with Ag atom and Cu atom are analyzed by DFT,and it is found that vanillin has stronger adsorption with Ag atom.The Tafel curve proves that vanillin increases the polarization of Ag⁺deposition on Ag,and promotes Ag⁺depositing on Cu surface,forming a uniform/dense Ag nano layer.The uniform/dense Ag nano layer facilitates the solid-solution Li/Ag alloying process and promotes seamless Li deposition（no dendrites）,which reduces the generation of multiple SEI,avoids excessive consumption of active Li metal and electrolyte,and improves the reversibility of Li deposition/stripping.Through XPS and electrochemical characterization,it is found that the Li/Ag alloying process occurred after the SEI formation,and does not interfere with the SEI formation,which indirectly stabilized the SEI.The half-cell based on Ag-0.1 host has an average Coulombic efficiency of99.26%after 180 cycles at 1 m A cm^-2/1 m Ah cm^-2.The full cell based on Ag-0.1host|NCM has a capacity retention of 80.6%at 1 C（～200 m A/g）rate for 200 cycles.This strategy can be extended to the research of Li/Zn,Li/Mg,Li/Sn,Li/Sb alloy host,which is suitable for large-scale production.The Ag nano layer modified 3D Cu host is prepared by combining the above optimal displacement plating process and 3D printing technology.It is verified by COMSOL simulation that the framework of the square structure is more conducive to the lateral growth of Li deposition.The 3D Cu host with square structure is constructed by 3D printing technology,and the density of skeleton/pore is optimized.Then,a Ag nano layer is constructed on the 3D printed Cu host by the above optimal displacement Ag plating process.The 3D structure reduces the effective current density,and the lateral Li deposition releases the vertical volume change.The Ag nano layer can still present a solid-solution Li deposition,which reduces the formation of multiple SEI and improves the cyclic reversibility of the Li metal anode.The half-cell based on Ag nano layer modified 3D Cu host has an average Coulombic efficiency of 99.61%after 300 cycles at 1 m A cm^-2/1 m Ah cm^-2.The full cell based on Ag nano layer modified 3D Cu host|NCM has a capacity retention rate of 91.7%and 77.8%for 200 and 500 cycles at 1 C（～200 m A/g）,respectively.Based on the above results,the lithiophilic advantage of Cu host modified by micronano CuO layer can achieve uniform Li deposition/stripping and stable long life of Li metal anode.However,the interface reaction of CuO also reduces the stability of SEI,and the existing electrolyte system has low ionic conductivity and insufficient utilization of foam space,resulting in limited volume energy density.The solid-solution Li/Ag alloying process of Cu host modified by Ag nano layer indirectly stabilizes SEI and improves the reversibility of Li cycling.In addition,the 3D Cu host modified by Ag nano layer induces lateral growth of Li deposition,limits the longitudinal change of volume,and improves the utilization rate of 3D space,which is conducive to improving the volume energy density,further improves the overall performance of Li metal anode.