Preparation And Electrochemical Performance Of 3D Porous Current Collectors For Li Metal Anodes

Li metal is the essential anode material for high-energy-density batteries due to its light weight,low electrochemical potential,high specific capacity.Despite these attractive properties,the practical application of Li metal anodes is still hindered by some problems.It has been troubled with the volume change and uncontrolled lithium dendritic growth during repeated plating/stripping,which leads to poor cycling performance and serious safety problems.To solve these problems,the 3D porous current collectors with large specific surface are used to improve Li plating/stripping by reducing surface local current densities,consequently,suppressing the growth of lithium dendrites.Based on this consideration,graphene,artificial graphite,carbon fibers,porous copper,and nickel foam with high specific surface areas are widely considered as the hosts for lithium deposition.Although encouraging results have been achieved by using 3D current collectors,there still remain some harsh problems for practical application.On the one hand,it is difficult to protect SEI film on the inner surface of 3D porous structure,resulting in micrometer-sized Li dendrites growth on the inner surface of 3D skeleton.On the other hand,the preferential lithium nucleation and growth occur at the top part of the3D current collectors,because the Li⁺diffusion from the top to the bottom is slower than electron transfer.Uneven deposition of Li throughout 3D current collector would happen.It will reduce the utilization of interior voids and leads to performance degradation.In order to improve the cycling performance of Li metal anodes,we fabricated a nitrogen-doped graphene modifed 3D porous Cu?designated as3DCu@NG?current collector and 3D duct-like graphene?designated as 3D-DG?current collector with uniform and continuous porous structure.The results show that the N-doped graphene could uniformize the electron distribution on the surface of the current collector,leading to a uniform Li deposition.In addition,the strong bonding between Li⁺in the electrolyte and N-doped graphene leads to a uniform Li⁺flux and regulates the nucleation of Li,finally contributing to a stable Li deposition.The Li-3DCu@NG composite anodes demonstrate a high areal capacity of 4.0 mAh cm^-2 without dendrite formation and low voltage hysteresis??19mV?.The results also show that the 3D-DG provides the pathway accelerating the Li⁺diffusion.Thus,fairly uniform deposition throughout 3D current collector and complete suppression of Li dendrites could be achieved.The continuously porous structure of 3D-DG current collector provides a space for the metallic Li deposition without dendrites formation and could effectually adjust the volume expansion during cycles.As a result,the Li@3D-DG?the 3D-DG current collectors deposited with Li?anode exhibits a high areal capacity 10 mA h cm^-2,high plating/stripping efficiency of?99%,low voltage hysteresis??24 mV?,and long lifespan?more than 1000 hours?.