Fabrication Of Three-dimensional Porous Copper Current Collector Via Dealloying And Investigation On Stabilizing Lithium Metal Anode

The rapid development of grid energy storage and electric vehicles has put forward higher requirements for battery energy density.Lithium(Li)metal is an ideal anode material for achieving high energy density batteries due to its high theoretical specific capacity(3860 mA h g-1)and low redox potential(-3.04 V,versus the standard hydrogen electrode(vs.SHE)).Nevertheless,the application of Li metal anode is hindered by dendrites proliferation,serious side reactions,large volume changes,and the resulting capacity decay and safety hazards.Constructing three-dimensional porous copper current collector is an effective strategy to stabilize the Li metal anode.It can not only reduce the local current density and inhibit the growth of Li dendrites,but also accommodate the deposited Li to alleviate the volume change.However,the present three-dimensional porous copper current collectors still have many deficiencies in structural design and fabrication strategies,and the stability of the electrodes are also facing certain challenges in long-term or high-rate cycles.Therefore,the rational design of the current collectors and the exploration of a simple process to fabricate stable porous copper current collectors are of great significance for achieving high energy density Li metal batteries.Focusing on the fabrication of three-dimensional porous copper current collector via dealloying,the effect of porous layer thickness on the electrochemical performance of Li metal anode was systematically investigated.A new fabrication method of three-dimensional porous copper current collector and electrode stability strategy were proposed,and the mechanism of three-dimensional porous copper current collector inhibiting Li dendrite was discussed.The main research contents of the thesis are as follows:1.A series of self-supported three-dimensional porous copper(A-3D Cu-2/5/8/14)current collectors with different porous layer thicknesses(3.2 to 34.5μm)were fabricated via the painting-alloying-dealloying and further annealing strategy.The results show that the interconnected porous structure of A-3D Cu can reduce local current density and provide abundant nucleation sites to reduce nucleation resistance and adapt to volume changes,achieving uniform Li deposition.And the electrochemical performance of the A-3D Cu current collector can be elevated with the thickness of the porous layer increasing.When the thickness is increased to 34.5 μm(A-3D Cu-14),it can keep an average coulombic efficiency of 97.3%for 200 cycles at 1 mA cm-2,and cycle for 430 h at 1 mA cm-2 with the capacity of 0.5 mA h cm-2 in the symmetrical battery.Moreover,A-3D Cu-14 exhibits capacity retention of 93.1%after 100 cycles at 0.5 C and excellent rate performance in full cells.As benchmarked with A3D Cu-2/5/8,the performance improvement of A-3D Cu-14 stems from the thickest porous layer,which possesses more void to accommodate the deposited Li,and larger surface area to optimize the Li plating/stripping characteristics.2.Based on the difference of saturated vapor pressure between Zn and Cu,threedimensional porous copper(3D porous Cu)was fabricated via vapor phase alloying-dealloying(VPA-VPD)strategy.This method is simple,environmentally friendly and economical,which is conducive to industrial production.As current collectors,the 3D porous Cu exhibit small voltage polarization,and long lifespan over 450 h at 1 mA cm-2 and 0.5 mA h cm-2 in the symmetrical battery.The 3D porous Cu also exhibits outstanding cycling stability and rate performance in full cells,further demonstrating its application potential.Moreover,the observation of Li deposition morphology shows that 3D porous Cu can induce uniform deposition of Li metal,limiting most of the Li plating/stripping process inside the current collectors,inhibiting the growth of Li dendrites and alleviating volume changes.3.Three-dimensional porous copper-nickel(3D porous CuNi)current collectors were fabricated via the combination of vacuum sealing-melting-cold rolling with VPA-VPD strategy.With uniform porous structure and higher mechanical stability,the coulombic efficiency and lifespan of 3D porous CuNi are improved compared to 3D porous Cu,delivering the long lifespan of 550 h and low overpotential of 22 mV at 1 mA cm-2 and 0.5 mA h cm-2 in the symmetrical battery.The 3D porous CuNi also exhibits superior cycling performance in full cells.Moreover,the effect mechanism of 3D porous CuNi on Li deposition behavior was revealed by observing the evolution of Li deposition morphology and combining with density functional theory(DFT)calculation simulation.The results show that the addition of Ni and the presence of residual Zn improve the Li affinity of 3D porous CuNi current collectors to a certain extent.Combined with its own structural advantages,the 3D porous CuNi can synergistically promote the uniform deposition of Li metal,showing enhanced Li dendrites inhibition.