Study On The Structure And Interface Regulation Of Copper-Based Porous Skeletons For Lithium Anodes And The Mechanism Of Lithium Deposition

Lithium（Li）metal,with an ultra-high theoretical specific capacity(3860 m Ah g^-1)and the lowest electrode potential（-3.040 V vs.standard hydrogen electrode）,is the ideal anode material for next-generation high specific energy Li batteries.However,the high reactivity with the electrolyte,large volume change and uncontrollable dendrite growth of the Li metal anode greatly limits its practical application.In view of the problems of Li metal anodes,copper-based three-dimensional（3D）porous skeletons are designed and prepared as Li anode current collectors,and the structure and interface of porous skeletons are further regulated.The effects of the skeleton structure and interface on alleviating anode volume change and inhibiting dendrite growth are studied.The main results are as follows:（1）3D copper（Cu）porous skeletons with different pore sizes are prepared by loose sintering method followed by adjusting sintering temperatures,and the Coulombic efficiencies（CEs）of different Cu porous skeletons are studied.The porous skeleton corresponding to the best performance is optimized with an average pore size of about 21.2μm.The nucleation and growth processes of Li on different porous structures are studied by phase field simulation,and the effects of porous skeleton structure on Li deposition morphology and the connectivity of internal pores are analyzed.The electrochemical properties of the porous Cu skeletons show 110 stable CE cycles at the current density of 1 m A cm^-2with the capacity of 1 m Ah cm^-2,and the symmetric cell with Li composite electrodes achieves a stable cycle of 970 h with no obvious dendrite growth on the surface.The full cell assembled with the Li Fe PO₄ cathode reaches64%capacity retention after 800 cycles at 0.5 C.（2）The double-layered porous Cu skeleton with the distribution of large pores and small pores is prepared by spreading two kinds of powders with different particle sizes and sintering.The larger pores in the upper layer provide enough space to ensure the efficient mass transfer of Li ions into the skeleton,while the smaller pores in the lower layer provide enough specific surface area to reduce the local current density of the skeleton.The superior performance is confirmed compared with the porous Cu skeleton with single pore structure,and the skeleton morphology with large-capacity Li storage confirms the uniform Li deposition in the interior of the double-layered porous skeleton.The composite electrode shows a stable cycle of 450 h under large current density and capacity(4 m A cm^-2,4 m Ah cm^-2).（3）A lithiophilic copper-zinc（Cu-Zn）alloy porous skeleton is prepared with Cu-Zn alloy（Cu-0.2Zn）powder.to regulate the Li deposition interface property of the porous skeleton.The contact angle of liquid Li on the surface of Cu-Zn alloy is smaller than that of pure Cu confirmed by the wettability test of molten Li,and a smoother electrochemical deposition morphology of Li on the surface of Cu-Zn alloy is observed by in-situ optical microscopy.It is confirmed that the Cu-Zn alloy structure surface gains a lower Li atom adsorption energy and a smoother Li nucleation and growth morphology through DFT calculation and phase field simulation.The electrochemical tests verify that the porous Cu-Zn alloy skeleton has more stable CE,and 150 stable cycles are achieved at the current density of 1 m A cm^-2 with the capacity of 1 m Ah cm^-2,and the Li nucleation overpotential is reduced to 26 m V,which is further improved compared with the porous Cu skeleton.（4）On the basis of the porous Cu skeleton,a layer of metallic silver nanoparticles（Ag NP）with the particle size ranging from 100 nm to 200nm is compounded on the surface of the porous Cu skeleton by electroless plating to prepare the Ag NP modified Cu skeleton,and the lithiophilicity modification of the Li deposition interface on the porous Cu skeleton is realized.Lithiophilic Ag NP provides a large number of nucleation sites for Li deposition,and the small capacity Li deposition confirms the significant improvement of Ag NP on Li deposition morphology,and the performance of the skeleton improved by the surface Ag NP is further confirmed by electrochemical tests.160 stable cycles are achieved during CE tests at the current density of 1 m A cm^-2 with the capacity of 1 m Ah cm^-2,with the Li nucleation overpotential as low as 10 m V,and the Li deposition/stripping overpotential of the electrode with prestored Li is reduced.（5）The enriched-sparse gradient distributed lithium fluoride（Li F）modified Cu foam skeleton is designed and prepared by single-side magnetron sputtering.With the help of the surface Li ion conductivity and electronic insulation of Li F,the ionic and electronic conductivity of the porous skeleton is regulated.It is determined that the uniform and dense Li deposition within the skeleton is achieved when the Li F-enriched surface is set near the separator（near the counter electrode）by analyzing the Li deposition behavior corresponding to different orientations of the Li F-enriched surface of the skeleton.Different sputtering time is controlled to reach the best synergistic effect of ionic and electronic conductivity of the porous skeleton,and 40 min is determined as the optimal sputtering time.The composite electrode of gradient-distributed Li F modified Cu skeleton with Li achieves stable cycling for 1700 h at the current density of 2 m A cm^-2 and the capacity of 2 m Ah cm^-2,which illustrates the mechanism of ionic and electronic conductivity of the porous skeleton on Li deposition behaviors.115 Figures,6 Tables,207 References...