| As the demand for multifunctional electronic devices becomes higher,flexible wearable electronic devices are considered to be the next generation portable smart devices with broad prospects.This poses a higher challenge to the energy density,flexibility and cyclic stability of the energy storage components.Metallic lithium has become the ideal material for flexible high-energy-density lithium-metal batteries because of its high theoretical specific capacity(3860 m Ah/g),low electrochemical potential(-3.04 V vs.SHE),and low mass density(0.534 g/cm~3).However,if there is no carrier for the metallic lithium,there will be the growth of lithium dendrites and fatigue fracture during electrochemical cycling and mechanical deformation.The application of bare lithium-metal anode results in the attenuation of the performance of batteries and severe safety issues,which limits the development and practical application of flexible high-energy-density lithium-metal batteries.In order to suppress the growth of lithium dendrites and enhance mechanical flexibility,it is an effective strategy to choose a three-dimensional flexible current collector to combine with metallic lithium.Commercial carbon fabric cannot achieve good cycling stability with high loading and good mechanical flexibility due to its poor lithiophilicity,monotonous micrometer pores and low specific surface area,while it has a three-dimensional network with many pore structures,higher elastic limits,lower mass density,and excellent electrochemical and thermodynamic stability.This means commercial carbon fabric is still not a good choice for the carrier of metallic lithium.Herein,porous carbon fibers(PCF)with different etching times were prepared through an orderly process which involved the growth of nitrogen-containing polymer molecular brushes,electroless metal deposition,heat treatment and acid etching.The physical and chemical properties of carbon fiber(such as morphology,the valence and proportion of elements and dynamic surface resistance)were systematically characterized by methods of transmission electron microscope,scanning electron microscope,X-ray diffraction,energydispersive X-ray spectroscopy,BET,Raman spectra and bending test,etc.The experimental results confirmed that the optimized PCF could be obtained by 5 minutes nickel deposition,4 hours heat treatment and 9 hours acid etching.The optimized PCF had high specific surface area(2.61 m~2/g),uniform pore size(average width 10.48 nm),rich nitrogen and nickel content(N: 2.09%,Ni: 5.26%)and relatively stable dynamic surface resistance(0.125±0.010 Ω).This PCF showed a low nucleation overpotential(36.5 m V)for electrodeposited lithium.Meanwhile,it could achieve rapid and uniform infiltration and adsorption of molten lithium(adsorbing 8 mg molten lithium within 8 seconds).The symmetrical batteries assembled by the as-obtained anode(PCF@Li)could be stably operated for 250 hours at 2 mA/cm~2@2 m Ah/cm~2 and for more than 75 hours at 4 m A/cm~2@4 m Ah/cm~2.When PCF@Li was matched with the high-loading and high-voltage cathode NCM622,the capacity retention rate of the full battery remained 53.4% after more than 100 cycles.This scientific and effective modification method achieves the construction of multilevel micro-nano pore structure on commercial carbon cloth,the adjustment of specific surface area and the doping of heterogeneous elements on the surface,and thus promotes the lithiophilicity for both molten lithium and electrodeposited lithium.Therefore,as a threedimensional flexible current collector,PCF is able to provide excellent mechanical flexibility and electrochemical stability for lithium metal and lithium-metal batteries.The as-obtained PCF with high lithiophilicity and high specific surface area has certain reference significance for the research of future flexible lithium-metal batteries.The orderly preparation process of flexible lithium anode(PCF@Li)is easy to be operated,which shows industrial potential. |
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