Interfacial Modification Of Zinc Metal Anode For Aqueous Zinc-ion Batteries

The Aqueous Zinc-ion Batteries（ZIBs）have the advantages of environment-friendly,high safety,low cost,high energy density,etc.,which is considered to have great value and prospects in the application of large-scale energy storage systems.However,the side reaction between Znanode and electrolyte,and the growth of Zndendrites during electrochemical cycling,expose the aqueous ZIBs to poor stability and poor safety,and limit its development space.Therefore,the study on modification of zinc anode for aqueous ZIBs is of great significance to the application and popularization of secondary aqueous ZIBs.At present,the main modification strategies for the dendrite growth and interface side reaction of Znanode include electrolyte optimization,host construction design of Zinc deposition and interfacial modification.In recent years,the interfacial modification has attracted much attention,which is considered as a simple and efficient method of Znanode modification.Based on this,two kinds of modified layers of different materials were constructed on the surface of Znanode to realize the interfacial modification of Znanode:1.In the study of interfacial modification of Zn_xV₂O₅·nH₂O modified Znanode,we used the zinc-ion intercalatable V₂O₅·nH₂O as the interfacial modification materials for the first time,and cleverly utilized the spontaneously-redox reaction between the pre-fabricated V₂O₅·nH₂O film and Znmetal foil to on-site built an ideal zinc-ion conductive Zn_xV₂O₅·nH₂O（hereinafter referred to as ZnVO）modified layer on the surface of Znanode.The experimental results show that the ZnVO-modified Znanode（ZnVO@Zn）shows a flat and dense deposition morphology compared to the rough and loose deposition morphology of the Bare Znanode without ZnVO modification.The high zinc ionic conductivity of ZnVO-modified layer can effectively promote the uniform diffusion of zinc ions on the surface of the Znanode,thereby guiding the uniform deposition of zinc ions and inhibiting the growth of dendrites;meanwhile,the uniform coverage of the ZnVO-modified layer on the surface of the Znanode can effectively isolate the direct contact between Znanode and the electrolyte to alleviate the occurrence of side reactions,thereby improving the interface stability of the zinc anode.Electrochemical test results show that,at the current density of 0.25 mA cm^-2,the ZnVO@Znsymmetrical cell can cycle stably with a lower polarization voltage for more than560 h,which is more than 10 times higher than that of Bare Zn.Even at a high current density of 5 mA cm^-2,the ZnVO@Znsymmetrical cell can also cycle stably for more than 50 h.Furthermore,the Zn|ZnSO₄+Li₂SO₄|LiFePO₄ full cells can also exhibit a high coulombic efficiency after 1000 cycles,in comparison,the full cell using Bare Znanode died at 250 th cycle.2.In the study of interfacial modification ofβ-PVDF modified Znanode,we used the PVDF（Polyvinylidene fluoride）as the interfacial modification materials for the first time.By simply coating theβ-PVDF-modified layer on the interface of Znanode,we finally obtained theβ-PVDF modified Znanode（β-PVDF@Zn）.The experimental results show that,compared with the uneven and rough deposition morphology of Bare Zn,theβ-PVDF@Znanode shows a highly uniform and flat deposition morphology.The electrochemical test results show that the cyclic life-span ofβ-PVDF@Znsymmetrical cell under the current density of 0.25 mA cm^-2 is more than 600 h,which is more than 10 times of that for Bare Zn（～52 h）.Even at a high current density of 5 mA cm^-2,theβ-PVDF@Znsymmetrical cell can also cycle stably for more than 600 h,which is more than 40 times higher than that of Bare Zn.Furthermore,the Zn|Ti asymmetric cells’cycle test results show that,at the current density of 1.0 mA cm^-2,theβ-PVDF@Ti asymmetric cell can cycle stably with a high Coulombic efficiency（average Coulomb efficiency～98.24%）for more than 450 cycles,which is more than 3 times higher than that of Bare Ti（～150 cycles）.These electrochemical test results show that theβ-PVDF-modified layer could significantly improve the cyclic stability and reversibility of Znanode.The mechanism ofβ-PVDF interfacial modification may be based on the following points:（1）the good mechanical properties of theβ-PVDF-modified layer make it able to adapt to the volume change of the anode while inhibiting the growth of dendrites;（2）there are abundant electronegative C-F functional groups inβ-PVDF,and the interaction between electronegative C-F functional groups and zinc ions can prevent the"tip effect"of Zn-ion deposition,thus promote the uniform deposition of zinc ions,（3）the chemical inertness of theβ-PVDF-modified layer in the electrolyte can effectively improve the interfacial stability of the Znanode.