Study On Interface Modification And Performance Of Zinc Metal Anode For Aqueous Zinc-ion Batteries

Zinc metal has the advantages of low cost,high safety,high theoretical specific capacity(820 m Ah g^-1)and low redox potential（-0.76 V vs.standard hydrogen electrode）.However,when used as an anode of the aqueous zinc ion batteries,the uneven zinc deposition leads to the formation and growth of zinc dendrites,punctures the separator,and causes a short circuit of the battery.Zinc dendrites have mechanical rigidity and structural heterogeneity,which are easy to fall off from the zinc anode to form"dead zinc",resulting in the reduction of active materials and the decline of battery capacity.In addition,corresponding side reactions,such as hydrogen evolution reaction（HER）,zinc metal corrosion,and passivation also occur,resulting in the reduction of battery stability.These side reactions take place at the interface of zinc metal anode/electrolyte,which limited the development and application of aqueous zinc ion batteries.Therefore,in this paper,zinc salt functionalized cellulose acetate coating,biomimetic articular cartilage composite coating and biomimetic ant nest composite coating were constructed to functionalize the surface of zinc anode to inhibit zinc dendrites and corresponding side reactions,improve the stability of zinc metal anode,and further improve the electrochemical performance of aqueous zinc-ion batteries.The details are as follows:（1）Constructing a cellulose acetate-based coating（CAZ@Zn）on the surface of zinc foil is to stabilize the zinc anode/electrolyte interface.The cellulose acetate has a large number of ester groups（C=O）,which can interact with Zn²⁺to regulate the rapid diffusion and uniform deposition of Zn²⁺on the zinc anode,thus inhibiting the formation and growth of zinc dendrites.In addition,the Zinc salt functionalized cellulose acetate coating can improve the wettability of the Zn anode and reduce the resistance of the electrode/electrolyte interface,thus improving the Zn²⁺transport kinetics.During the process of electrochemical cycling,the cellulose acetate coating can maintain close contact with the zinc anode and continuously protect it.Besides,the corrosion resistance and the ability to suppress the hydrogen evolution reaction of the optimized zinc anode CAZ@Zn were improved.Therefore,the CAZ@Zn zinc anode can work stably for more than 2800 h at 1 m A cm^-2 with a capacity of 1 m Ah cm^-2,which is about 7 times higher than pure Zn and has a lower overpotential.The full cell NH₄V₄O₁₀//CAZ@Zn achieves a capacity of 415.1 m Ah g^-1 at a current density of 0.1A g^-1and keep capacity retention of 110%after 2000 cycles at 1 A g^-1,superior to that of the full cell NH₄V₄O₁₀//Zn（300 cycles,50%capacity retention）.（2）The flexible articular cartilage can protect the bone under the cartilage from damage by cooperating with the characteristics of fiber reinforced solid phase and efficient mass transport fluid phase.Inspired by articular cartilage with high mechanical properties,which is known for combining efficient mass transport,the biomimetic articular cartilage composite coating was constructed on the surface of zinc anode using PVDF as matrix and Kevlar nanofiber network as reinforcement（ANFZ@Zn）to optimize the interface stability of zinc anode.On the one hand,the biomimetic coating achieves high mechanical strength with a tensile strength of～53 MPa,which can ensure its sufficient strength to inhibit the growth of Zn dendrites without damage during electrochemical cycling,and can adapt to the volume change of Zn anode;on the other hand,the biomimetic composite coating has high ionic conductivity,which can regulate the diffusion and distribution of Zn²⁺on the Zn anode surface,and thus control the homogeneous deposition.Besides,the biomimetic ANFZ composite coating improves the wettability of the zinc anode while enhancing its corrosion resistance.Therefore,the ANFZ@Zn anode cycles stably for more than 1000 h at a current density of 1 m A cm^-2,much higher than the bare Zn anode（～400 h）and achieves a high Coulombic efficiency of 99.7%with dendrite-free zinc deposition.Similarly,the full-cell ANFZ@Zn//MVO achieves high specific capacity,high rate performance,and excellent cycling life.（3）Ant nests have complex interconnecting channels,which can rapidly transport life necessities and air for ants to maintain survival and regulate body temperature.Ant-nest architecture provides a high-throughput network channel,which can be used in the design of porous coating to enhance ion diffusion.Therefore,a porous PVDF-HFP-based biomimetic ant-nest organic-inorganic composite protective coating reinforced by Zn-MMT nanoparticles was prepared on the surface of the zinc anode（PC@Zn）.The biomimetic coating achieves high mechanical strength and high ionic conductivity,simultaneously.The well-wettable PC@Zn delivers dendrite-free zinc deposition by regulating the distribution and diffusion of Zn²⁺at the zinc anode/electrolyte interface.The biomimetic composite coating also inhibits side reactions such as HER,corrosion and passivation,improving the stability of the zinc anode.The flexible biomimetic coating can adapt to the changes in the zinc surface and maintains close contact with the Zn anode during cycling.As a result,the PC@Zn can work stably for thousands of hours at various current densities of 0.25,1 and 5 m A cm^-2,respectively,with high Coulombic efficiency and cycle reversibility,due to the protection of the biomimetic composite coating.The capacity retention of 95.5%of the full cell PC@Zn//Mg VO was also delivered after 3000 cycles at 5 A g^-1.