Design And Regulation Of Zn Anode Host Based On Two-Dimentional ZIF-8 Material

The increasingly serious energy crisis and environmental pollution promote the development and use of renewable energy resources such as wind and solar.But these renewable energy resources are only intermittently available.In order to improve the utilization efficiency of renewable energy,it is necessary to research and develop efficient and sustainable large-scale energy storage systems.The aqueous electrolyte is safe,environmentally friendly and low-cost with wide stable potential window,and its ionic conductivity(～0.1 S·cm^-1)is 2 orders of magnitude higher than that of the organic electrolyte(～1-10 m S·cm^-1).Low-cost Zn metal exhibits a low redox potential（-0.76 V vs.SHE）,high H₂evolution overpotential,and high theoretical capacity(gravimetric capacity of 820 m Ah g^-1and volumetric capacity of 5855 m Ah cm^-3).In aqueous Zn-ion batteries（AZIBs）,metallic Zn can be directly adopted as a stable anode.So,the AZIBs have attracted more and more attention.However,there are still many problems for Zn anode AZIBs,such as H₂evolution,corrosion,passivation,and dendrite growth.Therefore,it is very crucial to develop stable Zn metal anode for improving the overall performance of the AZIBs.In this work,we constructed composite anode hosts based on two-dimensional（2D）ZIF-8 materials,which induced uniform Zn deposition and improved the performance of AZIBs.The details are as follows:（1）First,we used sodium dodecyl sulfonate（SDS）as templates to synthesize 2D ZIF-8 nanosheets（SDS-ZIF）with exposed（002）crystal plane.Then,we constructed GP/SDS-ZIF composite anode hosts by electrodeposition.The array of SDS-ZIF nanosheets on the surface of graphite paper（GP）was flat and compact for uniform distribution of electric field.In addition,a large number of N and Zn zincophilic sites were uniformly distributed on SDS-ZIF nanosheets,which could induce uniform and rapid nucleation of Zn on its surface.Besides,the few SDS surfactant on the SDS-ZIF nanosheets could reduce the surface tension at the interface between the host and the electrolyte,improving the wettability of the electrolyte and facilitating the rapid diffusion of Zn²⁺.Thanks to high lattice matching ratio between the（002）crystal plane exposed by SDS-ZIF and the（002）crystal plane of Zn,the composite anode host could induce continuous deposition of Zn on（002）crystal plane.The stability of（002）crystal plane could also effectively inhibit the occurrence of side reactions.Last but not least,the AZIB was assembled to test the electrochemical performance of the hosts.GP/SDS-ZIF half cells could stably sustain more than 330 cycles,and the average Coulombic efficiency reached 99.06%.Moreover,the GP/SDS-ZIF/Zn||GP/SDS-ZIF/Zn symmetrical cells exhibited a long cycle of 200 hours at a current density of 3 m Ah cm^-2and showed a low polarization of 60 m V.As a proof of concept,the full cell with the GP/SDS-ZIF/Zn anode and V₂O₅cathode delivered prominent cyclability of 1000 cycles at a current density of5 A g^-1.（2）In order to further improve the conductivity and zincophilicity of 2D ZIF-8 materials,we further explored Ag⁺doped SDS-ZIF（Ag-SZIF）with different Ag proportions.Next,GP/Ag-SZIF composite anode hosts with impact and flat surfaces were constructed by electrodeposition.Similarly,the uniform distribution of electric field and the zincophilic sites such as N,Zn and Ag on the GP/Ag-SZIF promoted the uniform nucleation of Zn.What’s more,the（002）crystal plane enabled the continues Zn deposition on the（002）plane,without dendrite growth and side reactions.The Ag sites improved the conductivity of the host,enhancing the overall performance of the battery.The GP/Ag50-SZIF composite anode hosts achieved an excellent average Coulombic efficiency（99.5%）over 1000 cycles.The GP/Ag50-SZIF/Zn||GP/Ag50-SZIF/Zn symmetric cells showed stable Zn plating/stripping for 500 h at the current density of 3 m A cm^-2.And it could still operate 90 cycles stably at a high current density of 5 m A cm^-2and a high depth of discharge（50%）with the voltage hysteresis of less than 100 m V.The GP/Ag50-SZIF/Zn||V₂O₅full cells exhibited a stable cycling performance over1200 cycles.