Preparation Of Cu-MOf Cathode Material And Investigation Of Its Electrochemical Performacne For Aqueous Zinc Ion Batteries

The urgent need for clean energies have evoked the enthusiasm to establish energy storage systems with low cost,environmentally friendliness,and high stability for grid-scale electrical applications.In comparison to lithium-ion batteries employing organic electrolytes,secondary aqueous zinc-ion batteries（AZIBs）have attracted extensive interests due to the merits of cost-effectiveness,eco-friendliness,high reliability,low electrochemical potential（-0.762 V vs.standard hydrogen electrode）,high theoretical gravimetric(820 m Ah g^-1)and volumetric capacity(5854 m A h cm^-3),and good stability of zinc in ambient atmosphere.Over the past few years,many inorganic cathodes have been reported for AZIBs,including manganese-based materials,vanadium-based materials,Prussian blue analogues,and,to a small extent,organic compounds materials.Among them,organic compounds with the merits of non-toxicity and environmental friendliness,low production cost,multiple-electron-transfer reactions and resource sustainability,have attracted extensive attention rencently.However,remaining issues,including dissolution in electrolyte,poor electronic conductivity and low working potential,hindered the adoption of organic compounds in AZIBs.Herein,copper-tetracyanoquinodimethane（Cu TCNQ）,a charge-transfer metal-organic framework（MOF）material is evaluated as zinc-ion battery cathode owing to the good electron acceptation ability in the cyano groups that improves the voltage output.Through electrochemical activation,electrolyte optimization and adoption of graphene-based separator,Cu TCNQ-based aqueous zinc-ion batteries deliver much improved rate performance and cycling stability with anti-self-discharge.The specific research content of this paper is as follows:（1）Cu TCNQ is synthesized using a liquid reaction method that acetonitrile solutions of Cu I and TCNQ were mixed and reacted under the protection of N₂.Through electrolyte optimization,Cu TCNQ delivers the best electrochemical performance in aqueous electrolyte system.The structural evolution of Cu TCNQ during charge/discharge are investigated by ex situ Fourier transform infra-red（Ex-situ FTIR）,ex situ X-ray photoelectron spectroscopy（Ex-situ XPS）and in situ ultraviolet visible（In-situ UV-vis）,revealing reversible redox reactions of both cuprous cations（Cu⁺）and organic anions(TCNQ^x-1).Next,the electrochemical performance in Zn//Cu TCNQ is further improved by using graphene-modified separator to inhibit Cu TCNQ dissolution and shuttle effect in effect in electrolyte.The cell using graphene-modified separator can deliver a outstanding energy density of 162 Wh kg^-1 at 102 W kg^-1 and a peak power density of 1600 W kg^-1 at 74.4 Wh kg^-1;at a current density of 2000 m A g^-1,capacity of about 61 m Ah g^-1can still be maintained after 500 cycles,which is much better than the pristine cell.（2）Using a liquid reaction method,Cu TCNQ is combined with carbon nanotubes（CNTs）.It can be observed that Cu TCNQ is embedded in the CNT conductive networks by scanning electron microscope（SEM）and transmission electron microscope（TEM）.When Cu TCNQ@CNT is applied as cathode material in AZIBs,it shows the electrochemical performance of Cu TCNQ@CNT with 75 mg CNTs improved the most,providing a specific capacity of 173.96 m Ah g^-1 at 100 m A g^-1current density in galvanostatic charge-discharge test and AC impedance test.