Chitosan-based Surface Coating Layers For Zinc Anode Of Aqueous Ion Battery

In recent years,aqueous zinc-ion batteries（AZIBs）have attracted wide attention because of their intrinsic safety,environmental friendliness,low cost and high volumetric capacity.However,as one of the main components of AZIBs,the zinc anodes are facing with Zn dendrites,hydrogen evolution,passivation and other issues which hinder their rejuvenation.Because of the hydrogen evolution,the increased air pressure inside the battery may cause it to swell and break,which brings safety risks.At the same time,the insoluble and insulating byproducts make the electric field on the electrode surface uneven and accelerates the dendrite growth.Therefore,suppressing hydrogen evolution is of great significance for improving the performance of AZIBs.In order to solve this problem,this paper selects chitosan as the surface coating material for zinc anode,using its rich interaction between amino acids and hydrogen ions to inhibit the surface hydrogen evolution reaction.Then,reduce the surface reaction overpotential by compounding with conductive carbon black（CTS）.Furthermore,by combining with nitrogen doped carbon black（NCB）,the synergistic effect of surface chemistry and electrochemistry can effectively inhibit hydrogen evolution reaction and improve the uniform deposition ability of zinc ions.The specific research content is as follows:（1）Study on the electrochemical effect of chitosan coating on metallic zinc anodes.Firstly,using chitosan as the active material and polyvinylidene fluoride（PVDF）as the adhesive,a chitosan coated anode was prepared using the traditional slurry method.The symmetrical battery can cycle for 1300 h with the capacity of 1 m A·h cm^-2at 1 m A cm^-2,whose lifespan was longer than zinc anode’s for 200 h.In order to reduce the overpotential,CB with high conductivity was added to the coating.Through a comparative study of the overpotential and cycle stability,the optimal ratio of CTS,CB,and PVDF in the surface coating material was determined to be 7:2:1.The CTS-CB symmetric battery was prepared by coating zinc foil with this ratio.Compared with the zinc anode symmetric battery,the CTS-CB symmetric battery had a lower overpotential after cycling for 200 h with the capacity of 0.05 m A·h cm^-2at 0.25m A cm^-2.Moreover,scanning electron microscope images and X-ray diffraction patterns indicated that there were no large dendrites on the surface of the CTS-CB anode after cycling,and fewer by-products generated.With the capacity of 0.05 m A·h cm^-2at 0.25 m A cm^-2,the CTS-CB symmetric battery could stably cycle for more than 800 h,while the lifespan of the zinc anode symmetric battery was only 120 h.The results of linear polarization and AC impedance tests indicated that the coating could reduce electrochemical corrosion and charge transfer resistance.This series of experimental results indicate that the adsorption of hydrogen ions by CTS inhibits hydrogen evolution side reactions,increases the cycle reversibility and cycle life of the battery,and the addition of CB increases the conductivity of the coating and reduces the deposition overpotential.（2）Study on the electrochemical effects of composite coatings on metallic zinc anodes.NCB materials were prepared by pyrolysis of g-C₃N₄.Furthermore,CTS,NCB,and PVDF were coated in a ratio of 7:2:1 to prepare a CTS-NCB symmetric battery.symmetric batteries CTS-NCB can also stably cycle with the capacity of 0.05 m A·h cm^-2at 0.25 m A cm^-2,and the overpotential during the cycle is further reduced.Scanning electron microscope images and X-ray diffraction patterns indicated that the size of zinc nucleation was further reduced,and the amount of by-products was further reduced.Electrochemical testing results such as linear polarization and AC impedance indicated that electrochemical corrosion was less likely to occur and the charge transfer resistance was further reduced.With the capacity of 1 m A·h cm^-2at 1m A cm^-2,the CTS-NCB symmetrical battery can stably cycle for more than 1440 h,and its cycle life was increased by 640 h compared to the chitosan carbon black symmetrical battery.These results indicate that under the effect of nitrogen doping,the interaction between the coating and hydrogen ions is enhanced,which can further inhibit the hydrogen evolution reaction and dendrite growth.Therefore,replacing CB with NCB can further improve the cycle reversibility and cycle life of the battery.