Development Of Electrolyte Additive And Zinc Anode Protection For Aqueous Zinc Ion Battery

Aqueous zinc-ion batteries have received much attention due to their inherent safety,low cost,and high capacity(5855 Ah g^-1).In addition,Aqueous batteries tend to provide a greater power output than that of non-aqueous batteries due to the faster ion transfer characteristics at the solid/liquid interface.However,zinc anodes are easy to form zinc dendrites during the cycle process,which leads to the increase of local current density,accelerating the rate of hydrogen evolution.The acceleration of hydrogen evolution will lead to the change of local p H and form the by-product of Zn₄SO₄（OH）₆?·x H₂O（ZHS）.However,the accumulation of ZHS on the surface of zinc anodes intensifies the surface inhomogeneity and increases the polarization,which in turn intensifies the growth of zinc dendrites.Therefore,the problems of zinc dendrites,hydrogen evolution and parasitic reaction affect and intensify each other.This vicious circle leads to the very low plating/stripping columbic efficiency of zinc anodes,which is not conducive to its commercialization and wide applications.Researchers have proposed several solutions to solve the problem of poor reversibility in the plating/stripping process of zinc anodes.Among them,the design of three-dimensional metal anode,artificial SEI film and the use of high concentration electrolyte are effective measures to improve the cyclic reversibility of zinc anodes.However,problems such as high cost,complex processing and unsuitable for commercial promotion still exist.Therefore,we have successfully solved the problems related to zinc anodes based on electrolyte additives.The main results are as follows:Firstly,Vanillin was selected as the electrolyte additive of 2 M Zn SO₄.Studies had shown that the reversibility of zinc plating/stripping could be significantly improved by a very small amount(2.0×10^-3 g L^-1)addition in the zinc sulfate system.On one hand,vanillin molecules adsorbed on the electrode surface could regulate the deposition process of zinc ions and reduce the two-dimensional diffusion time of zinc ions,which made zinc ions tend to nucleate directly at the adsorption site and inhibited the formation of zinc dendrites.On the other hand,the adsorbed molecules occupied the active sites for the formation of hydrogen adsorption,which inhibited the hydrogen evolution reaction and corrosion of zinc anodes.After using the minimum amount(2.0×10^-3 g L^-1)Vanillin,the circulation stability of Zn||Zn batteries has been greatly enhanced.Under a current density of 1 mA cm^-2,1 mAh cm^-2,more than 250 cycles were obtained,and the stable cycle time was more than 500 h.The results show that the battery also has excellent cycle stability under high current.At a current density of 4.4 mA cm^-2(0.88 mAh cm^-2)the cycle time was more than 2000 h.Zn||MnO₂ also shows the excellent cycle stability（360cycles）and high coulomb efficiency（99.35%）in 2 M Zn SO₄ electrolyte with Vanillin.Secondly,1,2,4-triazole-3-carboxylate（TMC）was selected as the electrolyte additive.The mechanism of TMC improving the stability of zinc anodes was explored through experiments,and the results were as follows:On the one hand,it changes the deposition behavior of zinc anodes,increasing the nucleation overpotential,which made zinc anodes compact and smooth.On the other hand,the use of TMC inhibited the occurrence of hydrogen evolution reaction and corrosion,and improved the coulombic efficiency of zinc plating/stripping.At a current density of 1 mA cm^-2(1 mAh cm^-2),more than 1000 h was obtained,and exhibited excellent cycle stability at a large current density（>2400 h）.