Modification Of Zinc Metal Anode And Their Electrochemical Performance

Aqueous zinc ion batteries have received a lot of attention in recent years as an efficient energy storage system and have been developed rapidly.However,zinc passivation,hydrogen precipitation reaction,corrosion,dendrite growth and other undesirable reactions of zinc metal anode in aqueous electrolyte seriously hinder their further development.The root causes of these phenomena are mainly the difficult mass transfer caused by the coordination environment of zinc,the non-uniform nucleation of zinc,and the non-uniform distribution of the electric field at the interface between the anode of zinc metal and the electrolyte.Therefore,it is important to develop effective strategies to suppress the adverse effects of zinc anode for research purposes.It has been shown that by enhancing the zincophilicity of the substrate can reduce the nucleation potential of zinc and induce homogeneous nucleation of zinc.On the other hand,carbon materials are able to redistribute the electric field distribution because of their good electrical conductivity.Therefore,modifying the substrate or compounding the zinc anode with carbon materials can effectively optimize the nucleation process of zinc and improve the cycling stability of zinc ion batteries.In the first work,induced deposition was used to improve the stability of zinc metal anode.A uniform distribution of metallic tin was deposited on the surface of a commonly used copper foil substrate by an electrodeposition method.The modification by metallic tin lowers the nucleation potential of zinc,allowing zinc to preferentially form zinc nuclei at tin sites;and the uniformity of the zinc nucleation process is improved by the uniform distribution of tin.The growth of zinc on different substrates was characterized by scanning electron microscopy to illustrate the effect of tin on Zn nucleation and growth.The electrochemical performance was tested,and the results showed that the tin-modified electrode exhibited small polarization and excellent stability in the symmetric cell test,achieving more than 270 h of stable cycling.In a full cell test assembled with Mn O₂,the cell maintained a high discharge specific capacity after 500 cycles at a current density of 1 A g^-1,exhibiting excellent electrochemical performance.In the second work,homogenized electric field distribution was used to improve the stability of zinc metal.Composite zinc anodes containing different ratios of carbon nanotubes were prepared by powder metallurgy.The incorporation of carbon nanotubes optimizes the electric field distribution at the electrode-electrolyte interface and regulates the zinc deposition/exfoliation behavior during the cell cycle.In the symmetric cell test,the composite electrode exhibited lower polarization and longer cycle life than the commercial zinc foil.Among them,the composite electrode incorporating 4%carbon nanotubes exhibited the best cycling stability due to the best dispersion of carbon nanotubes.In the test of the full cell composed with Mn O₂,the cell assembled by the composite electrode also exhibited high discharge specific capacity and good cycling stability,showing excellent electrochemical performance.