Preparation Of Polymer-based Composite Film And Its Application On Dendrite-free Zinc Anode

Aqueous zinc ion battery has attracted extensive attention in recent years because of its advantages of high energy density,low cost,and green safety,etc.However,in the charging and discharging process,the uneven deposition/stripping of Zn on the anode electrode will lead to the generation of zinc dendrites.With the continuous growth of zinc dendrites,they will eventually pierce the film and lead to the failure of the battery.In addition,the thermodynamic instability of Zn electrode in weak acid electrolyte will lead to hydrogen evolution reaction（HER）,which leads to electrode passivation and hydrogen precipitation.In order to achieve stable Zn stripping/deposition and limit HER and other side reactions,the structural design of zinc anode,the development of new electrolyte and the regulation of electrode-electrolyte interface have been proposed successively.Among them,the polymer coating with polar groups can adjust the electrode/electrolyte interface,guide the uniform deposition of Zn,and slow down the occurrence of HER.In addition,polymer coating is an effective solution to improve the cyclic stability of zinc anode due to its low cost,easy machining and diverse structure.Therefore,in this paper,polymer-coated with polar groups were designed to effectively solve the problems of dendrite and HER of Zn anode.（1）PA6/BMI composite films were prepared by dissolving nylon 6（PA6）with amide group and 1-butyl-3-methylimidazole-trifluoromethane sulfonate（BMI）with good conductivity and hydrophilicity in formic acid.Physical characterization and electrochemical performance test showed that PA6/BMI composite film could be used as a shielding layer to inhibit the HER and limit Zn²⁺two-dimensional diffusion,thus effectively regulating Zn deposition on the anode surface.The stable stripping/deposition cycle of symmetric cells was achieved with 110 mA overpotential at 0.5 mA cm^-2 current density for 700 h.（2）The dense polymer coating causes high resistance to the migration of Zn²⁺,which could increase cell polarization and even lead to the formation of Zn dendrites.SPA6/BMI nanofiber films were obtained by electrospinning PA6 and BMI matrix,which could effectively reduce the impedance of the electrode.Symmetric cells could be stabilized for stripping/deposition cycle 1000 h with 50 mA overpotential at0.5 mA cm^-2 current density.（3）β-PVDF/BMI nanofiber films with piezoelectric effect were prepared by oriented electrospinning with PVDF and BMI matrix.β-PVDF can generate an electric field directed under the action of pressure,which accelerates the migration of Zn²⁺and achieves the uniform and compact deposition of Zn.The electrode modified withβ-PVDF/BMI nanofiber films could stabilize the stripping/deposition cycle for 1000 h at a current density of 0.5 and 2 mA cm^-2 with 47 and 51 mA overpotential respectively.And when the current density gradually increased to 10 mA cm^-2,the overvoltage only increased from 47 mV to 80 mV.