Improved Performance Of Aqueous Zinc Ion Batteries

Aqueous zinc ion batteries have developed rapidly,due to their high theoretical capacity(820 m Ah g^-1 and 5854 m Ah cm^-3),low electrochemical potential（-0.76 V vs.standard hydrogen electrode）and rich storage.However,there are also some problems and challenges for aqueous zinc ion batteries.As for the negative electrode,in the process of zinc ion deposition,due to the influence of the electric field distribution on the surface of the negative electrode,this leads to the uneven deposition of zinc ions.Under the influence of the tip effect,further accumulation produces dendritic zinc dendrites.The further growth of zinc dendrites will pierce the separator and cause the short circuit of the battery.At the same time,in the aqueous electrolyte environment,the reaction of zinc anode with water will produce hydrogen and further cause electrode passivation,which seriously hinders the further development of the aqueous zinc ion battery.In this paper,it mainly improves the aqueous zinc ion battery performance by adding electrolyte additives and constructing the functional interface layer on the negative electrode.It is committed to protect the negative electrode of zinc,inhibit the growth of zinc dendrites and reduce the side reaction.The main contents of the two works in this paper are as follows:（1）The general electrolyte additive has a single function and generally only acts on the positive or negative pole.However,for a complete battery system,the positive and negative poles are inseparable.Therefore,the introduction of halogen iodine ion additive into the electrolyte can achieve the dual-function effect,which can not only act on the negative electrode to regulate the deposition of zinc ion and thus inhibit the growth of zinc dendrites,but also apply appropriate voltage to the positive electrode to achieve the transition from zero to negative one,and contribute a certain amount of capacity to improve the overall energy density of the supercapacitor.After research,when the iodine ion is introduced into the electrolyte system,it will replace the water molecules around the zinc ion in the electrolyte,reduce the binding energy of hydrated zinc ion,and promote its desolvation process.（2）Although the introduction of iodine ion additives into the electrolyte can play a certain role in protecting the zinc negative electrode,for the inorganic electrolyte additives,although they can play a certain role in protecting the zinc negative electrode at low current density,their effects become worse and worse with the increase of current density,showing the limitations of inorganic electrolyte additives in the protection of zinc negative electrode.Through many published works,it is found that the negative electrode interface improvement strategy can achieve uniform and stable deposition of zinc ions at high current density.Therefore,manganese trioxide,zinc manganese oxide and carbon mixed phase（Mn₂O₃/Zn Mn₂O₄@C）were successfully prepared by solid phase synthesis and apply it evenly on the surface of zinc sheet by the scraper method.Through the test,it is found that the contact angle between zinc sheet and water increases due to the introduction of interface protective layer,which weakens the side reaction between zinc sheet and water.In addition,the improved interface reduces the battery impedance and the nucleation point of zinc ions,which is beneficial to guide the uniform deposition of zinc ions.