Non-strong Alkaline Electrolyte For Zinc Anode And Its Electrochemistry Behavior

Metal zinc is a good anode material for chemical power due to its low standard potential,high specific capacity,abundant resources and friendly environment.Zinc batteries using strong alkaline electrolyte solution have been commercialized such as alkaline Zn-Mn,Zn-Ni and Zn-Ag battery,etc.,but the zinc anode still faces some problems such as dendrite precipitation,chemical corrosion,electrode deformation and limited cycle life.Therefore,non-strong alkaline zinc battery has become a research hotspot in recent years,but a passive film can be easily formed on the surface of metal zinc.Passive film is very important for the electrochemical process of cells.The growth and decline of the passive film are closely related to the pH value of the electrolyte solution.In this paper,the electrochemical behavior and passivation characteristics of metal zinc anode in low alkaline,weak alkaline and slightly acidic electrolyte solution were studied.The electrolyte solution for inhibiting the formation of passive film was designed,and the electrochemical properties of zinc anode materials such as LiZnPO4,ZnO and metal Zn were studied.The electrochemical behavior of zinc sheet in non-strong alkaline electrolyte solution were studied by CV,EIS and SEM,the results showed that a significant and dense passivation film was formed on the surface of zinc sheet in low alkaline electrolyte solution of 3 M KOH,the thickness of the passivation film was about 50nm.In the weak alkaline electrolyte solution of 1.0 M Li2SO4 with pH 9.0,the passivation behavior of zinc surface is not obvious.but it is obvious when the current density is high.In slightly acidic electrolyte solution of 1.9 M Li2SO4 with pH 5.0,the passivation film was thinner,and the passivation behavior may also appear on the zinc electrode surface when the oxidation current density is high.Porous LiZnPO4 anode materials withαandδcrystal structure were prepared and a low alkaline electrolyte solution of 3 M KOH was prepared.The first cycle charge-discharge specific capacities of porous LiZnPO4 electrode in this electrolyte solution was 94.5 m Ah·g^-1/79.4 m Ah·g^-1,and the capacity retention rate was 61%after 100 cycles.The mechanism of electrochemical reaction shows that Zn²⁺ions could be reversibly de intercalated in the porous LiZnPO4,but some Zn²⁺ions may be reduced and deposited on the surface of the electrode or separated from the electrode active material into the electrolyte solution,made it difficult to return to the electrode and caused the decline of the cycling capacity of the material.The weakly alkaline electrolyte solution Li2SO4-Na2SO4-（NH4）2SO4-Zn SO4 of pH 9.0 was prepared.Na2SO4 could effectively improve the ionic conductivity,and（NH4）2SO4 could effectively inhibit the formation of Zn（OH）2 coating film.The specific capacity of ZnO electrode in the electrolyte solution for the first charge/discharge cycle was 548.1 m Ah·g^-1/599 m Ah·g^-1,the capacity retention rate was 30.8%after 20 cycles,and the dissolution of Zn²⁺into the electrolyte solution leads to rapid capacity decay.The slightly acidic electrolyte solution of Li2SO4-Zn SO4-KHP was developed.The component KHP can inhibit the fluctuation of cycle capacity of Li Fe PO4 battery.When the pH of electrolyte solution was 5.0,the passivation film on the surface of zinc anode was weak and the impedance of electrolyte solution was small.The first cycle specific capacity of Zn/Li Fe PO4 battery could reach 131.2 m Ah·g^-1 at 0.25 C and 108.8 m Ah·g^-1 at 1 C.The mechanism study showed that the crystal structure of Li Fe PO4 degenerated during the charge discharge process,the released of a small amount of Fe²⁺and PO4^3-ions,and LiZnPO4 precipitate was formed on the electrode surface.