Construction Of Stable Zinc Anode Based On Polyethylene Glycol/polyethylene Glycol Monomethyl Ether Bifunctional Modified Electrolyte

Zinc metal has the advantages of high capacity,low redox potential,low cost and environmental friendliness,and zinc-ion batteries are excellent candidate materials for large-scale energy storage devices.However,zinc metal as anode suffers from poor cycle stability and low Coulomb efficiency in practical applications.The reasons for these problems can be summarized as follows:1)the existence of severe side reactions between zinc metal anode and aqueous electrolyte,which generates ion-insulating by-products,leads to the continuous consumption of zinc metal and the uneven deposition of zinc ions;2)Due to the inhomogeneous ion flux and electric field distribution on the zinc metal surface and the poor deposition kinetics of zinc ions,zinc ions cannot be nucleated uniformly during the deposition process,which leads to dendrite growth.To address the problems mentioned above,an electrolyte modification strategy is proposed in this paper,aiming to construct a bifunctional modified electrolyte.The modified electrolyte has two functions.On the one hand,it could modulate the solvation structure of zinc ions to suppress the side reactions;on the other hand,inducing the preferential deposition of zinc ions along the（002）crystal surface can suppress zinc dendrites and improve the cycling stability of zinc cathodes.And on this basis,the influence of the concentration of the terminal hydroxyl group of the system on the cycling performance is quantitatively studied to find the optimal concentration and further extend the cycle life of the battery.The specific research contents are as follows:1.To address the problem of poor cycle stability caused by the instability of the zinc anode interface,this paper introduces polyethylene glycol into the conventional zinc sulfate electrolyte to formulate a polyethylene glycol-modified electrolyte,the polyethylene glycol modified electrolyte can modulate the solvation structure of zinc ions and induce the preferential deposition of zinc ions along the（002）crystal plane to improve the stability of the zinc cathode and extend the battery cycle life.Compared with the conventional zinc sulfate electrolyte,the polyethylene glycol modified electrolyte can modulate the solvation sheath structure of zinc ions,while polyethylene glycol can interact with water molecules to reduce the activity of water molecules in the solution,so as to suppress the side reactions caused by the aqueous electrolyte and improve the transport kinetics of zinc ions;in addition,polyethylene glycol can induce the preferential deposition of zinc ions along the（002）crystal plane and promote the uniform deposition of zinc ions in horizontal layers,effectively inhibit the formation of dendrites,and improve the stability of zinc anode in a two-pronged way,which extends the cycle life of zinc anode from 60 h to 2100h at 0.5 m A cm^-2-0.5 m Ah cm^-2.Afterwards,it was tested in aqueous zinc ion battery,and the capacity retention rate was 94.0%after 1200 cycles in the polyethylene glycol modified electrolyte system at a current density of 1 A g^-1.2.In the above work,it has been determined through qualitative analysis that the introduction of polyethylene glycol,an organic alcohol polymer,into the conventional electrolyte can effectively improve the cycling stability of the zinc cathode.To further analyze the improvement of the modification on the battery performance,in this paper,zinc trifluoromethanesulfonate electrolyte was modified by different molecular weight polyethylene glycol derivatives-polyethylene glycol monomethyl ether,and a series of modified electrolytes with different end-hydroxyl concentrations were configured and tested for cycle life using the end-hydroxyl concentration as the descriptor.The test results showed that the cycle life of the battery was linked to the end-hydroxyl concentration,and the system showed the best cycle stability at the end-hydroxyl concentration of 1.6 mol L^-1.Among them,the symmetric battery cycle life of the polyethylene glycol monomethyl ether system with a molecular weight of 350 was up to 3980 h at the end-hydroxyl concentration of 1.6 mol L^-1,which was extended by 3700 h compared with the blank system,while the system Zn||Mn O₂ full cell at 1 A g^-1 current density after 1000 cycles,the capacity retention rate was 77.9%.The results indicate that regulating the terminal hydroxyl concentration of the system can further stabilize the zinc anode and enhance the cycle life.