Development Of Electrolyte Additives And Optimization Of Anode/Electrolyte Interface For Aqueous Zinc Ion Batteries

Rechargeable aqueous zinc ion batteries（ZIBs）have a broad application scenario and are expected to become the dominant player in the future energy storage field due to their inherent advantages of low cost,high safety,environmental friendliness and high theoretical capacity.Unfortunately,in practical applications,the Zn anode/electrolyte interface inevitably faces some thorny problems,mainly including dendrite growth caused by continuous two-dimensional diffusion of Zn²⁺ions,and hydrogen evolution and corrosion resulting from water decomposition.These problems interact and exacerbate each other,forming a vicious cycle that severely reduces the deposition/stripping efficiency of Zn anode,as well as destabilizes the cell and hinders the commercialization of aqueous ZIBs.To solve the above problems,various anode improvement strategies have been proposed.Among them,options such as constructing surface coatings,optimizing the anode structure and applying high concentration electrolyte have improved the stability and reversibility of the anode to some extent.However,they also have fatal drawbacks,such as high cost,cumbersome processing,and unsuitable for commercial dissemination.For this reason,we have chosen a simpler and effective optimization strategy,i.e.electrolyte additives,to successfully solve the problems related to zinc anodes.The main research contents and results are as follows:（1）α-Cyclodextrins（α-CD）was used as an electrolyte additive to stabilize the Zn anode/electrolyte interface.As an organic macromolecule,α-CD does not significantly change the coordination chemistry of Zn²⁺ions,but can spontaneously adsorb on the zinc electrode surface to form a dynamic adaptive adsorption layer.On the one hand,α-CD provides an abundance of electrons to the Zn（002）crystal surface,which triggers a charge density redistribution.This effect alleviates the aggregation of Zn²⁺ions and enhances the charge transfer process,thus regulating the uniform nucleation and growth of Zn.At the same time,α-CD molecules induce the orientation deposition of Zn²⁺ions along the Zn（002）crystal surface by selective adsorption on Zn-specific crystal surfaces,which achieves the surface texture of the Zn anode.On the other hand,the adsorbed layer can crowd out the water molecules in the electric double layer structure and act as a physical barrier to protect the Zn metal anode from them,increasing the corrosion potential.Based on the above properties,a very small amount ofα-CD additive can significantly improve the cycling performance of the cell.The Zn||Cu half-cell was stably cycled for 1980 cycles at a current density/capacity density of 2 m A cm^-2/0.5 m Ah cm^-2 with an average CE of 99.45%.Meanwhile,the Zn||Zn symmetric cell achieved up to 8000 h（over 330 days）of stable cycling at 1 m A cm^-2/1m Ah cm^-2,and even at high current and deep discharge(10 m A cm^-2,10 m Ah cm^-2)state,still achieved 570 h of stable cycling.（2）Pyridoxine（PN）was selected as an electrolyte additive to optimize the Zn anode.As a potential dibasic chelator,PN can chelate with Zn²⁺ions,thus destroying the solventized sheath of hydrated Zn²⁺ions and alleviating the hydrogen evolution and corrosion problems caused by desolvation.Additionally,PN molecules can electrostatically adsorbed on the Zn anode surface,thus improving the wettability of the electrolyte on the electrode,increasing the nucleation overpotential,homogenizing the Zn²⁺ion mass transfer,enhancing the Zn deposition/stripping kinetics,and finally inhibiting dendrites.Also,the adsorbed PN molecules can act as a natural barrier to isolate the Zn anode from free water,further increasing the hydrogen evolution overpotential and reducing the corrosion current,thereby maximizing the suppression of side reactions.As a result,the Zn||Zn symmetric cell exhibited excellent cycle reversibility and stability,with a stable cycle time of 2500 h at a high current density and capacity density of 5 m A cm^-2/4 m Ah cm^-2,and 1560 cycles even at a very high current density of 40 m A cm^-2(2 m Ah cm^-2).Furthermore,the Zn||NH₄V₄O₁₀ full cell was stably cycled 1500 times at a high current density of 5 A g^-1 with a specific capacity of 210.1 m Ah g^-1 and a capacity retention rate of 73.2%,demonstrating the practicality of PN additives.