Study On Stabilizing The Interface Of Zn Metal Anode By Zwitterionic Materials

Aqueous zinc-ion batteries have attracted widespread attention due to their high safety,low cost,and environmental benignity.However,Zn metal anode suffers from severe dendrite issues and passive by-products,which seriously affect the cycle life and Coulombic efficiency of the Zn anode.Therefore,solving these problems and obtaining high-performance Zn anodes is of great significance for the development of Zn-ion batteries.At present,researchers have proposed a variety of solutions,such as constructing structured anodes,using high-concentration electrolytes,and constructing（quasi）solid-state electrolytes.Although these methods effectively improve the stability of the Zn anode,the complex preparation process and high cost still limit the commercial promotion.Therefore,two simple and inexpensive methods were adopted to constructe high-performance Zn anodes（electrolyte additives and constructing a protective layer on Zn anode）,which successfully improved the interfacial stability and work life of the Zn anode.The main research contents and results are as follows:（1）Vinylimidazole and methyl chloroacetate were used as raw material to prepare zwitterionic substance 1-vinyl-3-（carboxymethyl）-imidazolium（VCI）.The optimal addition amount of VCI as an additive in 2 M ZnSO₄ electrolyte is 0.06 g m L^-1.In this case,the Zn anodes could be stabilized for 1400 hours at 1 m A cm^-2/1 m Ah cm^-2.The uniform and dense deposition Zn was observed on the surface of the Zn anode after cycling in the additive electrolyte.Meanwhile,the Zn anodes also show high cycle reversibility in zwitterionic additive electrolyte,Zn||Cu half-cell showed high reversible for 600 cycles with average Coulombic efficiency of 99.43%.（2）A uniform zwitterionic modified layer was obtained by simple radical polymerization of VCI and acrylamide on the Zn anode.The structure and morphology of the zwitterionic modified layer were analyzed by FTIR,XPS,SEM tests,which proved the successful preparation of the zwitterionic protective layer.Through the anti-corrosion test,the zwitterionic layer showed great protective effect for Zn anodes in the aqueous electrolyte.Cycling stability was tested by Zn||Zn symmetric cells,the symmetric cells assembled with zwitterionic-modified Zn anode could be cycled stably for 2600 hours with low polarization voltage at 1 m A cm^-2/1 m Ah cm^-2.Even the current density/deposition amount was increased to 8 m A cm^-2/8 m Ah cm^-2,zwitterionic modified Zn anode could still maintain a stable cycle for 300 hours.The reversibility of the zwitterionic-modified layer for Zn deposition/stripping was tested based on Zn||Cu half-cells.High reversible for 1000 cycles with an average Coulombic efficiency as high as 99.65%was achieved at 2 m A cm^-2.Meanwhile,the deposition behavior of Zn ions was analyzed by chronoamperometry,zwitterionic layer was beneficial to the formation of 3D diffusion of Zn ions on the Zn anode,which effectively avoided disordered diffusion and deposition of Zn ions.Combined with DFT theoretical calculations,it was confirmed that the stronger binding energy of Zn ions and zwitterions groups,which enables zwitterions groups to induce the deposition behavior of Zn ions.Finally,full battery was assembled using zwitterionic anode and MnO₂/CNT cathode to study electrochemical performance.The full battery with MnO₂/CNT as the cathode material can stably cycle at a current density of 3 C and maintain a high capacity of 205 m Ah g^-1 after 500 cycles,along with 90%capacity retention.