Employing EMImI Ionic Liquid Additive in Zn-Salt Solutions for Reversible Zn Stripping and Plating in Advanced Aqueous Zn-ion Battery

Abstract

Aqueous zinc ion batteries (ZIBs) have gained considerable interest owing to their low cost, intrinsic safety, and environmental friendliness. Nevertheless, their practical application is hindered by persistent challenges associated with the zinc anode, particularly dendritic growth and the accumulation of parasitic by-products. To overcome these limitations, this study proposes the use of a multifunctional ionic liquid (IL) additive comprising 1-ethyl-3-methyl imidazolium (EMIm⁺) cations to enable prolonged and highly reversible zinc plating and stripping. The EMIm⁺ cations modulate the Zn²⁺ solvation structure by reducing water activity and forming contact ion pairs, thereby suppressing the hydrogen evolution reaction (HER) and inhibiting by-product formation. The charge-shielding effect of EMIm⁺ promotes uniform zinc plating and mitigates dendrite formation. As a result, Zn||Zn symmetric cells exhibit stable cycling for over 2047 h at a current density of 1 mA cm⁻², with a low overpotential of 27 mV. This approach also markedly improves the cycling stability of full cells and hybrid supercapacitors employing manganese dioxide (MnO₂) and activated carbon (AC) cathodes, respectively. These findings highlight the incorporation of EMIm⁺-based ionic liquids as a promising electrolyte additive for enabling long-term, high-performance aqueous ZIBs.