Anion-Driven Interfacial Engineering and Solvation Structure Modulation of Imidazolium-Based Ionic Liquid Electrolyte Additives for Enhanced Zn Anode Reversibility

Abstract

Reversibility of Zn plating/stripping is greatly impacted by dendrite formation, hydrogen evolution reaction (HER) and passivation in zinc-ion battery. To effectively mitigate these challenges, it is essential to optimize the electrode-electrolyte interface, the Zn2+ ions solvation structure and its transport properties. In this work, the electrochemical performances of Zn||Zn symmetrical cells are investigated by using different electrolytes such as 1 M zinc tetrafluoroborate, 1 M zinc acetate and 1 M zinc chloride aqueous solution with addition of 0.1 M ionic liquids (ILs) as an electrolyte additive. We consider different types of imidazolium based ILs such as 1-ethyl-3-methylimidazolium tetrafluoroborate [EMIM][BF4], 1-ethyl-3-methylimidazolium acetate [EMIM][Ac] and 1-ethyl-3-methylimidazolium chloride [EMIM][Cl]. The molecular level intermolecular interactions between the anions and Zn2+ ions show an influence on the solvation structure and dynamic behavior of Zn2+ ions. As a result, the Zn||Zn symmetrical cell with 1-ethyl-3-methylimidazolium acetate as an electrolyte additive demonstrate cycling stability of more than 1350 h at a current density of 1 mA cm-2 and deposition capacity of 1 mAh cm-2. Detailed molecular dynamics simulations are performed to understand the underlying molecular mechanism regarding the structure and ion dynamic behaviour of Zn2+ ions, which agree with experimental results.

Keywords: ionic liquid electrolyte additive, zinc metal anode, dendrite formation, solvation structure, HER