A Novel “Water-in-Ionic Liquid” Electrolyte for Zn Metal Batteries
Zhiming Zhao, Joanne Lai, Duc Tam Ho, Yongjiu Lei, Jian Yin, Long Chen, Udo Schwingenschlögl, Husam N. Alshareef
Abstract
Success in the development of aqueous batteries hinges on strict design principles for the aqueous electrolyte: utilize the high ionic conductivity but limit the redox activity of water. Here we develop a new type of electrolyte, a “water-in-ionic liquid” electrolyte, where the water molecule is sealed in a water trap composed of ions by short-range intermolecular interactions. In this way, the water molecule is protected by the surrounding anion-abundant framework and simultaneously plays its lubricant role for ionic conduction, realizing a high stability together with a high ionic conductivity (1.18 × 10–2 S cm–1) of the electrolyte. This water-confined motif promotes the formation of an explicit interphase (SEI) on a Zn metal anode, which is clearly observed for the first time and contributes to a substantially reversible Zn electrochemistry. Notably, due to the intermolecular constraint, the volatilization of this electrolyte is alleviated, which is helpful for batteries with an open system. As a proof of concept, we demonstrate zinc–air batteries (ZABs) with superior longevity compared to those using typical aqueous electrolyte under lean-electrolyte conditions (300 h vs 72 h, respectively).