Tailoring zinc-ion deep eutectic electrolytes through dual regulation of solvation shell volume and solvent polarity

Abstract

The tunability of Lewis acid-base and hydrogen-bonding (HB) interactions in deep eutectic electrolytes (DEEs) is considered as effective platform for addressing vital challenges in zinc-ion batteries. However, in aqueous DEEs, undesirable intermolecular forces severely obstruct ion hopping, as reflected in high solute viscosity and transport behavior, which is only effective over short ranges. The Stokes-Einstein formula and Debye–Hückel theory based on Kohlrausch’s law describe the transport mechanism of cations in non-ideal fluids, where small solvation shell enables faster ion migration under electric field. The Et(30) parameter, which captures the trade-off between specific HB interactions and solvent polarity, serves as key descriptor for tailoring the desolvation kinetics of solvation sheath. Based on systematic screening of solvation shell volumes and solvent polarity, acetonitrile (AN) with small solvation shell volume and moderate polarity is the optimal choice. Furthermore, the system’s maximal decoupling from the environment validates the concept of long-range efficient ion transport. Ultimately, the DEE system achieves fourfold enhancement in ionic conductivity (8.3 mS cm−1) and exceptional cycling durability in Zn–I2 pouch cell, retaining reversible capacity of 95.4 mAh g−1 after 1,500 cycles at 1 A g−1. This work significantly narrows the theoretical gap between aqueous and non-aqueous battery systems.