Modulating Zn2+ bulk-interfacial kinetics via ionic eutectic network for high reversible Zn anode operated at 100 °C

Abstract

Deep eutectic electrolytes (DEEs) typically suffer from high viscosity and low ionic conductivity (<10 mS cm^-1), leading to severe battery polarization and limited cycle life, which significantly hinders their practical application in aqueous zinc-ion batteries (AZIBs). To overcome this bottleneck, this study developed an innovative "water-in-salt" ionic eutectic electrolyte (IEE). This design increases free ion concentration and reduces system viscosity (10.9 mPa s), significantly enhancing bulk ion transport and achieving an ionic conductivity (41.7 mS cm^-1) unattainable by conventional DEEs. Simultaneously, the low water activity of the IEE synergizes with its unique anion-cluster solvation structure to strongly suppress side reactions, enabling a Zn||PANI cell to achieve 100 % Coulombic efficiency even at 100 °C. Furthermore, replacing the conventional solid electrolyte interphase protection mechanism with electric double layer regulation and reducing the Zn²⁺ de-solvation energy barrier not only enabled dendrite-free Zn deposition but also substantially optimized interfacial kinetics. This resulted in stable cycling for 1000 h in a Zn||Zn half-cell under ultra-low polarization. Leveraging these combined advantages, the IEE-based full cell demonstrates exceptional rate capability and long-term cycling stability. This work provides a novel approach to overcoming the design limitations of DEEs.