Triple Regulation of Water Molecules Behavior to Realize High Stability and Broad Temperature Tolerance in Aqueous Zinc Metal Batteries via a Novel Cost-Effective Eutectic Electrolyte

Abstract

The high activity of water in aqueous electrolyte causes drastic side reactions on the Zn anodes, severely limiting the electrochemical performance of aqueous zinc metal batteries (AZMBs) under extreme conditions. Herein, levulinic acid is developed as the hydrated deep eutectic solvent (DES), to build a novel non-flammable and cost-effective ZnSO₄-based eutectic electrolyte with triple regulation of water molecules behavior, enabling highly stable AZMBs over a wide temperature. In situ experiments, molecular dynamics simulations, and spectroscopy analysis jointly reveal that the DES is capable of comprehensively lowering the water activity by simultaneously controlling the behavior of the free, solvated, and interfacial water molecules within the eutectic electrolyte system. Consequently, the Zn anodes exhibit ultralong cycling stability (4500 h at 1 mA cm⁻²/1 mA h cm⁻²), decent Coulombic efficiency of 99.39%, and excellent temperature tolerance (−20–50 °C). Notably, the designed 2.0 Ah Zn//VOX pouch cell exhibits a recorded actual energy density of 37.46 Wh Kg⁻¹ and 95.38 Wh L⁻¹ at the whole cell level, with a remarkable capacity retention of 81.01% after 150 cycles, demonstrating the potential for scale-up into real AZMBs. This work provides an in-depth understanding of the correlation between the water molecule behavior and electrochemical properties of AZMBs.