Ionic Liquid-Based Hydrogel Electrolytes Enabling High-Voltage-Plateau Zinc-Ion Batteries

Abstract

Aqueous zinc ion batteries (ZIBs) have been recognized as highly promising energy storage systems due to their high safety, low cost, and environmental benignity. However, low voltage platform of cathode, coupled with uneven Zn deposition, side reactions, and limited operational temperature range caused by free water molecules, has hampered the practical application of ZIBs. To address these issues, 1-ethyl-3-methylimidazolium acetate (EmimAc) ionic liquid (IL) is utilized to modify the active water in polyvinyl alcohol (PVA)-based hydrogel electrolyte. The abundant hydroxyl groups on PVA chains, along with strong interactions between IL and H₂O, disrupt hydrogen bonds between water molecules. This hydrogel electrolyte alleviates side reactions, and improves low-temperature performance through suppressing water crystallization and lowering the freezing point of the electrolyte. Furthermore, the strong binding of hydroxyl groups of PVA to Zn²⁺ restricts Zn²⁺ migration, ensuring the de-intercalation of Na⁺ at the Na₃V₂(PO₄)₃ (NVP) cathode, thereby maintaining a high voltage plateau (1.48 V) for improved energy density. Benefitting from these merits, a pouch cell of Zn||NVP achieves 100 cycles at 25 °C, and a coin cell achieves 81.3% capacity retention after 1600 cycles at −20 °C. This work represents a significant advance in designing expanded work voltage/temperature hydrogel electrolytes for ZIBs.