A Diethylene Glycol-Regulated Aqueous Electrolyte for Zinc-Ion Hybrid Capacitors Operating from −40 to 60 °C

Aqueous zinc-ion hybrid capacitors (ZIHCs) have attracted considerable attention for safe and sustainable energy storage; however, their practical application under variable temperature conditions remains challenging due to electrolyte freezing at low temperatures, accelerated water-related side reactions at elevated temperatures, and the instability of zinc electrode reactions. Herein, a diethylene glycol (DG)-based aqueous electrolyte was developed to improve the wide-temperature electrochemical performance of ZIHCs. The effects of different DG concentrations on electrolyte properties, molecular interactions, and electrochemical behavior were systematically investigated. The incorporation of an appropriate amount of DG regulates the hydrogen bond interactions among water molecules, thereby reducing water-related side reactions and improving zinc reversibility. Among the investigated electrolytes, the optimized DW80 electrolyte achieves balanced performance in terms of safety, low-temperature tolerance, and electrochemical stability. Benefiting from the optimized electrolyte composition, Zn||Zn symmetric cells exhibit stable long-term cycling performance, and the assembled ZIHCs demonstrate reliable operation over a wide temperature range from −40 to 60 °C. This work highlights the importance of optimizing cosolvent content and provides a simple strategy for improving the temperature adaptability of aqueous zinc-based energy storage systems.