Regulating Solvation Structures for Wide Voltage Window Chloride Electrolytes toward Low-Temperature Energy Storage

Abstract Chloride-based aqueous electrolytes exhibit low melting points, making them highly attractive for low-temperature electrochemical energy storage. However, the limited electrochemical stability window of chloride-based aqueous electrolytes results in unsatisfactory energy density, thereby hindering their practical application. Herein, a dual-salt Zn(ClO4)2 + CaCl2 gel electrolyte is developed by molecularly reshaping the ion–water–polymer network. By introducing Zn2+ into the CaCl2 electrolyte, a [ZnCl4]2–-dominated coordination environment is established, thereby suppressing the activity of free Cl– and free water molecules. Furthermore, ClO4– disrupts the long-range hydrogen-bonding network of water, lowering the melting point of the electrolyte. The resulting hydrogel electrolyte combines a widened electrochemical stability window, high ionic conductivity, and excellent water retention. An activated carbon symmetric supercapacitor assembled with this electrolyte operates stably over 0–1.8 V and retain 82.1% of its capacitance after 58,000 cycles at –40 °C. The devices also exhibit nearly complete capacitance recovery (∼99%) after temperature-switching tests and stable electrochemical behavior under bending from 0 to 135o. This work provides a molecular design strategy for low-temperature, high-energy, and flexible aqueous energy-storage devices.