Highly stretchable dual network hydrogel electrolytes for supercapacitors at −80 °C

The rapid development of wearable and portable electronics has driven an increasing demand for flexible energy storage devices. Hydrogel electrolytes with both mechanical robustness and high ionic conductivity are essential for achieving high-performance and safe flexible electronics. Here, we present a dual-network hydrogel electrolyte composed of zinc tetrafluoroborate (Zn(BF₄)₂), polyacrylamide (PAM), and gelatin (denoted as PGx-Zn). The PG₃-Zn hydrogel containing 3 wt% gelatin demonstrates exceptional mechanical properties with a high elongation at break of 1193 % and a tensile stress of 88 kPa, outperforming gelatin-free hydrogels by 1.67 and 2.26 times. The incorporation of Zn(BF₄)₂ effectively disrupts the hydrogen-bonding network of water, stabilizes the folded structure of gelatin, and maintains both outstanding mechanical strength and high ionic conductivity of the hydrogel. PG₃-Zn has an ionic conductivity of 0.26 S m⁻¹ at −80 °C, enabling supercapacitors to retain 73 %, 68 %, and 61 % of the room temperature capacitance at −40 °C, −60 °C, and −80 °C, respectively. This work offers a promising pathway for developing hydrogel electrolytes with superior mechanical and ionic conductivity for low-temperature, high-power energy storage applications.