Phase Transition-Induced Nanohydrogel Electrolytes with High Tensile Strength, Robust Adhesion, and Superior Antifreezing

Hydrogel electrolytes hold great potential as flexible all-in-one supercapacitor materials due to their excellent flexibility and safety features. However, the practical application of common hydrogels as electrolytes is severely restricted because of their inferior mechanical performance, insufficient adhesion to electrode materials, and poor antifreezing properties under harsh conditions. In this study, a hydrogel electrolyte is developed via a phase transition method. The presence of in situ-generated nanocrystals within the hydrogel electrolyte has been confirmed by multiple techniques, significantly enhancing their mechanical properties. Specifically, the toughness of the nanohydrogel electrolyte has been improved by 60-fold, while the elongation at break has tripled. Furthermore, the nanohydrogel electrolyte has strong adhesion to electrode materials. Subsequently, a nanohydrogel-based all-in-one supercapacitor is constructed using polyaniline as the electrode through a convenient powder-coating technique. The supercapacitor achieves an impressive specific capacitance of 527 F/g at 30 °C and maintains a capacitance retention of 97% even after 15,000 cycles. Additionally, the freezing point of the nanohydrogel electrolyte is dramatically decreased to approximately −80 °C with the synergistic introduction of glycol, demonstrating its superior antifreezing characteristics. This nanohydrogel electrolyte can be used to construct flexible supercapacitors in frigid environments, and our design strategy can be expanded to other conductive polymers.