In Situ Polymerization of Hydrogel Electrolyte on Electrodes Enabling the Flexible All‐Hydrogel Supercapacitors with Low‐Temperature Adaptability

Abstract All‐hydrogel supercapacitors are emerging as promising power sources for next‐generation wearable electronics due to their intrinsic mechanical flexibility, eco‐friendliness, and enhanced safety. However, the insufficient interfacial adhesion between the electrode and electrolyte and the frozen hydrogel matrices at subzero temperatures largely limit the practical applications of all‐hydrogel supercapacitors. Here, an all‐hydrogel supercapacitor is reported with robust interfacial contact and anti‐freezing property, fabricated by in situ polymerizing hydrogel electrolyte onto hydrogel electrodes. The robust interfacial adhesion is developed by the synergistic effect of a tough hydrogel matrix and topological entanglements. Meanwhile, the incorporation of zinc chloride (ZnCl 2 ) in the hydrogel electrolyte prevents the freezing of water solvents and endows the all‐hydrogel supercapacitor with mechanical flexibility and fatigue resistance across a wide temperature range of 20 °C to –60 °C. Such all‐hydrogel supercapacitor demonstrates satisfactory low‐temperature electrochemical performance, delivering a high energy density of 11 mWh cm −2 and excellent cycling stability with a capacitance retention of 90% over 10000 cycles at −40 °C. Notably, the fabricated all‐hydrogel supercapacitor can endure dynamic deformations and operate well under 2000 tension cycles even at −40 °C, without experiencing delamination and electrochemical failure. This work offers a promising strategy for flexible energy storage devices with low‐temperature adaptability.