Cation–π Hydrogel Electrolyte for Flexible All‐Solid‐State Supercapacitors with Excellent Mechanical Deformation and Low‐Temperature Tolerance

Flexible supercapacitors are promising power sources for new-generation wearable electronics. However, their electrochemical performance often deteriorates under mechanical deformation and low-temperature environments. Here, a flexible supercapacitor is developed by sandwiching a hydrogel electrolyte between two electrodes. To address performance challenges, cation-π crosslinking sites are incorporated into the hydrogel network. These dynamic crosslinking sites act as efficient ion-hopping centers, imparting the hydrogel electrolyte with high fracture strength (1.8 MPa), strong ionic conductivity (3.9 S m^-1), and excellent anti-freezing properties. Furthermore, the hydrogel forms cation-π interactions with carbon nanotube-based composite electrodes, facilitated by the reaction between the indole groups and Na⁺ in the electrodes. This strong interfacial bonding minimizes electrode-electrolyte displacement during deformation, reducing interfacial resistance and enhancing charge transport efficiency. As a result, the cation-π hydrogel electrolyte enables the supercapacitor to achieve high energy storage, outstanding mechanical deformation tolerance, and robust performance at low temperatures. The device maintains 89.8% of its initial capacitance after 5000 bending cycles and retains 70.9% capacitance at -40 °C-significantly surpassing previously reported methods. This work presents an innovative strategy for designing high-performance hydrogel electrolytes for advanced energy storage systems.