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

## TL;DR

A flexible supercapacitor is developed using a cation–π hydrogel electrolyte that performs well under mechanical stress and low temperatures.

## Contribution

The use of cation–π crosslinking in hydrogel electrolytes improves mechanical and electrochemical performance in supercapacitors.

## Key findings

- The hydrogel electrolyte achieves high fracture strength (1.8 MPa) and ionic conductivity (3.9 S m−1).
- The device retains 89.8% of its capacitance after 5000 bending cycles and 70.9% at −40 °C.
- Cation–π interactions between the hydrogel and electrodes reduce interfacial resistance and enhance charge transport.

## Abstract

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.

A flexible supercapacitor with outstanding low‐temperature and mechanical performance is developed using a cation−π hydrogel electrolyte and carbon nanotube composite electrodes. Na+−indole crosslinking sites within the hydrogel enhance mechanical strength, fatigue resistance, and ion transport, enabling it with excellent mechanical and electrochemical performance. Strong adhesion ensures reliable operation under bending and dynamic movements.