Stretchable, Wide-Temperature Gel Electrolytes Integrating Ionic Conduction and Heat Buffering for Flexible Supercapacitors

Abstract Traditional hydrogel electrolytes face multiple challenges in flexible energy storage applications, including poor mechanical properties, low ionic conductivity, and failure under extreme temperatures. Herein, this study designs and fabricates a composite gel electrolyte based on polyacrylic acid (PAA), cellulose nanofibers (CNF), and choline chloride (ChCl)/ethylene glycol (EG)/water. The CNF network provides mechanical support and ion transport channels, while an appropriate amount of EG constructs a reversible hydrogen bonding network, endowing the gel with excellent mechanical properties (fracture energy of 218.43 kPa at 780% strain), interfacial adhesion (37.41 kPa on NF and 14.8 kPa on CC), and ionic conductivity (37.93 mS cm−1). The high boiling point and abundant hydroxyl groups of EG impart the gel with outstanding water retention, flame resistance, and adequate self-healing properties and synergize with ChCl to confer good low-temperature adaptability. The flexible symmetric supercapacitor assembled based on this gel exhibits a wide voltage window (0–1.6 V) and excellent cycling stability (92.84% after 6000 cycles) and can operate normally within a temperature range of −20 to 60 °C. More importantly, owing to its high specific heat capacity, the gel possesses dual functionality of “ionic conductivity and thermal management”, significantly suppressing the temperature rise during battery charge/discharge processes. This work provides a novel electrolyte fabrication strategy for developing next-generation flexible energy storage devices with high performance, a wide temperature range, and thermal management capability.