Sulfuric Acid‐Dissolved Cellulose‐Induced Toughened Polyvinyl Alcohol Hydrogel Electrolyte for Flexible Energy Storage

Abstract

Polyvinyl alcohol (PVA)‐based hydrogel electrolytes are widely employed in flexible solid‐state supercapacitors owing to their biodegradability, nontoxicity, and low cost. However, the further application of pure PVA hydrogel is limited by its low mechanical properties, narrow electrochemical working window, and insufficient frost resistance. In this study, a cellulose solution dissolved in sulfuric acid was directly incorporated into the PVA hydrogel, and the PVA/cellulose composite hydrogel was prepared via a freeze–thaw cycling method. The resulting composite exhibited excellent mechanical properties, with a tensile strength of up to 0.66 MPa and an elongation at break of 896%, as well as remarkable self‐healing capability. After soaking in LiCl electrolyte, the obtained composite hydrogel electrolyte was used to assemble a supercapacitor, which delivered a specific capacitance of 248 mF cm −2 at a current density of 2 mA cm −2 and remained electrochemically operational at −25 °C. Even after 180° bending, the specific capacitance retention rate of the capacitor is as high as 98.4%, and the hydrogel still has 95% specific capacitance retention after fracture self‐healing. These results indicate that the PVA/cellulose composite hydrogel electrolyte has broad application prospects in flexible wearable energy storage devices.