A High-Voltage Supercapacitor Electrolyte Based on Zn²⁺-Driven Self-Adhesive Cellulose Hydrogel

The development of environmentally friendly energy storage devices with high performance has garnered significant attention; however, significant challenges persist in achieving excellent structural stability, high operating voltage, outstanding power density, and outstanding energy density. Here, cellulose was utilized to design hydrogel electrolytes for flexible supercapacitors (FSCs). A dual-network hydrogel was synthesized by interpenetrating cellulose with a poly(acrylamide-co-2-acrylamido-2-methylpropanesulfonic acid) (P(AM-co-AMPS)) network, which was cross-linked by Zn2+. The dissolution of cellulose was facilitated by Zn2+ coordination, while ZnCl2 served as both an ionic conductor and an inhibitor of water molecule electrolytic activity. The hydrogel electrolyte exhibited a significantly enhanced conductivity of 38 mS cm–1, attributed to ion migration channels formed by –SO3H from AMPS. Moreover, the maximum output voltage was increased to an unusual 2 V. Under this voltage, a high specific capacitance of 239.58 mF cm–2 at 0.5 mA cm–2 and an impressive energy density of 130.56 mW h cm–2 at a power density of 0.28 mW cm–2 were obtained. In addition to improved conductivity, AMPS also endowed the hydrogel with remarkable interfacial adhesion of 0.12 MPa to the electrode, enhancing the structural stability and energy storage efficiency of the device. This Zn2+-driven cellulose-based dual-network hydrogel offers valuable insights for the advancement of flexible hydrogel electrolytes.