Biomass Hydrogel Electrolytes toward Green and Durable Supercapacitors: Enhancing Flame Retardancy, Low-Temperature Self-Healing, Self-Adhesion, and Long-Term Cycling Stability
Nannan Zhu, Qijin Teng, Yibin Xing, Xiyao Wang, Zuocai Zhang, Xuejuan Wan
Abstract
Hydrogels have shown promise as quasi-solid-state electrolytes for flexible supercapacitors but face challenges such as poor self-repair, unstable electrode adhesion, limited temperature range, and flammability. Herein, an all-round green hydrogel electrolyte (silk nanofibers (SNFs)/peach gum polysaccharide (PGP)/borax/glycerol (SPBG)-ZnSO 4 ) addresses these issues through dynamic cross-linking of peach gum polysaccharide and silk nanofibers with borax, integrating varieties of key property including high water retention, broad temperature tolerance (−20 to 90 °C), excellent self-adhesion (60.7 kPa for carbon cloth electrodes), satisfactory flame retardancy (limited oxygen index of 51%), low-temperature self-healing (−20 °C), and good ionic conductivity (7.68 mS cm –1 ). The resulting supercapacitor exhibits excellent cycling stability with 98.2% capacitance retention after 40,000 long cycles at 25 °C. The specific capacitance retention remains above 90% even after 15,000 cycles at high/low temperatures (50 °C/–20 °C). Furthermore, the flexible supercapacitor demonstrates stable performance under mechanical stimuli (180° bending and perforation), highlighting the potential of biomass hydrogels in flexible energy storage devices.