Cellulose nanocrystals built multiscale hydrogel electrolyte for highly reversible all-flexible zinc ion batteries

Hydrogel electrolytes are promising for flexible and stable zinc ion batteries (ZIBs), but they lack fatigue resistance and still face challenges in terms of mechanical stability and durability. Herein, inspired by the hierarchical structure of biological networks, multiscale anti-fatigue hydrogel electrolytes with high toughness, high strength, and rapid recovery are constructed by introducing nanoscale cellulose nanocrystals (CNCs) as building blocks into dual-network cross-linking hydroxypropyl chitosan (HPCS) modified polyacrylamide (PAM) hydrogel (denoted as PHC-gel). As a result, the PHC-gel achieves a high fatigue threshold up to 356 J m- 2 and with a superior strength and stretchability up to 180 kPa and 3178 %, respectively. In addition, the assembled Zn//Zn cell exhibits long-term cycling stability of 1800 h at 1 mA cm- 2 / 1 mAh cm- 2 with a high Coulombic efficiency of 99.4 %. More importantly, the Zn//PHC-gel//MnO2 2 flexible cell shows remarkable flexibility and capacity retention under different stretching and deformation conditions. This work demonstrates a promising gel chemistry that improves anti-fatigue properties and controls zinc behavior, offering great potential for highperformance flexible and wearable ZIBs and beyond.