Cellulose Nanocrystals Built Multiscale Hydrogel Electrolyte for Highly Reversible All-Flexible Zinc Ion Batteries

Abstract

Hydrogel electrolytes are promising for flexible and stable zinc ion batteries (ZIBs), but it remains challenging to achieve synthetic hydrogels with mechanical stability and durability similar to those of the natural load-bearing tissues only at molecular level. Herein, inspired by the hierarchical structure of biological networks, multiscale hydrogel electrolytes with high toughness, high strength, rapid recovery, and high fatigue-resistance 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. Moreover, the assembled Zn//Zn cell showcases a 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 flexible cell exhibits remarkable flexibility and capacity retention under different stretching and deformation conditions. This work demonstrates a promising gel chemistry that improves mechanical stability and durability and controls zinc behavior, offering a great potential in high-performance flexible and wearable ZIBs and beyond.

Keywords: cellulose nanocrystals, multiscale hydrogel electrolyte, mechanical stability, all-flexible, zinc ion batteries