Tough Cellulose Hydrogel Electrolyte with Low Solvation for Highly Reversible and Flexible Aqueous Zinc-Ion Battery.

Abstract

Recent advancements in hydrogel electrolytes for aqueous zinc-ion batteries (AZIBs) have drawn considerable interest due to their soft nature, offering potential to overcome challenges including reversibility and flexibility. As the most abundant natural polymer, cellulose is ideal for AZIB hydrogel electrolytes due to rich hydroxyls with stable hydrogen-bonded networks for water retention. However, conventional cellulose hydrogels suffer from low Zn²⁺ conductivity and insufficient mechanical robustness, usually requiring additional polymers to meet practical demands. This work reports a chemically neutral dissolution system combined with Keggin-type polyoxometalate as a bifunctional crosslinker and electrolyte modulator. This approach results in ultra-low solvation of Zn²⁺ in cellulose hydrogel, contributing to a wide 2.48 V electrochemical stability window. The high-desolvation hydrogel exhibits balanced Zn²⁺ reaction stability and transport kinetics, effectively suppressing dendrite growth and parasitic reactions. The Zn electrode can be stably strapped/plated with this hydrogel for thousands of cycles with minimal Coulomb efficiency change. The hydrogel also shows excellent flexibility, with toughness of 1.5 MJ m^-3 and elongation at break of 80%. Pouch cells assembled with this hydrogel demonstrate high mechanical flexibility and stability under deformations. This pioneering cellulose dissolution and crosslinking chemistry paves the way for practical application of flexible, durable AZIBs.