Anisotropic and anti-freezing cellulose hydrogel electrolyte with aligned channels stabilizing Zn metal anode

Abstract

Aqueous zinc-ion batteries hold substantial promise, benefiting from their cost-effectiveness, high safety, and impressive power density. Nonetheless, their performance is compromised by Zn dendrites and by-product formation at the Zn anode. Hydrogel electrolytes are considered a viable solution to these issues. This study proposes to fabricate anisotropic carboxymethyl cellulose hydrogel electrolyte with aligned channels through a straightforward directional freezing technique, aiming to simultaneously achieve good mechanical properties and large ionic conductivity. Meanwhile, Zn(ClO₄)₂ is introduced into hydrogel electrolyte to establish ternary hydrogen-bonding network, so as to enhance frost resistance. Thanks to these benefits, the anisotropic hydrogel electrolyte (denoted as Ani-hydrogel) manifests improved Zn²⁺ ion transfer, expedited desolvation process, favored planar Zn²⁺ ion diffusion, and promoted interfacial kinetics. Accordingly, Zn dendritic growth and parasitic reactions can be efficiently impeded, contributing to significantly improved reversibility of Zn stripping/plating. With the use of Ani-hydrogel electrolyte, the duration of Zn//Zn cell is extended to 1200 h under 2 mA cm⁻² and 2 mAh cm⁻², and the Zn//Cu cell can be stably operated for 300 cycles. The Zn//MnO₂ battery with Ani-hydrogel electrolyte delivers superior cyclability at both room temperature and –10 ℃. This study underlines the importance of anisotropic architecture for hydrogel electrolytes.