Modulation of hydrogel electrolyte enabling stable zinc metal anode

Abstract

The uneven flux and strong solvation of Zn2+ ions in aqueous electrolytes bring undesirable dendritic deposition and side reactions to zinc metal anodes (ZMAs). Hydrogel electrolytes have considerable mechanical strength and limited water content, which can suppress dendrite growth and alleviate side reactions. Nevertheless, the design of hydrogel electrolytes with desired electrochemical and mechanical properties is still challenged due to the lack of understanding of how structural features affect performances. Herein, we systematically investigate the hydrogel electrolytes for ZMAs by regulating their crosslinking and grafting structures. Experiments and theoretical simulations emphasize the importance of the network structure and the polymetric anions bonded on the hydrogel. The PSX gel crosslinked by carboxyl-grafted polyvinyl alcohol and xanthan gum shows superior performance, contributed by its abundant -COO− groups and stable three-dimensional structure. The PSX electrolyte shows high ionic conductivity (18.86 mS cm−1) and a considerable Zn2+ transference number (0.8). Zn//Zn cells with PSX electrolytes deliver long cycle lives accompanied by uniform zinc deposition, few by-products, and suppressed hydrogen evolution. When paired with V2O5 or active carbon cathodes, the PSX electrolyte also shows good compatibility and excellent performance. Flexible pouch cells are further demonstrated to work normally under different deformation and stress conditions.