Hydration-mediated zwitterionic hydrogel electrolyte with hierarchical network for aqueous zinc ion batteries

Designing hydrogel electrolytes for aqueous zinc-ion batteries necessitates a delicate balance between retaining water for ion conduction and restricting its activity to prevent interfacial side reactions. Herein, we present a hydration-mediated hydrogel electrolyte with a supramolecular hierarchical network integrating poly(vinyl alcohol) (PVA) and a sulfonate-terminated zwitterionic polymer. Formed through freezing and thawing combined with dynamic Zn²⁺ coordination, this hierarchical framework achieves robust mechanical stability with the aid of strong intermolecular binding. At the molecular level, the zwitterionic moieties substantially reduce the content of free water and reconstruct the aqueous environment into a dynamic, bound-water layer via strong hydration. Benefiting from this engineered polymer-water interaction that facilitates Zn²⁺ desolvation and transport, alongside the spatial and electrostatic restriction of anion migration, the hydrogel achieves an exceptional ionic conductivity of 16.65 mS cm^-1 and a high Zn²⁺ transference number of 0.75. Consequently, a Zn||Cu cell achieves an average Coulombic efficiency of 99.2% over 600 cycles, while a Zn||Zn_xV₂O₅ full cell retains 78.4% capacity after 1000 cycles at 2.7 A g^-1. This work establishes a supramolecular design principle of constructing hydration-mediated ion channels within a hierarchical network, providing an effective strategy to reconcile fast, selective ion transport with high electrochemical and mechanical stability in hydrogel electrolytes for aqueous Zn²⁺ batteries.