Polyanionic hydrogel electrolytes to regulate ion transport behavior in long cycle life zinc-ion batteries

The practical implementation of aqueous zinc-ion batteries (ZIBs) is distinctly hindered by the intrinsic challenges concerned with Zn anodes, primarily manifested through two key issues: (1) the occurrence of irreversible side reactions at the electrode-electrolyte interface and (2) the formation and growth of dendritic structures during electrochemical cycles. Herein, a sulfonate-based polyanionic hydrogel electrolyte with good adhesion and mechanical properties is designed for building dendrite-free and long cycle life ZIBs. The introduction of anion moieties induces the partial substitution of coordinated water molecules in Zn (H₂O)₆²⁺, promoting the reorganization of the solvation environment around Zn²⁺ and facilitating the ion transport kinetics and Zn²⁺ diffusion. The anionic macromolecular structure effectively regulates the potential distribution at the electrode-electrolyte interface, minimizing parasitic reactions and alleviating dendrite growth. The Zn symmetric cells employing the polyanionic hydrogel electrolyte exhibit the long-term electrochemical stability, maintaining the stable zinc plating/stripping cycles over 3300 h at 1 mA cm⁻² and 1100 h at 5 mA cm⁻². When configured as full cells with Zn//NVO/MWCNTs cathodes, the system delivers superior specific capacity and remarkable cycling performance. This work provides new insights for developing the advanced hydrogel-based electrolyte systems to address the Zn anode instability and safety issues in aqueous ZIBs.