Polyzwitterionic hydrogel electrolytes based on imidazolium cations and sulfonate anions enable stable Zn-I₂...

Aqueous zinc-iodine batteries represent a promising candidate for new energy storage systems owing to their abundant resources and high energy density. However, the challenges associated with the polyiodide shuttle and zinc dendrite growth are the critical barriers to the large-scale energy storage system. Herein, polyzwitterionic hydrogel electrolytes (PMVP) are prepared from imidazolium cation monomers and sulfonate anion monomers for regulating dendrite growth and polyiodide shuttle. The sulfate anions restrict the diffusion of iodide ions through strong electrostatic repulsion while capturing free water molecules via strong coordination. Meanwhile, the imidazolium cations guide the uniform deposition of zinc ions to inhibit the dendrite formation and intercept those iodide ions that bypass the electrostatic repulsion barrier. This hydrogel electrolyte shows high ionic conductivity (33.89 mS cm^-1) and transference number (0.74). The Zn//PMVP//Zn symmetric cell cycles stably over 4500 h at 1 mA cm^-2/1 mA h cm^-2 and 1000 h at 10 mA cm^-2/1 mA h cm^-2. The capacity retention of the PMVP-based Zn//I₂ battery reaches 71.48% after 10 000 cycles (1.0 A g^-1), and the flexible pouch cell maintains stable operation under extreme conditions. These cation-anion synergistic polyzwitterionic hydrogel electrolytes provide a novel strategy for addressing dendrite growth and polyiodide shuttle issues in zinc-iodine batteries.