Anchoring Polyiodides: Microphase-Separated Gel Polymer Cathode for Zinc–Iodine Batteries

Zinc–iodine (Zn-I2) batteries are attractive for grid-scale energy storage owing to safety and low cost, yet practical deployment is hindered by shuttling of soluble polyiodide intermediates (I3–, I5–), which causes capacity decay, anode corrosion, and thermal instability. We report a universal electrode design using a microphase-separated gel cathode based on an amphiphilic acrylamide copolymer (a-PAM). The copolymer forms a 3D network with hydrophilic ion-transport channels and embedded nanoscale hydrophobic domains. These domains physically sequester and chemically anchor iodine species, effectively restraining their dissolution and cross-electrode shuttling. The cathode delivers 209.3 mAh g–1 and retains 87.7% of its initial capacity over 15,000 cycles (269 days) at 1 A g–1. It also sustains stable cycling at 80 °C with 80% capacity retention after 500 cycles. This work establishes a generalizable design principle to suppress soluble intermediates, enabling durable and safe aqueous batteries for practical applications.