Interface-Confined Cationic Polarization Enables Rapid and Reversible Polyiodide Conversion for High-Rate Zinc-Iodine Batteries

Aqueous zinc-iodine (Zn-I₂) batteries are promising for safe and sustainable energy storage, but their application is limited by sluggish polyiodide redox kinetics and severe shuttle effect. Many cathode-regulation strategies improve iodine chemistry through physical confinement and polar adsorption. However, simultaneously suppressing polyiodide shuttling and enabling rapid iodine conversion remains challenging, particularly under high-rate where fast interfacial redox kinetics are required. Here, interface-confined cationic polarization is established by integrating π-delocalized guanidinium cations (Gdm⁺) into iodine cathodes, where cation-π interactions with Ketjen Black (KB) sp² carbon domains confine Gdm⁺ on the KB surface. The delocalized positive charge of interface-confined Gdm⁺ electrostatically enriches polyiodides within the cathode, while its delocalized π-electron system polarizes the electron cloud of iodine species and promotes interfacial charge transfer, enabling reversible polyiodide conversion without irreversible trapping. The optimized I₂ cathode delivers 100 mAh g^-1 at an ultrahigh-rate of 50 A g^-1 (∼237 C) and sustains 40 000 cycles with only 0.002% decay per cycle. A 1.0 Ah pouch cell retains 82.6% capacity after 1200 cycles. This work demonstrates interface-confined cationic polarization as an effective strategy for regulating polyiodide redox chemistry, offering a new route toward high-rate and long-life Zn-I₂ batteries.