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

Aqueous zinc–iodine (Zn–I 2 ) 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) sp 2 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 I 2 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–I 2 batteries.