Electrostatic Confinement of Polyiodides by Cationic Biomass‐Binder Toward High‐Performance and Sustainable Aqueous Zinc–Iodine Batteries

Aqueous zinc–iodine batteries (AZIBs) hold great promise for sustainable energy storage, yet their practical viability is hindered by the uncontrolled shuttling of soluble polyiodide intermediates (e.g., I 3 − and I 5 − ), which causes severe cathode active‐material loss and zinc anode corrosion. Herein, hydroxypropyl trimethyl ammonium chloride chitosan (HTCC), a quaternized biomass derivative, is developed as a cationic binder that fundamentally suppresses the polyiodide shuttle effect. Unlike binders with weak hydrogen bonding that can only immobilize I 3 − , HTCC immobilizes both I 3 − and I 5 − through strong electrostatic interactions, complemented by hydrogen‐bonding interactions. The optimized aqueous AZIBs exhibit exceptional antiself‐discharge performance, as demonstrated by a stable open‐circuit voltage of 1.322 V and a Coulombic efficiency above 96.2% after a 72 h rest. Furthermore, they deliver a highly specific capacity of 216.4 mAh g −1 at 0.1 A g −1 and outstanding long‐term cycling stability, retaining 90.1% of their initial capacity after nearly 40,000 cycles at 5.0 A g −1 . Mechanistic studies reveal the functionality of HTCC in mitigating polyiodide shuttling and zinc anode corrosion, owing to substantially enhanced adsorption energies and accelerated iodine conversion kinetics. This work highlights the great potential of cationic biomass binders for high‐performance, sustainable aqueous iodine‐based energy storage.