Phase Inversion‐Engineered Ultrathick Electrodes With Intrinsic Hydrogel Interphase for High Areal Capacity Aqueous Zinc–Iodine Batteries at Room/Subzero Temperatures

ABSTRACT Thick cathodes are essential to maximize the practical energy density of zinc–iodine (Zn–I 2 ) batteries, yet their implementation is severely constrained by processing‐induced elemental iodine sublimation loss and aggravated polyiodide shuttling during cycling. Herein, unstable active iodine species are decoupled from the conventional cathode and incorporated into a ZnI 2 electrolyte, which is paired with an ultrathick polyethersulfone–polyvinylpyrrolidone@activated carbon (PES–PVP@AC) host electrode to achieve practical high‐areal‐capacity Zn–I 2 batteries. This scalable phase‐inversion electrode‐fabrication strategy using a PES–PVP binder blend not only creates highly interconnected electrolyte‐infiltration microchannels but also generates an intrinsic PVP‐containing hydrogel interphase, thereby simultaneously facilitating rapid ion transport and regulating I 3 − generation/dissolution. Mechanistically, the PVP‐containing hydrogel interphase coordinates with electrodeposited I 2 to form a stable PVP–I 2 complex, thereby increasing the Gibbs free energy of I 3 − formation and rendering the reaction thermodynamically less favorable, while concurrently reducing interfacial H 2 O availability to inhibit water‐mediated I 3 − dissolution/diffusion kinetics. Benefiting from the inherent anti‐freezing capability of the ZnI 2 ‐based electrolyte, the Zn–I 2 battery achieves an ultrahigh areal capacity of 7.5 mAh cm −2 over 3000 cycles at −20°C. Importantly, this strategy enables the direct assembly of Ah‐level single‐layer pouch cells (∼1.5 Ah) without complex multilayer stacking, offering a practical pathway toward scalable grid energy storage.