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

Thick cathodes are essential to maximize the practical energy density of zinc-iodine (Zn-I2) 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 ZnI2 electrolyte, which is paired with an ultrathick polyethersulfone-polyvinylpyrrolidone@activated carbon (PES-PVP@AC) host electrode to achieve practical high-areal-capacity Zn-I2 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 I3 - generation/dissolution. Mechanistically, the PVP-containing hydrogel interphase coordinates with electrodeposited I2 to form a stable PVP-I2 complex, thereby increasing the Gibbs free energy of I3 - formation and rendering the reaction thermodynamically less favorable, while concurrently reducing interfacial H2O availability to inhibit water-mediated I3 - dissolution/diffusion kinetics. Benefiting from the inherent anti-freezing capability of the ZnI2-based electrolyte, the Zn-I2 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.