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-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.