Monolithic Host‐Separator Continuum Decouples Polyiodide Confinement and Reversibility in Lithium‐Iodine Batteries

ABSTRACT Lithium‐iodine batteries are hindered by the polyiodide shuttle effect, where conventional mitigation strategies face a fundamental trade‐off between active material confinement and redox reversibility. Herein, we report a monolithic host‐separator continuum that address this dilemma through spatially organized compartmentalization. The architecture integrates an oxidized sulfonated lignin‐functionalized graphene aerogel (GA@SOL) core with an encapsulating sulfonated cellulose polymer (SCP) shell via sequential infiltration and freeze‐drying, minimizing the interfacial discontinuities inherent in stacked configurations. Within the conductive scaffold, iodine adsorption spontaneously generates a mixed‐valence iodine species (I − /I 2 /I 3 − ) via balanced Lewis acid‐base interactions, establishing a redox‐active environment that preserves electronic connectivity without compromising reaction kinetics. Concurrently, the sulfonate‐rich SCP shell establishes an electrostatic Donnan barrier that selectively repels polyiodide anions while facilitating Li + transport. The resulting GA@SOL‐I 2 @SCP cathode delivers 252 mAh g −1 at 1 C with 89.6% retention over 1500 cycles, a Li + transference number of 0.63, and mitigated self‐discharge (76.1% capacity retention after 120 h). Operando spectroscopy and in situ impedance monitoring confirm sustained polyiodide accessibility and suppressed anode corrosion. This work demonstrates that structural continuity and mixed‐valence‐enabled charge transport can decouple confinement from kinetic penalty, offering a design framework for conversion‐type energy storage systems plagued by soluble intermediates.