Synergistic Physicochemical Confinement in a Dual-Functional Separator for Long-Life Zn–I ₂ Batteries

Aqueous zinc–iodine (Zn–I2) batteries have attracted considerable interest as promising energy storage systems, owing to their high safety, low cost, and environmental friendliness. However, the practical development of aqueous zinc–iodine batteries is impeded by polyiodide shuttle and severe self-discharge. Herein, a dual-functional separator is prepared by coating biomass-derived nitrogen-doped carbon nanosheets (NCNS-5) onto glass fiber (NCNS-5/GF). This rational design leverages a synergistic “blocking-adsorption-reconversion” mechanism, integrating a dense nanosheet barrier with chemical adsorption at N-dopants. NCNS-5 layer functions as a physical barrier that restricts polyiodide migration and the nitrogen-rich sites strongly adsorb soluble I3–/I5– species and facilitate their reconversion into active iodine species, suppressing shuttle and alleviating self-discharge at the source. The resulting battery exhibits 85.1% capacity retention after long-term cycles, 87.6% Coulombic efficiency after 120 h rest, while maintaining high capacity retention at 60 °C or under high iodine loading. This work presents an effective interfacial-engineering strategy of integrating a physical barrier with chemical mediation in separator design for effectively managing soluble intermediates in conversion-type battery systems.