A Gradient Functionalized Separator for Unlocking Latent Cathode Host Sites and Enhancing Zinc Anode DOD in Ultrahigh‐Areal‐Capacity Static Zn‐I ₂ Batteries

The development of static aqueous zinc-iodine batteries (SAZIBs) is hindered by the polyiodide shuttling effect and poor zinc anode reversibility, issues that are exacerbated under high iodine loadings essential for high energy density. Herein, a gradient-structured separator (G-CCN@GF) is designed by modifying a glass fiber separator with 2D cyano-functionalized graphitic carbon nitride (CCN). Experimental and simulation results demonstrate that the dense CCN layer facing the cathode effectively anchors polyiodides and unlocks latent electrochemical active sites, thereby facilitating conversion kinetics under high iodine loading and I/C ratio. Meanwhile, the thin and uniform CCN layer on the anode side promotes a uniform Zn²⁺ flux, significantly improving the zinc reversibility under high depth of discharge (DOD). Consequently, the Zn/G-CCN@GF/I₂ battery with a conventional activated carbon (AC) host achieves exceptional performance under high I/C ratio (2:1) conditions, including a high areal capacity of 27.9 mAh cm^-2 at 150.1 mg cm^-2 iodine loading and remarkable stability over 7200 cycles at 40 mg cm^-2. A 60 cm² pouch cell further validates practicality, delivering 5.8 mAh cm^-2 and retaining 85.87% capacity after 1100 cycles. This work provides a feasible separator-engineering strategy for high-energy-density SAZIBs.