Taming the polyiodide shuttle <i>via</i> curvature engineering of cationic microenvironments for ultradurable Zn-I ₂ batteries

Aqueous zinc-iodine batteries (AZIBs) are promising candidates for grid-scale energy storage owing to their high safety and low cost. However, their practical application is hindered by severe polyiodide species shuttle. Herein, we constructed well-defined cationic microenvironments by assembling poly(diallyldimethylammonium chloride) (PDDA) onto multi-walled carbon nanotubes (PDDA@MWCNT) and flat graphite sheets (PDDA@GS). This design enables strong electrostatic anchoring of polyiodide species and allows systematic differentiation of curvature-dependent immobilization behaviors. The optimal PDDA@MWCNT cathode exhibits a high Coulombic efficiency of 98.3% at 0.1 A·g⁻¹, along with exceptional durability of 82,000 cycles at 3.0 A·g⁻¹ and 3,569 cycles at 0.1 A·g⁻¹ (nearly one year), far surpassing its planar PDDA@GS counterpart. Combined experimental characterizations and density functional theory (DFT) calculations reveal that the curvature-guided PDDA configuration markedly enhances iodine adsorption and accelerates interfacial charge transfer, thereby suppressing polyiodide shuttling and self-discharge. This work demonstrates molecular curvature engineering as a powerful and generalizable strategy for governing iodine chemistry, offering new design principles for high-performance AZIBs.