Anti‐Swelling Microporous Membrane for High‐Capacity and Long‐Life Zn−I2 Batteries

Abstract Zinc–iodine (Zn−I 2 ) batteries are gaining popularity due to cost‐effectiveness and ease of manufacturing. However, challenges like polyiodide shuttle effect and Zn dendrite growth hinder their practical application. Here, we report a cation exchange membrane to simultaneously prevent the polyiodide shuttle effect and regulate Zn 2+ deposition. Comprised of rigid polymers, this membrane shows superior swelling resistance and ion selectivity compared to commercial Nafion. The resulting Zn−I 2 battery exhibits a high Coulombic efficiency of 99.4 % and low self‐discharge rate of 4.47 % after 48 h rest. By directing a uniform Zn 2+ flux, the membrane promotes a homogeneous electric field, resulting in a dendrite‐free Zn surface. Moreover, its microporous structure enables pre‐adsorption of additional active materials prior to battery assembly, boosting battery capacity to 287 mAh g −1 at 0.1 A g −1 . At 2 A g −1 , the battery exhibits a steady running for 10,000 cycles with capacity retention up to 96.1 %, demonstrating high durability of the membrane. The practicality of the membrane is validated via a high‐loading (35 mg cm −2 ) pouch cell with impressive cycling stability, paving a way for membrane design towards advanced Zn−I 2 batteries.