Anti‐swelling Microporous Membrane for High‐capacity and Long‐life Zn–I2 Batteries

Zinc–iodine (Zn–I2) 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 Zn2+ deposition. Comprised of rigid polymers, this membrane shows superior swelling resistance and ion selectivity compared to commercial Nafion. The resulting Zn–I2 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 Zn2+ 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 mA h 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–I2 batteries.