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 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-I₂ batteries.