Confinement of Polyiodides by Dual‐Functional Tetrazine Cathodes in Zn–I 2 Batteries

Abstract Zinc–iodine batteries offer great potential for energy storage due to their long‐term cycle stability, flat voltage plateau, inherent safety, and cost‐effectiveness. However, their performance is limited by capacity fading and low Coulombic efficiency (CE) caused by the I 3 − shuttle effect. In this work, we propose a molecularly engineered tetrazine derivative, 3,6‐bis(2‐morpholinoethyl)‐1,2,4,5‐tetrazine (BMT) as a multifunctional cathode to address these challenges. BMT exhibits a reversible two‐electron redox process, boosting charge storage capacity, and forms stable precipitation with I 3 − ions at a 1:2 stoichiometric ratio, effectively inhibiting the shuttle of polyiodide by covalent‐electrostatic synergistic confinement. As expected, the BMT‐based cathode exhibits a CE of 99.6% at 2 A g −1 , a high specific discharge capacity of 207 mAh g −1 at 0.5 A g −1 as well as ∼100% capacity retention over 33 000 cycles at 2 A g −1 , achieving a record iodine anchoring efficiency. Furthermore, the Zn–I 2 pouch cell with high iodine mass loading (15.5 mg cm −2 ) delivers a practical cathode energy density of 145.2 Wh kg −1 and maintains 76.2% of its capacity after 800 cycles at 2 A g −1 . This work presents a mechanism‐driven cathode design strategy that integrates redox activity and polyiodide confinement, providing a blueprint for the development of stable iodine‐based batteries.