Towards Stable Metal–I 2 Battery: Design of Iodine–Containing Functional Groups for Enhanced Halogen Bond

Abstract The redox chemistries of iodine have attracted tremendous attention for charge storage owing to their high theoretical specific capacity and natural abundance. However, the practical capacity and cycle life are greatly limited by the active mass loss originating from the dissolved iodine species in either non‐aqueous or aqueous batteries. Despite intensive progress in physical and physicochemical confinements of iodine species (I 2 /I 3 − /I − ), less attention has been paid to confining iodine species beyond the host–iodine interface, inhibiting further development of iodine cathodes with high I 2 contents. Here a halogen bond (XB)– enhanced design concept is proposed between I 2 molecules to achieve stable cycling performances, as exemplified by the Na–I 2 battery. The enhanced XB is derived from the incorporation of –B(OH)I 3 groups in highly integrated porous carbon/I 2 cathode (HOCF–BI n ), which can generate extended interactions between –B(OH)I 3 and following I 2 molecules. Due to the strong intermolecular force between I 2 molecules, the HOCF–BI n cathodes exhibit substantially strengthened I 2 /I 3 − /I − confinement, enabling outstanding cycling stability at I 2 loading ranging from 1.8 to 6.2 mg cm −2 . This findings demonstrate a functional group to manipulate XB chemistry within I 2 molecules and polyiodides for stable and low‐cost metal–iodine batteries.