High Sodium Ion Storage by Multifunctional Covalent Organic Frameworks for Sustainable Sodium Batteries

Rechargeable sodium batteries hold great promise for circumventing the increasing demand for lithium-ion batteries (LIBs) and the limited supply of lithium. However, efficient sodium ion storage remains a great impediment in this field. In this study, we report the designed synthesis of a multifunctional two-dimensional covalent organic framework featuring hexaazatrinaphthalene cores linked by imidazole moieties and demonstrate its effective performance in sodium ion storage. Benzimidazole-linked covalent organic framework (BCOF-1) was synthesized by a condensation reaction between hexaazatrinaphthalenehexamine (HATNHA) and terephthalaldehyde (TA) and exhibited a high theoretical specific capacity of 392 mA h g^-1. BCOF-1 crystallizes, forming eclipsed AA stacking and mesoporous hexagonal one-dimensional channels with high surface area (840 m² g^-1), facilitating fast ionic mobility and charge transfer and enabling high-rate capability at high current rates. BCOF-1 exhibits pseudocapacitive-like behavior with a high specific capacity of 387 mA h g^-1, an energy density of 302 W h kg^-1 at 0.1 C, and a power density of 682 W kg^-1 at 5 C. Our results demonstrate that redox-active COFs have the desired structural and electronic merits to advance the use of organic electrodes in sodium-ion storage toward sustainable and efficient batteries.