Fully conjugated covalent organic frameworks with high conductivity as superior cathode materials for Li-ion batteries

Abstract

Covalent organic frameworks (COFs) exhibiting both high ion redox capability and high electronic conductivity show potential as cathode materials for Li-ion batteries (LIBs). Specifically, expanding the conjugation planes of the COF materials as well as incorporating redox-active groups can enhance their performance. Here, we developed a class of COF synthesis methods based on aldol condensation and realized the construction of fully conjugated conducting COF materials. In contrast to the majority of COFs synthesized through Schiff base reactions, COFs formed via aldol condensation feature interconnecting units joined by carbon–carbon double bonds. This structural characteristic results in an expanded conjugation plane, facilitating the synthesis of fully sp²-conjugated COFs, denoted as TBI-COF-O and TBI-COF-N. Notably, TBI-COF-O exhibits an electrical conductivity of 7.5 × 10⁻⁴ (±5 × 10⁻⁵) S cm⁻¹ and a maximum capacity of 320 mA h g⁻¹ at a discharge rate of 0.1C, which are among the highest values reported for COF-based LIBs. Moreover, TBI-COF-O based LIBs maintained 99.8% specific capacity even after 500 cycles, with 245 mA h g⁻¹ at a discharge rate of 1C. This study further expands the variety of conjugated COFs and provides a new perspective on their use in energy storage.