Tetrathiafulvalene-based covalent organic frameworks as high-voltage organic cathodes for lithium batteries

Abstract

Redox-active covalent organic frameworks (COFs) are promising electrode materials for metal-ion batteries owing to their tunable electrochemical properties, adjustable structure, and resource availability. Herein, we report a series of two-dimensional tetrathiafulvalene (TTF)-based COFs incorporating different organic linkers between the electroactive moieties. These COFs were investigated as p-type organic cathode materials for lithium-organic batteries. The electrical conductivity of both neutral and doped TTF-COFs was measured using a van der Pauw setup, and their electronic structures were investigated through quantum-chemical calculations. Binder-free buckypaper TTF-based electrodes were prepared and systematically tested as organic cathodes in lithium half-cells. The results revealed high average discharge potentials (∼3.6 V vs. Li/Li⁺) and consistent cycling stability (80% capacity retention after 400 cycles at 2C) for the three TTF-COF electrodes. In addition, the specific capacity, rate capability, and kinetics varied depending on the structure of the framework. Our results highlight the potential of TTF-COFs as high-voltage organic cathodes for metal-ion batteries and emphasize the importance of molecular design in optimizing their electrochemical performance.