A Bipolar Covalent Organic Framework Cathode Enabling a Six-Electron Redox Process for Wide-Temperature Sodium-Ion...

Sodium-ion batteries (SIBs) are promising for large-scale energy storage because of the natural abundance and low cost of sodium. However, the development of cathodes that combine high redox-site utilization with prolonged cycling across a wide temperature range remains challenging. Herein, we develop a heteroporous bipolar triphenylamine-benzoquinone covalent organic framework (TPBQ-COF)/carbon nanotube (CNT) composite cathode, TPBQ-COF@CNT, for wide-temperature SIBs. The framework incorporates carbonyl groups and triphenylamine units as complementary n-type and p-type redox centers, while the CNT network improves electrical connectivity throughout the electrode. The ordered porous skeleton further provides accessible pathways for electrolyte penetration and ion migration. TPBQ-COF@CNT exhibits an average capacity decay of only 0.0012% per cycle over 15000 cycles at 5 A g^-1. Even in the full-cell configuration, reversible capacities of 189 and 85 mAh g^-1 are preserved after 200 cycles at 50°C and 500 cycles at -20°C, respectively. We identify carbonyl reduction and triphenylamine oxidation as the complementary reactions underlying the overall six-electron redox process, with Na⁺ and PF₆ ^- participating at distinct states of charge. These findings clarify how molecularly encoded cation and anion storage can remain electrochemically accessible during prolonged cycling over a wide temperature range.