Tri(Thiophene-Nitrile) Covalent Organic Frameworks With Low HOMO/LUMO Donor/Acceptor for High-Potential-Plateau Zinc Batteries.

Covalent organic frameworks (COFs) featuring desirable redox-active sites have become competitive cathode materials for aqueous zinc-organic batteries (ZOBs). However, multi-active COFs, albeit with high capacity, are often confined to their sloping and low redox potential (<0.8 V) caused by high molecular orbital energy levels (HOMO/LUMO) of active moieties. Here we report a capacity-voltage trade-off-breaking design of COFs by pairing low-HOMO trithiophene donor (-6.04 eV) with low-LUMO trinitrile acceptor (-3.82 eV) via robust olefin linkages (TN-COF), using high-LUMO triazine acceptor (-1.75 eV) as the counterpart (TA-COF). The tri(thiophene-nitrile) donor-acceptor enables low HOMO/LUMO energy levels (-3.98/-5.94 eV) for TN-COF cathode, thus unlocking a flat and high redox potential of 1.2 V compared to TA-COF (0.9 V). An 18-electron CF3SO3 -/NH4 + (de)coordination process is activated per hexagonal tri(thiophene-nitrile) unit in TN-COF cathode with ultralow activation energy (0.17 eV). This facilitates 98.2% utilization of C-S/C≡N active sites to liberate high capacity of 335 mAh g-1 (vs. 80.1%/268 mAh g-1 for TA-COF). The ideal combination of high voltage and capacity gives TN-COF cathode superior energy density (402 Wh kg-1) and ultralong life (70,000 cycles). This finding widens the design philosophy of high-voltage-capacity COFs via HOMO/LUMO energy engineering for advanced ZOBs.