A Metal–Organic Framework with Mixed Electron Donor TTF and Electron Acceptor NDI Ligands for High-Performance Hybrid Lithium-Ion Capacitors

Integrating mixed electron donor (D) and electron acceptor (A) ligands into metal–organic frameworks (MOFs) is an effective yet relatively unexplored approach for improving the anode performance of hybrid lithium-ion capacitors (HLICs). In this study, using an electron donor 2,6-bis(4’-pyridyl)tetrathiafulvalene and an electron acceptor N,N’-bis(5-isophthalic acid) naphthalene diimide as ligands, a new Zn-TTF/NDI MOF (1) is constructed as a pseudocapacitive anode of HLICs. Crystallographic characterization revealed that MOF 1 adopts a two-dimensional (2D) coordination network. A three-dimensional (3D) supramolecular framework is formed through face-to-face TTF packing of the adjacent 2D layers. As a result, the 2D MOF 1 with both electron-donating TTF and electron-accepting NDI units not only has rich active sites and excellent charge conductivity for reversible Li⁺ storage but also, owing to its 3D-supramolecular architecture, provides open channels for ion transport, leading to the merits of enhanced capacity utilization and high power density. The MOF 1||activated carbon HLIC exhibited maximum specific energy (133.7 Wh kg^–1) and high specific power (12.9 kW kg^–1) with stable cycling performance. The remarkable performance originates from the synergistic effect of the mixed electron-donating TTF and electron-withdrawing NDI ligands, interligand charge transfer, and structural stability.