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.