Three-Dimensional Metal-Organic Frameworks with Selectively Activated Aromatic Rings for High-Capacity and High-Rate...

Metal-organic frameworks (MOFs) are considered promising candidates for anode materials in Li-ion batteries (LIBs) owing to their designable structure, abundant active sites, and well-organized porosity. However, the structural factors governing active site utilization and Li-ion storage kinetics remain inadequately understood. In particular, the Li-ion storage behaviors of aromatic rings with high LUMO energy levels and situated in varying chemical environments remain a highly debated issue. Herein, a new cobalt-based MOF (Co-NTTA, NTTA ligand: 5,5',5''-((4,4',4''-nitrilotris (benzoyl)) tris-(azanediyl)) triisophthalic acid), featuring aromatic rings situated in diverse local environments, is deliberately designed and synthesized. Experimental characterizations and first-principles calculations have verified the occurrence of a reversible electrochemical reaction involving a total of 51 electrons among the NTTA ligands, cobalt cations, and Li⁺ ions. Unlike the traditional concept of superlithiation, the three inner aromatic rings are selectively activated by π-aromatic conjugation networks and π $$ π stacking, contributing to a reversible 6-electron pseudocapacitive Li⁺ intercalation reaction. Conversely, the three outer aromatic rings remain inert toward Li⁺ ions. Impressively, the Co-NTTA MOF anode, with selectively activated aromatic rings, delivers a reversible capacity of up to 956 mAh g^-1 at 200 mA g^-1 and demonstrates exceptional high-rate durability, further supporting a 4.3 V lithium-ion hybrid electrochemical capacitor with high energy/power density.