Modulation of the ligands and coordination environment of metal-organic frameworks (MOFs) has been an effective and relatively unexplored avenue for improving the anode performance of lithium-ion batteries (LIBs). In this study, three MOFs are synthesized, namely, M4 (o-TTFOB)(bpm)2 (H2 O)2 (where M is Mn, Zn, and Cd; o-H8 TTFOB is ortho-tetrathiafulvalene octabenzoate; and bpm is 2,2'-bipyrimidine), based on a new ligand o-H8 TTFOB with two adjacent carboxylates on one phenyl, which allows us to establish the impact of metal coordination on the performance of these MOFs as anode materials in LIBs. Mn-o-TTFOB and Zn-o-TTFOB, with two more uncoordinated oxygen atoms from o-TTFOB8- , show higher reversible specific capacities of 1249 mAh g-1 and 1288 mAh g-1 under 200 mA g-1 after full activation. In contrast, Cd-o-TTFOB shows a reversible capacity of 448 mAh g-1 under the same condition due to the lack of uncoordinated oxygen atoms. Crystal structure analysis, cyclic voltammetry measurements of the half-cell configurations, and density functional theory calculations have been performed to explain the lithium storage mechanism, diffusion kinetics, and structure-function relationship. This study demonstrates the advantages of MOFs with high designability in the fabrication of LIBs.
Keywords: Coordination Modulation; Lithium-Ion Batteries; Metal-Organic Frameworks; Tetrathiafulvalene Ligands.
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