Tetrathiafulvalene-Based\nMetal–Organic Framework\nas a High-Performance Anode for Lithium-Ion Batteries

Abstract

Metal–organic\nframeworks (MOFs) have aroused great interest\nas lithium-ion battery (LIB) electrode materials. In this work, we\nfirst report that a pristine three-dimensional tetrathiafulvalene\nderivatives (TTFs)-based zinc MOF, formulated [Zn₂(py-TTF-py)₂(BDC)₂]·2DMF·H₂O (<b>1</b>) (py-TTF-py = 2,6-bis­(4′-pyridyl)­tetrathiafulvalene and H₂BDC = terephthalic acid), can work as a high-performance electrode\nmaterial for rechargeable LIBs. The TTFs-Zn-MOF <b>1</b> electrode\ndisplayed a high discharge specific capacity of 1117.4 mA h g^–1 at a current density of 200 mA g^–1 after 150 cycles along with good reversibility. After undergoing\nelevated discharging/charging rates, the electrode showed superior\nlithium storage performance in the extreme case of 20 A g^–1 and could finally recover the capability when the current rate was\nback to 200 mA g^–1. Particularly, specific capacities\nof 884.2, 513.8, and 327.8 mA h g^–1 were reached\nat high current densities of 5, 10, and 20 A g^–1 after 180, 175, and 300 cycles along with good reversibility, respectively.\nSuch an excellent performance is first reported for the LIB anode\nmaterials. TTFs-Zn-MOF <b>2</b>, namely, [Zn₂(py-TTF-py)\n(BDC)₂]·DMF·2H₂O (<b>2</b>),\nwas prepared as a contrast to explore the relationship between the\nstructures of the electrode materials and the electrochemical properties.\nBased on the structural analysis of <b>1</b> and <b>2</b> and ex situ X-ray photoelectron spectroscopy, the TTF moiety and\nthe twofold TTF pillar play a key role in the excellent electrochemical\nperformance. The full cell of MOF <b>1</b> with NMC 622 delivered\nthe capacity of 131.9 mA h g^–1 at 100 mA g^–1 with the Coulombic efficiency of 99.45% after 70 cycles and exhibited\nthe tolerance to high-current operation.