Drastically enhancing the cycle stability of copper-dicarboxylate as an anode material for lithium-ion batteries by rational fluorination

Metal-organic frameworks (MOFs) are extensively investigated in lithium-ion batteries because of their large specific surface area, adjustable chemical properties, porous structure, and rich reaction sites. However, the severe capacity attenuation of MOF electrodes has been one of the hardest obstacles hindering the further application of MOFs, due to the embedding and de-embedding of lithium ions during the cycles leading to the structural disintegration and volume fluctuation. Inspired by the wide application of fluorinated additives in commercial electrolytes, a typical carboxylate MOF, copper 1,4-benzenedicarboxylate is fluorinated molecularly to improve its cycle stability. Without enough fluorine source for a robust SEI film, the performance of fluorine -free copper 1,4-benzenedicarboxylate degrades rapidly to 99.5 mAh/g in the initial 21 cycles at a current density of 100 mA g-1, while its fluorinated counterpart, copper tetrafluoroterephthalate, delivers drastically enhanced cycle stability and maintains a reversible specific capacity of 575.5 mAh/g after 500 cycles, due to the SEI-promoting effect of fluorine in the framework. The present fluorination strategy is proved effective and can be extended in much wider applications of MOF materials.