MOF-derived Fe₇S₈–Fe₂O₃ heterojunction as separator coating for efficient catalysis of lithium polysulfide in Li-sulfur battery

In this paper, the Fe₇S₈–Fe₂O₃/NCF composite is vulcanized with Fe-BTT/NCF composite as the precursor and used as an overlay material of the separator for Li-sulfur batteries. Fe₂O₃ can rapidly capture lithium polysulfides, and Fe₇S₈ can effectively catalyze polysulfide lithium. Homogeneous Fe₇S₈–Fe₂O₃ heterostructures cooperate with each other to inhibit the shuttle effect of polysulfide lithium. In the condition of sulfur loading of 1.5 mg/cm², the Li-sulfur battery assembled with Fe₇S₈–Fe₂O₃/NCF as the overlay separator has an initial capacity of 1054.5 mAh/g at 1C, and the ultimate specific capacity is kept at 651.0 mAh/g after 300 long-term cycles. It can maintain 564.0 mAh/g even at a tremendous current density of 5 C. At the same time, even in the case of an excessive sulfur mass of 4.7 mg/cm², the reversible capacity density can still be maintained at 890.1 mAh/g for the following 50 cycles. An appropriate example of designing a functional separator from this work can inhibit shuttle effects efficiently.