Enhanced\nCatalytic Conversion of Polysulfides Using\nBimetallic Co₇Fe₃ for High-Performance Lithium–Sulfur\nBatteries

Abstract

Practical\napplications of lithium–sulfur (Li–S) batteries\nhave been severely hindered by their low capacity, poor rate performance,\nand fast capacity degradation, which mainly originate from the notorious\npolysulfide shuttle effect. Herein, with density functional theory\ncalculations, we show that the alloying of Fe into carbon-coated Co\nnot only provides moderate binding interactions with the polysulfides\nto hinder their diffusion but also serves as an active catalyst in\nthe spontaneous and successive lithiation of S₈ to Li₂S. Based on the fast migration of Li ions and the spontaneous\nlithiation of Li₂S₂ on the carbon-coated Fe–Co\nalloy, the entrapping–conversion processes of polysulfides\nare both thermodynamically and kinetically promoted in redox cycling.\nExperimentally, rationally designed Co₇Fe₃@porous\ngraphite carbon–carbon nanotubes (Co₇Fe₃@PGC–CNT) electrocatalysts are introduced into Li–S\nbatteries through separator functionalization. Consistent with theoretical\npredictions, Li–S batteries with Co₇Fe₃@PGC–CNT modified separators exhibit a dramatically enhanced\nrate capacity (788 and 631 mAh g^–1 at 10 and 15\nC rates, respectively) and cycling stability (a slow capacity decay\nof 0.05% per cycle over 1000 cycles at 2.0 C), which are superior\nto those of most reported Li–S batteries coupled with state-of-the-art\nseparators. Furthermore, it is shown that the excellent hindering\nof the shuttle effects enables a high areal capacity of 4.7 mAh cm^–2 after 90 cycles at a high sulfur loading of 6.7 mg\ncm^–2. Our work provides a feasible method for developing\nhigh-energy and long-life Li–S batteries, which might drive\nthe commercialization of Li–S batteries.