Electronic-structure modulation and interfacial chemistry of nickel doped Iron carbide for polysulfide conversion in lithium-sulfur batteries.

Abstract

Transition metal compound catalysts offer a promising route for advancing lithium-sulfur batteries. Nevertheless, achieving a balance of low toxicity, high abundance, cost-effectiveness, and high catalytic activity within a single material remains challenging. Herein, we report the preparation of iron carbide (Fe3C) using dicyandiamide and the regulation of its catalytic activity via nickel doping. X-ray photoelectron spectroscopy and density functional theory calculations reveal that nickel doping induces electron accumulation around Fe sites, triggering d-orbital reconstruction, enhanced metallicity, and an upward shift of the d-band center. Upon exposure to Li2S6, chemical adsorption and metal sulfide formation occur on both nickel doped Fe3C and Fe3C surface, accompanied by oxidation of Fe2+ to Fe3+ and electron transfer to Li2S6. Consequently, the system featuring the Ni-doped Fe3C separator coating delivers a specific capacity of 361 mAh g-1 after 800 cycles at 1C. This study provides a comprehensive understanding of both the electronic-structure modulation and the catalytic mechanism of nickel doped Fe3C, thereby offering valuable insights for the rational design of advanced polysulfide-conversion catalysts.

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