Electrospun carbon nanofibers loaded with sulfur vacancy CoS2 as separator coating to accelerate sulfur conversion in Lithium-Sulfur batteries

Abstract

Lithium–sulfur batteries (LSBs) have been sought after by researchers owing to their high energy density; however, the inevitable capacity decay and slow reaction kinetics have hindered their advancement. Here, we prepare a Prussian blue analog, Co3[Co(CN)6]2 and synthesize carbon nanofibers/S vacancy CoS2−x (CNFs/CoS2−x) as electrocatalysts for separator coating via electrospinning, carbonization, sulfurization, and hydrogen reduction. CNFs/CoS2−x exhibits excellent electrocatalytic activity, wherein S vacancies induce the partial oxidation of Co2+ to Co3+ in CoS2 and CNFs provide long-range electron transport pathways. Various electrochemical tests, such as Tafel, ion diffusion coefficient, Li2S precipitation, and Li2S6 symmetric cells, further confirm the enhanced electrocatalytic activity. The LSBs with CNFs/CoS2−x modified separator delivers an initial discharge capacity of 1056.7 mAh g−1 at 0.2C, maintaining 840.8 mAh g−1 after 100 cycles at 0.2C. When S loading is increased to 4.42 mg cm−2, the battery retains a discharge capacity of 687.9 mAh g−1 (3.04 mAh cm−2) after 70 cycles at 0.1C. Our work can provide a reference for synthesizing anion-vacancy materials and designing anion-vacancy electrocatalytic composites for LSBs.