Ionic‐Liquid‐Assisted Synthesis of N, F, and B Co‐Doped CoFe2O4−x on Multiwalled Carbon Nanotubes with Enriched Oxygen Vacancies for Li–S Batteries

Abstract The “shuttle effect,” sluggish redox kinetics, and short life cycle have seriously restricted the practical application of Li–S batteries. Herein, N, F, and B co‐doped NFBCoFe 2 O 4− x on multiwalled carbon nanotubes’ (MWCNTs) (NFBCoFe 2 O 4− x @MWCNTs) composite material with enriched oxygen vacancies (OVs) introduced by ionic liquids (ILs) does not only exhibit enhanced polysulfides trapping ability but also effectively accelerate the redox kinetics of polysulfides. A commercial Celgard polypropylene (PP) 2400 separator with NFBCoFe 2 O 4− x @MWCNTs coating layer is fabricated as a multifunctional barrier for Li–S batteries. As a result, the battery based on the NFBCoFe 2 O 4− x @MWCNTs separator demonstrates a stable electrochemical performance. Even under a high S loading of 8.0 mg cm −2 , a desirable areal capacity of 4.62 mAh cm −2 can still be maintained over 200 cycles at a current density of 0.2 C. The prospective strategy of engineering OVs introduced by ILs provides novel insights into the development of Li–S batteries.