Ionic-Liquid-Assisted synthesis of N, F, and P codoped FeNC/HSs on hollow carbon nanospheres for Li–S batteries

The severe shuttle effect and slow redox kinetics of polysulfides are major obstacles to the practical application of lithium sulfur batteries. In this study, we proposed a method for synthesizing hollow carbon nanospheres supported by iron single-atom catalysts using [HMIM] PF₆ ionic liquid (IL) as a promoter. Metal single atoms are embedded in carbon nanospheres to mitigateshuttle effects and enhance the bidirectional redox kinetics of sulfur. The incorporation of iron sites is beneficial for the reduction reaction of polysulfides, and the addition of ionic liquids not only increases the porosity of the catalyst but also enhances the loading of iron atoms. The sulfur cathode with metal single atom pairs exhibited an ultra-high capacity retention rate of 73.8 % after 150 cycles at 0.2C. Even under a high sulfur load of 6.58 mg cm⁻² and a current density of 0.2C, an ideal areal capacity of 4.64mAh cm⁻²can still be maintained. Impressively, the assembled button cell battery achieved a high discharge capacity of 1451mAh/g and maintained 867.9mAh/g after 150 cycles at 0.2C. This work provides new insights into designing loaded single-atom catalysts for application in lithium sulfur batteries.