Ionic-liquid-assisted synthesis of Fe/Co diatomic catalysts on hollow carbon nanospheres for lithium–sulfur batteries

Background Lithium-sulfur (Li-S) batteries are promising next-generation energy storage systems due to their high theoretical energy density. However, their practical deployment is hindered by the polysulfide shuttling effect and sluggish redox kinetics. Methods We demonstrate an ionic liquid (BMIM-BF4)-assisted strategy to synthesize hollow carbon nanospheres anchored with Fe-Co diatomic catalysts (NFB-FeCoNC/HSs). Significant findings Systematic characterization reveals that the dual-metal sites synergistically enhance bidirectional sulfur redox reactions, while the ionic liquid-derived heteroatoms (N, F, B) optimize catalyst porosity and metal loading density. Electrochemical evaluations show the sulfur cathode achieves remarkable cycling stability with 59.28% capacity retention after 200 cycles at 0.2 C. Notably, under high sulfur loading (8.89 mg cm⁻²) and lean electrolyte conditions (E/ S = 5.3 μL mg⁻¹), the battery delivers an exceptional areal capacity of 8.87 mAh cm⁻². Long-term cycling at 1 C exhibits a high initial discharge capacity of 1001.12 mAh g⁻¹ with 415.4 mAh g⁻¹ retained after 1000 cycles, corresponding to a minimal decay rate of 0.58% per cycle. This work establishes a paradigm for designing hierarchical diatomic catalysts to address critical challenges in Li-S systems.