Ionic-Liquid-Assisted Synthesis of Fe/Co Diatomic Catalysts on Hollow Carbon Nanospheres for Lithium–Sulfur Batteries

Abstract

The practical deployment of lithium-sulfur (Li-S) batteries remains hindered by polysulfide shuttling and sluggish redox kinetics. Herein, we demonstrate an ionic liquid (BMIM-BF4)-assisted strategy to synthesize hollow carbon nanospheres anchored with Fe-Co diatomic catalysts (NFB-FeCoNC/HSs). 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.

Keywords: ionic liquid, dopamine, hollow structures, diatomic catalyst, lithium-sulfur battery