Dual Active Sites of Oversaturated Fe-N₅ and Fe₂O₃ Nanoparticles for Accelerating Redox Kinetics of Polysulfides

The shuttling effect and sluggish reaction kinetics are the main bottlenecks for the commercial viability of lithium-sulfur (Li-S) batteries. Metal-nitrogen-carbon single atom catalysts have attracted much attention to overcoming these obstacles due to their novel electrocatalytic activity. Herein, a novel cooperative catalytic interface with dual active sites (oversaturated Fe-N-5 and polar Fe2O3 nanocrystals) are co-embedded in nitrogen-doped hollow carbon spheres (Fe2O3/Fe-SA@NC) is designed by fine atomic regulation mechanism. Both experimental verifications and theoretical calculations disclose that the dual active sites (Fe-N-5 and Fe2O3) in this catalyst (Fe2O3/Fe-SA@NC) tend to form "Fe-S" and "Li-N/O" bond, synchronically enhancing chemical adsorption and interface conversion ability of polysulfides, respectively. Specially, the Fe-N-5 coordination with 3D configuration and sulfiphilic superfine Fe2O3 nanocrystals exhibit the strong adsorption ability to facilitate the subsequent conversion reaction at dual-sites. Meanwhile, the nitrogen-doped hollow carbon spheres can promote Li+/electron transfer and physically suppress polysulfides shuttling. Consequently, Li-S battery with the Fe2O3/Fe-SA@NC-modified separator exhibits a high capacity retention of 78% after 800 cycles at 1 C (pure S cathode, S content: 70 wt.%). Furthermore, the pouch cell with this separator shows good performance at 0.1 C for practical application (S loading: 4 mg cm(-2)).