Redistribution of d-orbital in Fe-N4 Active Sites Optimizing Redox Kinetics of the Sulfur Cathode

Redistributing the d-orbital of single Fe atom catalysts (SFeACs) has been challenging to optimize redox kinetics of lithium sulfur batteries (LSBs). Here, the Fe-N4/S2C with mounting energy level of dz2 and partial occupation of dxz is controllably fabricated. The increased dz2, originating from thiophene sulfur, upshifts d band center compared to the Fe-N4/C with planar symmetric structure. That promotes electron transfer between Fe-N4 and sulfur, enhancing conversion of polysulfides and solid products. The lower fill of dxz develops hybridization between Fe and S atoms via the form of bonding and antibonding, with alleviating the loss of sulfur. Thus, the sulfur cathode with Fe-N4/S2C delivers a high capacity of 749 mAh g-1 at 2.0 C, accompanied by excellent stability with a lower capacity decay of 0.07% per cycle. This work has developed a novel coordination configuration towards SFeACs and uncovered the intrinsic mechanism of facilitated redox kinetics with SFeACs for LSBs.