Strengthening d-p Orbital-Hybridization via Coordination Number Regulation of Manganese Single-Atom Catalysts Toward Fast Kinetic and Long-Life Sodium-Sulfur Batteries

The practical application of room-temperature sodium-sulfur (RT Na-S) batteries is blocked by the notorious shuttle effect of sodium polysulfides (NaPSs) and sluggish refox reaction kinetics. Single-atom catalysts (SACs) have been widely studied for boosting the energy storage performance of RT Na-S batteries. Nevertheless, the catalytic centers of SACs reported so far have focused mainly on symmetrical metal-N-4 structures, which offer weak bonding affinity toward polar NaPSs, leading to detrimental shuttle effect and sluggish sulfur conversion kinetics. Herein, a novel asymmetrical Mn-N-2 structure is implanted into nitrogen-doped carbon nanofibers (Mn-N-2/CNs) through thermal NH3 etching of a symmetrical Mn-N2O2 structure. The Mn-N-2 structure promotes the bonding affinity and catalytic conversion of NaPSs due to the strengthened d-p orbital-hybridization between the d orbital of Mn in the Mn-N-2 structure and the p orbital of S in NaPSs. Consequently, Mn-N-2/CNs@S achieves a high capacity of 458 mAh g(-1) at 3.0 C with a capacity decay of 0.23% over 2300 cycles. This work offers a promising pathway for regulating the coordination number of SACs with strengthened d-p orbital-hybridization for high-performance RT Na-S batteries.