Enhanced d–p orbital hybridization accelerates two-step quasi-solid-state sulfur conversion in sodium–sulfur batteries

Abstract

Room-temperature sodium–sulfur (RT Na–S) batteries are promising for large-scale energy storage owing to the high capacity of sulfur and the abundance of sodium, yet their application is hindered by sluggish redox kinetics and poor sulfur utilization. Here, we realize a fast and reversible two-step quasi-solid-state redox pathway from sulfur through Na₂S₄ to Na₂S without detectable accumulation of Na₂S₂ through d–p orbital hybridization-induced interfacial electronic structure modulation. Ultrafine Mo₂C nanoparticles uniformly embedded in cross-linked carbon spheres activate the inert d_xy and d_x²–y² orbitals, allowing strong d–p hybridization with sulfur p states, which effectively promotes the sulfur conversion kinetics. Spectroscopic analysis reveals reversible valence evolution of Mo accompanied by dynamic changes in its local electronic structure, confirming the electronic structure modulation that accelerates charge transfer and stabilizes intermediates. Multi-scale in situ visualization further captures Na-ion transport and structural evolution in real time, directly linking interfacial stability with ultrafast redox kinetics. The resulting S@Mo₂C/C cathode delivers a high reversible capacity of 854 mAh g⁻¹ after 200 cycles at 200 mA g⁻¹ and remarkable durability of 314 mAh g⁻¹ after 10 000 cycles at 20 A g⁻¹, establishing orbital hybridization-driven catalysis and in situ visualization as new paradigms for next-generation Na–S batteries.