Optimizing s-p Orbital Overlap Between Sodium Polysulfides and Single-Atom Indium Catalyst for Efficient Sulfur Redox Reaction

P-block metal carbon-supported single-atom catalysts (C-SACs) have emerged as a promising candidate for high-performance room-temperature sodium-sulfur (RT Na-S) batteries, due to their high atom utilization and unique electronic structure. However, the ambiguous electronic-level understanding of Na-dominant s-p hybridization between sodium polysulfides (NaPSs) and p-block C-SACs limits the precise control of coordination environment tuning and electro-catalytic activity manipulation. Here, s-p orbital overlap degree (OOD) between the s orbitals of Na in NaPSs and the p orbitals of p-block C-SACs is proposed as a descriptor for sulfur reduction reaction (SRR) and sulfur oxidation reaction (SOR). Compared to NG and NG-supported InN4 (NG-InN4) SACs, the nitrogen-doped graphene-supported InN5 (NG-InN5) SACs show the largest s-p OOD, demonstrating the weakest shuttle effect and the lowest reaction energy barriers in both SRR and SOR. Accordingly, the designed catalysts allow the Na-S pouch batteries to retain a high capacity of 490.7 mAh g-1 at 2 A g-1 with a Coulombic efficiency of 96 % at a low electrolyte/sulfur (E/S) ratio of 4.5 mu l mg-1. This work offers an s-p orbital overlap descriptor describing the interaction between NaPSs and p-orbital-dominated catalysts for high-performance RT Na-S batteries.