Asymmetrically Coordinated p-Block Aluminum Single-Atom Sites for Stable Na─S Batteries.

Main-group metal single-atom catalysts (SACs) are promising for sodium-sulfur (Na─S) batteries owing to their low toxicity and economic viability, yet their inherently poor catalytic activity limits the electrochemical performance. Moreover, the electronic interplay involving p-p orbital hybridization between p-block metal SACs and sodium polysulfides (Na2Sn) remains unclear. Herein, we design efficient aluminum (Al) SACs with a planar asymmetrical Al─O3N coordination anchored on carbon materials (Al─O3N─C) for Na─S batteries. The introduced N ligand breaks the coordination symmetry, creating localized charge at the Al sites, which enhances p-p orbital hybridization between Al-3p and S-3p of Na2Sn. This effectively suppresses Na2Sn shuttling and accelerates sulfur redox kinetics. The resulting Al─O3N─C/S exhibits a high capacity of 1196 mAh g-1 at 0.1 C after 100 cycles, and an ultralow capacity decay of 0.017% per cycle over 2500 cycles, outperforming most reported d-block SACs for Na─S batteries. This strategy of regulating p-orbital charge distribution provides a general guideline for the rational design of other efficient main-group metal SACs.