Spin Polarization of Axial Oxygen-Enhanced Ferromagnetic Single-Atom Catalysts for Boosting Redox Kinetics in Room-Temperature Sodium-Sulfur Batteries.

Abstract

Room-temperature sodium-sulfur (RT Na-S) batteries are promising candidates for large-scale energy storage owing to their high energy density and low cost, yet their practical deployment is hindered by sluggish sulfur redox kinetics and severe polysulfide shuttling. Here, guided by density functional theory (DFT) calculations, we develop a class of axially oxygen-coordinated ferromagnetic single-atom catalysts (SACs) with enhanced spin polarization to accelerate sulfur conversion. Among Fe-, Co-, and Ni-based SACs, Co-N₂O₃ is theoretically identified as the most effective configuration, featuring an optimized electronic structure with a minimal energy offset (0.26 eV) between the Co d-band and S p-band centers, which facilitates Na⁺ diffusion and lowers the activation barrier for polysulfide conversion. Experimentally, Co-N₂O₃ atoms anchored on hollow mesoporous carbon spheres (Co-N₂O₃@MCS) exhibit outstanding catalytic activity as the sulfur host, achieving an ultrahigh rate capability (330.5 mAh g^-1 at 10 A g^-1) and excellent durability over 600 cycles at 1 A g^-1. In situ characterizations reveal that the enhanced ferromagnetism effectively suppresses polysulfide shuttling, underscoring the crucial role of coordination-engineered spin polarization in boosting the redox kinetics of RT Na-S batteries.