Electric-Field-Modulated 2D C 5 N 3  for Polysulfide Confinement and Conversion in RT Na–S Batteries

Room-temperature Na-S (RT Na-S) batteries are capable of attaining a theoretical energy density as great as 1274 Wh/kg and functioning within a relatively mild temperature range of 25-60 ℃. Nevertheless, the inferior oxidation-reduction kinetics and polysulfide shuttle effect in Na-S batteries significantly impede their practical applications. Consequently, the development of high-performance anchoring materials capable of both immobilizing polysulfides and catalyzing their conversion is therefore critical. Herein, first-principles calculations were utilized to assess the potential of a novel 2D material, C5N3, serving as a multifunctional host for sodium polysulfides in Na-S batteries. Through comprehensive analyses, including structural optimization, charge transfer evaluation, and van der Waals corrections, it is revealed that C5N3 exhibits moderate adsorption energies toward high-order sodium polysulfides (Na2Sx, x=8,6,4), with the values falling in the range of 1.543 to 1.812  eV, substantially larger than those of conventional electrolytes. This robust binding effectively suppresses polysulfide dissolution. Furthermore, the energy barrier of the rate-limiting step in the sodium polysulfide reduction reaction (SRR) is determined to be 1.168  eV. Notably, applying an external electric field reduces this barrier to 0.533 eV, thereby substantially expediting the catalytic breakdown of low-order polysulfides (Na2Sx, x=2,1). These findings collectively demonstrate that electric-field-modulated C5N3 shows promise as an advanced anchoring material for high-performance RT Na-S batteries.