First-principles screening of TM@C4N4 single-atom catalysts for lithium–sulfur batteries

Abstract

Single-atom catalysts (SACs) can regulate both polysulfide adsorption and sulfur-conversion kinetics in lithium–sulfur batteries, yet their structure–function relationships remain insufficiently compared at the atomic level. Here, a first-principles screening of 3d transition-metal single atoms embedded in a C₄N₄ monolayer (TM@ C₄N₄, TM = Sc–Zn) is performed to evaluate their roles in lithium polysulfide binding and sulfur conversion reactions. The calculations assess the stability and electronic properties of TM@C₄N₄, together with the adsorption of sulfur species and the energetics of sulfur reduction and Li₂S decomposition. Among the candidates examined, Ti@C₄N₄ exhibits moderate polysulfide binding combined with reduced free-energy barriers for both the rate-limiting sulfur reduction step and Li₂S decomposition, indicating bifunctional catalytic behavior. Electronic structure analysis shows that TM–S interactions arising from d–p hybridization play a key role in regulating sulfur intermediates. These results identify Ti@C₄N₄ as an effective single-atom catalytic motif for regulating sulfur redox processes and provide a comparative theoretical basis for screening SACs in lithium–sulfur batteries.