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 C 4 N 4 monolayer (TM@ C 4 N 4 , 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@C 4 N 4 , together with the adsorption of sulfur species and the energetics of sulfur reduction and Li 2 S decomposition. Among the candidates examined, Ti@C 4 N 4 exhibits moderate polysulfide binding combined with reduced free-energy barriers for both the rate-limiting sulfur reduction step and Li 2 S 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@C 4 N 4 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.