Theoretical Identification on Typical Fe3X (X=B, C, N) Compounds for Polysulfide Conversion in Lithium-Sulfur Batteries

Li−S batteries (LSBs) are considered as the attractive candidates for next-generation high-energy system due to their high energy and low cost. However, their practical application is hindered by several stubborn issues, including the poor electric conductivity of sulfur cathodes, the shuttle of lithium polysulfides (LiPSs) and the slow dynamics during charge/discharge cycles. Transitional iron (Fe)-based compounds are regarded as effectively electrocatalysts for polysulfide conversion by accelerating the reaction kinetics and enhancing the electric conductivity and electron/charge transfer. In this study, we investigate the typical transition Fe-based compounds (Fe₃X, X=B, C, N), known for their high catalytic ability, analyze their roles as sulfur host for LSBs using density functional theory (DFT). Our finding reveals that Fe₃C and Fe₃B surfaces exhibit more Fe-S bonds compared to Fe₃N surface, which explains the different electrochemical behaviors observed during battery testing with sulfur cathodes. Additionally, Fe₃N demonstrates greater structural stability and effective polysulfide adsorption according to DFT calculations, outperforming the other two compounds in these aspects. We believe that this theoretical investigation would guide the identification of highly efficient hosts for sulfur cathodes and open new avenues for sulfur host selection in LSBs.