Theoretical Design and Study of a Single-Atom Catalyst in Lithium–Sulfur Batteries: Edge-Type FeN<sub>4</sub> Active Site Electron Density Redistribution Driven by Heteroatoms
Chou Wu, Haiyan Zhu, Shaobo Jia, Jiezhen Xia, Wanlin Xu, Ping Liu, Wenli Zou, Bingbing Suo, Ghulam Meeladi, Yawei Li
Abstract
Lithium–sulfur (Li–S) batteries are considered to be the most promising next-generation high energy density storage systems. However, they still face challenges, such as the shuttle effect of lithium polysulfides (LiPSs) and slow sulfur oxidation–reduction kinetics. In this work, heteroatom (P and S)-doped edge-type Fe single-atom catalytic materials (FeN 4 S 2 /P 2 -DG) for sulfur reduction reactions (SRRs) and sulfur oxidation reactions in Li–S batteries are investigated using density functional theory calculations. Theoretical analysis suggests that compared to planar Fe–N 4 fragments, the charge density accumulation around edge-type Fe–N 4 fragments in S- or P-doped structures is higher. Furthermore, the doping of P or S reduces the electron filling state of Fe_3d orbitals, leading to a decrease in electron occupancy in the antibonding orbitals, which is beneficial for the formation of d–p orbital hybridization, strengthening the anchoring strength of FeN 4 P 2 /S 2 -DG for S 8 /LiPSs. Specifically, FeN 4 P 1,2 -DG showed the lowest free energy barriers (0.57 eV) for SRRs and reduced the dissociation energy barrier of Li 2 S from 1.85 eV (for planar FeN 4 -G) to 0.96 eV during the charging process, demonstrating excellent catalytic ability. Additionally, this theoretical study provides further insights into the application of graphene-supported single-atom catalyst materials as anchoring materials for Li–S batteries.