Selective elevation of d-orbital energies by Mn/Fe dual-atom catalyst accelerating sulfur redox kinetics in lithium-sulfur batteries

Practical application of lithium-sulfur (Li-S) batteries is hindered by the migration of lithium polysulfides (LiPSs), sluggish conversion kinetics, and anode instability. In these regards, with a novel strategy focusing on the selective elevation of d-orbitals, Mn/Fe dual-atom catalysts (MnFe DACs) embedded in N-doped carbon frameworks are designed. Theoretical calculations reveal that energy levels of dz2, dzx, and dyz orbitals participating in d-p hybridization are elevated closer to the Fermi level at both Mn and Fe sites, thereby reducing orbital occupancy in antibonding states. Consequently, these electronic features via the selective d-orbital elevation enable enhanced adsorption strength toward intermediate LiPSs and accelerate redox reaction during cell operation. Also, the MnFe DAC improves anode stability by regulating Li-ion flux with its lithiophilic active sites. Specifically, the cell equipped with MnFe DAC-modified separator maintains a capacity of 758.4 mAh g−1 after 400 cycles at 0.5 C. Notably, the cell demonstrates a high initial capacity of 822.7 mAh g−1 with only 0.047% decay rate over 1000 cycles at 1 C. Even under high sulfur-loading (5.0 mg cm−2) and low electrolyte-to-sulfur (E/S) ratio (6 μL mg−1), a high initial areal capacity of 4.94 mAh cm−2 with 92.5% retention after 50 cycles at 0.1 C is achieved. This study provides guidelines on selective modulation of d-orbitals in DACs for high-performance Li-S batteries.