Constructing Orbital Coupling-Modulated Homogeneous Dual-Atom Fe–Fe Sites for Boosting Bidirectional Conversion of Polysulfides

Homogeneous dual-atom catalysts (HDACs) have garnered significant attention for their potential to overcome the shuttling effect and sluggish reaction kinetics in lithium-sulfur (Li-S) batteries. However, modulating the electron structure of metal atomic orbitals for HDACs to dictate the catalytic activity toward polysulfides has remained meaningful but unexplored so far. Herein, an interfacial cladding strategy is developed to obtain a new type of dual-atom iron matrix with a unique FeN₂P₁-FeN₂P₁ coordination structure (Fe₂@NCP). The 3d orbital electrons of the Fe centers are redistributed by incorporating phosphorus atoms into the first coordination sphere. The theoretical calculations disclose that the strong coupling between the Fe d orbital and the S p orbital exhibits an enhanced Fe-S bond and improved reactivity toward polysulfides. Moreover, the Fe₂@NCP catalyst achieves robust adsorption ability toward Li₂S_n (1 ≤ n ≤ 8) and significantly boosts bidirectional sulfur redox reaction kinetics by lowering the Li₂S deposition/decomposition energy barriers. Consequently, the assembled Li-S batteries present a high retention ratio of 77.3% after 500 cycles at 1C. Furthermore, the Li-S pouch cell also exhibits good performance at 0.1C (80.2% retention over 100 cycles) for practical application with a sulfur loading of 4.0 mg/cm². The outcome of this study will facilitate the design of homogeneous dual-atom catalysts for Li-S batteries.