Tuning Redox Behavior of Sulfur Cathodes Via Ternary-Coordinated Single Fe Atom in Lithium-Sulfur Batteries

Modulating the coordination configuration of single Fe atom has been an efficient strategy to strengthen the redox dynamics for lithium-sulfur batteries (LSBs) but remains challenging. Herein, the single Fe atom is functioned with nitrogen and carbon atoms in the first shell, and simultaneously, oxidized sulfur (SOx) in the second shell, which presents a lower antibonding state and well address the redox activity of sulfur cathodes. In the ternary-coordinated single Fe atom catalyst (FeN2C2-SOx-NC), the binary structure of FeN2C2 provides a lower Fe-S bonding strength and d-p orbital hybridization, which obviously optimizes the adsorption and desorption behavior of sulfur species during the reduction and oxidation reaction processes. Simultaneously, the SOx redistributes the electron density of the coordinating nitrogen atoms, which possesses high electron-withdrawing ability and develops electrocatalytic activity. As a result, the sulfur cathodes with FeN2C2-SOx-NC present an excellent high-rate cyclic performance, accompanied by a capacity decay rate of 0.08% per cycle for 500 cycles at 4.0 C. This study provides new insights for optimizing the redox dynamics of sulfur cathodes in LSBs at the atomic level. In this work, the ternary-coordinated single Fe atom (FeN2C2SOxNC), consists of FeN2C2 structure and oxidized sulfur, is first constructed to address the redox behavior of sulfur cathodes in lithium-sulfur batteries. Expectedly, the sulfur cathodes with FeN2C2SOxNC present an excellent high-rate cyclic performance, accompanied by capacity decay rate of 0.08% per cycle after 500 cycles at 4.0 C.image