Experimental and Theoretical Insights on Interface Engineered FeS/rGO as Anode for Fast‐Charging Lithium‐ and Sodium‐Ion Batteries

Interface engineering facilitates the development of stable energy storage devices that can endure the severe changes encountered during operation. In the context of fast-charging anodes for lithium- and sodium-ion batteries (LIBs and SIBs), the interface needs to promote charge/ion transfer processes, enhance Li-/Na-ion storage capacity, and ensure good reversibility in order to function efficiently at high rates. Herein, a simple synthetic strategy is reported to design interfaces between transition metal sulfides and carbonaceous supports to generate high-performance fast-charging anodes. FeS/rGO nanostructures are synthesized via a simple solid-state annealing method by employing FeOOH/rGO, a metastable precursor, which is annealed at 600 °C in the presence of H₂S gas. Interface engineering between FeS and rGO significantly improved the electrochemical performance, particularly demonstrated by stable capacities at high rates (625 mAh g⁻¹ at 5 A g⁻¹ for LIBs and 708 mAh g⁻¹ at 10 A g⁻¹ for SIBs). The high-rate charge storage is primarily governed by capacitive processes. Density functional theory (DFT) calculations attributed the enhanced performance of the FeS/rGO anode to a lower diffusion energy barrier for Li- and Na-ion diffusion at the interface along with the presence of a built-in electric field at the heterointerface.