Synchronized CVD Growth of Iron Carbide Nanocatalysts within Carbon Nanotube Networks for Stable Lithium–Sulfur Batteries

Transition-metal carbides remain underexplored as catalytic phases in energy storage despite their rich electronic structure and tunable surface chemistry. Here, we demonstrate that Fe₅C₂ nanoparticles embedded in a carbon nanotube (CNT) network act as a bifunctional catalytic–anchoring phase, simultaneously immobilizing lithium polysulfides (LiPSs) and accelerating their conversion to Li₂S. Density functional theory and ab initio molecular dynamics simulations reveal that the (510) Fe₅C₂ surface provides strong adsorption sites and promotes stepwise dissociation of higher-order polysulfides. UV–vis adsorption, potentiostatic Li₂S deposition, cyclic voltammetry, and X-ray photoelectron spectroscopy confirm Fe–S bond formation and rapid polysulfide conversion, while dynamic electrochemical impedance spectroscopy (DEIS) tracks the reduction of charge-transfer resistance during cycling. The Fe₅C₂/S/CNT bilayer cathode delivers a high initial capacity of 1450 mAh g⁻¹ at 0.1C, excellent rate capability (700 mAh g⁻¹ at 1C), and stable cycling. This multiscale investigation establishes a direct link between atomic-level catalytic interactions and enhanced electrochemical kinetics, presenting Fe₅C₂ as a design paradigm for catalytic materials in lithium–sulfur and broader metal–sulfur battery systems.