Ab-Initio Studies on Fluorine–Sulfur Coterminated MXene–Reduced Graphene Oxide Composites for Fast Polysulfide Conversion in Flexible Sodium–Sulfur Batteries

Flexible, high-performance cathodes are essential for realizing practical room-temperature sodium–sulfur (Na–S) batteries, yet sluggish polysulfide conversion, poor retention, and mechanical limitations remain major barriers. Here, we introduce a sulfur/fluorine coterminated vanadium carbide MXene integrated with reduced graphene oxide, V<inf>2</inf>CF<inf>0.67</inf>S<inf>0.33</inf>(rGO), designed to enhance polysulfide anchoring, catalytic activity, and flexibility simultaneously. First-principles calculations reveal that this mixed-termination MXene–rGO composite exhibits markedly stronger polysulfide adsorption (0.8–3.90 eV) than single-terminated counterparts while preserving structural integrity and metallic conductivity for efficient charge transport. The material achieves the lowest Na<inf>2</inf>S decomposition barrier reported for MXene-based Na–S cathodes (0.287 eV) and a reduced Gibbs free energy pathway for the sulfur reduction reaction, enabling faster and more complete sulfur utilization. Charge density difference, partial density-of-states, and crystal orbital Hamilton population analyses confirm substantial charge transfer and strong interfacial chemical bonding with Na<inf>2</inf>S<inf>n</inf>species. Mechanical stress–strain simulations further demonstrate robust yet flexible behavior, highlighting its promise for wearable energy storage. This work establishes surface-termination engineering in MXene–graphene hybrids as a promising route toward high-capacity, durable, and mechanically compliant Na–S batteries.