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, V2CF0.67S0.33 (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 Na2S 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 Na2Sn 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.