Enhanced performance of Li–S batteries via dual cathode–interlayer engineering: hollow TiO2–sulfur with electrospun MXene–TMO interlayers

Official URL: https://dx.doi.org/10.1021/acsomega.5c11112

Lithium–sulfur (Li–S) batteries suffer from rapid capacity fading due to the polysulfide (LiPS) shuttle, sluggish redox kinetics, and the formation of insulating discharge products. Here, we report a dual-engineering strategy that integrates a hydrogen-treated hollow TiO2 (H–TiO2) sulfur host with conductive poly(vinylidene fluoride) (PVDF)-based MXene–TMO interlayers. Hydrogen treatment introduces Ti3+/oxygen vacancies and forms a hollow framework, imparting enhanced conductivity to TiO2 while providing abundant active sites for sulfur immobilization and redox catalysis. Complementarily, the best-performing MXene–TMO interlayer, PVDF/MXene–SnO2 (PV–MS), couples the high conductivity of MXene with the polar, catalytic activity of SnO2, enabling efficient LiPS adsorption and accelerated conversion. This synergy yields substantial performance improvements: LiPS charge-transfer resistance decreases by 93% (4.5 to 0.31 Ω), cycling stability is significantly enhanced (capacity retention >81% compared with 64% for the reference cell), Li+ diffusion rates nearly double, and fast kinetic reactions are maintained even at high scan rates without diffusion limitations. Additionally, the rate capability remains robust at high current densities. Density functional theory (DFT) calculations further confirm this synergistic behavior, showing that the adsorption free energy of Li2S6 follows the trend |ΔGads|H–TiO2 > |ΔGads|TiO2 > |ΔGads|graphene, indicating the strongest LiPS binding and the highest catalytic reactivity on H–TiO2 surfaces. Both DFT and XPS analyses reveal a distinct dual-site binding mechanism in H–TiO2, where Ti–S and Ti–O–Li interactions cooperatively enhance polysulfide anchoring, promote faster redox conversion, and improve sulfur utilization. To the best of our knowledge, this is the first demonstration of a dual-engineered Li–S cathode system in which defect-mediated sulfur hosts and catalytic interlayers operate synergistically. The resulting mechanism─controlled sulfur release at the cathode, shuttle suppression at the interlayer, and rapid electron/ion transport across the interface, establishes a powerful design guideline for achieving long-lived and high-rate Li–S batteries.