Vacancy‐Engineered Ceria Enables 4f‐Orbital‐Driven Redox Catalysis for Bidirectional Sulfur Conversion in Li─S Batteries

Abstract Redox‐flexible rare‐earth catalysts featuring partially filled 4f orbitals enable orbital‐level modulation of sulfur electrochemistry. Here, an oxygen‐vacancy‐engineered CeO 2 /carbon nanotube (O v ‐CeO 2 /CNT) composite is reported, configured as a conformal catalytic layer on a commercial separator, to regulate polysulfide redox reactions in lithium‐sulfur (Li─S) batteries. In situ and ex situ characterizations, corroborated by DFT calculations, reveal that oxygen vacancies dynamically modulate the Ce electronic environment, enabling reversible Ce 3+ (4f 1 )/Ce 4+ (4f 0 ) redox cycling and interfacial charge transfer. This vacancy‐induced orbital hybridization between Ce‐4f/S‐3p and Li‐2s/O‐2p states enhances LiPS adsorption, lowers the barriers for Li 2 S nucleation and decomposition, and facilitates ion transport, thereby accelerating bidirectional sulfur conversion and ensuring stable redox reversibility. As a result, the designed cell achieves long‐term durability (743.2 mAh g −1 after 1000 cycles at 0.5C), high‐rate capability (up to 5C), and high energy density in pouch cells. This work establishes 4f‐orbital‐mediated defect engineering as a scalable and effective strategy for designing redox‐regulating catalysts in high‐performance Li─S batteries.