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

Redox-flexible rare-earth catalysts featuring partially filled 4f orbitals enable orbital-level modulation of sulfur electrochemistry. Here, an oxygen-vacancy-engineered CeO₂/carbon nanotube (O_v-CeO₂/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 Ce³⁺(4f¹)/Ce⁴⁺(4f⁰) 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 Li₂S 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.