Hierarchical Confinement and Oxygen-Vacancy Catalysis for Highly Reversible Room-Temperature Sodium-Sulfur Batteries

Room-temperature sodium-sulfur (RT Na-S) batteries are attractive for grid-scale energy storage owing to their high theoretical energy density and elemental abundance, yet their practical application remains severely challenged by sluggish sulfur redox kinetics and the shuttle of sodium polysulfides. Herein, we establish a molten-salt-assisted strategy to construct a multifunctional cathode host (PNCNs@CeO_2-x), where oxygen-deficient CeO_2-x nanoparticles are confined within a hierarchically porous carbon framework and encapsulated by graphene-like carbon nanosheets. This deliberately orchestrated architecture unifies spatial confinement and oxygen-vacancy-enabled catalysis to form conductive microreaction domains featuring continuous ion/electron transport pathways and abundant active interfaces. Through in situ characterizations and machine-learning-assisted molecular dynamics simulations, we demonstrate that oxygen vacancies in CeO_2-x induce favorable charge redistribution, strengthen Na₂S_x adsorption, lower the energy barrier for Na₂S₂/Na₂S conversion, and promote a highly reversible solid-liquid-solid conversion process, thereby effectively suppressing polysulfide dissolution. Consequently, the PNCNs@CeO_2-x-S cathode exhibits an impressive reversible capacity of 1167 mAh g^-1 at 0.1 A g^-1 and outstanding cycling stability, maintaining 86.2% capacity retention after 9000 cycles at 5 A g^-1. This work establishes a confinement-catalysis design paradigm for regulating sulfur electrochemistry for long-life RT Na-S batteries.