A Freestanding Ce-MOF Separator with Synergistic Functions for Stable and Safe Room-Temperature Sodium–Sulfur Batteries

Room-temperature sodium-sulfur (RT Na-S) batteries offer great promise for grid-scale energy storage but face various challenges, such as polysulfide shuttling and sodium dendrite growth. This study develops a freestanding cerium-based metal-organic framework (Ce-MOF) separator (denoted as CM) to address these issues synergistically. The CM separator features hierarchical micromesopores that regulate uniform Na⁺ flux while physically blocking polysulfide diffusion. Abundant surface amino groups and the Ce³⁺/Ce⁴⁺ redox couple create dual-active sites that chemically adsorb and catalytically convert polysulfides. This integrated approach simultaneously promotes homogeneous sodium deposition and offers improved thermal stability, along with flame-retardant properties. Consequently, RT Na-S batteries with the CM separator deliver an initial discharge capacity of 920 mA h g⁻¹ at 0.2C and retain 86% capacity after 250 cycles, significantly outperforming conventional GF separators. This work presents an effective MOF-based separator strategy for stable and safe RT Na-S batteries.