Application of Y-MOF–CNT-Derived Y₂O₃–C@CNT Composites in Lithium–Sulfur Battery Separators

In order to mitigate the shuttle effect of lithium polysulfides in lithium-sulfur batteries, we propose a yttrium-metal-organic framework-carbon nanotube (Y-MOF-CNT)-derived Y₂O₃-C@CNT composite for modifying the separator in this study. The Y-MOFs, comprising yttrium (Y) rare earth metal and terephthalic acid, exemplify a prototypical category of metal-organic framework (MOF) materials. They manifest the advantageous attributes associated with MOFs while concurrently possessing distinctive catalytic traits ascribed to rare earth elements. In this study, Y-MOF nanoparticles were synthesized on carbon nanotube (CNT) substrates via a facile aqueous solution method, succeeded by high-temperature carbonization to yield Y₂O₃-C@CNT composite materials. These composites were subsequently employed as coatings on one side of polyethylene (PE) separators. The resultant Y₂O₃-C@CNT composite inherits the particle-like morphology and porosity from its precursor Y-MOF, alongside the inherent conductivity in carbon-based materials. This amalgamation is conducive to polysulfide capture and catalytic conversion processes within lithium-sulfur batteries. The application of the Y₂O₃-C@CNT-coated PE separator effectively mitigated polysulfide shuttle effects and significantly enhanced the battery electrochemical performance. At a sulfur loading level of 3 mg cm^-2 under a 0.5 C rate, an initial discharge specific capacity of 900 mAh g^-1 was achieved. After 400 cycles, the discharge specific capacity remained at 483.85 mAh g^-1 with a capacity retention rate of 53.7%. Upon increasing sulfur loading to 5 mg cm^-2, the discharge specific capacity at a lower rate (0.1 C) reached 817.8 mAh g^-1; even after 100 cycles, it maintained a value of 700 mAh g^-1 with a capacity retention rate of 85.6%. Notably, our modified Y₂O₃-C@CNT separator demonstrated exceptional cycling stability, even under conditions involving high sulfur loading.