Effects of UiO-66 metal clusters and defects on electrochemical performances of lithium-sulfur battery separators

Two metal-organic frameworks （MOFs）， Ce-UiO-66， and Zr-UiO-66， are synthesized using cerium ammonium nitrate （Ce（NH4）2（NO3）6） and zirconium tetrachloride （ZrCl4） as metal salts， and 1，4-benzenedicarboxylic acid （H2BDC） as the organic linker. The crystal structure and morphology of the MOFs are characterized by powder X-ray diffraction （XRD） and scanning electron microscopy （SEM）. The MOFs-modified functional separators are prepared by loading Ce-UiO-66 and Zr-UiO-66 onto one side of commercial Celgard PP separators via vacuum filtration. The electrochemical performance of lithium-sulfur batteries is assembled and tested. The results show that the Ce-UiO-66 modified separator batteries demonstrates optimal electrochemical performance. At a rate of 0.2 C， the initial discharge capacity reaches 1047 mAh·g-1， with a capacity retention rate of 77.5% after 200 cycles and Coulombic efficiency approaching 100%. Under various current rates， the Ce-UiO-66 modified cells deliver discharge capacities of 1281， 945， 768.1， 673.2， 604.7 mAh·g-1 at 0.1， 0.2， 0.5， 1， 2 C， respectively. When returning to 0.1 C， the capacity recovers to 951.6 mAh·g-1 with a capacity retention rate of 74.3%. The above results demonstrate that the redox-active Ce₆-oxo clusters in Ce-UiO-66 can effectively catalyze the conversion reactions of lithium polysulfides （LiPSs） and enhance the redox kinetics. Furthermore， Ce-UiO-66 possesses abundant defects and unsaturated coordination sites， which can effectively anchor LiPSs， mitigate the shuttle effect， and further enhance the electrochemical performance of batteries.