Fluorinated Zr-MOF-modified separators for Li-S batteries with enhanced electrochemical performance

Considering the asymmetric development of the demand for new energy, two Zr-based MOF materials were successfully synthesized using a solvothermal method. Using ZrCl₄ as the metal source, UiO-66-4F and UiO-66 were prepared with 2,3,5,6-tetrafluoroterephthalic acid (H₂BDC-4F) and terephthalic acid (H₂BDC) as ligands, respectively. These two Zr-based MOFs were coated onto one side of a commercial Celgard separator, and the electrochemical performance of the assembled lithium-sulfur (Li-S) batteries was tested. The influence of the electron-withdrawing group -F on the performance of Li-S batteries was explored. The test results showed that at a current density of 0.5C, the UiO-66-4F separator cell delivered an initial discharge specific capacity of 1182.9 mAh g^-1 and retained a reversible specific capacity of 400.7 mAh g^-1 after 1000 cycles. Even under a high sulfur loading of 4 mg cm^-2, the UiO-66-4F-modified separator cell still maintained a high reversible specific capacity of 961.28 mAh g^-1. These electrochemical properties are all superior to those of the UiO-66-modified separator. The UiO-66-4F-modified separator battery consistently demonstrated better cycling performance and a lower capacity decay rate. These improvements indicate that the electron-withdrawing group -F effectively inhibits the polysulfide shuttle effect and improves Li-S battery performance.