Benzothiadiazole-Functionalized Two-Dimensional Zr-MOF Nanosheets as Efficient Separator Coatings for Li–S Batteries

The shuttle effect caused by the migration of soluble polysulfides limits the practical applications of lithium–sulfur (Li–S) batteries. The employment of a functional coating on separators is an efficient strategy to alleviate the shuttle effect. Herein, we have developed an approach to enhance the electrochemical performance of Li–S batteries by incorporating benzothiadiazole-functionalized (BT) metal–organic framework (UiO-68-BT MOFs) nanosheets within the battery separator. The UiO-68-BT nanosheets were synthesized using a solvothermal method, employing 4,4′-(benzothiadiazole-4,7-diyl) diphenylcarboxylic acid (H₂BTDB) as the organic ligand and ZrCl₄ as the metal precursor. The incorporation of benzothiadiazole groups, known for their strong electron-withdrawing capabilities and high affinity for polysulfides, addresses the critical challenge of polysulfide shuttling in Li–S batteries. Electrochemical performances revealed that the modified separator Li–S battery delivered an initial discharge capacity of 1063.6 mAh g^–1, maintaining a capacity of 455.2 mAh g^–1 after 500 cycles at 0.5 C, with a Coulombic efficiency of 99.74% and an average capacity decay rate of only 0.114% per cycle. In contrast, a battery with a pristine Celgard polypropylene (PP) separator showed a significantly lower initial discharge capacity (610.8 mAh g^–1) and higher capacity decay rate (0.154%). Detailed experiments and density functional theory (DFT) calculations suggested that the enhanced performance is attributed to the effective capture of lithium polysulfides (LiPSs) by the BT-functionalized nanosheets, which suppresses the shuttling effect and facilitates Li⁺ charge transfer. This work demonstrates the potential of using MOF nanosheet-modified separators to significantly enhance the electrochemical performance of Li–S batteries.