Water-Scavenging Zr-Based Metal–Organic Framework-Decorated Functional Separator for Stable Lithium Metal Batteries

In lithium metal batteries (LMBs), even trace water can severely affect the battery performance and safety. Therefore, the removal of water from the electrolyte is important and necessary. In this study, the hydroxyl (−OH) functionalized metal–organic frameworks (MOFs), UiO-66-(OH)2 (noted as U66-OH) are applied as efficient and effective water scavengers in LMBs. The U66-OH crystals are pasted onto the conventional polypropylene (PP) to fabricate the U66-OH/PP separator. The results show that U66-OH can effectively capture trace water in cells, suppress the generation of acidic substances, and improve the cycling stability of the Li||NCM811 cells. Even with a 1000 ppm water-containing electrolyte, the Li||NCM811 cell equipped with a U66-OH/PP separator maintains 90% capacity retention after 300 cycles. In addition, U66-OH can effectively optimize the poor wettability of the PP separator and facilitate Li-ion transport. Consequently, the coated U66-OH layer can regulate Li+ deposition behavior and suppress the formation of lithium dendrites. The Li||Li symmetric cell employed by the U66-OH/PP separator shows stable cycling for over 750 h at 0.5 mA cm–2. This work paves a feasible route for water removal in advanced electrolytes toward high-performance LMBs.