Ethoxy/Amide-Functionalized UiO-66-(OH)2 MOF Composite Separators Enabling Water/HF scavenging and Li+ Regulation for Stable Lithium Metal Batteries

Abstract

To overcome the disadvantages of commercial polyolefin-based separators, such as inadequate electrochemical properties and dendrite growth, in lithium metal batteries, nanofiber separators coated with MOF are prepared using the electrospinning technique and a vacuum surface coating method. The Zr-based MOF (UiO-66-(OH)2) materials that scavenge H2O/HF in the electrolyte are synthesized via hydrothermal synthesis, and ethoxy/amide groups are introduced onto the MOF surface through a reaction between hydroxyl groups on UiO-66-(OH)2 surface and ICPTES (silane coupling agents). The fabricated MF-U66I separator exhibits excellent performance, including high porosity (68.2 %), substantial electrolyte absorption capacity (750 %), outstanding mechanical strength (27.5 N mm2), dimensional stability (<5% shrinkage at 200 °C), and significantly high electrochemical properties (σ = 2.85 mS cm−1, = 0.77). Moreover, Li metal-based cells using the MF-U66I separator show much greater capacity retention and cycle life than the other cells with PE and pristine MF separators. The NCM∥Gr full cell equipped with the MF-U66I separator also maintains more than 93.5 % of its initial discharge capacity after 500 cycles at 55 °C. These results demonstrate that the MF-U66I separator surpasses conventional PE and pristine MF separators and offers strong potential for practical application as a stable separator for lithium metal batteries.