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

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, <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics><mml:msub><mml:mi>t</mml:mi> <mml:mrow><mml:mi>L</mml:mi> <mml:msup><mml:mi>i</mml:mi> <mml:mo>+</mml:mo></mml:msup> </mml:mrow> </mml:msub> <mml:annotation>${{\mathrm{t}}_{{\mathrm{L}}{{\mathrm{i}}^ + }}}$</mml:annotation></mml:semantics> </mml:math> = 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.