含亞胺和環硼氧烷之共價有機框架(COFs): 合成與其在鋰金屬電池的人工固態電解質介面之應用

Abstract

共價有機框架（Covalent Organic Frameworks, COFs）是一種主要由C、H、O、N和B等輕元素組成的有機多孔材料。其為透過共價鍵結構形成二維或三維網絡結構，具有高孔隙率、大表面積、低密度以及優異的熱穩定性和化學穩定性。透過前驅物的選擇，即可調整COFs的官能基團和孔徑。在此研究中，我們使用4-formylphenylboronic acid 和 p-phenylenediamine作為前驅物，並採用一鍋法合成了同時具有亞胺和環硼氧烷的COFs。我們系統性的研究了包括溶劑、催化劑和反應環境在內的反應參數對COFs結構和性質(如形貌、顆粒大小、結晶度和孔隙率等)的影響。 在此研究中，我們還開發了利用超音波破碎技術，製備均勻分散COFs的液體電解質的方法。在此方法中，液體電解質會滲透到隔離膜中，均勻分散之COFs會在隔離膜和鋰金屬負極之間形成人工固態電解質界面。我們系統性的研究了COF的添加量和結晶度對A-SEI性能的影響。含有COF A-SEI之鋰對稱電池（LSC）的長期界面阻抗明顯低於不含COF的鋰對稱電池，表明COF A-SEI可以透過抑制化學SEI的形成來提高界面穩定性。COF A-SEI LSC的恆電流循環測試還顯示，在1 mA cm⁻²和2 mAh cm⁻²的電流密度下可穩定循環長達550小時，是不含COF的LSC的兩倍，證明了COF A-SEI優異的效能。由於亞胺和環硼氧烷對鋰離子的高親和力，可以促進鋰的均勻沉積和剝離，從而有效抑制鋰金屬表面的鋰枝晶形成。

Covalent Organic Frameworks (COFs) are a type of organic porous material composed primarily of light elements such as C, H, O, N, and B. They are structured through covalent bonds to form two-dimensional or three-dimensional networks possessing high porosity, large surface area, low density as well as excellent thermal and chemical stability. By varying the chemical structure of the precursors, the functional groups and pore size of COFs can be tailored. In this work, a one-pot chemistry using 4-formylphenylboronic acid and p-phenylenediamine as the precursors is adopted to synthesize COFs possessing both imine and boroxine groups. We systematically investigate the effects of reaction parameters including solvents, catalysts, and reaction environments on the structures and the properties of COFs, such as morphology, particle size, crystallinity, and porosity. In this research, we also developed a methodology to prepare liquid electrolytes containing homogeneously dispersed COFs with the help of ultrasonication. Upon infiltrating the liquid electrolytes into the separator, the dispersed COFs would feasibly form an artificial solid electrolyte interphase (A-SEI) between the separator and the lithium metal anode. We systematically investigate the influence of the amount and the crystallinity of COF on the performance of the corresponding A-SEI. The long term interfacial resistance of the optimized lithium symmetrical cell (LSC) containing COF A-SEI is obviously lower than the counterpart without COF, suggesting the COF A-SEI would improve the interfacial stability by inhibiting chemical SEI formation. Galvanostatic cycling of the COF A-SEI LSC also demonstrates up to 550 h stable cycling at 1 mA cm-2 and 2 mAh cm-2, twice longer than the COF-free LSC. The COF A-SEI proves the strong capability to facilitate homogeneous deposition and stripping of lithium owing to the high affinity of imine and boroxine to lithium ions, and thus to effectively suppress lithium dendrite formation at the lithium metal surface.