對苯二甲酸雙（2-羥乙基）酯衍生之鹼土族對苯二甲酸基金屬有機框架應用於鋰離子電池之負極

Abstract

能源和環境議題是二十一世紀裡非常重要的其中兩個議題。為了能同時解決這兩大議題，我們開發了一條透過簡單的水熱反應和使用聚對苯二甲酸乙二醇酯（PET）的乙二醇解產物，即對苯二甲酸雙（2-羥乙基）酯（BHET），作為配體以合成鹼土族對苯二甲酸基金屬有機框架(MOFs)，即Ca-和Ba-BDC，並將它們應用於鋰離子電池之負極。我們發現對苯二甲酸雙（2-羥乙基）酯會透過金屬氫氧化物溶解在水中產生的氫氧根離子水解為對苯二甲酸離子以合成鹼土族對苯二甲酸基金屬有機框架。在我們的合成技術下，兩種金屬有機框架都能在相對於文獻中較溫和的反應條件下合成，其中Ca-BDC可以在130 °C下15分鐘或50 °C下12小時內合成，而Ba-BDC可以在130 °C下1小時或50 °C下12小時內合成。除此之外，我們也在室溫下合成出Ba-BDC的新相，並透過從頭計算(Ab initio)粉末X光繞射結構分析法解出其晶體結構。而當我們將合成出的金屬有機框架應用於鋰離子電池之負極時，我們發現鋰離子在連續充放電過程中會造成結構失序，進而在結構中產生更多空間儲存鋰離子，因此其電容量會隨著循環圈數增加而上升，其中Ca-BDC_130°C15min和Ba-BDC_RT12h在50 mAg-1的電流密度下循環100圈後的電容量分別提升到403和390 mAhg-1。本研究除了開發了一條利用廢PET塑膠解聚之單體在溫和條件下合成Ca-和Ba-BDC的路徑外，也將合成的金屬有機框架應用於鋰離子電池之負極以期能同時解決環境和能源問題。

Environmental and energy issues are two of the most significant issues in the 21st century. To cope with these two issues simultaneously, we demonstrate that alkaline-earth BDC-based Metal-organic frameworks (MOFs), e.g., Ca- and Ba-BDC, can be synthesized through a simple and convenient hydrothermal technique by using bis(2-hydroxyethyl) terephthalate (BHET) as a linker source, which is the glycolysis product of polyethylene terephthalate (PET). Besides, the as-synthesized MOFs also show the potential of being applied as anodes for lithium-ion batteries (LIBs). We found that the hydrolysis of BHET to terephthalic acid ions (BDC) by OH– ions from the dissolved metal hydroxide (Ca(OH)2 or Ba(OH)2), i.e., the metal precursors used in this work, is the key for the crystal growth of Ca- and Ba-BDC MOFs. The results showed that while Ca-BDC can be synthesized just within 15 min at 130 °C or 12 h at 50 °C, Ba-BDC can be synthesized within 1 h at 130 °C or 12 h at 50 °C. These conditions were mild compared to the reported literature regarding the synthesis of Ca- and Ba-BDC MOFs. In addition, a new phase of Ba-BDC was observed when the material was synthesized under room temperature stirring for 12 h, and the crystal structure was successfully solved via ab initio powder XRD structural analysis. Moreover, the as-synthesized MOFs possessed unprecedented performances as anodes in LIBs, in which the disordered structure during the charge-discharge process led to the increase in capacity with increasing cycles, where the capacities of Ca-BDC_130°C15min and Ba-BDC_RT12h reached 403 and 390 mAhg-1 after 100 cycles at a current density of 50 mAg-1, respectively. This work not only realizes the idea of PET waste-to-MOFs with milder conditions, more convenience, and green compared to any reported solvent approaches but also reveals the potential of applying as-synthesized MOFs as anodes for LIBs to deal with the real-world environment and energy issues at the same time.