主鏈修飾三唑的高分子電解質之合成與物性探討

Abstract

近年來的研究指出，三唑具多種排列構形可幫助質子傳導，優於其它含氮雜環吡咯及咪唑。本研究將三唑應用於含鋰鹽的固態高分子電解質內，探討三唑在電解質內幫助鋰離子傳導的情形。我們製備三種高分子電解質，分別為PEG混摻三挫、PEG經速配接合化學與乙醚氧鏈段及碳鏈段偶合同時產生三唑於主鏈，分別摻入不同比例的鋰鹽和純PEG高分子電解質比較。 由FT-IR結果發現，含三唑的電解質內自由鋰離子的濃度都較純PEG高，表示三唑的加入可以幫助鋰鹽解離。若將三唑固定於主鏈上，可減少三唑上氫與鋰陽離子競爭鏈段上的氧原子。 但由DSC結果指出，三唑的加入會使高分子電解質Tg上升，尤其是在高鋰鹽濃度下，Tg上升的幅度更大。量測導電度後得知，摻入超過20 wt%的鋰鹽後，導電度較未加入三唑的PEG低約一個級數。所以只有在5 wt%低濃度的鋰鹽下，室溫導電度較不含三唑者高約0.5至1.5個級數，因此推測低溫下鋰離子在電解質內可利用鏈段運動及三唑間跳躍傳導，而高溫下以鏈段運動為主要的傳導方式，但鏈段運動及導電度皆受較高的Tg所限制。 因此高分子電解質內良好的電荷傳導並非僅依靠足夠的離子數，更需考慮鏈段運動的能力等因素。

These years, many research groups have pointed out that nitrogen-containing heterocycle (NCH), especially triazole, could help proton conduction in the polymer electrolyte. In this thesis we applied this concept to solid state polymer electrolyte to see if it works similarly as proton conduction. Here click chemistry was employed to synthesize polymer electrolyte based on polyethylene glycol (PEG), because it offers an easy way to fix triazole on the main chain with high yield. After estimating the amount of triazole in the polymer, we blended small molecule triazole into the PEG, and the resulting blends were compared with those having triazole group on the main chain and pristine PEG. From the results of FT-IR, we found that the appearance of triazole can help the dissociation of lithium perchlorate, which results in the increase in the fraction of free lithium cation in the electrolyte. It indicated that the incorporation of triazole led the polymer to possessing more charge carriers in the polymer electrolyte. In addition, the DSC data showed that with the appearance of triazole, Tgs of the polymer electrolyte were also increased, implying the difficulty in segmental motion, especially at high concentration of lithium perchlorate.The AC impedance results also confirmed that as the concentration of lithium perchlorate was increased over 20 wt%, the conductivity decreased about one order. Therefore, only under low lithium perchlorate concentration (5 wt%) at room temperature, the conductivities of those polymers with triazole were 0.5 to 1.5 orders higher than pristine PEG. Based on the above, the conduction of lithium at high temperature relies mainly on segmental motion while at low temperature there is another pathway of lithium hopping through triazole, which improves the conductivity at room temperature.