聚氧化乙烯摻合物和其蒙托土／奈米碳管複材固態電 解質之結構和電性相關性研究

Studies on Structure and Electric Property Relationship of PEO Blends and their MMT/MWCNT Composites as Solid Electrolytes

彭東仁(Dong-Ren Peng)

指導教授 ： 林金福

國立臺灣大學/工學院/材料科學與工程學研究所/碩士(2017年)

https://doi.org/10.6342/NTU201704307

摘要

本論文主要著重討論不同的高分子與其脫層蒙托土(Montmorillonite, MMT)混 摻PEO 及過氯酸鋰(LiClO4)應用在固態電解質中。首先，我們先利用無乳化聚合 (soap-free emulsion polymerization)製備聚丙烯酸甲酯(PMA)、聚乙烯酸乙酯 (PVAc)以及聚((寡聚乙二醇)甲基醚甲基丙酸酯) (POEGMEMA)。並用上述三種高 分子脫層MMT 製備出PMA-MMT、PVAc-MMT 以及POEGMEMA-MMT。利用 FTIR、DSC 及XRD 對其進行特性分析。參照文獻利用澆鑄法(Solvent casting method) 製備聚氧化乙烯(Polyethylene oxide, PEO)固態高分子電解質，在r=0.0625 時(r= [Li]/ [EO])，利用EIS 量測其離子導電度可達5.34*10-7 S/cm，並且仍可以維持良好的固 態特性。
我們以 r=0.0625 為基礎製備固態電解質，分別將PMA、PVAc 及POEGMEMA 混摻PEO 製備成固態高分子電解質。在PEO/PVAc/Li(r=0.0625)電解質系統中，添 加2.5%的PVAc 可以得到離子導電度為1.21*10-5 S/cm。PEO/PVAc/Li 系統的離子 導電性優於PEO/PMA/Li 的離子導電度，因為我們發現在5%添加量時，PEO/PVAc 系統的PEO 熔化溫度只有一個。但是，PEO/PMA 系統的PEO 熔化溫度卻有兩個。 我們推測是因為PEO/PMA 系統中形成兩相結晶，使Li 離子傳遞受到阻礙。
我們同樣以 r=0.0625 為基礎，分別將PMA-MMT、PVAc-MMT及POEGMEMAMMT 混摻PEO 製備成固態複合材料電解質。在PVAc-MMT 系統中，添加5%的 PVAc-MMT 可以得到離子導電度為9.71*10-6 S/cm。從FTIR 分析中，發現Li 離子 會和MMT 產生作用。所以，利用MMT 吸附離子的特性，幫助Li 離子在其上進 行氧化還原反應，提高離子導電度。另外，我們仍然發現在添加5%的PVAc-MMT 時，PEO 的熔化溫度只有一個。然而，在PMA-MMT 系統與POEGMEMA-MMT 系統卻出現兩個熔化溫度，這個現象與高分子混摻系統一樣。
在 DSC 分析中，我們利用線性規劃分別計算PEO/混摻物及PEO/混摻物 /Li(r=0.0625)系統之結晶度隨混摻物含量增加而下降之斜率(slope)，計算出混摻物因子。混摻物因子表示混摻物與PEO 競爭Li 離子的能力。在高分子混摻系統中， PVAc 可以得到最低值為0.49055。在複合材料混摻系統中，PVAc-MMT 系統可以 得到最高值為0.58845。在FTIR 分析中，10%混摻物以內的高分子混摻系統，ClO4 的吸收強度及C=O 的吸收強度的比值與PEO/PMA 系統以及PEO/PVAc 系統的離 子導電度趨勢相符。在10%混摻物以內的複合材料混摻系統，C=O 的吸收強度及 ClO4 的吸收強度的比值與PEO/PMA-MMT 系統及PEO/PVAc-MMT 的離子導電度 趨勢相符。不論從DSC 分析中或是FTIR 分析中，兩種系統中的趨勢剛好相反。 我們認為當系統中有混摻Polymer-MMT 時，主要藉由Li 離子在MMT 上進行氧 化還原來達到傳遞的效果。
接著，我們將電性表現最好的PVAc-MMT 系統，混摻酸化奈米碳管(CNT)， 製備出PEO/PVAc-MMT/CNT/LiClO4 固態電解質。在濃度25%的PVAc-MMT 混摻 下，可以使LiClO4 的添加量提高至r=0.125，仍然維持良好的固態性質。而且PEO 的結晶區塊完全被破壞，使離子導電度提高至3.22*10-4 S/cm。最後，加入0.001% 的CNT 可以幫助PEO/PVAc-MMT25/Li(r=0.125)提高導電度至3.84*10-4 S/cm。
本研究利用簡單、有效的方法製備上述固態電解質，並且克服固態電解質低離子導電度的缺點。

關鍵字

固態高分子電解質 ； 固態複合材料電解質 ； 脫層蒙托土 ； 聚氧化乙烯 ； 混摻物因子 ； 傅立葉轉換紅外光譜儀 ； 酸化多層奈米碳管

並列摘要

In this study, a variety of polymers and their composites with exfoliate montmorillonite (MMT) blending with polyethylene oxide (PEO) and LiClO4 were used for solid electrolytes. First, poly(methyl acrylate) (PMA), poly(vinyl acetate) (PVAc), and poly(oligo(ethylene glycol) methyl ether methacrylate) (POEGMEMA) were prepared by soap-free emulsion polymerization. And then, PMA-MMT, PVAc-MMT, and POEGMEMA-MMT were fabricated through the above-mentioned method in the presence of MMT. By following the method published in the literature, we successfully prepared the solid polymer electrolyte of PEO by using solvent casting method. At r=0.0625 condition (r= [Li]/ [EO]), the ionic conductivity of PEO/Li electrolyte could reach 5.34*10-7 S/cm and the property of solid state still remained well.
Based on r=0.0625 condition, PEO blending with PMA, PVAc, and POEGMEMA were employed to fabricate the solid-state polymer electrolyte respectively. The PEO/PVAc system achieved an ionic conductivity of 1.21*10-5 S/cm at 2.5 % PVAc. The ionic conductivity of PEO/PVAc system was better than PEO/PMA system because there is only one melting point in PEO/PVAc system. However, there are two melting points in PEO/PMA system. According to the above result, we speculate that there were two crystalline phases which blocked the movement of Li ion.
Similarly, based on r=0.0625 condition, PEO blending with PMA-MMT, PVAc- MMT, and POEGMEMA-MMT were employed to fabricate the solid-state composite electrolyte respectively. In PEO/PVAc-MMT system, the ionic conductivity of 9.71*10- 6 S/cm was obtained at 5 % PVAc-MMT. From FTIR anaylsis, we found that there existes certain interaction between MMT and Li ion. Li ions are believed to perform the redox reaction on the surface of MMT that makes ionic conductivity increase because of the potential cation exchange on MMT. In addition, we also found that there were two melting points in PEO/PMA-MMT and PEO/POEGMEMA-MMT systems similar to the polymer blending system.
In DSC anaylsis, we calculated the slope of descent in degree of PEO crystallization with the content of blending polymer and polymer-MMT respectively. The blending factor which represents the chelating capability of PEO on Li ions compared to the blending polymer or polymer-MMT. In polymer blending system, PVAc had the lowest blending factor (0.49055). In composites blending system, PVAc-MMT afforded the highest blending factor (0.58845). In FTIR anaylsis, within 10 % blending polymer in the PEO/polymer blending system, the ratio of ClO4 peak intensity with C=O peak intensity had the similar trend as the ionic conductivity. As to the PEO/polymer-MMT blending systems, the ratio of C=O peak intensity with ClO4 peak intensity had the similar trend as the ionic conductivity. Either from DSC analysis or FTIR analysis, the two kinds of system had the opposite trend. We speculate that it might be du to that the redox reaction of Li ions was maily through the surface of MMT for the PEO/polymer-MMT blending system.
Next, because PEO/PVAc-MMT system has the highest ionic conductivity among the PEO/polymer-MMT system, we futher incorporated different amount of oxided MWCNT to fabricate PEO/PVAc-MMT/CNT/LiClO4 solid-state electrolyte. At 25 % PVAc-MMT, the electrolyte could accommodate more Li ions up to r=0.125 and still remained the solid status. The ionic conductivity reached 3.22*10-4 S/cm and the crystalline phase of PEO was destructed completely. Finally, by further adding 0.001 % OCNT, the ionic conductivity increased to 3.84*10-4 S/cm.
Therefore, this research has demonstrated a simple and effective method to fabricate solid-state electrolyte and still can overcome the issue of low ionic conductivity in solid state.

並列關鍵字

solid polymer electrolyte ； solid composites electrolyte ； exfoliated montmorillonite ； polyethylene oxide ； blending factor ； FTIR ； oxided-MWCNT

參考文獻

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