高分子/黏土/鋰金屬鹽所組成之奈米級高分子電解質複合材料之研究

Abstract

本論文主要在研究蒙托黏土對於高分子電解質導電行為的影響。其研究結果可指出，添加經由有機分子改質過的有機黏土於高分子電解質中可大幅的提升系統的離子導電值。經由交流阻抗分析儀(a.c. Impedance)、DSC熱分析儀、紅外線光譜儀(FTIR)與固態核磁共振光譜(Solid-state NMR)的量測結果發現，黏土中的矽酸鹽片、金屬陽離子與高分子鏈上官能基間存在著特殊作用力，此種特殊作用力乃是屬於路易式酸鹼性的吸引力。因為黏土中的矽酸鹽片層帶有負電荷，其扮演著與高分子官能基相同的角色(路易士鹼)，因而可吸附鋰陽離子。在第四章PEO/LiTf/Clay系統中，添加有機黏土會使部份的鋰金屬陽離子與矽酸鹽片錯合，並因而改變了陽離子(Li+)的錯合型態，此錯合型態的改變亦伴隨著高分子鏈段的更自由性，並也導致了更高的結晶熔點(Tm)與更大的高分子結晶度(Xc %)。另外，於第五章PAN/LiTf/Clay系統中更可發現，有機黏土的存在可增加系統的極性，因此高極性的鋰金屬鹽離子將能更輕易地於此具有高極性的高分子環境中解離。 為了要更進一步的了解高分子/黏土間相容的行為對系統導電值的影響，在第六章中分別使用不同的界面活性劑來有機化黏土，以製造出不同性質的高分子電解質材料。雖然黏土中的矽酸鹽片與金屬陽離子間存在著特殊作用力，然而此作用力的大小主要主要決定於黏土於高分子鏈段間的分散情形。在(PEO)8LiClO4/DDAC-oClay此剝離型態黏土分佈的電解質系統下，有機黏土會產生眾多帶有負電荷的矽酸鹽片層並且均勻的分散於高分子間，矽酸鹽片表面上的電子能與鋰金屬陽離子作用並造成鋰金屬鹽離子鹽的解離與導電值的提高。當DDAC-oClay = 2.9 wt%時，系統不但擁有最高的導電值8×10-5 S/cm，亦具有相當不錯的薄膜機械性質。 為了要使高分子電解質薄膜具有高離子導電的實用價值，在第七章中，以EC當作可塑劑並組成PMMA/LiClO4/EC/Clay之膠態高分子電解質。研究結果指出，添加少量(5 wt%)經由DDAC分子改質過後的有機黏土於P(MMA)8LiClO4(75)/EC(25)電解質系統中，可有效的提升系統的離子導電值達50倍之多，此高分子電解質薄膜不但擁有高的離子導電值(6×10-4 S/cm)，並具有相當良好的機械性質，此類“奈米複合材料膠態高分子電解質”極具有可商業化的潛力。 添加有機黏土於高分子電解質中不但可提高系統的導電特性，亦仍能保持高分子原本優良的機械性質，本論文提出了由「高分子/鋰金屬鹽/黏土」所組成的“奈米複合材料高分子電解質”以期能對國內電池產業的發展有所助異。

The objective of this study is to investigate the effect of the montmorillonite on the ionic conductivity behavior. The result has demonstrated that the addition of optimum content of the organo-modified montmorillonite (oClay) is able to enhance the ionic conductivity drastically. Specific interactions among silicate layer, ethyl oxide and lithium cation have been investigated using alternating current impedance (a.c. Impedance), differential scanning calorimetry (DSC), Fourier-transform infrared (FT-IR), and Solid-state NMR. The specific interaction is attributed to the Lewis acid-base interaction. These negative charges on the silicate layers can play the same role as the polar functional group in polymer (Lewis base) to interact with lithium cations. In the chapter 4, PEO/LiTf/Clay system, the presence of the oClay tends to influence the complex form by drawing lithium cations away from the original polymer matrix into the silicate layers’ region. The shift of the complex form will also accompany with the higher chain flexibility, different melting point (Tm), and crystallinity (Xc%). Additionally, the results of chapter 5 reveal that the presence of the oClay in the PAN/LiTf/Clay system can also increase the system’s dipolar property, and results in the lithium salts more easily dissociated. In order to further understand the effect of intercalated property of polymer/oClay on the ionic conductivity. A model system based on poly(ethylene oxide) (PEO) doped with LiClO4 and incorporated with different oClay is investigated in the chapter 6. Although the strong interactions occur between the silicate layer and the dopant salt LiClO4 within the PEO/clay/LiClO4 system, however, the strength of this specific interaction depends on the extent of PEO intercalation. In the exfoliated clay system, (PEO)8LiClO4/DDAC-oClay, great numbers of the negative charges in the silicate layers can be dispersed homogeneously in the polymer matrix, huge numbers of negative charges on the silicate layers can interact with the lithium cation and results in the high ionic conductivity. When the DDAC-mClay = 2.9 wt%, the (PEO)8LiClO4/DDAC-oClay polymer film not only possesses the highest ionic conductivity (8×10-5 S/cm) but also maintains the excellent dimensionally stability. In order to achieve the commercial purpose, study on the effect of adding specific amount of ethylene carbonate (EC) to the P(MMA)8LiClO4/Dclay system has also been carried out in the chapter 7. This study has demonstrated that the addition of an optimum content (5 wt%) of the oClay increases the ionic conductivity of the PMMA-based electrolyte by nearly forty times (6×10-4 S/cm) relative to the plain P(MMA)8LiClO4(25)/EC(75) system. These novel plasticized nanocomposite films not only give significantly higher conductivity but also possess improved dimensional stability for potential commercial applications. Adding clay not only enhances the ionic conductivity, but also sustains the mechanical property of the electrolytes.