聚偏二氟乙烯/聚乙烯乙酸系高分子電解質導電行為與分子間作用力之研究

Abstract

本論文旨在藉由紅外線光譜(FT-IR),微分掃描熱卡計(DSC),X光繞射儀 (X-Ray)及固態核磁共振儀(NMR)來探討聚偏二氟乙烯(Poly(vinylidene floride);PVDF)與聚乙烯乙酸(Poly(vinyl acetate;PVAc)複合性高分子電解質導電度行為.由交流阻抗圖譜(Ac-Impedance)可PVDF/PVAc/LiClO4 組成比例時於室溫下可得到最大的導電度(7.1×10-7),足足比純的PVDF系高分子電解質大了兩個等級.由DSC,X-Ray研究分析結果可知PVAc的加入可大幅降低抑制PVDF本身結晶.由FT-IR結果預測PVDF的C-F鍵結能提功額外的電子雲給PVAc的羰基(C=O),造成羰基電子雲密度上升而本身也變得更鹼(Base).此項結果可幫助鋰鹽的大量解離並進一步的增加電荷載子的濃度.由NMR中發現當高分子電解質主體PVDF/PVAc組成為80/20時,鋰原子的化學位移會往上磁場(upfield)的方向偏移,而隨PVAc的增多,此化學位移會呈現不連續的化學位移往下磁場(downfield)方向偏移,此項結果與我們所分析的FT-IR數據中當PVDF/PVAc組成為80/20羰基有最強鹼度前後呼應.由NMR中自旋-空間弛緩時間T1數值知道鋰離子的移動率隨著PVAc含量增多而增多,我們推測此乃因高分子主體本身玻璃轉換溫度的上升所造成.

In this work the ionic conductivity of PVDF/PVAc/LiClO4 solid polymer electrolyte has been studied by DSC,X-ray, FT-IR,7Li (CP/MAS) solid state NMR instrument.Ac-Impedance measurements showed that the concentration dependence of the ionic conductivity underwent maximum(σ=7.1×10-7 Scm-1) at the 80/20/16.35 composition ratio at room temperature, which is two order larger than the neat PVDF/LiClO4 polymer electrolyte. It is found that the degree of crystalinity of PVDF decreases as increasing amount of PVAc in the composite,which was evidenced by DSC and X-Ray examination. .However, in the FT-IR measure ment,it is found that CF2 groups of PVDF are able to donate its lone pair electrons toward the C=O groups, resulting in higher basicity of the C=O group and higher amount of free charge carrier. 7Li NMR spectra shows jump discontinuity of different chemical shift, and it shifts toward upfield at the blends of PVDF/PVAc(80/20) .This result provides a powerful evidence in the trend of FT-IR data, since it confirms the enhanced basicity we suggested in FT-IR,spectrum ,and the conductivity behavior.7Li (CP/MAS)Spin-lattice relaxation time (T1) indicate the mobility of mobile lithium ion for different composition polymer host.We supposed that the major reason of this phenomena was caused by the increasing glassy transition temperature of the host.