| 摘要: | 近年來，對聚氧化乙烯（PEO）的研究焦點集中在利用不同的化合物或鹽類以摻合的方式來改善聚氧化乙烯本身易結晶的缺陷，使鋰離子自由運動的範圍增加。本研究中，將具有半導體性質與良好分子特性的二氧化鈦粒子（TiO2）以混摻的方式加入到高分子電解質的系統中。觀察奈米級二氧化鈦結晶粒子對鋰鹽解離速率的影響，並探討在聚氧化乙烯上結晶區塊與非結晶區塊當中鋰離子的運動情形。 研究結果發現Anatase晶型之奈米二氧化鈦結晶粒子在固態電解質系統當中的影響主要作用是在與鋰鹽作用後形成鹽類錯合物解離鋰鹽，對於降低聚氧化乙烯結晶性質的影響並不大。依據導電度數據結果可以發現，在添加5％奈米粒子可獲得最高之離子導電度。當奈米粒子含量增加至10％以上時，離子導電度降低。其成因是因為在高鹽類組成中鋰離子與奈米二氧化鈦作用形成錯化合物，熔融之高分子鏈段會包覆在二氧化鈦與鹽類作用之錯合物的表面形成錯合物微結晶，使得離子導電度降低。此表面微結晶現象在奈米二氧化鈦與鹽類混摻比例增加至15％時最為明顯。配合NMR、DSC、TGA、POM、SEM、TEM、AC-Impedance等儀器，本研究成功的解析了TiO2奈米粒子/PEO作為高分子電解質的可行性，其優缺點以及詳細的分子結構和鋰離子導電運動的關係。 Nano-particle composite polymer has demonstrated effective to improve various polymer mechanical properties. Using Nano-particle to improve solid polymer electrolyte (SPE) has also been reported, however, the specific role of the nano-particle in presence of the salt to the ion conductivity has never been clearly identified, apart from hand-waving speculations. In this research we present detailed SEM, TEM, POM and solid NMR studies regarding the function of TiO2 particle in the modification of ion conductivity, surface morphology, crystallization, and ion mobility in solid polymer electrolyte, PEO. The TiO2 nano-particle is made from the sol-gel preparation route from Ti(OBu)4 which bears Anatase structure with size in the order of 20 to 30 nm. The large surface potential, which prevents TiO2 from aggregation, is reduced in presence of the salt. On the one hand, it facilitated the lithium salt dissociation, and improved the free-ion content. But on the other hand, the surface charged particle tends to aggregate and trapped amorphous PEO in the clusters via the interaction between Li and PEO, as clearly demonstrated by SEM and solid NMR studies. The stronger interaction of TiO2 with salt reduces the amount of lithium to reduce PEO crystallinity. As a result, the PEO crystalline redevelops in the SPE’s at moderate TiO2 content of 5wt%, with high salt content. With increasing TiO2 content, however, it produces more aggregates and reduces PEO crystallinity, but the ion conductivity is not improved since the lithium is consumed by the TiO2 surface. The surface charged TiO2 particle and aggregates (dimension close to 0.5um) served as physical tie between PEO domains, and is found to also improve the mechanical properties, yielding a rubber-like polymer. Variable temperature conductivity measurements show the ion conductivity have all been improved with the addition of nano-TiO2. The best conductivity behavior occurs at the composition of 5wt% TiO2 and 18wt% LiClO4 salt, where the PEO crystallinity is about 5%. |
