| 摘要: | 本研究以(3-glycidyloxypropyl)trimethoxysilane (GLYMO)對中孔洞分子篩MCM-41進行表面修飾，並利用X光粉末繞射儀以及固態核磁共振儀鑑定其化學結構。另外，將經修飾後的中孔洞分子篩MCM-41以不同比例摻混於高分子與鋰鹽 (PEO/LiClO4) 的系統中，得到複合式高分子電解質。利用交流阻抗分析儀、X光粉末繞射儀、微差式熱分析儀、掃描式顯微鏡以及多核固態核磁共振儀對此系統進行鑑定與分析。 這些分析結果顯示在摻混少量修飾後的中孔洞分子篩 (5 wt% G-MCM-41) 於固態高分子電解質中，因為高分子與經表面修飾的MCM-41的環氧環 (epoxy ring) 進行交聯反應，使得高分子與中孔洞分子篩相容性 (Compatibility) 增加。所以在<60oC時，導電度有明顯地上升。 而當摻混高比例的G-MCM-41於固態高分子電解質中，導電度反而下降。這是因為填充物扮演阻礙鋰離子運動的角色，使得鋰離子運動變差。在微差式熱分析儀的結果中顯示高分子鏈段的運動性和非結晶相的比例，受到G-MCM-41的影響，因而增加高分子鏈段的運動並降低結晶相的比例。以路易士酸－鹼之間的作用力解釋聚氧化乙烯鏈鍛 (PEO chain) 、G-MCM-41和鋰鹽 (LiClO4) 之間的關係，如何影響PEO結晶相的變化。 藉由固態7Li NMR的測量，在溫度小於玻璃轉化溫度時，7Li的譜寬開始明顯的變窄，這指出7Li離子除了經高分子傳導之外，鋰離子也可能沿著MCM-41的中孔洞通道表面或在MCM-41的中孔洞通道表面外移動。對於複合式高分子電解質來說，這個額外的導電機制是特殊的，這是在一些以PEO為基材的高分子摻混球狀填充物（如Al2O3、SiO2粒子）所看不到的。在去氫偶合7Li NMR光譜也證明在複合式高分子電解質中鋰離子存在於不同的化學環境。 在本研究中的第二部分，以未鍛燒及鍛燒後的MCM-41以不同比例摻混於高分子電解質的系統中，得到複合式的高分子電解質。再這一系列的高分子電解質，從其導電度與微差示熱分析儀的結果中，可以知道摻合5 wt% 的未鍛燒的MCM-41時，對高分子電解質並無助益，相反的是降低導電度。而在摻合同樣比例鍛燒後的MCM-41時，由於中孔洞表面提供許多的氫氧基，這些氫氧基將和高分子電解質中的鋰鹽作用，會增加高分子的結晶度，並且幫助鋰鹽的解離，因此導電度的結果顯示導電度提高。 另外，加入10 wt% 未鍛燒或鍛燒後的MCM-41於高分子電解質中時，均可以觀察到結晶度下降，並且導電度下降的結果。而以加入鍛燒後MCM-41結晶度下降程度較高，這是因為系統中存在路易式酸-鹼之間的作用力所形成之錯合物，由於錯合物量過多，抑制了高分子鏈鍛的再結晶。在這一部分的研究中，仍可藉由去氫偶合7Li NMR光譜也證明在複合式高分子電解質中鋰離子存在於不同的化學環境。 The thesis divided into two parts. First, we are interested that the effect of addition of Mesoporous silica MCM-41 with surface modification of (3-glycidyloxypropyl)trimethoxysilane (GLYMO) to poly(ethylene oxide) (PEO) complexed with LiClO4 has been explored by alternating current (AC) impedance, powder X-ray diffraction (XRD) , differential scanning calorimeter (DSC), and multinuclear solid-state NMR measurements. The presence of small quantity of GLYMO modified MCM-41 enhances the ionic conductivity of the resulting composite electrolyte as compared to present PEO/LiClO4 electrolyte. The enhancement in conductivity is directly correlated with the improved compatibility between PEO and surface modified MCM-41 as a result of blending PEO with GLYMO group. Addition of high concentration of surface modified MCM-41 leads to a decrease in the conductivity of the composite electrolyte, mainly because MCM-41 filler acts an insulator that impedes the lithium ion transport. DSC results show that both the polymer segmental motion and the proportion of amorphous PEO phase are affected by addition of MCM-41 filler. The change of portion of crystalline PEO phase can be explained by Lewis acid-base interactions between PEO chain, MCM-41 surface, and lithium cation. Solid-state 7Li NMR measurements show that the 7Li linethwidth narrowing begins at temperature much lower than the glass transition temperature of PEO chains, indicative of the presence of an additional conduction mechanism with lithium ions moving along (both interior and exterior) the mesoporous channels of MCM-41.The additional mechanism is unique for the composite electrolytes doped with mesoporous silica MCM-41, and is absent in the case of other spherical fillers such as Al2O3 and SiO2 particles in PEO-based electrolytes. Variable temperature proton decoupled 7Li MAS (magic angle spinning) NMR spectra reveal that at least two different lithium environments are present in the composite electrolyte, serving as an evidence for the existence of interaction between lithium cation and MCM-41 surface. In the second part of my thesis, the effect of addition of uncalcined or calcined mesoporous silica MCM-41 to poly(ethylene oxide) (PEO) complexed with LiClO4 has been explored by alternating current (AC) impedance, powder X-ray diffraction (XRD) , differential scanning calorimeter (DSC), and multinuclear solid-state NMR measurements. The present of small quantity of uncalcined MCM-41 do not enhance the ionic conductivity of the resulting composite electrolyte as compared to present PEO/LiClO4 electrolyte. However, the present of small quantity of calcined MCM-41 enhances the ionic conductivity of the resulting composite electrolyte as compared to present PEO/LiClO4 electrolyte. The enhancement in conductivity is directly correlated with Lewis acid-base interactions between PEO chain, MCM-41 surface, and lithium cation. Addition of high concentration of uncalcined or calcined MCM-41 leads to a decrease in the conductivity of the composite electrolyte, mainly because uncalcined or calcined MCM-41 filler acts an insulator that impedes the lithium ion transport. Variable temperature proton decoupled 7Li MAS (magic angle spinning) NMR spectra reveal that at least two different lithium environments are present in the composite electrolyte, serving as an evidence for the existence of interaction between lithium cation and MCM-41 surface. |
