| 摘要: | 針對固態高分子電解質在組成電池的應用性方面，限制最大的離子導電度與機械性能不佳的因素，本研究利用交聯劑六甲烯基四氨（Hexamethylene Tetramine, (CH2)6N4）的添加來交聯酚醛樹酯，使其產生網狀結構，以增加固態高分子電解質的機械性質、尺寸安定性，並提昇導電度。由於影響導電度的因素，除了PEO的結晶性之外，還有可移動鋰離子的量及其擴散速率與活化能大小，以及高分子自由體積變化的因素。因此，本研究利用IR、DSC、TGA、NMR、SEM、AC-impedance等分析儀器來探討交聯前、後固態高分子電解質的結構特性、表面型態與分子運動型態的變異性對導電性質之影響。 結果發現交聯之後電解質的表面型態良好，並無相分離的現象，且熱裂解溫度提高到420℃至460℃之間，這不僅提升電解質的機械性能，更藉由酚醛樹酯網狀結構所形成之微孔區塊，來降低PEO結晶性，並促進鋰鹽解離速率。而高分子鏈段的運動性亦因為交聯網狀結構產生，使其自由體積變大而增加分子鏈段的運動性促使玻璃轉移溫度降低，有利於鋰離子的傳遞。尤其在高鋰鹽含量組成，當交聯比例增加時，如樣品D4y(composition?) 的玻璃轉移溫度更是降低為-46.9℃。此新型固態高分子電解質的導電度，並沒有因交聯提升機械性能而被犧牲。本研究中，交聯後的高分子電解質之導電度皆達10-3S/cm左右，而樣品D3y展現全溫區最佳的導電行為及優良之機械性，值得進行實際電池之組裝及性能測試。此一結果，特別是反應在常溫下導電度的大幅提昇，對固態高分子電解質之發展具有重大意義。 Low ion conductivity and mechanical property limits the utility of solid polymer electrolyte in solid sate electrochemical device applications. Current research approach is to modify the solid polymer electrolyte to improve mechanical stability and ion conductivity by cross-liking PEO/phenolic polymer electrolyte with Hexamethylene Tetramine (CH2)6N4). The cross-linking is found to be more affect on mechanical property, dimension stability, ion conductivity, PEO crystallinity and surface morphology. To investigate surface morphology, molecule structure, segmental motion, lithium transport and ion conductivity before and after cross-linking with Hexamine modified SPE were carried by using variety of experimental techniques like IR, DSC, TGA, NMR, SEM, AC-impedance measurements etc. The surface morphology is improved dramatically and thermal stability increased to 420 to 460 oC after cross-linking, which corroborates the improved mechanical property. Compared to pure PEO and PEO/phenolic without cross-linking, PEO crystallinity is reduced due to the constraint micro-domain. Furthermore the PEO chain motion is increased after cross-linking due to the expanded free-volume, as reflected in the reduction of glass temperature. For example, Tg for sample D4y (composition) is —46.9 ℃. However, the ion conductivity is not sacrificed by the improved mechanical property, instead it exhibited more superior room temperature conductivity, reaching the order of 10-3S/cm.. These results, especially the substantial improvement in room temperature conductivity, are significant to the development of solid polymer electrolyte technology. Sample D3y shows the most promising balance of mechanical and electrical properties and should be explored for battery assembly tests. |
