聚輪烷側鏈接枝聚乙二醇：合成及其在固態高分子電解質的應用

Polyrotaxane-graft-poly(ethylene oxide)：Syntheses and Applications in Solid Polymer Electrolytes

彭晨瑜(Chen-Yu Peng)

指導教授 ： 趙基揚

國立臺灣大學/工學院/材料科學與工程學研究所/碩士(2021年)

https://doi.org/10.6342/NTU202102261

摘要

聚環氧乙烷(poly(ethylene oxide), PEO)具有靈活的醚鍵鏈段和有助於解離鋰鹽的醚基氧原子，因此成為被廣泛研究的鋰離子電池之固態電解質(solid polymer electrolyte, SPE)材料；然而因為PEO具有半結晶的性質，使它在室溫下的離子傳導度小於10-5 S cm-1，在高溫下又會喪失機械強度而不利於實際電池運作。
在本研究中，我們使用聚輪烷(polyrotaxane, PR)作為基材，將短鏈的PEO接枝於PR的α-環糊精(a-cyclodextrin, α-CD)上來開發新型態的SPE。PR是一種超分子聚合物，有多個CD環串在PEO主鏈上，透過CD環上的OH基產生鏈與鏈之間的氫鍵而形成超分子網路結構，而且CD環可沿著PEO主鏈移動形成獨特的滑環效應，使PR具有低結晶性、良好的機械強度、自癒行為(self-healing)及超高的延展性的性質，因此我們以PR為骨幹，透過短鏈PEO側鏈修飾於CD環上以調控分子間作用力，並建立主鏈PEO之外的第二個離子傳導通道，所獲得的SPE同時能夠具有高的室溫離子傳導度、良好的機械強度及薄型化的特性。我們使用三種不同長度的PEO側鏈修飾在CD環上並調控PEO的接枝率，開發出帶有聚乙二醇側鏈接枝的聚輪烷(PEO-PR)，並改變鋰鹽(lithium perchlorate, LiClO4)的濃度以得到SPE，並探討PEO側鏈長度、接枝率及鋰鹽濃度對SPE的熱性質、微結構、機械性質與電化學性質的影響。所得之SPE薄膜的厚度約50至70 μm，拉伸率能夠超過200%，最佳的室溫離子傳導度可達2.89×10-5 S cm-1，80℃下則可達1.11×10-4 S cm-1，而且改變溫度並不會影響其機械性質，60℃時仍具有高韌性及高於PEO(Mv 600,000) 7倍的楊氏係數，以上結果顯示PEO-PR是一種可有效提升鏈段運動能力及降低活化能以提高SPE的柔韌性和離子傳導度的材料。

關鍵字

鋰電池 ； 固態高分子電解質 ； 聚環氧乙烷 ； 聚輪烷 ； 側鏈接枝

並列摘要

Poly(ethylene oxide) (PEO) is the mostly studied materials for solid polymer electrolytes in lithium ion batteries because its high chain mobility and good capability to dissociate lithium salts could facilitate lithium ion transport. However, the intrinsic semi-crystallinity of PEO leads to low conductivity less than 10-5 S cm-1 at room temperature while the mechanical strength is lost at high temperature, which are disadvantageous to real battery application.
In this study, we adopt polyrotaxane (PR) as the substrate and graft short PEO side chains to a-cyclodextrins of PR to develop novel SPEs. PR is classified as a supramolecular polymer, in which a PEO main chain tethering through multiple CDs, and the hydroxyl groups in the CD rings could form hydrogen bonding to allow the interconnection between different PR chains to form supramolecular network structure. Because CD rings could move along the PEO main chain to generate unique “slide ring effect”, PRs possess low crystallinity, good mechanical strength, self-healing capability and ultra-high ductility. Therefore, by grafting short PEO side chains to PR, the strength of intermolecular forces could be tailored and additional lithium ion conducting pathways could be constructed for the resulting SPEs. It is anticipated that the SPEs should exhibit high ionic conductivity at room temperature and good mechanical strength as a thin membrane. Hereby, PEO side chains with three different lengths are incorporated in various grafting densities to prepare the PEO modified PR, termed as PEO-PR. We also alter the concentration of lithium salts LiClO4 in the resulting SPEs to systematic study the effect of the length and grafting density of PEO side chains in PEO-PR as well as the lithium salt concentrations on the microstructure, the mechanical properties, and the electrochemical properties of the SPEs. The obtained SPE membranes prepare from solvent casting are in 50-70 μm thick. Among all SPEs, the best ionic conductivities are 2.89×10-5 S cm-1 at 30℃ and 1.11×10-4 S cm-1 at 80℃. In addition, the mechanical properties of PEO-PR SPEs are not temperature sensitive, and a more than 200% elongation and a Young’s modulus 7 times higher than PEO based SPE are observed at 60℃. These observations suggest PEO-PR is highly potential for SPEs for the enhanced segmental motion to improve the ionic conductivity with lowered activation energy as well as for the high ductility.

並列關鍵字

lithium batteries ； solid polymer electrolyte ； poly(ethylene oxide) ； polyrotaxane ； side chain grafting

參考文獻

[1] Tarascon, J.-M.; Armand, M., Issues and challenges facing rechargeable lithium batteries. Materials for sustainable energy: a collection of peer-reviewed research and review articles from Nature Publishing Group 2011, 171-179.

[2] Long, L.; Wang, S.; Xiao, M.; Meng, Y., Polymer electrolytes for lithium polymer batteries. Journal of Materials Chemistry A 2016, 4 (26), 10038-10069.

[3] Ngai, K. S.; Ramesh, S.; Ramesh, K.; Juan, J. C., A review of polymer electrolytes: fundamental, approaches and applications. Ionics 2016, 22 (8), 1259-1279.

[4] Arya, A.; Sharma, A. L., Polymer electrolytes for lithium ion batteries: a critical study. Ionics 2017, 23 (3), 497-540.

[5] Armand, M., The history of polymer electrolytes. Solid State Ionics 1994, 69 (3-4), 309-319.