交聯式PVA-g-SBMA/PEDOT:PSS作為於固態電解質的應用

Abstract

鋰電池在現今的儲能裝置中因為優秀的能量密度和循環壽命，佔有重要的地位，故受到廣泛的討論。但傳統鋰離子電池存在洩漏與穩定性不足等問題，因此有研究指出，使用固態電解質的全固態鋰電池能有效解決這樣的缺點。其中，固態聚合物電解質 (SPEs) 具備優異的安全性與柔韌性，為極具發展的一個議題，但由於以聚合物為基底的電解質會面臨導電度相對不足的狀況，因此本研究旨在開發並合成一種接枝共聚物 PVA-g-SBMA，透過將兩性離子甲基丙烯酸磺機甜菜鹼 (sulfobetaine methacrylate, SBMA) 接枝至聚乙烯醇 (poly(vinyl alcohol), PVA) 上，成功合成 PVA-g-SBMA。聚乙烯醇具有良好的成膜性與機械強度，能提升固態器件的柔性與穩定性，而 SBMA 的雙離子結構促進高效離子傳輸，進而提高離子導電率與固態電解質在能量儲存應用中的性能。我們透過 ¹H NMR 光譜分析，我們探討了 PVA-g-SBMA 雙離子接枝共聚物的質子化學位移。水相 GPC 測試結果顯示，該接枝共聚物的Mn為 15,755，PDI為 1.17，而 SBMA 的接枝率為 25%。然而，該材料的機械性能不足，導致薄膜脆裂。為解決此問題，本研究透過交聯方式提升其機械性能，使用導電高分子 PEDOT:PSS 並以3-環氧丙氧丙基三甲氧基矽烷 (3-glycidoxypropyltrimethoxysilane, GOPS) 作為交聯劑，二甲基亞碸 (DMSO) 作為溶劑，完成交聯反應。交聯機制涉及 PVA 及 PSS 上的羥基反應，GOPS 與 PSS 鍵結，形成穩固的交聯網絡。交聯反應經過 120 ℃ 加熱完成。本研究亦比較不同交聯比例對薄膜性能的影響。此外，我們摻入鋰鹽，以探討不同鋰鹽濃度對材料的影響。根據EIS測試結果，最佳導電系統為摻雜 0.1 wt.% PEDOT:PSS 及 0.015 wt.% LiTFSI 之交聯 PVA-g-SBMA，其在室溫下的離子導電率達 4.9 × 10⁻⁴ S/cm。此外，本研究亦探討了薄膜的熱學性質、形態結構與分子鏈間作用力。

Conventional lithium-ion batteries face issues like leakage and instability. Solid-state lithium batteries with solid electrolytes address these, while solid-state polymer electrolytes (SPEs) offer safety and flexibility. This study primarily aimed to develop and synthesize a graft copolymer, PVA-g-SBMA, which was successfully synthesized by grafting [2-(methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl)ammonium hydroxide (SBMA) onto poly(vinyl alcohol) (PVA). PVA provided excellent film-forming ability and mechanical strength, enhancing flexibility and stability in solid-state devices. Meanwhile, SBMA’s zwitterionic structure promoted efficient ion transport, improving ionic conductivity and solid electrolyte performance in energy storage applications. From the results, the proton assignment of the PVA-g-PSBMA zwitterionic graft copolymers was investigated via 1H NMR spectra. The molecular weight of the graft copolymer was determined through aqueous GPC; the number average molecular weight (Mn) was 15,755, and the PDI was 1.17. The grafting efficiency of SBMA was calculated as 25 %. However, the material lacked sufficient mechanical properties, leading to brittle membranes. To solve this problem, we crosslinked the film to enhance its mechanical performance. The grafted copolymer was crosslinked with the conductive polymer PEDOT:PSS using (3-glycidyloxypropyl)trimethoxysilane (GOPS) as the crosslinker and dimethyl sulfoxide (DMSO) as solvent to complete the crosslinking reaction. The crosslinking mechanism involved the reaction between hydroxyl groups on PVA and PSS, while the GOPS bonded with PSS, forming a robust crosslinked network. The crosslinking process was completed by heating the mixture to 120 °C. We also compared different crosslinking ratios to discuss film performances. Lithium salts were incorporated to investigate the effect of varying lithium salt concentrations. According to EIS measurements, the best-performing system was crosslinked PVA-g-SBMA with PEDOT:PSS 0.1 wt. % and LiTFSI 0.015 wt. %, which reached conductivities of 4.9 × 10-4 S/cm at room temperature. We also explored the film's thermal properties, morphologies, and chain interactions in this research.