聚氨酯基高分子的功能設計作為超級電容器與鋰電池的黏著劑、膠態高分子電解質及界面修飾層

Functions Design of Polyurethane-Based Polymers as a Binder, Gel Polymer Electrolyte, and Modified Layer for Supercapacitors and Lithium Batteries

王莉茜(Li-Qian Wang)

指導教授 ： 胡啟章

國立清華大學/工學院/化學工程學系/碩士(2020年)

摘要

本論文旨在設計功能性高分子並應用於儲能裝置，依高分子製備方式可分為兩部分，PUPAA和PU-co-AA。

1. 雙功能高分子PUPAA於超級電容器之應用
為增進用於儲能裝置之超級電容器的性能，此研究製備了具雙功能之黏性共聚物聚氨酯-聚丙烯酸（PUPAA），不僅可作為超級電容器中之膠態高分子電解質，亦可作為電極材料中之黏著劑。由此透明且機械性質良好的PUPAA薄膜為基質，吸取有機液體電解質（四乙基四氟硼酸銨鹽溶於碳酸丙烯酯溶劑）形成之膠態電解質，結合了有機液體和高分子固態電解質的優點，在無電解液洩漏風險的同時，具有3.2 mS cm-1之高離子電導率。且根據電化學分析，當在2.5 V之電位窗，0.5 A g-1之電流密度時，使用活性炭作為電極活性材料之可撓式全固態超級電容器表現優異，具有139.84 F g-1之比電容值， 30.35 Wh kg-1之能量密度，並在彎曲條件下具有良好的撓曲穩定性，當彎曲角度90o時，依舊保有超過94 %的電容保持率。
此外，為了在電極材料內部形成離子通道，進而提升超級電容器之性能。本研究採用製備之黏性PUPAA高分子取代電極材料中常用之黏著劑聚偏二氟乙烯（PVDF），除了具備固定活性材料之功能，PUPAA在吸取電解液後可形成深入電極層之離子通道，提升電解質層與電極層之接觸面積並優化活性材料之利用率。結果表明，以PUPAA和PVDF混合作為黏著劑時，隨著電極活性材料沉積量的提升，由於離子通道的作用，在單位面積下比電容值亦與沉積量呈現正比的提升。

2. UV固化PU-co-AA於超級電容器和鋰電池之應用
為改善膠態高分子電解質(GPE)和多孔電極之間的接觸問題，本研究將包含電解液和單體的液相混合物透過UV照射於電池中原位凝膠化，使GPE能深入電極材料顆粒和隔離膜的孔隙。相較於傳統預先製備的薄膜，此原位製備GPE之方式成功解決電極和電解質間的接觸問題。當應用於超電容時，在與PUPAA電極黏著劑協同下，已得到最佳化結果。於0.5 ~ 5 A g-1電流密度下，皆具有相較於商用液態系統更佳的電化學表現，0.5A g-1時，電容值高達143.5 F g-1。
而當應用於鋰電池時，UV固化PU-co-AA不僅可作為膠態高分子電解質，亦可作為液態系統中的界面修飾層。除了具有與電極緊密接觸之原位聚合優勢，PU-co-AA因富含醚基而具有高離子導電度，更透過引入帶負電之羧酸根離子而有高鋰離子轉移數(tLi+ = 0.86)，實現均勻的鍍鋰/剝鋰行為。作為GPE在Cu||Li和Li||Li電池中皆有優於液態系統的效果，有效降低初始成核過電位與極化現象。且在Li||LFP全電池中，羧酸根離子的引入提高容量保持率，使至100圈時保有71 %。此外，為穩定液態系統的電極電解質界面，亦將PU-co-AA作為Li||NMC811電池中的界面修飾層，並藉由添加Al2O3?進一步提高離子導電度與鋰離子轉移數(tLi+ = 0.92)。未經修飾的電池循環至約100圈即無法運作，而於Li塗覆界面修飾層則可穩定循環至150圈。且在第100圈時容量仍有125.3 mAh g-1，明顯大於未經修飾的88.5 mAh g-1。

關鍵字

聚氨酯聚丙烯酸 ； 可撓 ； 電雙層電容器 ； 鋰電池 ； 膠態高分子電解質 ； 黏著劑 ； 界面修飾層 ； 原位聚合

並列摘要

This thesis aims to design functional polymers and apply to energy storage devices. According to the preparation method, it can be divided into two parts, PUPAA and PU-co-AA.
1. Bi-functional polymer PUPAA for organic supercapacitors
To enhance the performance of the supercapacitor for energy storage devices, in this study, the sticky copolymer polyurethane-polyacrylic acid (PUPAA) was prepared and used not only as a gel polymer electrolyte in supercapacitor but also as a binder. The freestanding and transparent PUPAA film as the matrix, and swelled using an organic liquid electrolyte (TEABF4 in propylene carbonate solvents) combines the advantages of the organic liquids and of conventional polymers. Guaranteeing high ionic conductivity, which is recorded to be as high as 3.2 mS cm-1 without the risk of electrolyte leakage. According to electrochemical analysis, when operated within 0-2.5 V, the quasi-all solid-state supercapacitors using activated carbon as electrode material showed rather good capacitance, energy densities and flexibility, that is, a high specific capacitance of 139.84 F g-1 at 0.5 A g-1, a large energy density of 30.35 Wh kg-1, and a remarkably flexible performance under bending conditions (over 94 % specific capacitance retention at a bending angle of 90o).
Moreover, to develop a high performance supercapacitor by generating ionic tunnels in the electrode material. The commercial binder, poly(vinylidene fluoride) (PVDF) was also substituted by PUPAA in electrodes, which can more deeply bring electrolyte ions into the inner site of active materials, and thus increase the effective area between the interface of electrodes and electrolyte. The results showed that the areal specific capacitance of the electrode, which used PUPAA mixed with PVDF as the binder, was increased with the increasing of mass loading in the same ratio.
2. UV-cured PU-co-AA for supercapacitors and lithium batteries
To improve the contact problem between gel polymer electrolytes (GPE) and porous electrodes, in this study, liquid mixtures containing liquid electrolyte and monomers were in situ gelled in batteries through UV irradiation. So that GPEs can penetrate into the pores of electrode materials and the separator. Compared with the traditional pre-prepared film, using this in-situ method to prepare GPEs successfully solves the contact problem between the electrode and electrolyte. When applied to supercapacitors, optimized results have been obtained in cooperation with PUPAA binder. Having better electrochemical performance than the commercial liquid system under current densities of 0.5 ~ 5 A g-1, and the specific capacitance is as high as 143.5 F g-1 at 0.5 A g-1.
When applied to lithium batteries, UV-cured PU-co-AA can be used not only as gel polymer electrolytes, but also as modified layers in liquid systems. In addition to the high ionic conductivity endowed by abundant ether groups, through introducing negatively charged carboxylate ions, it shows a high lithium transfer number (tLi+ = 0.86) and achieves uniform lithium plating/ stripping behavior. As a GPE, it effectively reduced the nucleation overpotential and polarization phenomenon in Cu||Li and Li||Li cells. And in Li||LFP full cells, the introduction of carboxylate ions enhanced the capacity retention, which still retained 71% at the 100th cycle. Moreover, to stabilize interfaces between electrodes and electrolyte in a liquid system, PU-co-AA was also used as modified layers for Li||NMC811 cells. And by adding Al2O3 nanoparticles, ionic conductivities and the lithium transfer number (tLi+ = 0.92) were further increased. Unmodified cells can no longer work after 100 cycles, while with a modified layer coated on Li, stably cycled to 150 times can be achieved. And at the 100th cycle, the discharge capacity was still 125.3 mAh g-1, which was significantly larger than the unmodified one, 88.5 mAh g-1.

並列關鍵字

polyurethane-polyacrylic acid ； flexible ； electric double-layer capacitor ； lithium battery ； gel polymer electrolyte ； binder ； modified Layer ； in-situ polymerization

參考文獻

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