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標題: | 有機人工固態電解液界面膜於高電壓水溶液電池之研究 Research on Artificial Solid-Electrolyte Interphase for High-Voltage Battery in Aqueous Electrolytes |
作者: | Yu-Hsiang Lin 林玉祥 |
指導教授: | 吳乃立(Nae-Lih Wu) |
關鍵字: | 水系鋰離子電池,水溶液電解液,人工固態電解質界面,鋰鈦氧,硫化鉬, Aqueous Li-ion batteries,Aqueous electrolyte,Artificial solid electrolyte interphase,Lithium titanate,Molybdenum sulfide, |
出版年 : | 2018 |
學位: | 碩士 |
摘要: | 在發展鋰離子電池的過程中,現今面臨最大的挑戰是安全性和成本的問題。首先,安全的顧慮來自於電池中的有機電解液大多具有可燃性,且充放電過程中又必須承受高伏特的工作電壓,例如常用的酯類(ester)溶劑的問題是具可燃性且會與電極產生反應,鋰鹽六氟磷酸鋰(LiPF6)的問題是熱穩定性差、遇水易分解及具有高毒性,因此,使用上可能會有過熱或是爆炸的問題。再者,傳統製造的鋰電池生產成本高、生產條件要求高,需在低濕度和精密準確監控的環境下才可進行電池的組裝,因此,上述之問題已成為鋰離子電池無法推廣於大規模儲能裝置上的阻礙。
然而,使用水溶液電解液應用在鋰離子電池上可以解決上述提到的顧慮,其安全性高、對環境友善、成本低、離子傳導能力好…等優點,最重要的是在生產過程中,對於外界空氣和水分的要求程度較為寬鬆,容易實現低成本和大規模生產,因此,水溶液電解液的開發對於鋰離子電池的發展是勢在必行的。 儘管水溶液電解液具有上述優點與特性,然而水溶液電解液面臨最大的問題在於穩定的電壓區間只有1.23伏特,超過這範圍即會產生水的分解反應,如此小的電壓區間無法使水系鋰離子電池滿足現今高蓄電效能之期待。 因此,在這項研究中,實驗的構想是使用安全、低毒性、低濃度的水溶液電解液,並利用簡單且方便的高分子塗層(polymer-coating)的方式,在電極和材料表面上,建造一層人工固態電解質界面(Artificial SEI),這層界面的功用主要是隔絕電極片和阻礙水分子的接觸,但仍能讓鋰離子(Li+)通過,間接的抑制水分子和電極片產生水分解的反應,而這樣的方法能直接擴展鋰離子電池的整體工作電壓。 在實驗的第一部分,先尋找適當的高分子作為人工固態電解質界面,分別為聚四氟乙烯(PTFE)和聚偏二氟乙烯(PVDF),利用這兩種高分子本身具備疏水的特性,在電極表面建立一層與水分子隔絕的界面膜,並藉由循環伏安法的測試,證實這兩層膜皆具有抑制產氫反應功效,達到擴張整體工作電位的效果。 在實驗的第二部分,嘗試多種的負極材料來驗證聚偏二氟乙烯界面膜的效用,我們選用鋰鈦氧、二氧化硫和硫化鉬來進行實驗,由於這三種材料的電位皆低於產氫反應的電位,是相當適合用來觀察界面膜抑制產氫的效用,且由結果顯示這界面膜確實能有效減緩產氫反應的發生,幫助低電位的負極材料在低電位進行氧化還原。在鋰鈦氧的實驗中,界面膜可減緩氧化還原反應衰退的現象,並降低產氫反應所造成的影響,而在硫化鉬的實驗中,首先自行合成出硫化鉬材料,觀察材料只在高濃度的電解液中才有完整氧化還原的訊號,但可藉由塗層界面膜,來降低使用的電解液的濃度,使得硫化鉬材料在低濃度的電解液下也能進行完整的氧化還原反應。 Nowadays, the serious problems in the development of Li-ion batteries were the safety concern and high cost. First of all, the safety concern is derived from the use of organic-based electrolytes, and these electrolytes are flammable and needed to withstand at high voltage. For example, the ester-based solvents are highly flammable and reactive with electrodes. Also, the lithium salt (LiPF6) is thermally unstable, easily decomposed and toxic. Thus, the overheat and explosion problem might occur while batteries go the thermal run away. Second, the manufacturing cost of Li-ion batteries is expensive since the manufacturing process is required under the specific environment with low moisture. As a result, these problems hinder the development of energy storage devices for high energy applications, such as electric vehicles and energy grids. However, the aqueous electrolytes for Li-ion batteries can resolve these concern as I mention above. Aqueous electrolytes are much safer, environmentally friendly, low cost and higher ionic conductivity. And the most important thing is the manufacturing process can operate in the air instead of the specific environment, which is beneficial to realize to low cost and mass production. Consequently, the development of aqueous electrolyte is important and necessary for Li-ion batteries in the future. Even though aqueous electrolytes have those advantages in above, the narrow electrochemical stability window (1.23V) is the most serve shortcoming which causes aqueous Li-ion batteries cannot be commercialized. And if the cells operate beyond this range, the water-splitting reaction will happen unwillingly. That is to say, aqueous Li-ion batteries with the narrow electrochemical window cannot satisfy the demand and the requirement of the high voltage batteries technology. In this research, our idea is constructing an artificial solid-electrolyte interphase (SEI) on the electrode surface by polymer coatings to enable the use of aqueous electrolyte with low salt concentration. The artificial SEI is expected to prevent the access of water molecules to electrode surface for water splitting, while allowing Li-ions transport through the interphase. Therefore, the overall working potential can be enlarged to become wider. In my first part of the experiment, we try the two different polymers (PTFE & PVDF) as artificial SEIs. We take advantage of the hydrophobic property of these two polymers to hinder the passage of water molecules to the electrode surface. Cyclic voltammetry (CV) tests prove the sufficient inhibition of hydrogen evolution reaction. And the electrochemical window is enlarged by these two kinds of polymer coatings, no matter on the aluminum or titanium current collectors. In the second part of the experiment, the applicability of the polymer coatings is tested with few kinds of anode materials in aqueous electrolyte. Those materials are lithium titanate, titanium disulfide and molybdenum sulfide. Since these potentials are all lower than the potential of hydrogen evolution reaction, they are suitable for evaluating the effect of the artificial film. The final result shows that the film can reduce hydrogen evolution and make these anode materials to undergo the redox reaction. For lithium titanate, the film alleviates the decay of redox reaction and the side effect of hydrogen evolution. For the synthesized molybdenum sulfide materials, the entire redox reaction can only undergo in the highly concentrated electrolyte. However, the coatings help the second redox reaction reappear instead of hydrogen evolution reaction in low concentrated (1m LiTFSI(aq)) electrolyte. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/79027 |
DOI: | 10.6342/NTU201801075 |
全文授權: | 有償授權 |
電子全文公開日期: | 2023-08-23 |
顯示於系所單位: | 化學工程學系 |
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