碳系超級電容器用耐高壓電解液研發;Development of High Withstand Voltage Electrolyte for Carbon Supercapacitors

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Title:	碳系超級電容器用耐高壓電解液研發;Development of High Withstand Voltage Electrolyte for Carbon Supercapacitors
Authors:	張靖雍;Chang, Ching-Yung
Contributors:	材料科學與工程研究所
Keywords:	超級電容器;活性碳;耐高壓電解液;碸類添加劑;SBPBF4
Date:	2019-08-22
Issue Date:	2019-09-03 14:51:03 (UTC+8)
Publisher:	國立中央大學
Abstract:	本研究主要利用Propylene carbonate (PC)為主要有機溶劑，並分三階段開發耐高壓電解液：(一)比較不同碸類添加劑對耐電壓能力的影響，包含 A、B、C，固定以1.0 M溶質莫耳濃度的Tetraethylammonium tetrafluoroborate (TEABF4)作為鹽類，加入相同體積百分比x%的不同碸類添加劑。結果顯示B的添加能保持PC低黏度與高導電度的特性，同時有效提升電解液之耐壓能力。(二)選取第一階段比較出的最佳碸類添加劑B，以y%、x%、z%三不同體積百分比加入電解液，比較不同體積百分比的添加劑和未添加前(1.0 M TEABF4/PC)各電性與耐壓能力。結果顯示x%為最適當比例，再提高體積百分比亦無法提高耐壓能力，同時還會造成電解液黏度上升，降低導電度。(三)根據前二階段實驗結果，調配出最佳有機溶劑，並比較不同種類溶質對電性與耐壓能力的影響，包含TEABF4與5-Azoniaspiro[4,4]nonane tetrafluoroborate (SBPBF4)，結果指出SBPBF4在電性與耐電壓能力上，都顯著優異於TEABF4。接著選用SBPBF4為固定鹽類，配製1.0 M、1.5 M二不同溶質莫耳濃度，探討不同溶質濃度對耐電壓能力的影響，結果顯示提高濃度至1.5 M後耐壓能力有所提升，推測是電解液的溶劑化作用所導致。本研究最終合成1.5 M SBPBF4/PC+x%B此最為優異的耐高壓電解液。由材料分析可觀察其高導電度(15.2 mS/cm)、低交流阻抗(Rs : 1.6 ohm；Rct : 2.3 ohm)等特性，使其整體電容值高，在1 A/g電流密度3.0 V下擁有113 F/g之電容值，20 A/g尚有83 F/g，電容維持率表現優異，同時具備耐高壓能力，電位窗高達3.3 V，且於3.3 V時庫倫效率可高達97.x%。本研究在最後一章節將開發之最佳電解液，與其他商用電解液組裝之超級電容器，經過老化測試後進行各材料結構與電性分析。發現以純PC作為溶劑之電解液，老化後在3.0 V的高速電容值衰退十分嚴重，根據SEM結果顯示，經過3.0 V老化過後正負極便會被大量PC裂解所生成的聚合物披覆，其中以負極被覆蓋的程度較大，顯示電解液的裂解反應在負極影響較大；本研究開發之1.5 M SBPBF4/PC+x%B和商用高電壓電解液1.5 M SBPBF4/SL+EMS，老化後在3.0 V高速電容值衰退程度較前二者小，其中又以1.5 M SBPBF4/PC+x%B 較佳，由SEM結果顯示3.0 V老化後兩者正負極碳材完整性高，且都是負極完整性高於正極，顯示耐壓能力的關鍵在於電解液於負極端裂解的程度大小，而根據Raman負極結構完整性結果，1.5 M SBPBF4/PC+x%B的負極結構較1.5 M SBPBF4/SL+EMS還完整，與老化後3.0 V高速電容值結果相呼應。綜合所有數據結果指出，本研究開發之1.5 M SBPBF4/PC+x%B，具備低黏度與高導電度特性，同時耐壓能力優於商用高電壓電解液。關鍵詞：超級電容器、活性碳、耐高壓電解液、SBPBF4、碸類添加劑 ;In this study, we use PC as the main solvent in our organic electrolyte which is used for carbon EDLCs, and develop the high-withstand voltage electrolyte in three stages: (1) Compare the effects of different types of sulfone additives on withstand voltage including A, B, and C. All additives will be added at 5 vol% in PC with 1.0 M TEABF4, to discuss high rate performances and the withstand voltage. (2) Select the best additive compared in the first stage and add the additive into the electrolyte at y%, x%, z% three different volume percentages. Compare high rate performances and the withstand voltage between different volume percentages of additives and before adding, which is 1.0 M TEABF4/PC. (3) According to the results of the first two stages of experiments, the optimal organic solvent was modificated. Next, compare the effects of different types of solute including TEABF4 and SBPBF4 to figure out the correlation with high rate performances and the withstand voltage. In this part, all the data indicates that SBPBF4 is superior to TEABF4 in all electrochemical performances. Next step, use SBPBF4 to prepare 1.0 M and 1.5 M two different solute molar concentration, investigating the association between the solute concentration and withstand voltage. After the final modification of the electrolyte, compare the best of the high withstand voltage electrolyte with the high-voltage commercial electrolyte, 1.5 M SBPBF4/SL+EMS. In this study, we finally synthesized 1.5 M SBPBF4/PC+x% B, which is the most excellent high withstand voltage electrolyte. It can be observed high conductivity (15.2 mS/cm) and low resistance (Rs: 1.6 ohm; Rct: 2.3 ohm) by material analysis, result in good capacitance performance. It shows a capacitance of 113 F/g at 1 A/g and 83 F/g at 20 A/g for 3.0 V, demonstrating the excellent capacitance retention. For the withstand voltage, the potential window is up to 3.3 V and the coulombic efficiency is up to 97.5% at 3.3 V. In the last chapter of this study, we compare the material analysis and electrochemical performances after aging tests of carbon EDLCs, assembled with our best high withstand voltage electrolyte and other commercial electrolytes, to understand the key improving high withstand voltage for EDLCs in organic systems.
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