能量與功率值為工作電壓的平方比是眾所皆知的事情，所以工作窗口的大小極大影響電容器的儲存能力。而我們將證明合適的窗口大小不再一直是影響儲存能量的唯一原因，本次研究，我們探討離子液體[EMIM][TFSI]嵌入奈米碳管對於指叉式微型電容器的能量儲存影響。
原則上，可操作電位窗口受到電解液分解限制，離子液體[EMIM][TFSI]以白金片當電極測量可用電為範圍：-1.8  2.6 V (vs. RHE)。然而，一維奈米碳管是層狀結構，奈米碳管經受陽離子[EMIM]和陰離子[TFSI] 的嵌入，導致剝離或是管破裂，嵌入的電位範圍小於離子液體[EMIM][TFSI]分解電位。我們用循環伏安探討上界與下界電位，且以拉曼光譜解析出嵌入限制電位，嵌入的上界電位決定在1.5和1.7 V (vs. RHE)之間，下界電位決定於-1.6 和-1.7 V (vs. RHE)之間，在循環穩定分析進一步驗證嵌入的上界與下界電位的影響。
當操作電位窗口2.0 V，微型電容器充放電10000圈後的保留率約100 %，代表有很好的循環穩定性，且庫倫效率也很快提升且穩定於100 %。然而，當操作電壓設在2.8 V或3.8 V，電容器的循環穩定逐漸下降，因為電極的電位已達到離子嵌入的電位境界，且奈米碳管有部分破裂。當電容器電壓設在2.8 V，正極的電位達到嵌入的上界內，且隨著圈數增加比電容值逐漸下降，在電流密度8 A g-1充放電10000圈後，保留率為90.8 % 。另外一方面，當電容器窗口設在3.8 V，而電流密度30 A g-1充放電10000圈後，保留率為77.5 %，由於循環測定中正負極都受到並非只有正極，造成低保留率。因此，電化學電容器的循環穩定性，主要是受電壓窗口，少數影響來自於電流密度，因此兩個因素能改變的正負電極的電位界限。

It is well-known that the energy and power values of an ultracapacitor are proportional to the square of its working voltage window. The size of working window influences the storage capability tremendously. As we shall demonstrate, the answer of proper window size is not a straightforward one. In this work, we investigate the influences of ionic liquid [EMIM][TFSI] intercalation in carbon nanotubes (CNT) on energy storage of a miniature electrochemical capacitor with interdigitated electrodes.
In principle, the workable potential window is governed by decomposition potential limits of the electrolyte. For ionic liquid [EMIM][TFSI], the measured potential range with a platinum working electrode is -1.8  2.6 V (vs. RHE). Nevertheless, one-dimensional CNT is a layer structure material. [EMIM] cation and [TFSI] anion may undergo intercalation into CNT, resulting in exfoliation or tube rupture. The potential range of intercalation is narrower than the decomposition limits of ionic liquid [EMIM][TFSI]. We explore the potential upper and lower limits with cyclic voltammetry and resolve the intercalation limits with Raman spectroscopy. The upper potential limit of intercalation is determined between 1.5 and 1.7 V (vs. RHE), while the lower potential limit is decided between -1.6 and -1.7 V (vs. RHE). The upper and lower potential limits for intercalation are further validated in the cycle stability analysis.
When operated in the potential window 2.0 V, the miniature ultracapacitor was charged and discharged with excellent cycle stability, typified by a retention ratio 100% after 104 cycles. Their coulombic efficiencies quickly rise up, and hold steady at 100%. However, when the applied voltage is set at 2.8 V or 3.8 V, the cycle stability of capacitor gradually declines, because the electrode potential has reached the potential limits of ion intercalation and ruptured a fraction of CNT structure. When the capacitor window is set 2.8 V, the positive electrode potential can reach the intercalation upper limit, and the capacitance value gradually decreases with increasing cycle number. The retention ratio, after 104 cycles, is 90.8% at current density 8 A g-1. On the other hand, when the capacitor window is set 3.8 V, the capacitor energy is cycled at current density 30 A g-1, the retention ratio is only 77.5% after 104 cycles. The lower retention ration results from both of the electrodes, not just positive electrode, which experienced intercalation during energy cycling. Hence the cycle stability of this electrochemical capacitor is mainly affected by the voltage window, less influenced by the current density, since both factors can change the potential boundaries of positive and negative electrodes.

1. 胡啟章：電化學原理和方法 五南圖書出版公司出版
2. Electropaedia,” http://www.mpoweruk.com/performance.htm
3. Simon, P., and Y. Gogotsi. "Materials for Electrochemical Capacitors." Nature materials 7, no. 11 (2008): 845-854.
4. Armand, M., F. Endres, D. R. MacFarlane, H. Ohno, and B. Scrosati. "Ionic-Liquid Materials for the Electrochemical Challenges of the Future."
Nature materials 8, no. 8 (2009): 621-629.
5. Carlin, R. T., H. C. De Long, J. Fuller, W. J. Lauderdale, T. Naughton, P. C. Trulove, and C. S. Bahn. "Dual Intercalating Molten Electrolyte Batteries." 393, 201-206, 1995
6. Hardwick, L. J., M. Hahn, P. Ruch, M. Holzapfel, W. Scheifele, H. Buqa, F. Krumeich, P. Novak, and R. Kotz. "An in Situ Raman Study of the Intercalation of Supercapacitor-Type Electrolyte into Microcrystalline Graphite." Electrochimica Acta 52, no. 2 (2006): 675-680.
7. Hardwick, L. J., P. W. Ruch, M. Hahn, W. Scheifele, R. Kotz, and P. Novak. "In Situ Raman Spectroscopy of Insertion Electrodes for Lithium-Ion Batteries and Supercapacitors: First Cycle Effects." Journal of Physics and Chemistry of Solids 69, no. 5-6 (2008): 1232-1237.
8. Zhao, Xin, Beatriz Mendoza Sanchez, Peter J. Dobson, and Patrick S. Grant. "The Role of Nanomaterials in Redox-Based Supercapacitors for Next Generation Energy Storage Devices." Nanoscale 3, no. 3 (2011): 839-855.
9. Zhang, Li Li, and X. S. Zhao. "Carbon-Based Materials as Supercapacitor Electrodes." Chemical Society Reviews 38, no. 9 (2009): 2520-2531
10. Arbizzani, Catia, Maurizio Biso, Dario Cericola, Mariachiara Lazzari, Francesca Soavi, and Marina Mastragostino. "Safe, High-Energy Supercapacitors Based on Solvent-Free Ionic Liquid Electrolytes." Journal of Power Sources 185, no. 2 (2008): 1575-1579
11. Helical microtubules of graphitic carbon Nature, Vol. 354 (November 1991), pp. 56-58 by S. Iijima
12. Chen, Qiao-Ling, Kuan-Hong Xue, Wei Shen, Fei-Fei Tao, Shou-Yin Yin, and Wen Xu. "Fabrication and Electrochemical Properties of Carbon Nanotube Array Electrode for Supercapacitors." Electrochimica Acta 49, no. 24 (2004): 4157-4161
13. C. Niu, Sichel, E.K., Hoch, R., Moy, D., Tennent, H. "High Power Electrochemical Capacitors Based on Carbon Nanotube Electrodes." Applied Physics Letters 70, (1997): 1480-1482.
14. An, K.H., Kim, W.S., Park, Y.S., Moon, J.-M., Bae, D.J., Lim, S.C., Lee, Y.S., . "Electrochemical Properties of High-Power Supercapacitors Using Single-Walled Carbon Nanotube Electrodes." Advanced Funtional Materials 11, no. 5 (2001): 387-392
15. 陳金銘：高容量碳粉材料.工業材料雜誌 100：57,1997
16. Maldonado, Stephen, Stephen Morin, and Keith J. Stevenson. "Structure, Composition, and Chemical Reactivity of Carbon Nanotubes by Selective Nitrogen Doping." Carbon 44, no. 8 (2006): 1429-1437.
17. Shi, H., J. Barker, M. Y. Saidi, R. Koksbang, and L. Morris. "Graphite Structure and Lithium Intercalation." Journal of Power Sources 68, no. 2 (1997): 291-295.
18. Chemical engineering(The Taiwan I. Ch. E.)Vol. 58, No.3 JUN. 2011.
19. 李汝雄 編著 綠色溶劑-離子液體的合成與應用 化學工業出版社
20. Seddon, Kenneth R. "Ionic Liquids for Clean Technology." Journal of Chemical Technology & Biotechnology 68, no. 4 (1997): 351-356.
21. Barrosse-Antle, L. E, A. M Bond, R. G Compton, A. M O'Mahony, E. I Rogers, and D. S Silvester. "Voltammetry in Room Temperature Ionic Liquids: Comparisons and Contrasts with Conventional Electrochemical Solvents." Chemistry – An Asian Journal 5, no. 2 (2010): 202-230.
22. Greaves, Tamar L., Asoka Weerawardena, Celesta Fong, Irena Krodkiewska, and Calum J. Drummond. "Protic Ionic Liquids:  Solvents with Tunable Phase Behavior and Physicochemical Properties." The Journal of Physical Chemistry B 110, no. 45 (2006): 22479-22487.
23. Holzapfel, M., C. Jost, A. Prodi-Schwab, F. Krumeich, A. Wursig, H. Buqa, and P. Novak. "Stabilisation of Lithiated Graphite in an Electrolyte Based on Ionic Liquids: An Electrochemical and Scanning Electron Microscopy Study." Carbon 43, no. 7 (2005): 1488-1498
24. Chemical engineering(The Taiwan I. Ch. E.)Vol. 58, No.5 OCT. 2011
25. Edited by Scott Handy, Middle Tennessee State University, USA, ISBN 978-953-307-605-8, Hard cover, 516 pages, Publisher: InTech, Chapters published September 22, 2011 under CC BY-NC-SA 3.0 license DOI: 10.5772/1769
26. Khomenko, V., E. Raymundo-Pinero, and F. Beguin. "High-Energy Density Graphite/Ac Capacitor in Organic Electrolyte." Journal of Power Sources 177, no. 2 (2008): 643-651.
27. Zheng, Honghe, Kai Jiang, Takeshi Abe, and Zempachi Ogumi. "Electrochemical Intercalation of Lithium into a Natural Graphite Anode in Quaternary Ammonium-Based Ionic Liquid Electrolytes." Carbon 44, no. 2 (2006): 203-210.
28. Aida, T., K. Yamada, and M. Morita. "An Advanced Hybrid Electrochemical Capacitor That Uses a Wide Potential Range at the Positive Electrode." Electrochemical and Solid-State Letters 9, no. 12 (2006): 534-536.
29. Aida, T., I. Murayama, K. Yamada, and M. Morita. "Analyses of Capacity Loss and Improvement of Cycle Performance for a High-Voltage Hybrid Electrochemical Capacitor." Journal of The Electrochemical Society 154, no. 8 (2007): A798-A804.
30. Ishihara, T., M. Koga, H. Matsumoto, and M. Yoshio. "Electrochemical Intercalation of Hexafluorophosphate Anion into Various Carbons for Cathode of Dual-Carbon Rechargeable Battery." Electrochemical and Solid-State Letters 10, no. 3 (2007): A74-A76.
31. Wei, Di, Pritesh Hiralal, Haolan Wang, Husnu Emrah Unalan, Markku Rouvala, Ioannis Alexandrou, Piers Andrew, Tapani Ryhanen, and Gehan A. J. Amaratunga. "Hierarchically Structured Nanocarbon Electrodes for Flexible Solid Lithium Batteries." Nano Energy, no. 0.
32. Placke, Tobias, Olga Fromm, Simon Franz Lux, Peter Bieker, Sergej Rothermel, Hinrich-Wilhelm Meyer, Stefano Passerini, and Martin Winter. "Reversible Intercalation of Bis (Trifluoromethanesulfonyl) Imide Anions from an Ionic Liquid Electrolyte into Graphite for High Performance Dual-Ion Cells." Journal of The Electrochemical Society 159, no. 11 (2012): A1755-A1765
33. Lu, Wen, Liangti Qu, Kent Henry, and Liming Dai. "High Performance Electrochemical Capacitors from Aligned Carbon Nanotube Electrodes and Ionic Liquid Electrolytes." Journal of Power Sources 189, no. 2 (2009): 1270-1277
34. Balducci, Andrea, Wesley A. Henderson, Marina Mastragostino, Stefano Passerini, Patrice Simon, and Francesca Soavi. "Cycling Stability of a Hybrid Activated Carbon//Poly(3-Methylthiophene) Supercapacitor with N-Butyl-N-Methylpyrrolidinium Bis(Trifluoromethanesulfonyl)Imide Ionic Liquid as Electrolyte." Electrochimica Acta 50, no. 11 (2005): 2233-2237
35. Lazzari, M., F. Soavi, and M. Mastragostino. "High Voltage, Asymmetric Edlcs Based on Xerogel Carbon and Hydrophobic Il Electrolytes." Journal of Power Sources 178, no. 1 (2008): 490-496.
36. Balducci, A., R. Dugas, P. L. Taberna, P. Simon, D. Plee, M. Mastragostino, and S. Passerini. "High Temperature Carbon–Carbon Supercapacitor Using Ionic Liquid as Electrolyte." Journal of Power Sources 165, no. 2 (2007): 922-927.
37. Mastragostino, M., and F. Soavi. "Capacitors | Electrochemical Capacitors: Ionic Liquid Electrolytes." In Encyclopedia of Electrochemical Power Sources, edited by Garche Editor-in-Chief: Jurgen, 649-657. Amsterdam: Elsevier, 2009.
38. Balducci, Andrea, Ugo Bardi, Stefano Caporali, Marina Mastragostino, and Francesca Soavi. "Ionic Liquids for Hybrid Supercapacitors." Electrochemistry Communications 6, no. 6 (2004): 566-570.
39. El-Kady, M. F., and R. B. Kaner. "Scalable Fabrication of High-Power Graphene Micro-Supercapacitors for Flexible and on-Chip Energy Storage." Nature Communications 4, (2013).
40. Kang, Y. J., H. Chung, C. H. Han, and W. Kim. "All-Solid-State Flexible Supercapacitors Based on Papers Coated with Carbon Nanotubes and Ionic-Liquid-Based Gel Electrolytes." Nanotechnology 23, no. 6 (2012).
41. Kim, B., H. Chung, and W. Kim. "High-Performance Supercapacitors Based on Vertically Aligned Carbon Nanotubes and Nonaqueous Electrolytes." Nanotechnology 23, no. 15 (2012).
42. Seel, J. A., and J. R. Dahn. "Electrochemical Intercalation of Pf6 into Graphite." Journal of The Electrochemical Society 147, no. 3 (2000): 892-898.
43. Hahn, M., O. Barbieri, F. P. Campana, R. Kotz, and R. Gallay. "Carbon Based Double Layer Capacitors with Aprotic Electrolyte Solutions: The Possible Role of Intercalation/Insertion Processes." Applied Physics A 82, no. 4 (2006): 633-638.
44. Smart, L.E., and E.A. Moore. Solid State Chemistry: An Introduction, Third Edition: Taylor & Francis, 2005. p296
45. Scott Handy, Middle Tennessee State University, USA "Applications of Ionic Liquids in Science and Technology", ISBN 978-953-307-605-8, Published: September 22, 2011 under CC BY-NC-SA 3.0 license
46. Mitani, Satoshi, Marappan Sathish, Dinesh Rangappa, Atsushi Unemoto, Takaaki Tomai, and Itaru Honma. "Nanographene Derived from Carbon Nanofiber and Its Application to Electric Double-Layer Capacitors." Electrochimica Acta 68, no. 0 (2012): 146-152.
47. Tamailarasan, P. and S. Ramaprabhu, Carbon Nanotubes-Graphene-Solidlike Ionic Liquid Layer-Based Hybrid Electrode Material for High Performance Supercapacitor. The Journal of Physical Chemistry C, 2012. 116(27): p. 14179-14187.
48. Herstedt, M., M. Smirnov, et al. (2005). "Spectroscopic characterization of the conformational states of the bis(trifluoromethanesulfonyl)imide anion (TFSI−)." Journal of Raman Spectroscopy 36(8): 762-770.
49. Rey, I., P. Johansson, et al. (1998). "Spectroscopic and Theoretical Study of (CF3SO2)2N- (TFSI-) and (CF3SO2)2NH (HTFSI)." The Journal of Physical Chemistry A 102(19): 3249-3258.
50. Mihkel Koel , Tallinn University of Technology, Tallinn, Estonia Professor Emeritus, Duke University, Durham, NC, USA, "Ionic Liquids in Chemical Analysis", October 9, 2008, ISBN-10: 1420046462, ISBN-13: 978-1420046465
51. Endo, M., T. Hayashi, et al. (2001). "Scanning tunneling microscope study of boron-doped highly oriented pyrolytic graphite." Journal of Applied Physics 90(11): 5670-5674.
52. 成會明 編著 張勁燕 校訂 "奈米碳管 Catbon nanotube" 五南圖書出版公司 印行