Van Aken Katherine L, McDonough John K, Li Song, Feng Guang, Chathoth Suresh M, Mamontov Eugene, Fulvio Pasquale F, Cummings Peter T, Dai Sheng, Gogotsi Yury
Department of Materials Science and Engineering & A J Drexel Nanomaterialstechnology Institute, Drexel University, Philadelphia, PA 19104, USA.
J Phys Condens Matter. 2014 Jul 16;26(28):284104. doi: 10.1088/0953-8984/26/28/284104. Epub 2014 Jun 12.
While most supercapacitors are limited in their performance by the stability of the electrolyte, using neat ionic liquids (ILs) as the electrolyte can expand the voltage window and temperature range of operation. In this study, ILs with bis(trifluoromethylsulfonyl)imide (Tf2N) as the anion were investigated as the electrolyte in onion-like carbon-based electrochemical capacitors. To probe the influence of cations on the electrochemical performance of supercapacitors, three different cations were used: 1-ethyl-3-methylimidazolium, 1-hexyl-3-methylimidazolium and 1,6-bis(3-methylimidazolium-1-yl). A series of electrochemical characterization tests was performed using cyclic voltammetry (CV), galvanostatic cycling and electrochemical impedance spectroscopy (EIS). Diffusion coefficients were measured using EIS and correlated with quasielastic neutron scattering and molecular dynamics simulation. These three techniques were used in parallel to confirm a consistent trend between the three ILs. It was found that the IL with the smaller sized cation had a larger diffusion coefficient, leading to a higher capacitance at faster charge-discharge rates. Furthermore, the IL electrolyte performance was correlated with increasing temperature, which limited the voltage stability window and led to the formation of a solid electrolyte interphase on the carbon electrode surface, evident in both the CV and EIS experiments.
虽然大多数超级电容器的性能受电解质稳定性的限制，但使用纯离子液体（ILs）作为电解质可以扩大工作电压窗口和温度范围。在本研究中，研究了以双（三氟甲基磺酰）亚胺（Tf2N）为阴离子的离子液体作为洋葱状碳基电化学电容器中的电解质。为了探究阳离子对超级电容器电化学性能的影响，使用了三种不同的阳离子：1-乙基-3-甲基咪唑鎓、1-己基-3-甲基咪唑鎓和1,6-双（3-甲基咪唑鎓-1-基）。使用循环伏安法（CV）、恒电流循环和电化学阻抗谱（EIS）进行了一系列电化学表征测试。使用EIS测量扩散系数，并将其与准弹性中子散射和分子动力学模拟相关联。这三种技术并行使用，以确认三种离子液体之间的一致趋势。结果发现，阳离子尺寸较小的离子液体具有较大的扩散系数，从而在更快的充放电速率下导致更高的电容。此外，离子液体电解质性能与温度升高相关，这限制了电压稳定窗口，并导致在碳电极表面形成固体电解质界面，这在CV和EIS实验中均很明显。
