Largeot Celine, Portet Cristelle, Chmiola John, Taberna Pierre-Louis, Gogotsi Yury, Simon Patrice
Université Paul Sabatier, CIRIMAT UNM CNRS 5085, 118 route de Narbonne, 31062 Toulouse Cedex 4, France.
J Am Chem Soc. 2008 Mar 5;130(9):2730-1. doi: 10.1021/ja7106178. Epub 2008 Feb 8.
The research on electrochemical double layer capacitors (EDLC), also known as supercapacitors or ultracapacitors, is quickly expanding because their power delivery performance fills the gap between dielectric capacitors and traditional batteries. However, many fundamental questions, such as the relations between the pore size of carbon electrodes, ion size of the electrolyte, and the capacitance have not yet been fully answered. We show that the pore size leading to the maximum double-layer capacitance of a TiC-derived carbon electrode in a solvent-free ethyl-methylimmidazolium-bis(trifluoro-methane-sulfonyl)imide (EMI-TFSI) ionic liquid is roughly equal to the ion size (approximately 0.7 nm). The capacitance values of TiC-CDC produced at 500 degrees C are more than 160 F/g and 85 F/cm(3) at 60 degrees C, while standard activated carbons with larger pores and a broader pore size distribution present capacitance values lower than 100 F/g and 50 F/cm(3) in ionic liquids. A significant drop in capacitance has been observed in pores that were larger or smaller than the ion size by just an angstrom, suggesting that the pore size must be tuned with sub-angstrom accuracy when selecting a carbon/ion couple. This work suggests a general approach to EDLC design leading to the maximum energy density, which has been now proved for both solvated organic salts and solvent-free liquid electrolytes.
对电化学双层电容器（EDLC）的研究进展迅速，这种电容器也被称为超级电容器或超电容器，因为其功率输出性能填补了介电电容器和传统电池之间的空白。然而，许多基本问题，例如碳电极的孔径、电解质的离子大小与电容之间的关系，尚未得到充分解答。我们发现，在无溶剂的乙基甲基咪唑双（三氟甲烷磺酰）亚胺（EMI-TFSI）离子液体中，导致碳化钛衍生碳电极达到最大双层电容的孔径大致等于离子大小（约0.7纳米）。在500摄氏度下制备的TiC-CDC在60摄氏度时的电容值超过160 F/g和85 F/cm³，而具有较大孔径和更宽孔径分布的标准活性炭在离子液体中的电容值低于100 F/g和50 F/cm³。在比离子大小仅大或小一埃的孔径中，已观察到电容显著下降，这表明在选择碳/离子对时，必须以亚埃精度调整孔径。这项工作提出了一种实现最大能量密度的EDLC设计通用方法，目前已在溶剂化有机盐和无溶剂液体电解质中得到验证。
