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arXiv 1706.09263cond-mat.mtrl-sci
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纳米多孔碳基超级电容器的电容是离子浓度和可分离性之间的权衡

Capacitance of Nanoporous Carbon-Based Supercapacitors is a Trade-Off Between the Concentration and the Separability of the Ions

Ryan Burt, Konrad Breitsprecher, Barbara Daffos, Pierre-Louis Taberna, Patrice Simon, Greg Birkett, X. S. Zhao, Christian Holm, Mathieu Salanne

摘要:

纳米多孔碳基超级电容器通过在电极表面吸附来自电解质的离子来存储电力。在有机液体电解质中显示出最大离子浓度的室温离子液体原则上应产生更大的电容。在这里,我们通过使用电化学测量表明,当从纯离子液体切换到使用相同离子种类的常规有机电解质时,电容不会受到显著影响。通过进行额外的分子动力学模拟,我们解释这个结果作为一个增加的困难,分离相反电荷的离子时,他们更集中,即在没有溶剂,屏幕库仑相互作用。充电机制始终随离子浓度而变化,从稀释的有机电解质中的反离子吸附切换到纯离子液体中的离子交换。与电容相似,孔内扩散系数在很大程度上取决于组成,纯离子液体中的动力学明显减慢。

英文摘要:

Nanoporous carbon-based supercapacitors store electricity through adsorption of ions from the electrolyte at the surface of the electrodes. Room temperature ionic liquids, which show the largest ion concentrations among organic liquid electrolytes, should in principle yield larger capacitances. Here we show by using electrochemical measurements that the capacitance is not significantly affected when switching from a pure ionic liquid to a conventional organic electrolyte using the same ionic species. By performing additional molecular dynamics simulations, we interpret this result as an increasing difficulty of separating ions of opposite charges when they are more concentrated, i.e. in the absence of a solvent which screens the Coulombic interactions. The charging mechanism consistently changes with ion concentration, switching from counter-ion adsorption in the diluted organic electrolyte to ion exchange in the pure ionic liquid. Contrarily to the capacitance, in-pore diffusion coefficients largely depend on the composition, with a noticeable slowing of the dynamics in the pure ionic liquid.

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