Capacitance of Nanoporous Carbon-Based Supercapacitors Is a Trade-Off between the Concentration and the Separability of the Ions.
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, that is, in the absence of a solvent that screens the Coulombic interactions. The charging mechanism consistently changes with ion concentration, switching from counterion 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.
School of Chemical Engineering, University of Queensland , St. Lucia, Brisbane, Queensland 4072, Australia.
Ryan
R
Burt
Institute for Computational Physics, University of Stuttgart , Allmandring 3, 70569 Stuttgart, Germany.
Konrad
K
Breitsprecher
CIRIMAT, Université de Toulouse, CNRS, INPT, UPS , 118 route de Narbonne, 31062 Toulouse Cedex 9, France.|Réseau sur le Stockage Electrochimique de l'Energie (RS2E), FR CNRS 3459, 80039 Amiens, France.
Barbara
B
Daffos
CIRIMAT, Université de Toulouse, CNRS, INPT, UPS , 118 route de Narbonne, 31062 Toulouse Cedex 9, France.|Réseau sur le Stockage Electrochimique de l'Energie (RS2E), FR CNRS 3459, 80039 Amiens, France.
Pierre-Louis
PL
Taberna
CIRIMAT, Université de Toulouse, CNRS, INPT, UPS , 118 route de Narbonne, 31062 Toulouse Cedex 9, France.|Réseau sur le Stockage Electrochimique de l'Energie (RS2E), FR CNRS 3459, 80039 Amiens, France.
Patrice
P
Simon
School of Chemical Engineering, University of Queensland , St. Lucia, Brisbane, Queensland 4072, Australia.
Greg
G
Birkett
School of Chemical Engineering, University of Queensland , St. Lucia, Brisbane, Queensland 4072, Australia.
X S
XS
Zhao
Institute for Computational Physics, University of Stuttgart , Allmandring 3, 70569 Stuttgart, Germany.
Christian
C
Holm
Réseau sur le Stockage Electrochimique de l'Energie (RS2E), FR CNRS 3459, 80039 Amiens, France.|Sorbonne Universités, UPMC Univ Paris 06 , CNRS, Laboratoire PHENIX, F-75005 Paris, France.|Maison de la Simulation, CEA, CNRS, University Paris-Sud, UVSQ, Université Paris Saclay , F-91191 Gif-sur-Yvette, France.
Mathieu
M
Salanne