Abstract : The recent demonstration that in supercapacitors ions from the electrolyte could enter sub-nanometer pores increasing greatly the capacitance opened the way for valuable improvements of the devices performances. Despite the recent experimental and fundamental studies on that subject, the molecular mechanism at the origin of this capacitance enhancement is still not quite clear. We report here molecular dynamics simulations including two key features: the use of realistic electrode structures comparable with carbide-derived carbons and the polarization of the electrode atoms by the electrolyte. This original design of an electrochemical cell allows us to recover capacitance values in quantitative agreement with experiment and to gain knowledge about the local structure and dynamics of the ionic liquid inside the pores. Then, from the comparison between planar (graphite) and porous electrodes, we propose a new mechanism explaining the capacitance enhancement in nanoporous carbons. We also set up some simulations where, starting from 0V, an electric potential is applied between the electrodes. It is then possible to follow the dynamical aspects of the charging of supercapacitors.

Biographie : Matthieu SALANNE Mathieu Salanne is assistant professor at University Pierre and Marie Curie (Paris). He graduated in chemical engineering from Chimie ParisTech in 2004 and obtained his PhD in 2006 at UPMC. His research focuses on the modelling of molten salts (for energy production) and ionic liquids (for electrochemical storage of energy). He has published more than 60 peer-reviewed journal articles and has received the award of the French magazine La Recherche for the research work carried on the modelling of supercapacitors (in 2013).