Influence of solvation on the structural and capacitive properties of electrical double layer capacitors

We use molecular dynamics simulations to explore the impact of a non-ionic solvent on the structural and capacitive properties of supercapacitors based on an ionic liquid electrolyte and carbon electrodes. The study is focused on two pure ionic liquids, namely 1-butyl-3-methylimidazolium hexafluorophosphate and 1-butyl-3-methylimidazolium tetrafluoroborate, and their 1.5 M solutions in acetonitrile. The electrolytes, represented by coarse-grained models, are enclosed between graphite electrodes. We employ a constant potential methodology which allows us to gain insight into the influence of solvation on the polarization of the electrodes as well as the structural and capacitive properties of the electrolytes at the interface. We show that the interfacial characteristics, different for two distinct pure ionic liquids, become very similar upon mixing with acetonitrile. ∗Corresponding author Email address: [email protected] (Céline Merlet) ISE member UPMC Univ Paris 06 and CNRS, UMR 7195, PECSA, F-75005, Paris, France Réseau sur le Stockage Electrochimique de l’Energie (RS2E), FR CNRS 3459, France Department of Materials, University of Oxford, Parks Road, Oxford OX1 3PH, UK Laboratoire PECSA CC51, Université Pierre et Marie Curie, 75005 Paris, France (tel) +33 1 44 27 31 17, (fax) +33 1 44 27 32 28 Preprint submitted to Elsevier August 26, 2013