Simulating Supercapacitors: Can We Model Electrodes As Constant Charge Surfaces?
Supercapacitors based on an ionic liquid electrolyte and graphite or nanoporous carbon electrodes are simulated using molecular dynamics. We compare a simplified electrode model in which a constant, uniform charge is assigned to each carbon atom with a realistic model in which a constant potential is applied between the electrodes (the carbon charges are allowed to fluctuate). We show that the simulations performed with the simplified model do not provide a correct description of the properties of the system. First, the structure of the adsorbed electrolyte is partly modified. Second, dramatic differences are observed for the dynamics of the system during transient regimes. In particular, upon application of a constant applied potential difference, the increase in the temperature, due to the Joule effect, associated with the creation of an electric current across the cell follows Ohm's law, while unphysically high temperatures are rapidly observed when constant charges are assigned to each carbon atom.
†UPMC Université Paris 06, CNRS, ESPCI, UMR 7195, PECSA, F-75005 Paris, France.|‡Réseau sur le Stockage Electrochimique de l'Energie (RS2E), FR CNRS 3459, France.
Céline
C
Merlet
†UPMC Université Paris 06, CNRS, ESPCI, UMR 7195, PECSA, F-75005 Paris, France.|‡Réseau sur le Stockage Electrochimique de l'Energie (RS2E), FR CNRS 3459, France.|¶CIRIMAT, UMR CNRS 5085, Université Paul Sabatier, Bat. 2R1, 118 route de Narbonne, 31062 Toulouse Cedex 9, France.
Clarisse
C
Péan
†UPMC Université Paris 06, CNRS, ESPCI, UMR 7195, PECSA, F-75005 Paris, France.|‡Réseau sur le Stockage Electrochimique de l'Energie (RS2E), FR CNRS 3459, France.
Benjamin
B
Rotenberg
§Department of Materials, University of Oxford, Parks Road, Oxford OX1 3PH, United Kingdom.
Paul A
PA
Madden
‡Réseau sur le Stockage Electrochimique de l'Energie (RS2E), FR CNRS 3459, France.|¶CIRIMAT, UMR CNRS 5085, Université Paul Sabatier, Bat. 2R1, 118 route de Narbonne, 31062 Toulouse Cedex 9, France.
Patrice
P
Simon
†UPMC Université Paris 06, CNRS, ESPCI, UMR 7195, PECSA, F-75005 Paris, France.|‡Réseau sur le Stockage Electrochimique de l'Energie (RS2E), FR CNRS 3459, France.
Mathieu
M
Salanne
electrolyte; graphite; molecular dynamics; nanoporous carbon electrode; supercapacitor