Highly confined ions store charge more efficiently in supercapacitors

Céline Merlet (1, 2) , Clarisse Péan (1, 2, 3) , Benjamin Rotenberg (1, 2) , Paul Anthony Madden (4) , Barbara Daffos (2, 3) , Pierre-Louis Taberna (2, 3) , Patrice Simon (2, 3) , Mathieu Salanne (1, 2)

1 PECSA - Physicochimie des Electrolytes, Colloïdes et Sciences Analytiques
2 RS2E - Réseau sur le stockage électrochimique de l'énergie
3 CIRIMAT - Centre interuniversitaire de recherche et d'ingenierie des matériaux
4 University of Oxford

Liquids exhibit specific properties when they are adsorbed in nanoporous structures. This is particularly true in the context of supercapacitors, for which an anomalous increase in performance has been observed for nanoporous electrodes. This enhancement has been traditionally attributed in experimental studies to the effect of confinement of the ions from the electrolyte inside sub-nanometre pores, which is accompanied by their partial desolvation. Here we perform molecular dynamics simulations of realistic supercapacitors and show that this picture is correct at the microscopic scale. We provide a detailed analysis of the various environments experienced by the ions. We pick out four different adsorption types, and we, respectively, label them as edge, planar, hollow and pocket sites upon increase of the coordination of the molecular species by carbon atoms from the electrode. We show that both the desolvation and the local charge stored on the electrode increase with the degree of confinement.

Mots clés: Ions store charge; Supercapacitors

Domaines: Matériaux; Matériaux

Céline Merlet, Clarisse Péan, Benjamin Rotenberg, Paul Anthony Madden, Barbara Daffos, et al.. Highly confined ions store charge more efficiently in supercapacitors. Nature Communications, 2013, vol. 4 (n° 2701), pp. 1-6. ⟨10.1038/ncomms3701⟩. ⟨hal-01157828⟩