title: Effect of cation on diffusion coefficient of ionic liquids at onion-like carbon electrodes.
abstract: While most supercapacitors are limited in their performance by the stability of the electrolyte, using neat ionic liquids (ILs) as the electrolyte can expand the voltage window and temperature range of operation. In this study, ILs with bis(trifluoromethylsulfonyl)imide (Tf2N) as the anion were investigated as the electrolyte in onion-like carbon-based electrochemical capacitors. To probe the influence of cations on the electrochemical performance of supercapacitors, three different cations were used: 1-ethyl-3-methylimidazolium, 1-hexyl-3-methylimidazolium and 1,6-bis(3-methylimidazolium-1-yl). A series of electrochemical characterization tests was performed using cyclic voltammetry (CV), galvanostatic cycling and electrochemical impedance spectroscopy (EIS). Diffusion coefficients were measured using EIS and correlated with quasielastic neutron scattering and molecular dynamics simulation. These three techniques were used in parallel to confirm a consistent trend between the three ILs. It was found that the IL with the smaller sized cation had a larger diffusion coefficient, leading to a higher capacitance at faster charge-discharge rates. Furthermore, the IL electrolyte performance was correlated with increasing temperature, which limited the voltage stability window and led to the formation of a solid electrolyte interphase on the carbon electrode surface, evident in both the CV and EIS experiments.
authors.affiliation: Department of Materials Science and Engineering & A J Drexel Nanomaterialstechnology Institute, Drexel University, Philadelphia, PA 19104, USA.
authors.forename: Katherine L
authors.initials: KL
authors.lastname: Van Aken
authors.forename: John K
authors.initials: JK
authors.lastname: McDonough
authors.forename: Song
authors.initials: S
authors.lastname: Li
authors.forename: Guang
authors.initials: G
authors.lastname: Feng
authors.forename: Suresh M
authors.initials: SM
authors.lastname: Chathoth
authors.forename: Eugene
authors.initials: E
authors.lastname: Mamontov
authors.forename: Pasquale F
authors.initials: PF
authors.lastname: Fulvio
authors.forename: Peter T
authors.initials: PT
authors.lastname: Cummings
authors.forename: Sheng
authors.initials: S
authors.lastname: Dai
authors.forename: Yury
authors.initials: Y
authors.lastname: Gogotsi
mesh_terms: D040761:Biomimetic Materials / Q000737:chemistry*; D002244:Carbon / Q000737:chemistry*; D002412:Cations / Q000737:chemistry; D003198:Computer Simulation; D004058:Diffusion; D025802:Electric Capacitance; D004566:Electrodes; D004867:Equipment Design; D019544:Equipment Failure Analysis; D052578:Ionic Liquids / Q000737:chemistry*; D008422:Materials Testing; D008956:Models, Chemical
chemical_list: D002412:Cations; D052578:Ionic Liquids; D002244:Carbon