Electrical conductivity and dynamics of quasi-solidified lithium-ion conducting ionic liquid at oxide particle surfaces

Atsushi Unemoto, Yoshiki Iwai, Satoshi Mitani, Seung Wook Baek, Seitaro Ito, Takaaki Tomai, Junichi Kawamura, Itaru Honma

Research output: Contribution to journalArticlepeer-review

25 Citations (Scopus)

Abstract

Lithium ion conducting solid-state composites consisting of lithium ion conducting ionic liquid, lithium bis(trifluoromethanesulfonyl)amide (Li-TFSA) dissolved 1-ethyl-3-methyl imidazolium bis(trifluoromethylsulfonyl)amide (EMI-TFSA), denoted by [yMLi+][EMI+][TFSA-] in this study, and various oxide particles such as SiO2, Al 2O3, TiO2 (anatase and rutile) and 3YSZ are synthesized via a liquid route for the molar concentration of lithium, y, to be 1. The composite consists of SiO2 and the ionic liquid with y = 0.2 was also prepared. The ionic liquid are quasi-solidified at the above oxide particle surfaces when x is below 40 for y = 1 and x is below 30 for y = 0.2, corresponding to the confinable thickness of the ionic liquid at the oxides' surfaces to be approximately 5-10 nm regardless of the oxide compositions. The electrical conductivities of x vol.%[yMLi+][EMI+] [TFSA-]-SiO2, Al2O3, TiO 2s or 3YSZ composites are evaluated by ac impedance measurements. The quasi-solid-state composites exhibited liquid-like high apparent conductivity, e.g. 10- 3.3-10- 2.0 S cm- 1 in the temperature range of 323-538 K for SiO2-ionic liquid composites with y = 1. The self-diffusion coefficients of the constituent species of x vol.% [yMLi +][EMI+][TFSA-] (x is below 40, y = 0.2 and 1) - SiO2 are evaluated by the Pulse Gradient Spin Echo (PGSE)-NMR technique in the temperature range of 298-348 K. By the quasi-solidification of the ionic liquid at SiO2 particle surfaces, the absolute values of the diffusion coefficients of all constituent species decreased. The SiO 2 surfaces work to promote ionization of ion pair, [EMI +][TFSA-], while significant influence on the solvation coordination, [Li(TFSA)n + 1]n-, was not observed. The apparent transport numbers of Li-containing species both in the bulk and the quasi-solidified ionic liquid showed similar values with each other, which was evaluated to be in the range of 0.010-0.017 for y = 0.2 and 0.051-0.093 for y = 1 in the abovementioned temperature range.

Original languageEnglish
Pages (from-to)11-20
Number of pages10
JournalSolid State Ionics
Volume201
Issue number1
DOIs
Publication statusPublished - 2011 Oct 19

Keywords

  • Composites
  • Interface
  • Ionic liquid
  • Lithium-ion conductor
  • Quasi-solidification

ASJC Scopus subject areas

  • Chemistry(all)
  • Materials Science(all)
  • Condensed Matter Physics

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