Insulator:conductor interfacial regions — Li ion dynamics in the nanocrystalline dispersed ionic conductor LiF:TiO2

M. Gombotz, K. P. Pree, V. Pregartner, I. Hanzu, B. Gadermaier, K. Hogrefe, H.M.R. Wilkening*

*Corresponding author for this work

Research output: Contribution to journalArticle

Abstract

Lithium fluoride is known to be a very poor ionic conductor. Here, we used it as a model substance to investigate the influence of the insulator TiO2 on ion dynamics in nanocrystalline composites of LiF and TiO2. In such two-phase systems a percolation network of fast Li+ pathways at the conductor:insulator interfaces may lead to enhanced overall, through-going ionic (and electronic) transport. Indeed, we observed such an effect and characterized it by conductivity spectroscopy as well as by variable-temperature 7Li and 19F Nuclear Magnetic Resonance (NMR) line shape measurements and diffusion-induced NMR relaxometry. Compared to nanocrystalline LiF, a remarkable increase in total conductivity of almost four orders of magnitude, that is, from 6×10−11 S cm−1 up to 2×10−7 S cm−1 (100 °C) was observed for LiF:TiO2 containing 40 vol.-% of TiO2. Direct current polarization measurements revealed that principally ionic charge carriers are responsible for this enhancement. As both ions in LiF, Li+ and F, might be mobile, NMR helped revealing that Li+ is the charge carrier being mainly responsible for the increase in ionic conductivity. Compared to SiO2 and Al2O3 [see, S. Breuer et al. J. Phys. Chem. C, 2019, 123, 5222], with TiO2 the largest increase in conductivity was achieved. Hence the introduction of heterogeneous conductor:insulator contacts turned out to be a highly suitable tool to effectively engineer the interfacial regions in such two-phase systems. In general, such a composite effect is important for ion transport in components for energy storage devices and in the solid electrolyte interphase region that generally passivates the anode material in lithium-ion batteries.

Original languageEnglish
Article number115726
JournalSolid State Ionics
Volume369
DOIs
Publication statusPublished - 15 Oct 2021

Keywords

  • Conductivity
  • Interfacial effects
  • Nanocrystalline materials
  • NMR
  • Solid electrolytes

ASJC Scopus subject areas

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

Cooperations

  • NAWI Graz

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