Extremely Fast Interfacial Li Ion Dynamics in Crystalline LiTFSI Combined with EMIM-TFSI

Bernhard Stanje, H. Martin R. Wilkening*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review


Materials providing fast transport pathways for ionic charge carriers are at the heart of future all-solid state batteries that completely rely on sustainable, nonflammable solid electrolytes. The mobile ions in fast ion conductors may take benefit from structural disorder, cation and anion substitution, or dimensionality effects. While these effects concern the bulk regions of a given material, one may also manipulate the surface or interfacial regions of a polycrystalline poorly conducting electrolyte to enhance its transport properties. Here, we used 7Li NMR to characterize interfacial effects in crystalline lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) to which a small amount of ionic liquid EMIM-TFSI (EMIM: 1-ethyl-3-methylimidazolium cation, C6H11N2+) was added. We recorded longitudinal spin-lattice relaxation (SLR) curves Mz(td) that directly mirror the 7Li spin-fluctuations controlled by motional processes in such ionic-liquids-in-salt composites. Already at room temperature we observe strongly bimodal buildup curves Mz(td) leading to two distinct SLR rates differing by a factor of 100. While the slower rate does exactly reflect the temperature behavior expected for poorly conducting LiTFSI, the faster rate mirrors rapid motional processes that are governed by an activation energy as low as 73 meV. We attribute these fast processes to highly mobile Li+ ions in or near the contact area of crystalline LiTFSI and EMIM-TFSI. By using a method that characterizes motional processes from the atomic-scale point of view, we emphasize the importance of interfacial regions as reservoirs for fast Li+ ions in such solid composite electrolytes.

Original languageEnglish
Pages (from-to)136-142
Number of pages7
JournalACS Physical Chemistry Au
Issue number2
Publication statusPublished - 23 Mar 2022


  • diffusion
  • ionic liquids
  • lithium
  • NMR
  • solid electrolytes
  • transport

ASJC Scopus subject areas

  • Chemistry (miscellaneous)
  • Physical and Theoretical Chemistry
  • Computational Theory and Mathematics
  • Computer Science Applications


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