The effect of coordinating and non-coordinating additives on the transport properties in ionic liquid electrolytes for lithium batteries

Abstract

In the present study we expand our analysis of using two contrasting organic solvent additives (toluene and THF) in an ionic liquid (IL)/Li NTf₂ electrolyte. Multinuclear Pulsed-Field Gradient (PFG) NMR, spin-lattice (T₁) relaxation times and conductivity measurements over a wide temperature range are discussed in terms of transport properties and structuring of the liquid. The conductivity of both additive samples is enhanced the most at low temperatures, with THF slightly more effective than toluene. Both the anion and lithium self-diffusivity are enhanced in the same order by the additives (THF > toluene) while that of the pyrrolidinium cation is marginally enhanced. ¹H spin-lattice relaxation times indicate a reasonable degree of structuring and anisotropic motion within all of the samples and both ¹⁹F and ⁷Li highlight the effectiveness of THF at influencing the lithium coordination within these systems.