Unusual Li⁺Ion Solvation Structure in Bis(fluorosulfonyl)amide Based Ionic Liquid

Abstract

Raman spectra of 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)amide [C 2 mIm + ][FSA − ] ionic liquid solutions dissolving LiFSA salt of various concentrations were measured at 298 K. FSA − ((FSO 2 ) 2 N − ) is an analogue anion of bis(trifluoromethanesulfonyl)amide ((CF 3 SO 2 ) 2 N − ; TFSA − ). We found that a solvation number of the Li + ion in [C 2 mIm + ][FSA − ] is 3, though it has been well established that Li + ion is solvated by two TFSA − anions in the corresponding ionic liquids below the Li + ion mole fraction of x Li + < 0.2. To yield further insight into larger solvation numbers, Raman spectra were measured at higher temperatures up to 364 K. The Li + ion solvation number in [C 2 mIm + ][FSA − ] evidently decreased when the temperature was elevated. Temperature dependence of the Li + ion solvation number was analyzed assuming an equilibrium between [Li(FSA) 2 ] − and [Li(FSA) 3 ] 2− , and the enthalpy ΔH°and the temperature multiplied entropy TΔS°for one FSA − liberation toward a bulk ionic liquid were successfully evaluated to be 35(2) kJ mol −1 and 29(2) kJ mol −1 , respectively. The ΔH°and ΔS°suggest that the Li + ion is coordinated by one of bidentate and two of monodentate FSA − at 298 K, and that the more weakly solvated monodentate FSA − is liberated at higher temperatures. The high-energy X-ray diffraction (HEXRD) experiments of these systems were carried out and were analyzed with the aid of molecular dynamics (MD) simulations. In radial distribution functions evaluated with HEXRD, a peak at about 1.94 Å appeared and was attributable to the Li + −O(FSA − ) correlations. The longer Li + −O(FSA − ) distance than that for the Li + −O(TFSA − ) of 1.86 Å strongly supports the larger solvation number of the Li + ions in the FSA − based ionic liquids. MD simulations at least qualitatively reproduced the Raman and HEXRD experiments.

Modelling the mobility of positive ion clusters in normal liquid helium over large pressure ranges

“…Along the saturated vapour pressure line the radius, r, varies from 0.53 nm to 0.68 nm. Using N = nV = n 4 3 πr 3 we obtain N = 14 and 19 atoms for r = 0.53 nm and N = 29 and 40 atoms for r = 0.68 nm in the lower and higher number density limit, respectively.…”

“…(3) can be used for calculating the radii, r. Since the dynamic viscosity of helium, η, is well documented for a wide pressure range and temperatures in normal liquid helium 44 , it is possible to calculate the mobility via the Stokes-Einstein equation (4) µ Stokes = e 6πrη (4)…”

Experimental and Computational Analysis of the Solvent‐Dependent O2/Li+‐O2− Redox Couple: Standard Potentials, Coupling Strength, and Implications for Lithium–Oxygen Batteries

“…[50] As Li + solvation structures can vary greatly among similar solvents (for example, glymes), [51,52] and across different classes of solvents such as ionic liquids, [53] À potentials. These results highlight the importance of the interplay between ion-solvent and ion-ion interactions in understanding and controlling the intermediate species energetics, reaction product morphology, discharge capacity, and solvent stability in aprotic metal-O 2 batteries.…”

Design and Materialization of Ionic Liquids Based on an Understanding of Their Fundamental Properties

“…Unfortunately, the addition of lithium salts into ILs significantly increases the viscosity of the mixtures because the strongly Lewis acidic Li + cations require strong coordination by the anions to form bulky ion-multiplets. [85][86][87][88] Furthermore, the Li + -transference number is low due to the presence of at least two different cations (Li + and IL cation) and one anion (the common anion of Li-salt and IL). [85][86][87][88] The Li + -conducting IL electrolytes may improve the safety issue of lithium batteries, but their performance is not good due to poor transport properties.…”