Molecular Environment and Enhanced Diffusivity of Li⁺ Ions in Lithium-Salt-Doped Ionic Liquid Electrolytes

Abstract

Lithium salts dissolved in ionic liquids (ILs) are interesting alternatives to the commonly used electrolytes for Li-ion batteries. In this study, the solution of Li [bis-(trifluoromethanesulfonyl)imide] (LiTFSI) in N-butyl-N-methylpyrrolidinium TFSI (PYR14TFSI) ionic liquid in the 0.1:0.9 molar ratio is studied by heteronuclear NOE and NMR diffusion measurements. The main purpose is to spot on the interions organization and mobility. NOE data support the existence of strongly coordinated Li+ species, whereas variable temperature measurements of the self-diffusion coefficients D show large, selective, and unexpected enhancement of Li+ mobility with T. The measured activation energy for Li+ diffusion is significantly larger than those of TFSI− and PYR14 +. These findings can be related to the mechanism of Li+ diffusion in ILs based on disruption formation of the coordination shells of Li+ with TFSI anions rather than on the Brownian motion of the whole Li+ coordinated species.

Molecular Modeling of Electrolytes

“…Figure 8.8 shows the ion self-diffusion coefficients from MD simulations [87] employing an APPLE&P [91] many-body polarizable force field. While the self-diffusion coefficient of pyr 14 TFSI was found to be in an excellent agreement with the experiments, the Li + cation self-diffusion coefficient in the pyr 14 TFSI doped with LiTFSI was noticeably slower than the experimental data from Castiglione et al [92], which indicates that further force field refinement is needed. Solano et al [86] published similar results.…”

On the parallelism between the mechanisms behind chromatography and drug delivery: the role of interactions with a stationary phase

“…The measurement of diffusivity could be done experimentally using 1 H NMR spectroscopy 58 . This well known technique is very reliable for liquid solutions, on the contrary 1 H NMR spectrum of hydrogels is characterized by broad signals due to the residual solid-state effects related to the dipole-dipole coupling.…”

Determination of Transport Parameters in Liquid Binary Lithium Ion Battery Electrolytes

“…10 In Castiglione et al, 7 the selfdiffusion coefficients of all ions in an electrolyte composed of LiTFSI (lithium bis(trifluoromethanesulfonyl)imide) dissolved in the ionic liquid PYR 14 TFSI (N,N-dimethyl pyrrolidinium) at a molar ratio of 1:9 were determined, whereas Capiglia et al 9 investigated LiPF 6 , LiBF 4 , and LiN(C 2 F 5 SO 2 ) 2 in ethylene carbonate (EC) ethyl-methyl carbonate (EMC) solvent mixture (EC:EMC at 2:8 v:v). A theoretical discussion of the experimental method is given in Price.…”