7 research outputs found
The local structure organization and dynamics in lithium borate ionic liquids using molecular dynamics simulation
Despite significant progress in the development of lithium-ion batteries, the
majority still rely on electrolytes based on organic solvents. However,
single-ion conducting electrolytes offer a promising alternative by mitigating
overpotential at the electrode and, thus, increasing the device's lifespan. In
a recent study, Guzman-Gonzalez et al. (Adv. Energy Mater., 2022, 2202974)
presented a novel approach to designing a new class of lithium ionic liquids,
based on tetracoordinated boron atom with oligoethylene glycol groups and
different fluorinated electron-withdrawing groups. To gain insights into the
structural and dynamic aspects underlying the high ionic conductivity of these
electrolytes, molecular dynamics simulations were employed. Our results
establish a relationship between the variation in ionic conductivity and the
extent of uncorrelated motion among the counterions. This phenomenon was
explained by differences in the rate of ion coordination dynamics
Local Structure in Terms of Nearest-Neighbor Approach in 1-Butyl-3-methylimidazolium-Based Ionic Liquids: MD Simulations
Description of the local microscopic
structure in ionic liquids
(ILs) is a prerequisite to obtain a comprehensive understanding of
the influence of the nature of ions on the properties of ILs. The
local structure is mainly determined by the spatial arrangement of
the nearest neighboring ions. Therefore, the main interaction patterns
in ILs, such as cationâanion H-bond-like motifs, cationâcation
alkyl tail aggregation, and ring stacking, were considered within
the framework of the nearest-neighbor approach with respect to each
particular interaction site. We employed classical molecular dynamics
(MD) simulations to study in detail the spatial, radial, and orientational
relative distribution of ions in a set of imidazolium-based ILs, in
which the 1-butyl-3-methylimidazolium (C<sub>4</sub>mim<sup>+</sup>) cation is coupled with the acetate (OAc<sup>â</sup>), chloride
(Cl<sup>â</sup>), tetrafluoroborate (BF<sub>4</sub><sup>â</sup>), hexafluorophosphate (PF<sub>6</sub><sup>â</sup>), trifluoromethanesulfonate
(TfO<sup>â</sup>), or bisÂ(trifluoromethanesulfonyl)Âamide (TFSA<sup>â</sup>) anion. It was established that several structural
properties are strongly anion-specific, while some can be treated
as universally applicable to ILs, regardless of the nature of the
anion. Namely, strongly basic anions, such as OAc<sup>â</sup> and Cl<sup>â</sup>, prefer to be located in the imidazolium
ring plane next to the CâH<sup>2/4â5</sup> sites. By
contrast, the other four bulky and weakly coordinating anions tend
to occupy positions above/below the plane. Similarly, the H-bond-like
interactions involving the H<sup>2</sup> site are found to be particularly
enhanced in comparison with the ones at H<sup>4â5</sup> in
the case of asymmetric and/or more basic anions (C<sub>4</sub>mimOAc,
C<sub>4</sub>mimCl, C<sub>4</sub>mimTfO, and C<sub>4</sub>mimTFSA),
in accordance with recent spectroscopic and theoretical findings.
Other IL-specific details related to the multiple H-bond-like binding
and cation stacking issues are also discussed in this paper. The secondary
H-bonding of anions with the alkyl hydrogen atoms of cations as well
as the cationâcation alkyl chain aggregation turned out to
be poorly sensitive to the nature of the anion
Local Structure in Terms of Nearest-Neighbor Approach in 1Butyl-3-methylimidazolium-Based Ionic Liquids: MD Simulations
Local structure organization in ionic liquids and molecular solvents mixtures : a molecular dynamics simulation
Ce travail est motivĂ© par lâutilisation dans de nombreux dispositifs Ă©lectrochimiques des mĂ©langes de liquides ioniques (LIs) Ă base du cation 1-butyl-3-mĂ©thylimidazolium (C4mim+) couplĂ©s Ă des anions perfluorĂ©s (BF4â, PF6â, TFOâ, TFSIâ), avec dâautre part des solvants aprotiques polaires tels que l'acĂ©tonitrile (AN), la Îł-butyrolactone (Îł-BL), le carbonate de propylĂšne (PC). Nous avons rĂ©alisĂ© des simulations de dynamique molĂ©culaire afin de caractĂ©riser la structure locale de ces mĂ©langes. Les variations de la structure microscopique en fonction de la composition du mĂ©lange ont Ă©tĂ© calculĂ©es via lâutilisation dâun arsenal de fonctions statistiques avancĂ©es, basĂ© sur la structure locale. Celle-ci est largement dĂ©terminĂ©e par la distribution radiale et orientationelle des plus proches voisins Ă un ion ou une molĂ©cule de rĂ©fĂ©rence. Dans un premier temps, la structure locale dans les LIs purs et dans les solvants molĂ©culaires a Ă©tĂ© analysĂ©e. Pour l'ensemble des LIs, il a Ă©tĂ© Ă©tabli que les interactions de liaison H de type C-HÎÎÎX impliquant les atomes dâhydrogĂšne H2,4,5 du cycle imidazolium et les atomes Ă©lectronĂ©gatifs de lâanion sont faibles et peuvent ĂȘtre classĂ©s dans lâordre suivant TFO-, BF4-, PF6-, TFSI-. Pour le solvant pur, nos rĂ©sultats montrent que les interactions dipĂŽle-dipĂŽle jouent un rĂŽle important dans la structure locale des solvants Ă©tudiĂ©s, alors que les interactions liaison H dans le PC et le Îł-BL sont faibles.Les rĂ©sultats montrent que dans tous les mĂ©langes LI/solvant molĂ©culaire Ă©tudiĂ©s, la distribution de l'anion autour du cation n'est pas fortement affectĂ©e lorsque la fraction molaire du LI, xIL, varie entre 0,3 et 1,0. Mais pour les valeurs de xIL infĂ©rieures Ă 0,3 les interactions entre cation et anion sont fortement diminuĂ©es. Ces rĂ©sultats corroborent les donnĂ©es publiĂ©es sur le comportement du dĂ©placement chimique du proton HÂČ en fonction de xIL. Nos rĂ©sultats soulignent aussi l'importance des interactions anion-solvant dans la description de la structure locale des mĂ©langes LI/solvant molĂ©culaire.Mixtures of imidazolium ionic liquids (ILs) with perfluorinated anions and dipolar aprotic solvent are promising candidates for electrolytic components used in different electrochemical applications. Current state of technologies requires detailed information on the influence of the mixture composition on the physical and chemical properties of the mixture. This thesis presents a molecular dynamics simulation analysis of the local structure organization of the mixtures of 1-butyl-3-methylimidazolium (C4mim+) ILs with perfluorinated anions (BF4â, PF6â, TFOâ, TFSIâ) and dipolar aprotic solvents such as acetonitrile (AN), Îł-butyrolactone (GBL) and propylene carbonate (PC). As a first step, the local structure in the neat ILs and molecular solvents has been analyzed. For the set of ILs it was established that H-bonding interactions at the H2 site is strongly enhanced compared to the H4-5 sites in the case of asymmetric and/or strongly basic anions like TFOâ or TFSIâ. The cation-cation contacts via the aggregation of the butyl chains is much stronger and less anion-dependent than the Ï+-Ï+ stacking of the imidazolium rings. For the pure solvent our results show that although the dominant dipole-dipole orientation between a reference molecule and first neighbor is the antiparallel one, while for the subsequent neighbors the antiparallel orientation is gradually weakened in favor of the parallel one. More distant neighbors tend to be parallel to the reference molecule. A deep analysis of the local structure made it possible to identify the presence of weak hydrogen bonds in the selected dipolar solvents. For the mixtures of imidazolium-based ILs the results show that in all the studied IL/molecular solvent mixtures, the distribution of the anion around the cation is not drastically affected in the range of xIL between 1.0 and 0.3 and for further decrease of xIL noticeable changes in the distance characteristics describing the cation and anion hydrogen bonding interactions, occur. These changes are associated with the expected weakening of the cation and anion interactions. These results are in good agreement with the behavior of the 2H chemical shift as a function of xIL. Furthermore, our results point out to the importance of the anion-solvent interactions in describing the local structure in these mixtures
Fluorescent probe dependence of the solvation dynamics in ionic liquid BmimBF4 and propylene carbonate mixtures: a time-resolved fluorescence and quantum chemistry study
A new potential model for acetonitrile: Insight into the local structure organization
International audienceThorough understanding of the microscopic organization and dynamics of individual constituents is a crucial step in the description and the prediction the properties of electrolyte solutions based on dipolar aprotic solvents such as acetonitrile. For this aim, a new potential (force field) model for acetonitrile was developed on the basis of comprehensive approach comprising quantum chemical calculations, ab initio molecular dynamics simulations and empirical parameterization. The developed potential model is able to reproduce the experimental thermodynamic and dynamic properties of neat acetonitrile in the range of temperatures between 228.15 and 348.15 K. The local structure of neat liquid acetonitrile then was analyzed in a framework of the nearest neighbor approach. It was shown that the distance standard deviations relative to the average distance between the nearest neighbors have a non-linear behavior that was traced back to the changes in the mutual orientation between acetonitrile molecules. The closest neighbors have a dominant antiparallel dipoles orientation with respect to a reference acetonitrile molecule, while for the further nearest neighbors perpendicular and parallel mutual orientation is observed. The nearest neighbors approach in combination with angular distribution functions was used for the estimation of the Kirkwood factor. Our results show that in order to reproduce the corresponding experimental values derived in the framework of the Onsager-Kirkwood-Fröhlich theory, it is necessary to take into account the mutual orientation of the 5â6 nearest neighbors. Although the atomic charges, on N and the methyl group hydrogen atoms, are negative, the values of the N ⯠H distance and the N ⯠HâC (methyl group), are compatible with a weak hydrogen bond between the two atoms
New Force Field Model for Propylene Glycol: Insight to Local Structure and Dynamics
In
this work we developed a new force field model (FFM) for propylene
glycol (PG) based on the OPLS all-atom potential. The OPLS potential
was refined using quantum chemical calculations, taking into account
the densities and self-diffusion coefficients. The validation of this
new FFM was carried out based on a wide range of physicochemical properties,
such as density, enthalpy of vaporization, self-diffusion coefficients,
isothermal compressibility, surface tension, and shear viscosity.
The molecular dynamics (MD) simulations were performed over a large
range of temperatures (293.15â373.15 K). The comparison with
other force field models, such as OPLS, CHARMM27, and GAFF, revealed
a large improvement of the results, allowing a better agreement with
experimental data. Specific structural properties (radial distribution
functions, hydrogen bonding and spatial distribution functions) were
then analyzed in order to support the adequacy of the proposed FFM.
Pure propylene glycol forms a continuous phase, displaying no microstructures.
It is shown that the developed FFM gives rise to suitable results
not only for pure propylene glycol but also for mixtures by testing
its behavior for a 50 mol % aqueous propylene glycol solution. Furthermore,
it is demonstrated that the addition of water to the PG phase produces
a homogeneous solution and that the hydration interactions prevail
over the propylene glycol self-association interactions