Classical molecular dynamics simulations have been performed in polarizable and nonpolarizable force fields for series of electrolytes based on MeTFSI (Me = Li, Na) salts dissolved in EMIM−TFSI ionic liquid. Structure and dynamics of the solvation shell of Me + ions have been investigated. Contributions to the total conductivity of the electrolyte arising from motions of different ions and cross-correlations between them have been analyzed. The analysis has indicated that regardless of the type of Me + cation, motions of Me + ions and ionic liquid anions are positively correlated, contributing toward conductivity decrease and leading to negative transference numbers of metal ions. The results have confirmed experimental findings of negative transference numbers of Li + and have suggested that the effect of Me-anion correlations in certain concentration range is a general feature of Me + solutions in ionic liquids.

Classical and ab initio molecular dynamics (MD) simulations have been performed for electrolytes based on LiTFSI and NaTFSI solutions in ethylene carbonate and its mono- and difluoro derivatives. Differences between electrolytes with Li+ or Na+ ions and the effect of fluorination on the structure and transport properties have been analyzed. The observed differences are related to the strength of Me+–carbonate binding, which is weaker for the Na+ cation and/or fluorinated solvents. Infrared spectra have been computed from ab initio MD and density functional tight binding (DFTB) MD trajectories. The changes of vibrational frequencies have been related to the local structure of the electrolyte and to interactions between salt cations and solvent molecules. The frequency shifts obtained from the AIMD simulations agree with experimental data, whereas DFTB underestimates Na+–carbonate interactions.

Classical and ab initio molecular dynamics simulations have been performed for a series of electrolytes for Na-ion devices based on sodium bis­(fluorosulfonyl)­imide (NaFSI) solutions in 1-ethyl-3-methylimidazolium FSI (EMIM-FSI) ionic liquid. Viscosities and conductivities estimated in a polarizable force field agree with experimental data. Fourier transform of the autocorrelation function of the dipole moment obtained in ab initio simulations has been used to calculate the IR spectra of electrolytes. Computed shifts of the vibrational band originating from the S–F stretch of the FSI anion are in very good agreement with experimental data measured for electrolytes with increasing NaFSI mole fraction. Fourier transform of geometrical parameters of FSI anions has been applied to probe locally the frequency changes. Results show the correlation between the local environment of the FSI ion and vibrational frequencies, corroborating the deconvolution of the experimental spectrum into contributions from “free” and “bound” ions.

Quantum-chemical calculations and classical and ab initio molecular dynamics simulations have been performed to study the Mg2+-conducting electrolytes based on Mg­(TFSI)2/MgCl2 solutions in dimethoxyethane. It has been shown that depending on the TFSI/Cl– ratio, the Mg2Cl2 2+ or Mg3Cl4 2+ complexes are preferred as stable ion aggregates. In the initial stages of the ion association process, MgCl+, MgCl2, and Mg2Cl3 + are formed as intermediate species. Calculations of harmonic frequencies and simulations of the IR spectrum of the electrolyte from the ab initio MD trajectories have been used to identify the spectral range of vibrations of ion aggregates found in the modeled electrolyte. The results have been discussed in the context of experimental data.

Simulations of ab initio molecular dynamics have been performed for mixtures of ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMIM-TFSI) ionic liquid and water. Statistics of donors and acceptors of hydrogen bonds has revealed that with increasing water content, hydrogen bonds between EMIM cations and TFSI anions are replaced by bonds to water molecules. In the mixture of liquids, the total number of bonds (from EMIM cations or water molecules) formed by TFSI acceptors increases. IR spectra obtained from ab initio molecular dynamics trajectories are in good agreement with literature data for ionic liquid/water systems. Analysis of oscillations of individual C–H and O–H bonds has shown correlations between vibrational frequencies and hydrogen bonds formed by an EMIM cation or water molecule and has indicated that the changes in the IR spectrum result from the decreased number of water–water hydrogen bonds in the mixture. The tests of DFTB methodology with tailored parameterizations have yielded reasonably good description of the IR spectrum of bulk water, whereas available parameterizations have failed in satisfactory reproduction of the IR spectrum of EMIM-TFSI/water mixtures in the region above 3000 cm–1.