Water in Protic Ionic Liquid Electrolytes: From Solvent Separated Ion Pairs to Water Clusters.

The large electrochemical and cycling stability of "water-in-salt" systems have rendered promising prospective electrolytes for batteries. The impact of addition of water on the properties of ionic liquids has already been addressed in several publications. In this contribution, we focus on the changes in the state of water.

Water in Protic Ionic Liquids: Properties and Use of a New Class of Electrolytes for Energy-Storage Devices.

In this work, the properties of "water-in-PIL" (PIL=protic ionic liquid) electrolytes are reported based on 1-butylpyrrolidinium bis(trifluoromethanesulfonyl)imide (Pyr TFSI). Taking advantage of experimental and theoretical investigations, it is shown that the amount of water inside the electrolyte has a dramatic effect on the viscosity, conductivity, density, cation-anion interplay, and electrochemical stability of Pyr TFSI. The impact of water on the properties of this ionic liquid also affects its use as an electrolyte for electrochemical double-layer capacitors (EDLCs).

Cation influence on heterocyclic ammonium ionic liquids: a molecular dynamics study.

Four different ionic liquids (ILs) consisting of the bis(trifluoromethanesulfonyl)imide ([NTf2]-) anion, with structurally similar systematically varying cations, are investigated herein through classical molecular dynamics. The following cations were examined: pyrrolidinium ([pyrHH]+), piperidinium ([pipHH]+), N-butyl-pyrrolidinium ([pyrH4]+) and N-butyl-N-methyl-pyrrolidinium ([pyr14]+). The focus herein is on understanding the effect of increased ring size and alkyl chain addition, resulting in three protic ILs and one aprotic IL ([pyr14][NTf2]), on the physicochemical properties of the liquids studied herein.

Molecular Dynamics Simulations of Lithium-Doped Ionic-Liquid Electrolytes.

Lithium bis(trifluoromethanesulfonyl)imide (LiNTf) doped ionic liquids (ILs) are investigated herein, as potential electrolytes for lithium-ion batteries, via scaled-charge molecular dynamics simulations. Four model ILs based on the [NTf] anion and heterocyclic ammonium cations were studied with varying concentrations, ranging from 0 to 1 M solutions, of the dissolved lithium salt. The pyrrolidinium ([pyrHH]), piperidinium ([pipHH]), N-butyl-pyrrolidinium ([pyrH4]), and N-butyl- N-methyl-pyrrolidinium ([pyr14]) cations were considered to evaluate the combined effects of increased ring size, as well as the introduction of apolar groups on the nitrogen atom of the cations, on the liquid structure properties of the electrolytes.

Finding the best density functional approximation to describe interaction energies and structures of ionic liquids in molecular dynamics studies.

Ionic liquids raise interesting but complicated questions for theoretical investigations due to the fact that a number of different inter-molecular interactions, e.g., hydrogen bonding, long-range Coulomb interactions, and dispersion interactions, need to be described properly.

Structural Investigations on Lithium-Doped Protic and Aprotic Ionic Liquids.

Solutions of lithium bis(trifluoromethanesulfonyl)imide (LiNTf), in four different [NTf]-based ionic liquids, are extensively investigated as potential electrolytes for lithium-ion batteries. Solvation of the [Li] ions in the ionic liquids and its impact on their physicochemical properties are studied herein with the aid of molecular dynamics simulations. The cationic components of the investigated liquids were systematically varied so as to individually evaluate effects of specific structural changes; increase in ring size, the addition of an alkyl chain and absence of an acidic proton, on the solvation and mobility of the [Li] cations.