From molten salts to room temperature ionic liquids: Simulation studies on chloroaluminate systems

TL;DR

This study uses advanced simulation techniques to analyze the structure and transport properties of chloroaluminate ionic liquids, especially EMI-AlCl4, showing strong agreement with experimental data and exploring effects of different cations.

Contribution

It introduces a first-principles-based interaction potential for simulating chloroaluminate melts and compares classical and electronic structure simulations, providing new insights into their structure and transport properties.

Findings

Excellent agreement between classical and electronic structure simulations.

Chloroaluminate speciation becomes more complex with smaller inorganic cations.

Transport properties of EMI-AlCl4 match experimental measurements.

Abstract

An interaction potential including chloride anion polarization effects, constructed from first-principles calculations, is used to examine the structure and transport properties of a series of chloroaluminate melts. A particular emphasis was given to the study of the equimolar mixture of aluminium chloride with 1-ethyl-3-methylimidazolium chloride, which forms a room temperature ionic liquid EMI-AlCl 4. The structure yielded by the classical simulations performed within the framework of the polarizable ion model is compared to the results obtained from entirely electronic structure-based simulations: An excellent agreement between the two flavors of molecular dynamics is observed. When changing the organic cation EMI+ by an inorganic cation with a smaller ionic radius (Li+, Na+, K+), the chloroaluminate speciation becomes more complex, with the formation of Al2Cl 7- in small amounts. The calculated transport properties (diffusion coefficients, electrical conductivity and viscosity) of EMI-AlCl4 are in good agreement with experimental data.