Development of coarse-grained force field to investigate sodium-ion transport mechanisms in cyanoborate-based ionic liquid

RM de Souza and TC Lourenco and LJA de Siqueira and M Karttunen and JLF Da Silva and LG Dias, JOURNAL OF MOLECULAR LIQUIDS, 338, 116648 (2021).

DOI: 10.1016/j.molliq.2021.116648

Sodium-ion batteries have a great potential for energy storage applications, however, its realization depends strongly on a deep atomistic understanding of the sodium-ion transport mechanisms, which is a key step to optimize its performance. A complete characterization of sodium-ion transport mechanism requires large time-scale calculations, which is a challenge even for classical atomistic force-field molecular dynamics simulations. Thus, in this work, we performed a calibration of a coarse-grained force-field to describe the thermodynamic and transport properties of sodium-ion for the particular case of cyanoborate-based ionic liquid using different molar fractions of sodium tetracyanoborate salt dissolved in 1-ethyl-3-methyl-imidazolium tetracyanoborate. The results from coarse-grained modeling were found to be in fair agreement with atomistic simulations and experimental data, and they captured concentration dependence of Na-xAnion(y)(x-y) aggregate sizes. In particular, two distinct populations of sodium-ions were identified inside the Na-xAnion(y)(x-y) aggregates: 1) a slow one in vehicular diffusion and 2) a fast one in hoping diffusion. Both of them contribute to sodium ion transport and occur preferentially at different sodium-ion concentrations. The present findings were obtained for a cyanoborate- based ionic liquid, however, we expect that our insights can be used to understand similar ionic liquids. (C) 2021 Elsevier B.V. All rights reserved.

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