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Correlation Length in Concentrated Electrolytes: Insights from All-Atom Molecular Dynamics Simulations

preprint
submitted on 12.11.2019 and posted on 25.11.2019 by Samuel Coles, Chanbum Park, Rohit Nikam, Matej Kanduč, Joachim Dzubiella, Benjamin Rotenberg

We study the correlations length of the charge-charge pair correlations in concentrated electrolyte solutions by means of all-atom, explicit-solvent molecular dynamics simulations. We investigate LiCl and NaI in water, which constitute highly soluble, prototypical salts for experiments, as well as two more complex, molecular electrolyte systems of lithium bis(trifluoromethane)sulfonimide (LiTFSI), commonly employed in electrochemical storage systems, in water and in an organic solvent mixture of dimethoxyethane (DME) and dioxolane (DOL). Our simulations support the recent experimental observations as well as theoretical predictions of a non-monotonic behavior of the correlation length with increasing salt concentration. We observe a Debye-Hückel like regime at low concentration, followed by a minimum reached when d/λD = 1, where λD is the Debye correlation length and d the effective ionic diameter, and an increasing correlation length with salt concentration in very concentrated electrolytes. As in the experiments, we find that the screening length in the concentrated regime follows a universal scaling law as a function d/λD for all studied salts. However, the scaling exponent is significantly lower than the experimentally measured one, and lies in the range of the theoretical predictions based on much simpler electrolyte models.

Funding

Ville de Paris (Emergences project: Blue Energy)

People Programme (Marie Curie Actions) PCOFUND-GA-2013-609102

Alexander von Humboldt foundation via the Bessel research award

Slovenian Research Agency (research core funding No. P1-0055)

History

Email Address of Submitting Author

samuel.william.coles@gmail.com

Institution

Sorbonne Université

Country

France

ORCID For Submitting Author

0000-0001-9722-5676

Declaration of Conflict of Interest

The authors declare no competing interest

Version Notes

This manuscript was submitted for review on 10/11/2019. To allow for ease of reading the supporting information is appended to the manuscript. These documents compile separately from the tex.

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