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Solvent-dependent iodide interactions in LiO₂ electrolytes - a molecular dynamics study.

ABSTRACT: Iodide-based redox mediation in Li-O₂ batteries is regarded as a promising system due to its relatively high round-trip efficiency, compared to alternative systems. Here we explore the role of electrolyte composition in the solvation of I^-, which has been shown to be critical for the efficient operation of this redox mediator, using a molecular dynamics approach. A combinatorial exploration of I^- and H₂O concentrations was performed, for a fixed concentration of Li⁺, across a series of glymes, with increasing chain length (mono- to tetraglyme). The resulting radial distribution functions show that shorter glymes allow for a closer packing of the I^- redox mediator. Furthermore, increasing the I^- concentration also reduces the solvation of Li⁺ in the glymes, especially in G2. The presence of water further pulls the I^- and Li⁺ together. With increasing water content, its presence in the iodide's coordination shell increases markedly - an effect most pronounced for monoglyme. Competition between Li⁺ and I^- for the coordination of water is modulated by the different solvents as they perturb the local coordination shell of these important complexes, with longer chain lengths being less affected by increases in water concentrations.

SUBMITTER: Jonsson E

PROVIDER: S-EPMC10823488 | biostudies-literature | 2024 Jan

REPOSITORIES: biostudies-literature

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Solvent-dependent iodide interactions in LiO2 electrolytes - a molecular dynamics study.

Jónsson Erlendur E Berge Astrid H AH Grey Clare P CP Temprano Israel I

Faraday discussions 20240129 0

Iodide-based redox mediation in Li-O2 batteries is regarded as a promising system due to its relatively high round-trip efficiency, compared to alternative systems. Here we explore the role of electrolyte composition in the solvation of I-, which has been shown to be critical for the efficient operation of this redox mediator, using a molecular dynamics approach. A combinatorial exploration of I- and H2O concentrations was performed, for a fixed concen ...[more]

PMID: 37812402

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Project description:Ferrocene is commonly used as an internal redox couple in electrochemical measurements. Therefore, understanding how the absolute oxidation potential of ferrocene is modulated by different solvents and ion concentrations is important for the comparison of experimental measurements between different electrochemical systems. While standard implicit solvation models may provide relatively good predictions in bulk solvents, they lack the ability to describe ion coordination effects that can substantially alter redox potentials in practical electrolyte systems. In this work, we utilize molecular dynamics simulations to compute absolute oxidation potentials for the ferrocene and decamethylferrocene redox couple in bulk solvents of water, acetonitrile, 1,2-dichloroethane, and trichloromethane, as well as organic electrolytes consisting of mixtures of [BMIM+][BF4-] ionic liquid and acetonitrile and 1,2-dichloroethane solvents, for a wide range of ion concentrations. The goals are twofold: first, for the bulk solvents, we compare and evaluate the consistency of redox potential predictions for polarizable and nonpolarizable force fields from explicit solvent, free energy simulations, with predictions from an implicit solvent model. Second, we evaluate how ion coordination within the organic electrolytes modulates the redox potential of ferrocene and decamethylferrocene as a function of the ionic concentration and solvent dielectric constant. Utilizing linear response theory, we analyze the solvation contribution to the redox potential in terms of distributions of anion coordination number and how the anion coordination modulates the vertical ionization energy. We show that inclusion of liquid-vacuum interfacial potentials is essential for consistent prediction/interpretation of redox potentials across different solvents and force fields in order to compensate for the artificial quadrupole trace contribution to the solute cavity interfacial potential; this important consideration was previously proposed by Harder and Roux [J. Chem. Phys. 2008, 129, 234706].

Dataset Information

Solvent-dependent iodide interactions in LiO₂ electrolytes - a molecular dynamics study.

Publications

Solvent-dependent iodide interactions in LiO<sub>2</sub> electrolytes - a molecular dynamics study.

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