Molecular dynamics studies of the structure–dynamics relationship in concentrated nonaqueous electrolytic solutions

Farag, Hossam Mostafa Abdelhamid Mostafa

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https://hdl.handle.net/2142/113235 Copy

Description

Title

Molecular dynamics studies of the structure–dynamics relationship in concentrated nonaqueous electrolytic solutions

Author(s)

Farag, Hossam Mostafa Abdelhamid Mostafa

Issue Date

2020-12-14

Director of Research (if dissertation) or Advisor (if thesis)

Zhang, Yang

Committee Member(s)

Heuser, Brent J.

Department of Study

Nuclear, Plasma, & Rad Engr

Discipline

Nuclear, Plasma, Radiolgc Engr

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

M.S.

Degree Level

Thesis

Keyword(s)

• Nonaqueuous electrolytic solutions
• MD
• association
• solvation

Abstract

Energy storage is essential for maintaining power grid stability while integrating diverse sources of energy, e.g., nuclear, renewable, and others. Such diversity of sources is essential for energy security. The solution phase of electrolytes provides the medium for ionic charge transport between the electrodes of electrochemical systems used in energy storage. The chemically-specific equilibrium spatial distribution of ionic species in electrolytic solutions, and the chemical equilibrium that exists between dissociated and associated charged entities are the main challenging factors contributing to the lack of a universal description for electrolytes properties in terms of microscopic molecular properties, and we need a system (or class of systems)-specific collective descriptors through which we can understand and guide the design of liquid electrolytes with desirable properties. Understanding the physical and electrochemical rate processes occurring in the bulk of concentrated nonaqueous electrolytic solutions is a major step towards the control and design of electrochemical systems, e.g., nonaqueous redox flow batteries which are indispensable part of a sustainable power grid . Herein, a combination of computational molecular dynamics carried by myself, Hossam Farag, and conductance measurements and experimental SAXS provided by our collaborators (Dr. Ilya Shkrob, Dr. Tao Li, Dr. Susan Odom, and Lily Robertson), is used to probe the dynamics of nonaqueous electrolytic solutions as a varying function of the battery state of charge (SOC) and the electrolyte concentration. Two solutions were compared: one containing metal cation electrolyte prone to form rigid hetero-charge network, and the other containing phenothiazine organic catholyte preferring softer homo-radical stacking. For the latter, conductivity data show that a faster charge transport is present at high electrolyte concentrations. This difference in behavior becomes less pronounced as the concentration is lowered and absent in the dilute limit. Our findings indicate enhanced dynamics in terms of bulk ionic conductivity driven by a softer medium-range emergent homo-radical stacking structure as revealed by the MD simulations results.

Graduation Semester

2020-12

Type of Resource

Thesis

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http://hdl.handle.net/2142/113235

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Copyright 2020 by Hossam Farag. All rights reserved.

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