Modeling transport and dynamics in redox-active polymer electrolytes for flow battery applications

Walker, Dejuante W.

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https://hdl.handle.net/2142/129432 Copy

Description

Title

Modeling transport and dynamics in redox-active polymer electrolytes for flow battery applications

Author(s)

Walker, Dejuante W.

Issue Date

2025-04-23

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

Sing, Charles E

Doctoral Committee Chair(s)

Sing, Charles E

Committee Member(s)

• Schroeder, Charles M
• Guironnet, Damien S
• Su, Xiao

Department of Study

Chemical & Biomolecular Engr

Discipline

Chemical Engineering

Degree Granting Institution

University of Illinois Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

• Flow Battery
• Battery
• Electrolyte
• Polymer
• Polymer Electrolyte
• Simulation
• Charge Transport
• Polymer Dynamics
• Ion Transport

Abstract

Redox flow batteries (RFBs) are a candidate technology for grid-scale energy storage due to advantages such as independently scalable power and capacity, long operation time, and instantaneous charging. To overcome detrimental material crossover that limits performance, redox-active polymers (RAPs) have been investigated since they can be paired with an inexpensive size-exclusion membrane that prevents crossover while still conducting both electrons and ions. RAPs, a subclass of polyelectrolytes, are of great interest in RFBs due to their fast charging/discharging, chemical modularity, and molecular size. However, designing RAPs for flow batteries at the molecular level requires a fundamental understanding of how their redox-activity couples to their polymer dynamics in non-equilibrium conditions. This dissertation develops a Brownian Dynamics–Monte Carlo simulation to systematically investigate charge transport, out-of-equilibrium polymer dynamics, and ion/nanoparticle transport relevant to RAP flow battery systems. We demonstrate that hydrodynamic interactions (HI) enhance charge transport when charge hopping is not dominant, accelerating polymer segmental and translational motion at low concentrations. In dilute concentrations, we show that flow can promote charge transport by extending polymer conformations, but can also suppress non-adjacent charge hopping processes that are important for transport at high charge fractions. Shear flows can similarly enhance charge transport through chain extension, but tumbling dynamics lead to oscillatory displacements that become a dominant feature with high charge fractions and strong flows. In semidilute concentrations, we show that both extensional and shear flows promote charge transport by extending the polymer conformation, and the overall charge displacement is decreased at increasing charge fraction due to charge localization. We also use this semidilute shear flow model to show that we can quantitatively capture trends in rheological properties as other large scale simulations, how the extension and orientation of chains couple to give rise to tumbling dynamics, and how these tumbling dynamics are reduced due to topological constraints from neighboring chains. We then study ion transport in equilibrium RAP solutions and show that the fraction of condensed counterions is a major feature that affects not only the counterion distribution, but also the size of the RAP and leads to diminished ion transport. Finally, to understand the impact of flow on uncharged nanoparticle transport, we show that the transport of such particles is significantly enhanced with flow at intermediate concentrations due to hydrodynamic backflows that arise amongst extended polymer chains. Overall, these insights provide a foundation for improving RAP-based flow battery performance through rational polymer design and careful consideration of flow conditions. Future research directions include extending these modeling approaches to investigate ion transport in flowing systems to study how counterion condensation and hydrodynamic backflows couple in such systems. Additionally, a method for cell-level modeling of RAP-based flow batteries will be proposed to establish structure-property relationships that inform the design of next-generation energy storage systems from the molecule up.

Graduation Semester

2025-05

Type of Resource

Thesis

Handle URL

https://hdl.handle.net/2142/129432

Copyright and License Information

Copyright 2025 Dejuante Walker

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