Doctoral Dissertations

Orcid ID

Date of Award


Degree Type


Degree Name

Doctor of Philosophy


Energy Science and Engineering

Major Professor

Tomonori Saito

Committee Members

Jagjit Nanda, Alexei Sokolov, Thomas A. Zawodzinski, Brian Long


Many countries have enacted renewable energy targets of 32% or more by 2040 to reduce their carbon footprint. However, due to the intermittent nature of renewable energy sources, long-duration energy storage systems are vital for providing a secure electricity supply. To meet this demand, new battery technologies utilizing earth-abundant and low-cost components are necessary. Among them, non-aqueous redox flow batteries represent a transformative energy storage system due to their flexible material selection and wide operating voltage window. A membrane plays a critical role in these next-generation energy storage technologies as it separates the anode and cathode while allowing for facile transport of the charge carrier. In addition to designing and synthesizing novel polymer membranes with improved ion transport, it is imperative to gain a greater understanding of the impact of a non-aqueous electrolyte on membrane properties. The goal of this study is to synthesize new high performance membranes and gain insight into the impact of non-aqueous electrolytes on membrane properties.

In this dissertation, membranes of various composition and architecture are synthesized, and a systematic evaluation of membrane properties in various electrolyte solutions unravels their structure-property relationships. Tailored crosslinking of poly(ethylene oxide) (PEO), a commonly utilized polymer electrolyte, was found to enhance sodium-ion conductivity and mechanical robustness over a wide temperature range compared to the linear polymer. Building upon these findings, a Lewis basic functional group was incorporated to the crosslinked PEO network. The Lewis basic functional group facilitates lithium salt dissolution and enables higher cation transport. Then a trifluoromethanesulfonimide functionalized cation exchange membrane was synthesized and the critical relationships between membrane ion transport and electrolyte salt concentration are unraveled. Tailoring the electrolyte salt concentration enables over an order of magnitude increase in membrane ionic conductivity, while maintaining a transport number >0.75.

Finally, the synthesis of a mechanically robust anion exchange membrane with excellent chemical stability is demonstrated. The membrane is evaluated for use in an aqueous and non-aqueous environment. Insights gained into the effect of organic electrolytes on membrane properties will provide strategies for the development of new polymer electrolyte membranes and performance improvements for a variety of electrochemical technologies.

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