Collaborative Research: Establishing Design Principles for Molecular Engineering of High Concentration Redox Electrolytes

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This project focuses on a type of battery called non-aqueous redox flow batteries (RFBs) that are promising for large-scale, stationary energy storage applications. RFBs have advantages for electrical grid-scale energy storage options that would reduce overall energy consumption when linked with an electrical grid. Non-aqueous RFBs that contain organic electro-active species have the following unique features relative to other RFB designs: higher operating voltages, non-corrosive electrolytes, smaller size, and use of scalable organic active materials (which are more environmentally friendly and potentially lower cost). This collaborative project addresses fundamental research to support the design of electrolytes for non-aqueous RFBs with high energy density, better stability, and acceptable fluid flow properties. This project will not only establish the foundational knowledge necessary to design electrolytes for next-generation grid storage batteries but will also provide fundamental insights into other electrochemical technologies necessary for a sustainable energy economy. The Principal Investigators Brushett and Odom have worked extensively with underrepresented groups in STEM fields and with mentoring undergraduate and graduate students in both research groups. Further, the PIs will establish summer student exchange programs with each other's institutions. At MIT, Dr. Brushett will engage with the THINK program, which seeks to foster exceptional innovation, networking, and knowledge in high school students working on projects that benefit the community. At University of Kentucky (UK), Dr. Odom will focus on Mixing Art & Science, which will introduce non-scientists to concepts and issues in energy collection and storage by attracting them with an accessible activity and will continue to serve as a co-organizer for UK's Expanding Your Horizons Annual Conference. Fundamental knowledge gaps exist both in (1) the molecular design of stable concentrated redox active solutions and (2) the electrochemical characterization of these concentrated electrolytes. At present, most investigations have focused on molecular discovery and electrochemical characterization under dilute conditions followed by direct integration into an unoptimized laboratory flow cell for preliminary cycling analysis. This approach has led to uneven advances in the field as, to date, most nonaqueous flow cells have shown poor performance and durability. It is unclear whether the observed results are due to fundamental instabilities of the redox organic materials, concentration-dependent changes in the physical and electrochemical properties of redox electrolytes, or failures in cell design and engineering. This collaborative research project focuses on the development of soluble and stable redox active molecules, based on substituted phenothiazines, as a platform chemistry for characterizing physical and electrochemical properties of solutions containing high concentrations of redox active materials and supporting salts in organic electrolytes - referred to as "redox electrolytes" - for use in nonaqueous flow batteries. The major scientific outcome of this research will be fundamental understanding of the role of chemical structure and surrounding electrolytes on the performance and durability of redox active organic materials at high concentrations in aprotic organic electrolytes. Further, new electrochemical methods will be developed to enable unambiguous characterization of concentrated nonaqueous redox electrolytes.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.