(Invited) Understanding Fluid Structure and Properties of Eutectic and Microemulsion Electrolytes for Energy Storage

Abstract

The increase of adding intermittent renewable energy sources like solar and wind to the electricity grid requires a commensurate need for large scale energy storage. Flow batteries are the most likely storage technology to meet this need because of its ability to decouple power load from energy storage capacity, and its promise for longer-term storage capacity. Flow battery electrolytes are mostly based on aqueous systems with limited voltage window for energy storage redox couples, with some systems based on organic solvents that are volatile and often toxic. The BEES (Breakthrough Electrolytes for Energy Storage) EFRC (a DOE Emerging Frontier Research Center), in its first four years (2018 to 2022), studied two classes of electrolytes, more specifically reported here is work on deep eutectic solvents (DESs) and microemul sions (µEs). While each class of liquid presents a unique aspect that can be leveraged for energy storage, collectively they represent novel electrolytes that are structured at the molecular (DESs) to meso-scale (µEs) level. The motivation to explore DES for electrolytes is the potential for high energy density, safety, and sustainability.1 The motivation to explore µEs for electrolytes is the ability to decouple power and energy density through composition.2 A fundamental understanding of the physical, transport, and electrochemical properties of model systems representative of each class of electrolytes in relation to their bulk and interfacial structure was achieved through collaborative experimental and theoretical studies within BEES. This presentation will describe our motivation and approach, and give examples of a few research highlight from BEES. Detailed results of BEES in developing standards and identifying the key structure-property relations and mechanisms, as well as intrinsic limitations and prospects are reported in BEES affiliated peer-reviewed publications.3 Acknowledgment: This work was funded by Breakthrough Electrolytes for Energy Storage (BEES) - an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences under Award # DE-SC0019409. 1 Ghahremani, Savinell, Gurkan, J Electrochem Soc, 2022, 169, 3 2 Barth, Imel, Nelms, Goenaga, Zawodzinski, Front Chem, 2022, 10, 831200 3 In Google Scholar search the DOE award number: DE-SC0019409