Improving Electrolyte Characterization Methods/Tools: What the Data Really Means

Electrolyte formulations are frequently perceived to be a linchpin for enabling the use of new battery electrode chemistries. The electrolyte serves as the medium for the transport of active ions to and from the electrodes as the electrodes undergo redox reactions, but the molecular-level interactions which govern solvent-ion (solvation) and ion-ion (ionic association) interactions remain poorly understood. New electrolyte characterization methods/tools, or improvements for existing evaluation methods, are needed to obtain detailed information about such interactions...and how they, in turn, are determinants for bulk electrolyte properties. The interpretation of the data from many electrolyte characterization methods, however, is often flawed due to incorrect assumption and/or limitations of the techniques. This can result in a gross misunderstanding of the actually solution structure which exists for electrolyte formulations of interest thus leading researcher astray. This talk will thus explore the challenges associated with the use of solvent polarization parameters (e.g., dielectric constant (ε), Gutmann donor number (DN), etc.) and Raman spectroscopy for obtaining solvation numbers and ionic association interactions. New electrolyte characterization tools will be demonstrated and examples will be provided which explore how the conventional wisdom regarding electrolyte properties and behavior is often inaccurate.

ACKNOWLEDGEMENT

The authors wish to express their gratitude to the U.S. Department of Energy (DOE) Office of Basic Energy Science-Division of Materials Sciences and Engineering which fully supported the experimental research under Award DE-SC0002169.