UC Berkeley

An important parameter in determining battery charging rates is the electrolyte’s transference number, the fraction of the current that the cation carries as opposed to the anion. For decades, others have attributed trends in mobility and transference such as negative transference numbers to ion complexation. In chapter one, I introduce the fundamental concepts of ion transport in battery electrolytes, emphasizing the importance of the transference number, the fraction of current carried by cations versus anions. I discuss the limitations of traditional measurement techniques and set the stage for advanced nuclear magnetic resonance (NMR) methods to directly observe ion complexation and transport phenomena. In chapter two, I investigate methanol-based zinc triflate electrolytes as alternatives to aqueous systems, using electrophoretic NMR (ENMR) and conductivity measurements to determine ion mobilities and transference numbers. Results show zinc cation transference numbers around 0.4 and high ionic conductivity, supporting the viability of these electrolytes for high-rate, sustainable zinc batteries. In chapter three, I explore aluminum triflate electrolytes, revealing multiple long-lived ion clusters through NMR spectroscopy. ENMR experiments demonstrate that, within the same experiment, anions and cations simultaneously undergo both charge-consistent and charge-inverted migration. This behavior results from the specific environment in which each species resides: some anions migrate in the expected direction (opposite to cations), while others migrate like cations, and vice versa for cations. These findings provide direct evidence that strong ion correlation and complexation lead to transport polarity inversion. In the conclusion, I highlight how direct NMR observation of ion complexation and migration advances the understanding of electrolyte transport mechanisms. The work underscores the impact of ion associations and cluster formation on battery performance and suggests future directions for exploiting NMR resolution in designing next-generation electrolytes.