(435j) Modulating Entropic Driving Forces to Guide Ion Structuring and Tune Metal Ion Coordination

Ionic liquids and organic ionic plastic crystals are two classes of salts that have gained increased interest for energy storage applications over the last few decades. These materials offer safer, nonflammable alternatives to the organic electrolytes currently used in battery technologies. However, the performance of ionic liquids and organic ionic plastic crystals as battery electrolytes has been hindered by their poor lithium transport behavior. Recent studies suggest that anion coordination to lithium cations can even drive formation of a negative complex, which may cause lithium species to move opposite of the desired direction. Similar ion coordination exists in systems that contain sodium, magnesium, and calcium. In this talk, I will discuss our work on tuning the nanostructures of ionic liquid inspired electrolytes to promote organic cation-anion affinity via incorporation of rigid moieties called “diamondoids”. Diamondoids are molecular diamond templates forming three-dimensional cage-like structures. The smallest diamondoid, adamantane, is composed of ten carbon atoms. By leveraging the unique self-assembly properties of diamondoids, we show that metal cation-anion coordination can be reduced, and possibly removed, resulting in enhanced mobility of redox species. Specifically, investigating system phase behavior, vibrational modalities, and magnetic environments demonstrates that metal salt solubility can remain high while metal cation-anion coordination is hampered. Our results provide a new paradigm for enhancing redox species mobility in ionic liquid-derived electrolytes by engineering cation functional groups to enhance organic cation-anion interactions, suppress metal coordination, and leverage packing mismatches to enhance redox species mobility.