(531b) Tuning Molecular Rigidity to Modulate Lithium Coordination and Enhance Mobility in Ionic Liquids

As lithium-ion battery deployment rapidly expands, increases in battery safety and sustainability are becoming critical. Currently, battery flammability is a growing problem, which is exacerbated by the high flammability of organic electrolytes. Ionic liquid-derived electrolytes offer safe, nonflammable alternatives, but the performance of ionic liquids as battery electrolytes has been hindered by poor lithium transport, which arises from formation of strong lithium-anion coordination complexes. For example, recent studies suggest that anion coordination to lithium can even drive formation of negative complexes in ionic liquids, which may cause lithium species to move opposite of the desired direction. In this talk, I will discuss our work on tuning ionic liquid nanostructures to suppress lithium-anion coordination via incorporation of rigid functional groups. By leveraging the unique self-assembly properties of rigid molecular clusters, we show that lithium coordination can be suppressed and organic cation mobilities can be minimized, resulting in dramatically enhanced lithium mobilities compared to the surrounding organic ion matrix. Specifically, we use studies of phase behavior, vibrational spectroscopy, and magnetic spectroscopy to demonstrate that rigid groups can be tuned to maintain high lithium solubility while concurrently minimizing lithium-anion coordination. Further, we show that lithium mobilities can be enhanced through rational incorporation of molecular packing mismatches. Our results provide a new paradigm for enhancing lithium mobility in ionic liquid-derived electrolytes by tuning self-assembly of cation functional groups to enhance organic cation-anion interactions, suppress lithium coordination, and enhance lithium mobility.