(263e) Ionic Liquid Battery Electrolytes with Functional Organic Cations to Enhance Lithium Mobility

Sustainable energy storage devices, such as batteries, are key for decarbonization of transportation and energy grids, which can help lower global carbon emissions and mitigate climate change. However, the performance and safety of modern batteries are greatly hindered by a lack of electrolytes that enable efficient transport of Li⁺ ions while retaining safety and nonflammability. Ionic liquids (ILs) have excellent thermal and electrochemical stability and are promising as next-generation battery electrolytes, but detrimental coordination between conventional IL anions and Li⁺ ions often leads to poor lithium mobility and long charging times. Here, we will discuss our molecular design, synthesis, and characterization of a series of imidazolium IL electrolytes containing [NTf₂]^- anions and unique oxygen- and fluorine-containing cation side chains in the place of conventional hydrocarbon groups. We show that these electrolytes and their equimolar blends with Li[NTf₂] have much lower volatility and higher thermal stability than conventional electrolytes. Further, we use Raman spectroscopy to reveal that, oxygen-containing cation substituents can exhibit remarkable disruption of the Li⁺-[NTf₂]^- coordination that compromises conventional ILs. In contrast, we find that addition of fluorine segments to imidazolium cations exacerbates Li⁺-[NTf₂]^- coordination. Our work demonstrates that imidazolium cation substituents provide an unexplored way to tune lithium coordination and mobility at the molecular level to substantially improve the performance of ILs for safe, high-performance batteries.