(450e) Direct Visualization of Lithium Transport in Nanostructured Ionic Liquid Electrolytes

Battery fires are a growing problem as most modern batteries are composed of large amounts of flammable organic electrolytes. One avenue to resolve this issue is replacing volatile organic liquids with ionic liquids, which are non-flammable and chemically stable. However, typical ionic liquids exhibit slow battery charging kinetics, which is thought to arise from high viscosity causing poor lithium transport. Next generation ionic liquids that facilitate selective lithium transport by decoupling ion mobility from bulk viscosity promise key advantages in battery safety and performance. Yet, poor understanding of lithium transport in ionic liquids hinders control over lithium transference, in large part due to a lack of methods that selectively probe lithium mobility. Here, I will discuss a new diffusion-front mapping method that quantifies lithium diffusion in ionic liquids using fluorophores that change color with lithium concentration. Notably, this approach yields diffusion coefficients of metal ions in ionic liquids as a continuous function of concentration, contrasting prior methods that sample one concentration at a time. Further, we can evaluate concentration regimes that are inaccessible with other methods. Remarkably this approach promises to reveal more diffusion coefficients in a few months than have been reported in the previous decade and enables systematic investigation of lithium transport mechanisms in ionic liquids to determine why bulk viscosity is a poor predictor of lithium mobility. I will conclude by showing how this method opens the door to exploring new classes of ionic liquids that can bridge the advantages of traditional liquid and solid electrolytes.