Unraveling Ion Dynamics and Interactions in an Ionic Liquid Electrolyte with a Protonated Anion for Lithium Batteries

The ion associations in two ionic liquid (IL) electrolytes based on the novel asymmetric anion (difluoromethanesulfonyl) (trifluoromethanesulfonyl)­imide (DFTFSI) are probed in detail using a combination of nuclear magnetic resonance (NMR) methods [heteronuclear overhauser enhancement spectroscopy (HOESY), relaxation, and diffusion] and molecular dynamics (MD) simulations. The ¹H–⁷Li HOESY NMR technique and MD simulations give insights into the lithium interactions with the IL anions and cations, while the measured ¹H–¹⁹F HOESY cross-relaxation rates and MD simulations indicate that the Li–H (anion) proximity disrupts the hydrogen bonding interaction previously observed between the DFTFSI anion and the ether oxygen of the N-methyl-N-methoxyethylpyrrolidinium (C_2O1mpy) cation in the pure IL. Preliminary electrochemical behavior shows excellent Li compatibility of the C₃mpyr DFTFSI-based IL electrolyte for future lithium-battery applications.