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 (C2O1mpy) cation in the pure IL. Preliminary electrochemical behavior shows excellent Li compatibility of the C3mpyr DFTFSI-based IL electrolyte for future lithium-battery applications.