Molecular Structure, Chemical Exchange and Conductivity Mechanism of High Concentration LiTFSI Electrolytes

High concentration lithium electrolytes have been found to be good candidates for high energy density and high voltage lithium batteries. Recent studies have shown that limiting the free solvent molecules in the electrolytes prevents the degradation of the battery electrodes. However, the molecular level knowledge of the structure and dynamics of such an electrolyte system is limited, especially for electrolytes based on typical organic carbonates. In this article, the interactions and motions involved in lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) in carbonyl containing solvents are investigated using linear and time-resolved vibrational spectroscopy and computational methods. Our results suggest that the overall structure and the speciation of the three high concentration electrolytes are similar. However, the cyclic carbonate based electrolyte presents an additional interaction as a result of dimer formation. The time-resolved studies reveal similar and fast dynamics for the structural motions ...