Molecular Motions, Structure, and Composition of Carbonates in the Solvation Shell of the Lithium Ion, Via Infrared Spectroscopies

摘要

Structure property relations of lithium ion battery electrolytes have not been derived because fundamental questions about the lithium ion solvation shell structure and composition remain unanswered. We present a study of lithium hexafluorophosphate in pure carbonate solvents, of cyclic and linear structure, at commercial battery concentrations. Using a combination of infrared spectroscopies we have studied the solvation dynamics of the lithium ion in linear and cyclic carbonate solvents. Infrared experiments show the carbonyl stretch of the cyclic carbonate is broader than that of its linear analogue. In addition, the FFCF dynamics derived from the peak shift photon echo reveal that cyclic carbonates have much slower dynamics than linear carbonates. The contrasting differences observed in the organization, motions and composition of the lithium ion solvation shell for the cyclic and the linear carbonates can be explained with the insertion of a second solvation shell in the case of cyclic carbonates.