Glyme-Li Salt Solvate Ionic Liquids for Advanced Lithium Batteries

Monday, 20 June 2016: 16:30
Grand Ballroom (Hyatt Regency)
M. Watanabe (Yokohama National University)
Certain molten complexes of Li salts and solvents can be regarded as ionic liquids. In this study, the local structure of Li+ ions in equimolar mixtures ([Li(glyme)]X) of glymes (G3:triglyme and G4: tetraglyme) and different Li salts was investigated to discriminate between solvate ionic liquids and concentrated solutions. Raman spectroscopic analysis allowed us to estimate the fraction of the free glyme in [Li(glyme)]X. The amount of free glyme was estimated to be a few percent in [Li(glyme)]X with perfluorosulfonylamide-type anions, and thereby could be regarded as solvate ionic liquids. Other equimolar mixtures of [Li(glyme)]X were found to contain a considerable amount of free glyme, and they were categorized as traditional concentrated solutions. The activity of Li+ in the glyme-Li salt mixtures was also evaluated by measuring the electrode potential of Li/Li+ as a function of concentration. At a higher concentration of Li salt, the amount of free glyme diminished in the solvate ionic liquids, leading to a drastic increase in the electrode potential. Unlike conventional electrolytes (dilute and concentrated solutions), the solvation of Li+ by the glyme forms stable and discrete solvate ions ([Li(glyme)]+) in the solvate ionic liquids. This anomalous Li+ solvation had a great impact on the electrolyte properties and electrode reactions, which enhanced the utility of the solvate ionic liquids in advanced lithium batteries such as Li-S batteries.