Thermodynamic and Structural Aspects of Solvate Ionic Liquid Formation

Development of the electrolyte solution plays a key role in realization for lithium-sulfur (Li–S) battery. The lithium ion local structure and the liquid structures of an electrolyte solution have direct influence on the battery performance because of the electromotive force, the charging/discharging speed and the life time. The activity for the free solvent directly contributes to the electrode potential in the concentrated electrolyte such as the solvate ionic liquid. Lithium-glyme solvate ionic liquid consists of only the glyme-solvated lithium ion and its counter ion; similarly a super-concentrated electrolyte solution contains no full solvated Li⁺ ion. However, it is unclear whether both electrolyte solutions should be regarded the same. From a thermodynamic point of view, the activity and/or the activity coefficient for the solvent is useful for the distinction among them. In this chapter, the liquid structures and the thermodynamic parameters like an activity coefficient are described for solvate ionic liquid.