Standard partial molar volumes of some electrolytes in ethylene carbonate based mixtures
Introduction
The volumetric behavior of solutes has been proved to be very useful in elucidating various interactions occurring in solutions. Studies on the apparent molar volumes of electrolytes have been widely used to examine the ion–ion and ion–solvent interactions. With the increased interest in high energy and low environmental impact batteries in recent years, a great variety of solvents and electrolytes have been employed in an effort to improve battery characteristics [1]. It is more interesting that molar volumes of electrolytes are relevant to developing an understanding of lithium battery behavior because of their effect on solution properties such as conductivity and viscosity, etc. [2].
Molar volumes of some electrolytes have been reported in ethylene carbonate (EC) [3], acetonitrile (AN) [4] and dimethoxyethane (DME) [4]. However, no data are available in the mixed solvents involving EC. In this paper, we report the partial molar volume of lithium salts (LiClO4 and LiBr), tetraethylammonium bromide (Et4NBr), tetrapropylammonium bromide (Pr4NBr) and tetrabutylammonium bromide (Bu4NBr) in solvent mixtures of EC with tetrahydrofuran (THF), AN, ethyl acetate (EA), DME at 298.15 K. Since our final purpose is to understand the nature of ionic solvation and ionic association in practical lithium battery electrolyte solutions, volumetric ratio of EC to the co-solvents was chosen to be 1:1. The results have been discussed from ion–solvent interactions and the dielectric effect of the solvents.
Section snippets
Experimental
LiClO4 · 3H2O (Beijing Baili Chem. Co., A.R.) was recrystallized twice from ethanol or acetonitrile, and dried at 453 K under vacuum for four days. LiBr · 2H2O (Beijing Chem. Co., A.R.) was recrystallized from ethanol, and dried at 423 K under vacuum for three days. Et4NBr (Shanghai Chem. Co., A.R.) was recrystallized from ethanol, and dried at 333 K to 353 K under vacuum for two days. Pr4NBr (Fluka, AT) was recrystallized from acetone or methanol, and dried at 383 K under vacuum for two days. Bu4
Results and discussion
Apparent molar volumes of lithium salts and tetraalkylammonium salts in a given solvent mixture were calculated from the solution densities bywhere M and m are, respectively, molar mass and molality of salts, ρ and ρ0 are densities of the ternary solutions and the binary solvents, respectively. Apparent molar volumes of these salts in EC based solvent mixtures are given in TABLE 1, TABLE 2, TABLE 3, TABLE 4 as a function of molality of the electrolytes. Since there is
Acknowledgements
We wish to acknowledge the financial support from the National Natural Science Foundation of China (Grant No. 29973009) and the Research Foundation of Ministry of Education of China.
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