Ion solvation in lithium battery electrolyte solutions. 1. Apparent molar volumes

Single Ionic Volumes in Acetonitrile–Organic Cosolvent Mixtures at 298.15 K

Densities of binary nonaqueous mixtures of acetonitrile (AN) with 2-methoxyethanol (ME), N,N-dimethylacetamide (DMA) and propylene carbonate (PC) were determined over the whole composition range at 298.15 K. The excess molar volumes and the partial molar volumes of both components were calculated from these data. Densities of solutions of NaI, NaBPh4 and Ph4PI in solvent mixtures AN + ME and AN + DMA and of NaI solutions in mixtures of AN + PC were measured over the whole composition range of the mixed solvents at an electrolyte concentration equal 0.05 mol dm−3. From these densities, apparent molar volumes of electrolytes and ions were evaluated and analyzed. The relationship between the apparent molar volumes of ions and (κT /ε) parameter was tested and discussed.

Volumetric studies of ion solvation in propylene carbonate + N,N-dimethylformamide electrolyte solutions

Apparent molar volumes V2,ϕ and standard partial molar volumes V°2,ϕ for tetraethylammonium bromide (Et4NBr), tetrapropylammonium bromide (Pr4NBr), tetrabutylammonium bromide (Bu4NBr), and tetrahexylammonium bromide (Hex4NBr) have been determined at 298.15 K from precise density measurements in solvent mixtures of propylene carbonate (PC) with N,N-dimethylformamide (DMF). Combined with our previous data for LiClO4 and LiBr in the same solvents, ionic molar volumes of Li+, Et4N+, Pr4N+, Bu4N+, Hex4N+, and related anions have been deduced from the extrapolation method suggested by Conway and co-workers. It is shown that the molar volumes of these cations are quite independent of the nature of the solvent and the composition of the solvent mixtures, in contrast to those of ClO4– and Br– anions. This suggests that the Lewis-base-type solvents with similar molecular volumes have similar interactions with Li+. The constancy in partial molar volume for tetraalkylammonium ions provides helpful evidence for the lack of solvation of large tetraalkylammonium cations in organic solvents. These findings have been interpreted using scaled-particle theory. The results are discussed in terms of ion solvation, packing effects of solvent molecules in the solvation shell, and the electrostriction of solvents.Key words: ionic volumes, propylene carbonate, N,N-dimethylformamide, solvent mixtures, solvation, lithium batteries.

A partial-molar volume study of electrolytes in propylene carbonate-based lithium battery electrolyte solutions at 298.15 K

Apparent molar volumes (V2, ϕ ) and standard partial-molar volumes (V20, ϕ ) of LiClO4 and LiBr at 298.15 K have been determined from precise density measurements in solvent mixtures of propylene carbonate (PC) with dimethylformamide (DMF), tetrahydrofuran (THF), acetonitrile (AN), and methyl formate (MF). The scaled particle theory is used to calculate the contributions of the cavity formation and the electrolyte-solvent interactions to the standard partial-molar volumes. It is shown that V20, ϕ is strongly dependent on the nature of the solvents, and the trends in V20, ϕ with composition of the solvent mixtures are determined by the interaction volumes of electrolytes with solvents. The results are discussed in terms of ionic preferential solvation, packing effect of solvents in the solvation shell, and electrostriction of solvents by ion.Key words: partial-molar volume, scaled particle theory, lithium salts, propylene carbonate, solvent mixtures, lithium battery electrolytes.