THERMODYNAMIC, STRUCTURAL, AND CONDUCTANCE STUDIES OF LITHIUM CORONAND ELECTROLYTES RELEVANT TO LITHIUM BATTERY TECHNOLOGY

Gibbs energies, enthalpies, and entropies of coronand macrocycles (15- crown-5 and 1-aza-12-crown-4) and lithium salts containing highly pola rizable anions (hexafluoroarsenate, tetrafluoroborate, and trifluorome thanesulfonate) in acetonitrile and in propylene carbonate at 298.15 K are reported. These titration calorimetry studies ate accompanied by C-13 and H-1 NMR measurements in acetonitrile (CD3CN). On the basis of the stability of the complexes, six new coronand electrolytes were is olated. The thermochemical behavior of these electrolytes as assessed from the standard enthalpies of solution is compared with correspondin g data for common lithium salts. Interpretation of these data reveals that the new coronand electrolytes are much less solvated by these sol vents than the latter. The implications of these results on the conduc tivity enhancement observed by the addition of 15-crown-5 and 1-aza-12 -crown-4 to nonaqueous lithium solutions are demonstrated leading to t he conclusion that the use of these electrolytes in lithium batteries shows promise. Enthalpies of coordination referred to reactants and pr oducts in their pure physical state for these systems are first report ed. A notable feature of the data is the higher enthalpic stability ob served for the coordination of 1-aza-12-crown-4 and lithium trifluorom ethanesulfonate with respect to that of the same ligand and other Lith ium salts. The observed enhancement of stability is within the range e xpected for hydrogen bond formation likely to be attributed to a speci fic interaction between the hydrogen atom of the aza crown ligand and the anion. Further investigations in this area are suggested with part icular emphasis on fundamental research where more efforts should be g eared to overcome some of the problems encountered in lithium battery technology.