ION SOLVATION IN LITHIUM BATTERY ELECTROLYTE-SOLUTIONS .1. APPARENT MOLAR VOLUMES

Apparent molar volumes, V-phi(MX), of seven electrolytes (NaClO4, NaCF3SO3, NaBPh4, LiClO4, LiAsF6, Ph4AsCF3SO3 and KCF3SO3) have been determined by vibrating-tube densimetry in nonaqueous solvent mixtures of propylene carbonate (PC) with acetonitrile (AN), dimethoxyethane (DME) and tetrahydrofuran (THF). V-phi(MX) was measured at an electrolyte concentration of 0.05M over the entire solvent composition range wherever possible. Ionic apparent molar volumes of transfer, DELTA-tV-phi(ion), were obtained via the tetraphenylarsonium tetraphenylborate (TATB) assumption. DELTA-tV-phi(ion) from PC to the mixed solvents are generally strongly negative for both cations and anions consistent with the greater compressibilities and lower dielectric constants of the cosolvents. In PC/AN mixtures cations and anions have similar values of DELTA-tV-phi but in PC/DME and PC/THF mixtures they differ considerably. Cationic volumes show the expected dependence on ion-size but the differences among the anion volumes are much greater than expected at high cosolvent compositions. These effects are discussed in terms of preferential solvation and other solvent interactions. The implications of these findings for lithium batteries are briefly discussed.