SOME THERMODYNAMIC AND TRANSPORT-PROPERTIES OF LITHIUM-SALTS IN MIXEDAPROTIC-SOLVENTS AND THE EFFECT OF WATER ON SUCH PROPERTIES

In a continuing study on the optimization of the electrolyte medium fo r high-energy lithium batteries, volumes, heat capacities, and specifi c conductivities of LIClO(4) and LiBr were measured in mixtures of gam ma-butyrolactone (BUTY) and 1,2-dimethoxyethane (DME) and of propylene carbonate (PC) and BUTY. These results are compared with those of the electrolytes in the pure solvents. Phase diagrams are also reported w hen appropriate. The effect of addition of water to these binary and t ernary systems was investigated with the same techniques. The mixtures DME-BUTY, PC-DME, DME-H2O, and BUTY-H2O are typical of mixtures of ap rotic solvents and mixtures of aprotic solvents and water. The electro lytes at high concentrations in aprotic solvents of low dielectric con stants are largely associated. The medium still conducts electrolytica lly since the ion pairs are in a state that resembles to a large exten t that of a molten salt. With some systems at high concentration, stab le solvates persist in the solution medium, as evidenced mostly by hea t capacities, and are in equilibrium with either the excess solvent or unsolvated molten salts. In mixed solvents, the properties of electro lytes can largely be predicted from the binary systems and by the coex istence of these solvates. The properties of water in DME, BUTY, or mi xtures of the two solvents are modified significantly in the presence of LiBr but only slightly with LiClO4. These specific interactions, wh ich affect the heat capacities much more than the volumes and which ar e especially large with the system LiBr-DME, could be responsible for the decrease in reactivity of water with lithium metal in an aprotic m edium in the presence of certain electrolytes.