1993 Volume 1993 Issue 11 Pages 1217-1224
Electrolytic properties in mixed binary solutions of 3-propylsydone(3-PSD)tetrahydrofuran (THF) and 1, 2-dimethoxyethane (DME) containing five kinds of lithium salts (LiPF6, LiCl04, LiBF4, LiCF8S03 and LiBPh4 (Ph: phenyl)) have been examined from solvent composition and molar conductivity of the solutions. The theoretical energy density of Li/MnO2 test cell and the cycling efficiency of the lithium electrode were also investigated in these mixed binary solutions. The molar conductivity (λ ) in mixed binary electrolyte solutions gradually increased with increasing THF and DME mole fractions (XTHF and XDME). However, the conductivity maxima were observed at 0.7-0.9 XTHF and XDME for four kinds of electrolytes except for LiBPh4. The increase in molar conductivity depended on the decrease in viscosity (η ° ) of mixed solvents. It is considered that the conductivity maxima observed is dependent on the ion pair formation due to the decrease of dielectric constant in the mixed solvents with increase of XTHF and XDME. On the contrary, no conductivity maximum was observed for LiBP114 solution. It means that the ion pair formation in LiBPh4 solution is hard because BPh4- ion is a very stable and a big anion. The order of λ among five kinds of electrolytes was LiPF8> LiCl04> LiBF4> LiCF8S03> LiBPh4 at XTHF and XDME=0.6. The electrolyte solutions of O.5 mol dm-3 LiBPh4 at XTHF=XDME=0.7 showed maximum coulombic efficiencies of lithium cycling more than 80%. The efficiency in four kinds of electrolyte solutions became higher at XTHF or XDME=0.5 than in the solutions showing conductivity maxima. The energy density for Li/MnO2 test cell with the electrolyte solutions showing conductivity maxima was higher than those with the solutions for any XTHF= XDME. On the other hand, the energy density for the cell with LiBP114 solution was fairly lower than those with other electrolytes.
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