Conductivity and Viscosity of PC-DEC and PC-EC Solutions of LiBOB

Conductivity κ of propylene carbonate-diethyl carbonate (PC-DEC) and propylene carbonate-ethylene carbonate (PC-EC) solutions of lithium bis(oxalato)borate (LiBOB) was experimentally determined at temperatures θ from 60 to salt molalities from 0.04 to and solvent compositions from 0 to 0.7 weight fraction of DEC and EC. Viscosity η of LiBOB in PC-EC was studied through measuring its glass transition temperature in the same ranges of and was found to rise with and of EC, indicating a concurrent change in the η of the solution. The κ of the PC-DEC solution of LiBOB peaked in both and thus forming a "dome" in its 3D presentation in the coordinates of and while that of the PC-EC solution peaked only in resulting in an "arch"-shaped surface. As the θ was lowered, these κ surfaces fell in height and shifted in the direction of low η. These observations correlated well with the changes of dielectric constant of the solvents and η of the solutions with the same set of variables. The measured data for the PC-DEC solution was fitted with the Vogel-Tamman-Fulcher equation for an evaluation of its vanishing mobility temperature and apparent activation energy. The results of κ and η of the LiBOB solutions were further compared with those of solutions from a previous study. © 2004 The Electrochemical Society. All rights reserved.