Conductivity and viscosity of PC-DEC and PC-EC solutions of LiBOB

Conductivity kappa 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 theta from 60 to -80 degreesC, salt molalities m from 0.04 to 1.1 mol kg(-1), and solvent compositions w from 0 to 0.7 weight fraction of DEC and EC. Viscosity eta of LiBOB in PC-EC was studied through measuring its glass transition temperature T-g in the same ranges of m and w. T-g was found to rise with m and w of EC, indicating a concurrent change in the eta of the solution. The kappa of the PC-DEC solution of LiBOB peaked in both m and w thus forming a dome'' in its 3D presentation in the coordinates of m and w, while that of the PC-EC solution peaked only in m resulting in an arch''-shaped surface. As the theta was lowered, these kappa surfaces fell in height and shifted in the direction of low h. These observations correlated well with the changes of dielectric constant of the solvents and h of the solutions with the same set of variables. The measured kappa(T) 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 k and h of the LiBOB solutions were further compared with those of LiPF6 solutions from a previous study. (C) 2004 The Electrochemical Society.