How Conductivities and Viscosities of PC-DEC and PC-EC Solutions of LiBFsub 4, LiPFsub 6, LiBOB, Etsub 4NBFsub 4, and Etsub 4NPFsub 6 Differ and Why

Electrolytes of LiBOB, and in propylene carbonate-diethyl carbonate (PC-DEC) and propylene carbonate-ethylene carbonate (PC-EC) binary solvents were compared for their electrolytic conductivity (κ) and viscosity (η) to assist their application to the batteries and capacitors and to understand the mechanisms underlying the differences in these properties. For η, the -salts resulted in considerably higher values than the -salts, and the influence of an anion was such that the larger its size, the higher the η of the electrolyte. Correspondingly, κ of the -electrolytes was substantially higher than the -electrolytes, and a larger anion was accompanied by a lower κ, except for electrolytes at the low-η end. Toward this end, the order of κ tended to be in reverse: the κ of an electrolyte with a larger anion rose relative to one with a smaller anion. All evidence presented leads to the conclusion that the η, and thereby the κ, of the electrolytes are dominantly affected by the number of unassociated ions through their solvation by the carbonate solvent molecules, the different anions of the Li-salts exerting their influence only through altering the number by their different powers for associating with the © 2004 The Electrochemical Society. All rights reserved.