A comparison of ionic conductivity behaviour in various ethylene oxide based polymer electrolytes

Glass transition temperatures T-g and ionic conductivities sigma have been measured as a function of salt concentration m for LiCF3SO3 complexes of three types of ethylene oxide (EO) based materials: (i) low molecular weight poly(ethylene oxide)s, viz. tetraglyme, PEG300 and PEG600 and end-esterified PEG300, (ii) higher molecular weight amorphous polymer electrolytes, poly(methoxy polyethylene glycol monomethacrylate) (PEM), methyl oxyethylene extended poly(propylene oxide) (Me-xPPO), and (iii) some [12] and [13]-crown-4 polymethacrylates (CEP). The variation of sigma with temperature T has been fitted to the VTF equation sigma = AT(1/2)exp{-B/(T-T-o)}. It is found (a) that the salt dependent behaviour of all the amorphous PEO materials is very similar but very different from that of the CEPs; (b) that (T-g-T-o) is related to B in an approximately linear manner for all salted systems independent of polymer type; (c) that for PEO systems, where the formation of ionic cross links is insignificant, T-o is independent of salt concentration, but that for the crown ether polymers in which ionic cross links are expected, T-o increases with m; and (d) that for the crown ether polymers, Aim and B vary weakly with rn and that the A/m and B values for all the ethylene oxide based materials appear to converge to common high values at high salt concentrations. This is compatible with the idea that the solvated cations, incorporated intrahelically, cause the PEO to form crown like configurations. (C) 1998 Published by Elsevier Science Ltd. All rights reserved.