TRANSPORT PROPERTY AND RAMAN-SPECTROSCOPIC STUDIES OF THE POLYMER ELECTROLYTE SYSTEM P(EO)(N)-NATFSI

Concentration dependences of a complete set of ionic transport propert ies are reported for the binary solid polymeric ion conductor poly(eth ylene-oxide) [P(EO)], complexed with NaTFSI, [TFSI = (bis)trifluoromet hanesulfonate imide, (CF3SO2)(2)N]. Measured transport properties incl ude the ionic conductivity to), the differential salt diffusion coeffi cient (D-s), and the cationic transference number (t(+)(0)). To measur e t(+)(0), a recently developed technique based on concentrated soluti on theory is used. Under this framework no assumptions need to be made concerning Ideality of the electrolytic solution. We find that for th e P(EO)(pi)-NaTFSI complexes the ionic conductivities, and differentia l salt diffusion coefficients are much higher than those of the previo usly reported P(EO)(pi)-NaCF3SO3 system. D-s also varies less with com plex composition in concentrated solutions. Interestingly, the cationi c transference numbers are found to be negative over a wide concentrat ion range, i.e., t(+)(0) decreases with increasing salt concentration and reaches a low of -1.15 +/- 0.25 at a composition corresponding to an ether-oxygen to sodium-ion ratio of 7:1. This implies that the cati onic current is mainly carried by complexed ions. Complementary Raman spectroscopic studies directly probing cation-anion and cation-polymer molecular interactions show that extensive interionic interactions oc cur in this system.