TONIC DIFFUSIVITY AND CONDUCTIVITY OF PLASTICIZED POLYMER ELECTROLYTES - PMFG-NMR AND COMPLEX IMPEDANCE STUDIES

Novel polymer electrolytes (LiBF4/plasticizer/PE) based on the interpe netrating network approach, were obtained starting from functionalized polyether network precursors, in the presence of LiBF, and PC (propyl ene carbonate) or TGME (tetraethylene-glycol dimethyl-ether) as plasti cizers. Self-consistent and easily handled membranes were obtained as thin films by a dry procedure using UV radiation to polymerize and cro sslink the network precursors, directly on suitable substrates. These membranes were studied by complex impedance and H-1, F-19, Li-7 PMFG ( Pulsed Magnetic Field Gradient)-NMR was used to determine the self-dif fusion coefficients (D) of the cation (D-Li), anion (D-F) and plastici zer (D-pl). Comparison of data from the two techniques allowed calcula tion of the deviation from the Nernst-Einstein equation (Delta(NE)) an d information on ion associations. Ionic conductivities (sigma) were m easured for PC and TGME-based membranes at various plasticizer and sal t contents as a function of T (60 to - 20 degrees C). LiBF4/PC/PE with 9% (w/w) salt and 59% PC has the highest sigma (2.4 X 10(-3) and 1.0 X 10(-3) S/cm at 20 degrees C and - 3 degrees C, respectively), Membra nes with PC have higher a than those of TGME due mainly to the greater amount of ion associations (correlated motions of ions) in TGME syste ms as evidenced by Delta(NE). Li+ in PC seems to interact preferential ly with the polymer. NMR shows that LiBF4/TGME/PE have higher cationic transport number(t(+) = ca. 0.5), little affected by changing salt or TGME contents, and faster polymer chain motions than the correspondin g PC system. Delta(NE) decreases with increasing T indicating that ion associations are favoured at high T. Simple binary electrolytes (LiBF 4/plasticizer) were also studied by conductimetry and PMFG-NMR. The di fferences between PC and TGME electrolytes regarding sigma, Delta(NE) and t(+) were the same as found for ternary systems. D data show a lar ger Li+ solvation shell in LiBF4/PC and on increasing the salt content above 10% (w/w) a drops rapidly (attributed to increased viscosity an d ion associations).