F. Croce et al., IMPEDANCE AND LI-7 NMR-STUDIES OF POLYMER ELECTROLYTES BASED ON POLY(VINYLIDENE FLUORIDE), Solid state ionics, 86-8, 1996, pp. 307-312
Composite polymer electrolytes consisting of at least 35 mol% poly(vin
ylidene fluoride) (PVdF) and mixtures of propylene carbonate (PC) and
dimethyl formamide (DMF), lithium salts (LiAsF6, LiN(CF3SO2)(2), or Li
C(CF3SO2)(3), and small amounts (similar to 5 mol%) of plasticizer, ei
ther diethylphthalate (DEP) or dibutylphthalate (DBP), were investigat
ed by differential scanning calorimetry, complex impedance analysis an
d Li-7 NMR spectroscopy. Despite the composite nature of these materia
ls, they all exhibit a single glass transition temperature (T-g). Sign
ificant variations of T-g with the two different plasticizers were not
ed. The sample containing the LiC(CF3SO2)(3) salt has the highest elec
trical conductivity of the series, similar to 3X10(-4) S/cm at 25 degr
ees C. Time-dependent impedance measurements utilizing cells with lith
ium electrodes revealed the growth of a passivating interface layer co
mparable to those observed with other polymer electrolytes. The onset
of NMR motional line-narrowing is correlated with T-g for all samples
prepared with DBP, as is known to occur in 'single component' polyethe
r-based electrolytes. However the onset of narrowing for the samples c
ontaining DEP occurs about 30 K above T-g. Lithium-7 spin-lattice rela
xation measurements exhibit non-exponential recovery profiles below T-
g, with about similar to 15% of the Li species relax differently than
the majority. Activation energies extracted from 7LiT(1) data show tha
t localized Li motion is significantly impeded in the DEP-containing s
amples, relative to those prepared with DBP.