Composite polymer electrolytes consisting of at least 35 mol% poly(vinylidene fluoride) (PVdF) and mixtures of propylene carbonate (PC) and dimethyl formamide (DMF), lithium salts (LiAsF6, LiN(CF3SO2)2, or LiC(CF3SO2)3, and small amounts (∼ 5 mol%) of plasticizer, either diethylphthalate (DEP) or dibutylphthalate (DBP), were investigated by differential scanning calorimetry, complex impedance analysis and 7Li NMR spectroscopy. Despite the composite nature of these materials, they all exhibit a single glass transition temperature (Tg). Significant variations of Tg with the two different plasticizers were noted. The sample containing the LiC(CF3SO2)3 salt has the highest electrical conductivity of the series, ∼ 3 × 10 4S/cm at 25°C. Time-dependent impedance measurements utilizing cells with lithium electrodes revealed the growth of a passivating interface layer comparable to those observed with other polymer electrolytes. The onset of NMR motional line-narrowing is correlated with Tg for all samples prepared with DBP, as is known to occur in 'single component' polyether-based electrolytes. However the onset of narrowing for the samples containing DEP occurs about 30 K above Tg. Lithium-7 spin-lattice relaxation measurements exhibit non-exponential recovery profiles below Tg, with about ∼ 15% of the Li species relax differently than the majority. Activation energies extracted from 7Li T1 data show that localized Li motion is significantly impeded in the DEP-containing samples, relative to those prepared with DBP.

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