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Impedance and lithium-7 NMR studies of polymer electrolytes based on poly(vinylidene fluoride)

TitleImpedance and lithium-7 NMR studies of polymer electrolytes based on poly(vinylidene fluoride)
Publication TypeArticolo su Rivista peer-reviewed
Year of Publication1996
AuthorsCroce, F., Appetecchi Giovanni Battista, Slane S., Salomon M., Tavarez M., Arumugam S., Wang Y., and Greenbaum S.G.
JournalSolid State Ionics
KeywordsDibutylphthalate, Dimethylformamide, Impedance spectroscopy, Lithium batteries, Lithium compounds, Lithium salts, Nuclear magnetic resonance spectroscopy, Organic solvents, Plasticizers, Polyelectrolytes, Polyvinylidene fluoride, Spectroscopy, Vinyl resins

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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Citation KeyCroce1996307