Cation dynamics in PVdF-based polymer electrolytes

Poly(vynilidene fluoride) P(VdF)/hexafluoropropylene (HFP) copolymers are well suited to prepare hybrid electrolytes which can be useful in solid-state electrochemical devices. We study with modulated differential scanning calorimetry (MDSC) and nuclear magnetic resonance (NMR) the polymer-solution interactions in 30 wt% P(VdF-HFP)-70 wt% (ethylene carbonate-propylene carbonate-LiN(CF3SO2)(3)) hybrid electrolyte. We show that both Li-7-NMR lineshape narrowing and spin-lattice relaxation are driven by the ion dynamics. The behaviour of the longitudinal relaxation times, T-1,, confirms that the host polymer matrix simply behaves like an inert cage for the cations, at least at the polymer-to-solution ratio examined in the present study. These results are confirmed by C-13-NMR-MAS data, which show that the presence of the polymer does not significantly affect the chemical shift changes induced in the EC/PC carbons by the imide salt. (C) 1999 Elsevier Science B.V. All rights reserved.