Host-guest interactions in fluorinated polymer electrolytes:: A 7Li-13C NMR study

Gel-type electrolytes based on fluorinated polymers are of interest for electrochemical devices. We present a Li-7-C-13 solid-state NMR and modulated differential scanning calorimetry (MDSC) study of gel electrolytes based on a copolymer poly(vinylidene fluoride) (PVdF)-hexafluoropropylene (HFP) activated with a nonaqueous solution ethylene carbonate (EC)-propylene carbonate (PC)-LiN(CF3SO2)(2). We show that the narrowing of the Li lineshape is decoupled from the glass transition. The behavior of the longitudinal relaxation times, T-1, confirms that the host polymer matrix simply behaves like a quasiinert cage for the solution. These results are confirmed by C-13 NMR at the magic angle (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 American Institute of Physics. [S0021-9606(99)50331-0].