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

摘要

Gel-type electrolytes based on fluorinated polymers are of interest for electrochemical devices. We present a ~7Li-~(13)C 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(CF_3SO_2)_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 ~(13)C 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.