A multinuclear NMR study of ion transport in P(EO)nLiBETI complexes

A study of ion transport in P(EO)nLiBETI complexes was undertaken, using both AC impedance and nuclear magnetic resonance (NMR) spectroscopy. 1H, 7Li and 19F NMR techniques were used to investigate structure and dynamics as a function of temperature for n=3, 6, 8, 12 and 20. Spin–lattice relaxation times (T1) and spectral information were obtained from −50 to 100 °C. Variable temperature self-diffusion coefficients (D) and ionic conductivity (σ) measurements were also performed. Anion diffusion (DF) results displayed a dependence on available free volume, increasing with decreasing salt concentration. On the other hand, cation diffusion (DLi) results did not follow this trend. DLi for n=3 and 6 suggest the presence of ionic mobility in the crystalline phase, with a significant rise above the melting point. A transition from a crystalline to amorphous phase dominated ion transport occurs at n=8. This is supported by σ results, which exhibited a VTF type of behavior for n≥8 that is associated with ion transport in the amorphous phase.