Multinuclear solid-state NMR characterization, ion dissociation, and dynamic properties of lithium-doped organic-inorganic hybrid electrolytes based on ureasils

Solid organic-inorganic hybrid electrolytes based on diureasils doped with LiClO4 have been obtained by the sol-gel process through the reaction of poly(propylene glycol)-block-poly(ethylene glycol)-block-poly(propylene glycol) bis(2-aminopropyl ether) (H2N-PPG-PEG-PPG-NH2) with 3-isocyanatepropyltriethoxysilane (ICPTES), followed by co-condensation of an epoxy trialkoxysilane, 3-(glycidyloxypropyl)-trimethoxylsilane (GLYMO). The structural and dynamic properties of the materials were systematically investigated by a variety of techniques including ac impedance, Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), multinuclear (C-13, Si-29, Li-7) solid-state NMR, H-1-C-13 2D WISE (wide-line separation) NMR, and Li-7 pulsed gradient spin-echo (PGSE) NMR measurements. The length of backbone PEG chain, the extent of GLYMO cross-linking, and the salt concentration were varied in order to obtain the materials with high conductivities. A maximum ionic conductivity value of 1.37 x 10(-5) S/cm was obtained at 30 degrees C for the hybrid electrolyte with a [O]/[Li] ratio of 32. This ionic conductivity value is 1 order of magnitude higher than that of previously characterized electrolytes based on ureasils without incorporation of GLYMO. The results of C-13 cross-polarization magic-angle spinning (CPMAS) NMR with varying contact times and H-1-C-13 WISE NMR provided a microscopic view of the effects of salt concentrations on the dynamic behavior of the polymer chains. Only one distinct Li-7 local environment was detected by variable temperature Li-7-{H-1} MAS NMR. The temperature dependence of Li-7 static line widths and self-diffusion coefficients showed that there is a strong correlation between the dynamic properties of the charge carriers and the bulk ionic conductivity.