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 LiClO 4 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) (H 2 N−PPG−PEG−PPG−NH 2 ) 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 ( 13 C, 29 Si, 7 Li) solid-state NMR, 1 H− 13 C 2D WISE (wide-line separation) NMR, and 7 Li 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 × 10 -5 S/cm was obtained at 30 °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 13 C cross-polarization magic-angle spinning (CPMAS) NMR with varying contact times and 1 H− 13 C WISE NMR provided a microscopic view of the effects of salt concentrations on the dynamic behavior of the polymer chains. Only one distinct 7 Li local environment was detected by variable temperature 7 Li−{ 1 H} MAS NMR. The temperature dependence of 7 Li 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.