Multinuclear Solid-State NMR, Self-Diffusion Coefficients, Differential Scanning Calorimetry, and Ionic Conductivity of Solid Organic-Inorganic Hybrid Electrolytes Based on PPG-PEG-PPG

ABSTRACT: Organic-inorganic hybrid electrolytes based on poly(propylene glycol)-block-poly(ethylene glycol)-block-poly(propylene glycol) bis(2-aminopropyl ether) (D2000) complexed with LiClO4 via the co-condensation of an epoxy trialkoxysilane and tetraethoxysilane have been prepared and characterized. The hybrid electrolytes thus obtained were rubbery thin films with good mechanical strength and a good degree of elasticity. Characterization was made by a variety of techniques including alternating current impedance, Fourier transform infrared spectroscopy, differential scanning calorimetry (DSC), multinuclear solid-state NMR spectroscopy, and pulse-gradient spin-echo (PGSE) NMR measurements. A VTF (Vogel-Tamman-Fulcher)-like temperature dependence of ionic conductivity was observed for all the compositions studied, implying that the diffusion of charge carriers was assisted by the segmental motions of the polymer chains. A maximum ionic conductivity value of 6.23 10-5 S/cm was obtained at 30 °C. 13C cross-polarization/magic angle spinning NMR results from variable contact time measurements along with 2D wide-line separation NMR indicated that a significant decrease in the mobility of the polymer chains as the salt content was increased, consistent with the increase in Tg as observed by DSC. Solid-state 7Li NMR characterization was performed to study ionic mobility by measuring spectral line widths, T1 relaxation times, and diffusion coefficients. The results of the lithium diffusion coefficient measurements indicated that the ionic conductivity in the present electrolytes was mainly dominated by the mobility of the lithium cations