Increased lithium-ion conductivity in (PEG)46LiClO4 solid polymer electrolyte with δ-Al2O3 nanoparticles

The effect of delta-Al2O3 nanoparticles (size similar to 10 nm) on the ionic conductivity and related properties of a solid polymer electrolyte (SPE) that consists of low molecular weight (M-w = 2000) poly(ethylene) glycol (PEG) complexed with LiCIO4 is studied in detail using XRD, DSC, TPD, NMR, and complex impedance methods. The maximum ionic conductivity sigma = 7.3 x 10(-7) S cm(-1) observed for pristine (PEG)(46)LiCIO4 is found to be dependent on the content of delta-Al2O3 filter; it shows a peak value of sigma = 4.5 x 10(-6) S cm(-1) for 10 mol% filler. This is nearly an order of magnitude enhancement of the ionic conductivity and is found by DSC studies to be related to a decrease in the crystalline regions in the SPE, while the glass transition temperature T-g and the melting temperature T-m, remain essentially unchanged. Li-7 NMR motional narrowing points to an increase in the effective mobility of the lithium ions on doping with the nanoparticles. The temperature dependence of sigma can be divided into two regions, one consistent with the Arrhenius behavior and the other with the Vogel, Tamman and Fulcher equation. The activation energy is found to be the lowest for the 10 mol% doped sample. It is concluded that doping with nanoparticles leads to an enhancement of conductivity due to a decrease in the crystallinity and the activation energy, as well as to an increase in the effective mobility of Li ions. (C) 2003 Elsevier B.V. All rights reserved.