Morphology and conductivity studies of a new solid polymer electrolyte: (PEG)_xLiClO₄

Abstract

A new solid polymer electrolyte, (PEG)_xLiClO₄, consisting of poly(ethylene)glycol of molecular weight 2000 and LiClO₄ was prepared and characterized using XRD, IR, SEM, DSC, NMR and impedance spectroscopy techniques. XRD and IR results show the formation of the polymer-salt complex. The samples with higher salt concentration are softer, less opaque and less smooth compared to the low salt concentration samples. DSC studies show an increase in the glass transition temperature and a decrease in the degree of crystallinity with increase in the salt concentration. Melting temperature of SPEs is lower than the pure PEG 2000. Room temperature¹H and⁷Li NMR studies were also carried out for the (PEG)_xLiClO₄ system. The¹H linewidth decreases as salt concentration increases in a similar way to the decrease in the crystalline fraction and reaches a minimum at aroundx = 46 and then increases.⁷Li linewidth was found to decrease first and then to slightly increase after reaching a minimum atx = 46 signifying the highest mobility of Li ions for this composition. Room temperature conductivity first increases with salt concentration and reaches a maximum value (σ = 7.3 × 10⁻⁷ S/cm) atx = 46 and subsequently decreases. The temperature dependence of the conductivity can be fitted to the Arrhenius and the VTF equations in different temperature ranges. The ionic conductivity reaches a high value of ∼10 ⁻⁴S/cm close to the melting temperature.