Enhanced lithium-ion transport in PEG-based composite polymer electrolyte with Mn_{0. 03}Zn_0.97Al₂O₄ nanoparticles

Abstract

The ion conduction and thermal properties of composite solid polymer electrolyte (SPE) comprising Poly(ethylene) Glycol (PEG, mol wt. 2000), lithium perchlorate (LiClO₄) and insulating Mn_0.03Zn_0.97Al₂O₄ nanoparticle fillers were studied by complex impedance analysis and DSC techniques. The average size of the nanoparticles was determined by powder X-ray diffraction (XRD) using Scherrer's equation and was found to be~8 nm. The same was also determined by TEM imaging and found to be~12 nm. The glass transition temperature T_g, as measured by differential scanning calorimeter (DSC), showed a minimum at 5 mol% of nanoparticles. Fractional crystallinity was determined using DSC. NMR was used to determine crystallinity of a pure PEG sample, which was then used as the standard. Fractional crystallinity X_c was the lowest for 5 mol% and beyond. The ionic conductivity of the composite polymer electrolyte containing 5 mol% Mn_0.03Zn_0.97Al₂O₄ nanoparticles was found to be 1.82× 10^-5 S/cm, while for the pristine one, it was 7.27×10^-7 S/cm at room temperature. As a function of nanoparticle content, conductivity was observed to go through two maxima, one at around 5 mol% and another shallower one at around 12 mol%. The temperature dependence of conductivity could be divided into two regions, one consistent with Arrhenius behaviour and the other with VTF. We conclude that the enhancement of ionic conductivity on the addition of Mn_0.03Zn_0.97Al₂O₄ nanoparticles is a result of reduction in both the T_g and the crystallinity.