[PEI–SiO2]:[LiTFSI] nanocomposite polymer electrolytes:Ion conduction and optical properties

Ion conductivity and optical properties were investigated for polymer electrolytes based on poly (ethyleneimine) and lithium bis(trifluoromethylsulfonyl)imide and also containing up to 9 wt.% of 7-nm-diameter SiO2 nanoparticles. The [N]:[Li] molar ratio was kept constant at 50:1. Impedance measurements were performed in the frequency range 10−2–107 Hz and between the temperatures 20 and 70 °C with an applied ac voltage of 1 V. Spectrophotometric data of total and diffuse transmittance were taken between the wavelengths 300 and 2500 nm. The bulk impedance was fitted to a conductive Havriliak-Negami circuit model. The ion conductivity increased monotonically for increasing SiO2 contents; specifically its room temperature value went from 8.5×10–7 S/cm without nanoparticles to 3.8×10–5 S/cm for 8 wt.% of SiO2 while the diffuse transmittance remained at ∼1% so that optical clarity prevailed.