An ionic conductivity and spectroscopy study of ionic transport mechanism in fire-retardant polyacrylonitrile-based gel electrolytes for Li polymer batteries

Solvation reaction and the Li+ ion conduction mechanism in fire-retardant poly[acrylonitrile] (PAN)-based gel electrolytes complexed with ethylene carbonate (EC), proplylene carbonate (PC), and LIPF6 were investigated using Fourier transform Raman scattering spectroscopy (FT-Raman) and conventional complex impedance measurements. FT-Raman spectroscopy eliminated the fluorescence problem of the gel electrolytes, showing that the mole fraction of EC-solvating Li+ ions is significantly affected by the LiPF6 concentration rather than the PAN ratio. Based on deconvolution analysis, the solvation numbers of Li+ ions were estimated to be 4.0 to 5.4 in the salt concentration range of 0.28 to 1.35 mol kg,which is corresponding to that in liquid electrolyte-based EC and PC. As for the ionic conduction property of PAN-based gel electrolytes, the activation energy of ionic conduction estimated from the Arrhenius equation is more strongly dependent on the LiPF, concentration than the PAN ratio in the temperature range from -20 degrees C to room temperature. These results confirm that Li+ ions dominantly interact with EC and PC dispersed in the network structure of the gel electrolytes and also the polymer chains of PAN make a rigid framework which scarcely interacts with the Li+ ions at ambient temperature.