Laser Raman and FTIR studies on Li+ interaction in PVAc–LiClO4 polymer electrolytes

The polymer electrolytes composed of poly(vinyl acetate) (PVAc) with various stoichiometric ratios of lithium perchlorate (LiClO4) salt have been prepared by solution casting method. The techniques Fourier transform infra-red (FTIR) and Laser Raman spectroscopy have been used to monitor polymer–salt complex formation, ion–ion and ion–polymer interactions as a function of salt concentration. Significant changes in both Laser Raman and FTIR spectra are observed which reveals an interaction between ester oxygens with lithium cation coordination. These results strongly suggest the interaction of lithium cation and network polymer chains. When the salt content is increased, the intensity of the internal Raman modes of the ClO4− increases. The ClO4− stretching mode observed at 934 cm−1 in Laser Raman shows some additional shoulder peaks with increase in salt concentration. This reveals the presence of free anions, ion contact pairs and higher order ionic clusters. From the FTIR and Laser Raman results the transport mechanism of ions in PVAc:LiClO4 polymer electrolytes has been discussed.