Investigation on Ionic Conductivity and Raman Spectroscopic Studies of Ionic Liquid Immobilized PEO-Based Polymer Electrolytes

The ionic conductivity and Raman spectroscopic studies are reported for ionic liquid (IL)-based polymer electrolyte [PEO:LiPF₆ (as salt)] + BMIMPF₆ (as IL) in which the dopant salt and IL have common anion \({\text{PF}}_{6}^{ - }\). These results are compared with another IL-based polymer electrolyte system with mixed anions (\({\text{ClO}}_{4}^{ - }\, \& \,{\text{PF}}_{6}^{ - }\)). X-ray diffraction (XRD) results showed that the structural modification in the polymer PEO matrix due to the change in its crystalline structure after the incorporation of salt and/or IL that gives reduced crystallinity (or enhanced amorphous content) of the polymer electrolyte films which, in turn, is accountable for enhancement in ionic conductivity. Raman spectroscopic analysis confirmed the occurrence of ion–polymer and ion–ion association/interaction phenomena in these polymer electrolyte membranes which is partly responsible for determining the number of mobile ions concentrations and hence ionic mobility. Furthermore, composition-dependent ionic conductivity results are discussed on the basis of changes in ion–polymer and ion–ion interactions as well as changes in the degree of crystallinity/amorphicity of the membranes.