Effect of ionic liquids on the electrical, structural and morphological properties of P(VdF-HFP)–NaTF electrolytes

Polymer electrolytes with different ionic liquids, 1-methyl-3-propylimidazolium iodide (PMII) and 1-butyl-3-methylimidazolium trifluoromethanesulfonate (BMImTf), were prepared. Poly(vinylidene fluoride-co-hexafluoropropylene) (P(VdF-HFP)) was used as polymer and sodium trifluoromethanesulfonate (NaTf) as salt. Maximum ionic conductivity for the polymer electrolyte was observed as 1.03 × 10−3 Scm−1 and 1.37 × 10−3 Scm−1 for the addition of 20 wt% of BMImTf and for 40 wt% of PMII respectively. The dielectric behaviour of the samples was studied by analysing the complex dielectric permittivity. It was observed from the XRD studies that the amorphicity of the PMII added system was greater than the system added with BMImTf. FTIR analysis confirmed the occurrence of complexation and interaction among the components. Quantity of free ion and contact ion pairs was calculated using the deconvolution of the FTIR spectrum which supported the determined ionic conductivity of the polymer electrolytes. The BMImTf-added system was identified as more thermally stable than the PMII-added system. DSC confirmed the enhancement of amorphous phase in polymer electrolyte after the addition of ionic liquid. SEM images illustrated the role of porous structures on the ionic conductivity of the films. AFM analysis of the polymer electrolytes showed that the morphological change induced by PMII was higher than BMImTf.