Effect of lithium salt concentration on crystallinity of poly(vinylidene fluoride-co-hexafluoropropylene)-based solid polymer electrolytes

The X-ray Diffraction (XRD), Horizontal Attenuated Total Reflection-Fourier Transform Infrared Spectroscopy (HATR-FTIR) and Differential Scanning Calorimetry (DSC) have been employed to study the correlation between the concentration of lithium trifluoromethanesulfonate (LiTf) salt with the conversion of crystalline to amorphous nature in poly(vinylidene fluoride-co-hexafluoropropylene) [P(VdF-HFP)]. Results obtained from selected samples with low, intermediate and high concentrations of LiTf salt incorporated in P(VdF-HFP) suggest that the LiTf salt effectively reduces the degree of crystallinity in P(VdF-HFP)-based solid polymer electrolytes. The addition of LiTf to P(VdF-HFP) creates an interaction between cations and the fluorine atom of the copolymer. All the results corroborate each other and supported by impedance spectroscopy and photoluminescence studies (PL). This signifies that LiTf is well dissociated to complex with P(VdF-HFP). It effectively disrupts the crystalline domain and gives rise to new P(VdF-HFP)/LiTf amorphous phase.

► LiTf salt reduces the degree of crystallinity in P(VdF-HFP).
► New P(VdF-HFP)/LiTf amorphous phase is formed.
► LiTf is well dissociated to complex with P(VdF-HFP).