Dielectric behaviour, ionic conductivity and structure of high energy ball mill blended melt pressed and solution cast solid polymeric nanocomposite electrolytes

Abstract

The high energy ball mill blended solid polymeric nanocomposite electrolytes (SPNEs) comprising poly(ethylene oxide) (PEO), lithium perchlorate (LiClO₄) and montmorillonite (MMT) clay as nanofiller (PEO₂₀-LiClO₄–x wt% MMT; where EO:Li⁺ = 20:1, and x = 0, 1, 2, 3 and 5) were prepared by melt pressing and solution casting techniques. The complex dielectric function, ac ionic conductivity, electric modulus and impedance spectra of these SPNE films have been investigated by dielectric relaxation spectroscopy in the frequency range 20 Hz – 1 MHz at ambient temperature. The values of dielectric relaxation strength, relaxation time of Li⁺ cation coordinated PEO segmental motion and dc ionic conductivity have been determined and their correlations with ion transportation in these materials have been explored. Results reveal that the dc ionic conductivity of solution cast SPNE films has gradual increase with loading of MMT concentration up to 5 wt%. In case of melt pressed SPNE films, the dc ionic conductivity shows anomalous variation with MMT concentration and it is maximum at 1 wt% MMT. The X-ray diffraction study of these SPNE films confirms the formation of ion-dipolar complexes between the ether oxygen atoms of PEO chain, the lithium cations and the siloxane groups of MMT nano-platelets. The d₀₀₁-spacing of intercalated MMT, crystallite size of PEO and the relative changes in PEO peaks intensity with MMT concentration have been evaluated from the XRD patterns. These XRD parameters were discussed in relation to the MMT intercalated structures and amorphicity of the electrolyte materials. The correlation between ionic conductivity and the structural properties of these electrolytes has also been explored.