Effect of nanoscopic confinement on improvement in ion conduction and stability properties of an intercalated polymer nanocomposite electrolyte for energy storage applications

Nanoscopic confinement of a cation coordinated polymer in the channels of organo-modified montmorillonite clay results in substantial improvement in conductivity, cation transport and stability properties required for energy storage/conversion devices. X-ray diffraction analysis confirms composite formation as evidenced by: (i) intercalation of PEO8–LiClO4 into the clay channels for clay loading ≥7.5 wt.% and (ii) partial intercalation/exfoliation for a lower clay loading (≤5 wt.%). Transmission electron microscopy analysis corroborates these findings as indicated by an enhancement in clay gallery width from 6 to 9 Å for 20 wt.% clay providing evidence for intercalation at higher clay loadings. Energy dispersive X-ray dot-mapping images confirm the homogeneous distribution of clay in nanocomposites. Thermal analysis indicates a strong dependence of thermodynamic parameters, e.g., glass transition (Tg), crystalline melting (Tm), melting enthalpy, glass transition width (ΔTg), and thermal relaxation strength (ΔCp), on clay concentration. These observations agree well with changes in electrical properties on nanocomposite formation. Substantial enhancement in ambient conductivity (∼208 times) occurs in a nanocomposite film (2 wt.% clay) relative to a clay-free film. The temperature dependence of conductivity obeys Arrhenius behaviour below Tm and the VTF (Vogel–Tamman–Fulcher) relationship above Tm. The ionic transport number (∼99.9%) confirms ionic charge transport with a cation contribution (tLi+)∼0.5(tLi+)∼0.5 for 2 wt.% clay. It represents an increase by ∼65% in comparison with PEO8–LiClO4. Improvement in voltage and thermal stability is also observed with the nanocomposites.