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

摘要

Nanoscopic confinement of a cation coordinated polymer in the channels of organo-modified montmo-rillonite 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 PEO_8-LiClO_4 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 A 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 (T_g), crystalline melting (T_m), melting enthalpy, glass transition width (ΔT_g), and thermal relaxation strength (ΔC_P), 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 T_m and the VTF (Vogel-Tamman-Fulcher) relationship above T_m. The ionic transport number (～99.9%) confirms ionic charge transport with a cation contribution (t_(Li~+)) ～ 0.5 for 2 wt.% clay. It represents an increase by ～65% in comparison with PEO_8-LiClO_4). Improvement in voltage and thermal stability is also observed with the nanocomposites.