Conductivity enhancement mechanism of the poly(ethylene oxide)/modified-clay/LiClO4 systems

Improved Conductivity in Gellan Gum and Montmorillonite Nanocomposites Electrolytes

Nanocomposite polymer electrolytes (NPEs) were obtained using gellan gum (GG) and 1 to 40 wt.% of montmorillonite (Na⁺SYN-1) clay. The NPEs were crosslinked with formaldehyde, plasticized with glycerol, and contained LiClO₄. The samples were characterized by impedance spectroscopy, thermal analyses (TGA and DSC), UV-vis transmittance and reflectance, X-ray diffraction (XRD), and continuous-wave electron paramagnetic resonance (CW-EPR). The NPEs of GG and 40 wt.% LiClO₄ showed the highest conductivity of 2.14 × 10^-6 and 3.10 × 10^-4 S/cm at 30 and 80 °C, respectively. The samples with 10 wt.% Na⁺SYN-1 had a conductivity of 1.86 × 10^-5 and 3.74 × 10^-4 S/cm at 30 and 80 °C, respectively. TGA analyses revealed that the samples are thermally stable up to 190 °C and this did not change with clay addition. The transparency of the samples decreased with the increase in the clay content and at the same time their reflectance increased. Finally, CW-EPR was performed to identify the coordination environment of Cu²⁺ ions in the GG NPEs. The samples doped with the lowest copper concentration exhibit the typical EPR spectra due to isolated Cu²⁺ ions in axially distorted sites. At high concentrations, the spectra become isotropic because of dipolar and exchange magnetic effects. In summary, GG/clay NPEs presented good ionic conductivity results, which qualifies them for electrochemical device applications.

Structural, electrical and electrochemical studies of ionic liquid-based polymer gel electrolyte using magnesium salt for supercapacitor application

In the present studies, the effect of ionic liquid 1-Ethyl-2,3-dimethylimidazoliumtetrafluoroborate (EDiMIM)(BF4) on ionic conductivity of gel polymer electrolyte using poly(vinylidene fluoride-co-hexafluoropropylene) [PVdF(HFP)] and magnesium perchlorate [Mg(ClO4)2] as salt was investigated. The maximum room temperature ionic conductivity for the optimized system was found to be of the order of 8.4 × 10–3 S cm−1. The optimized composition reflects Vogel-Tammann-Fulcher (VTF) behavior in the temperature range of 25 °C to 100 °C. The X-ray diffraction, Fourier transform infrared spectroscopy and scanning electron microscopy studies confirm the uniform blending of ionic liquid, polymer, and salts along with the enhanced amorphous nature of the optimized system. Dielectric and modulus spectra studies provide the information of electrode polarization as well as dipole relaxation properties of polymeric materials. The optimized electrolyte system possesses a sufficiently large electrochemical window of the order of 6.0 V with stainless steel electrodes.

Hybrid Solid Polymer Electrolytes with Two-Dimensional Inorganic Nanofillers

Solid polymer electrolytes are of rapidly increasing importance for the research and development of future safe batteries with high energy density. The diversified chemistry and structures of polymers allow the utilization of a wide range of soft structures for all-polymer solid-state electrolytes. With equal importance is the hybrid solid-state electrolytes consisting of both "soft" polymeric structure and "hard" inorganic nanofillers. The recent emergence of the re-discovery of many two-dimensional layered materials has stimulated the booming of advanced research in energy storage fields, such as batteries, supercapacitors, and fuel cells. Of special interest is the mass transport properties of these 2D nanostructures for water, gas, or ions. This review aims at the current progress and prospective development of hybrid polymer-inorganic solid electrolytes based on important 2D materials, including natural clay and synthetic lamellar structures. The ion conduction mechanism and the fabrication, property and device performance of these hybrid solid electrolytes will be discussed.

Polymer-Ion Interaction Weakens the Strain-Rate Dependence of Extension-Induced Crystallization for Poly(ethylene oxide)

The crystallization of poly(ethylene oxide) (PEO)-sodium iodine (NaI) composites is investigated by differential scanning calorimetry (DSC), extensional rheology, and in situ small-angle X-ray scattering (SAXS) with the aim of demonstrating versatile roles played by polymer-ion interactions. In the isothermal quiescent crystallization process, a decrease in the crystal growth rate is observed for PEO-NaI and is attributed to slow chain movement caused by the coordination between cations and polymer. In situ SAXS on extensional flow-induced crystallization (FIC) exhibits enhanced kinetics and orientation for both PEO and PEO-NaI with increasing strain rate. However, an overall weaker strain-rate dependence of FIC is observed for PEO-NaI, which can be interpreted as a synergistic consequence of promoted nucleation under flow and impeded crystal growth by polymer-ion interaction. A possible microscopic mechanism is proposed to account for the experimental observation based on the formation of transient cross-linking points in PEO-NaI and their influence on the entanglement network of polymer under various flow fields. The disclosed strain-rate dependence and various ion effects on the behavior of PEO-salt composites contribute to a comprehensive understanding of polymer-ion solid polyelectrolytes.

Nanostructure enhanced ionic transport in fullerene reinforced solid polymer electrolytes

We report a 6-fold ion conductivity enhancement in PEO/LiTFSI-based solid electrolytes upon the addition of fullerene derivatives.

Synthesis and Properties of High Strength Thin Film Composites of Poly(ethylene Oxide) and PEO-PMMA Blend with Cetylpyridinium Chloride Modified Clay

Ion-conducting thin film composites of polymer electrolytes were prepared by mixing high MW poly(ethylene oxide) (PEO), poly(methyl methacrylate) (PMMA) as a polymer matrix, cetylpyridinium chloride (CPC) modified MMT as filler, and different content of LiClO4by using solution cast method. The crystallinity, ionic conductivity (σ), and mechanical properties of the composite electrolytes and blend composites were evaluated by using XRD, AC impedance, and UTM studies, respectively. The modification of clay by CPC showed enhancement in thed-spacing. The loading of clay has effect on crystallinity of PEO systems. Blend composites showed better mechanical properties. Young’s modulus and elongation at break values showed increase with salt and clay incorporation in pure PEO. The optimum composition composite of PEO with 3.5 wt% of salt and 3.3 wt% of CPMMT exhibited better performance.

Hierarchical structure and crystal orientation in poly(ethylene oxide)/clay nanocomposite films

Water-cast nanocomposite films formed by poly(ethylene oxide) (PEO) and Laponite clay were found to display three characteristic levels of structure with large-scale orientation. The first level with the length scale of ca. 30-50 nm was the clay lamellar bundles, which tended to stack perpendicularly to the film surface. The second level with the characteristic length of 1.8 nm was associated with the alternating stacking of the silicate layers and the PEO chains sandwiched between them. The preferred orientations of these two levels of structure were independent of clay content, solvent removal rate for the film preparation, and the crystallization temperature of the PEO chains situating outside the clay bundles. The third level of structure was characterized by the preferred orientation of the PEO crystalline stems with respect to the surface of the silicate layers. Perpendicular orientation always dominated in the nanocomposite films prepared by slow solvent removal irrespective of crystallization temperature. In the films prepared by fast solvent removal, however, parallel crystal orientation set in as the clay concentration exceeded ca. 33 wt %. The preferred crystal orientation was ascribed to the confinement effect imposed by the clay bundles to the crystallization of the PEO chains situating in the interbundle region. In the films cast by slow solvent removal, the weaker confinement associated with the larger interbundle distance led to perpendicular crystal orientation. When the interbundle distance was reduced to ca. 30 nm in the films prepared by rapid solvent evaporation, the strong confinement directed the crystals to form parallel orientation.