Effects of different inorganic nanoparticles on the structural, dielectric and ion transportation properties of polymers blend based nanocomposite solid polymer electrolytes

Abstract

Nanocomposite solid polymer electrolyte (NSPE) films consisted of poly(ethylene oxide) (PEO) and poly(methyl methacrylate) (PMMA) blend (50/50wt%) as host polymer matrix with 20wt% lithium perchlorate (LiClO4) as dopant salt and 3wt% inorganic nanoparticles (i.e., Al2O3, SiO2, SnO2 or ZnO) as filler have been prepared by solution cast method followed by melt-press technique. The X-ray diffraction (XRD) study confirms that the electrolyte films without nanofiller and with Al2O3 and SiO2 nanofillers have predominantly amorphous structures, whereas the characteristic diffraction peaks of SnO2 and ZnO crystallites are observed in the respective NSPEs. Fourier transform infra-red (FTIR) spectra of these NSPE films confirm the formation of ion-dipolar coordination between the functional groups of polymers and the lithium ions throughout the material which completely suppressed the crystalline region absorption peaks of the PEO. The metal oxides of the nanoparticles mainly exhibit van der Waals type interaction with the polymers chains and the ions in the NSPE materials. Effects of a lithium salt as a dopant and the nanoparticles as fillers on the crystalline phase and thermal behaviour of PEO–PMMA blend in these electrolyte materials have also been examined by their differential scanning calorimetry (DSC) measurements.Dielectric and electrical dispersion behaviour of the NSPE films have been characterized by employing dielectric relaxation spectroscopy (DRS) over the frequency range from 20Hz to1MHz and at temperatures 27, 35, 45 and 55°C. The single relaxation peak appeared in the dielectric loss tangent spectra of these electrolytes confirms the ion-dipolar coordinated coupled cooperative chain segmental motion of the PEO and PMMA macromolecules. Lowering in the values of dielectric polarization strength and ionic conductivity has been observed for all the NSPE films as compared to that of the SPE film without nanofiller. A linear correlation between the crystallite sizes of different nanofillers and the dielectric permittivity of NSPE materials has been revealed. It is found that the cooperative polymers chain segmental dynamics becomes slower with the dispersion of nanoparticles in the ion-dipolar complexes which causes a decrease of ionic conductivity of the NSPE films. The correlation observed between the dielectric relaxation time and the ionic conductivity confirms that the ions transport occurs by intra- and inter-chain hopping in these PEO–PMMA blend based electrolytes. Temperature dependent values of relaxation time and dc ionic conductivity of the electrolyte films obey the Arrhenius relation and their activation energies are found in the range 0.22eV to 0.40eV which differ with the types of inorganic nanoparticles dispersed in the NSPEs. The comparative results confirm that the polymers chain segmental dynamics mask the effect of amorphous phase of these materials which contributes in the lithium ions transportation and their mobility. Linear correlation observed between the dielectric permittivity and ionic conductivity values of these NSPEs suggests that the strength of dielectric polarization also plays an important role for the ion transportation process in the solid ion-dipolar complexes. The room temperature ionic conductivity values of these NSPE films are found of the order of 10−5Scm−1 which confirms their suitability as potential candidates in the design and development of all-solid-state devices including the rechargeable lithium-ion batteries. Finally, these experimental results explain in depth the fundamental issues of nanomaterials science that confront the use of various kind of inorganic nanoparticles in the preparation of NSPEs, and the dependence of their ion transportation process on the amorphous phase, dielectric permittivity and the cooperative polymers chain segmental motion, especially for the polymers blend based electrolytes.