Effectively improved ionic conductivity of montmorillonite clay nanoplatelets incorporated nanocomposite solid polymer electrolytes for lithium ion-conducting devices

Abstract

Synergistic effects of lithium salt concentration and inorganic nanofiller incorporation on the ionic conductivity of polymer blend matrix based nanocomposite solid polymer electrolytes (NSPEs) have been examined. The montmorillonite (MMT) clay nanoplatelets incorporated NSPE films based on poly(ethylene oxide) and poly(methyl methacrylate) blend matrix with lithium tetrafluoroborate (LiBF4) ionic salt have been prepared by the solution-cast method followed by melt-press technique. The 1, 3, and 5 wt% MMT amounts along with 13.3 wt% LiBF4 amount as compared to the weight of polymer blend have been used for the preparation of NSPE films. X-ray diffractometer (XRD) and the Fourier transform infrared (FTIR) spectrometer have been employed for structural characterization of these NSPE films. The complex permittivity and ac electrical conductivity spectra are investigated by using the dielectric relaxation spectroscopy, whereas the electrochemical performance of these materials has been characterized by the electrochemical analyzer. The XRD patterns reveal that the NSPEs are predominantly amorphous and have the intercalated and exfoliated MMT platelets, whereas the relative changes in their FTIR spectra confirm the ion–dipolar–nanofiller interactions between the functional groups of the blended polymers, lithium ions, and the MMT nanoplatelets. The permittivity and conductivity spectra of these materials are analyzed for exploring the dominant contribution of electrode polarization and dipolar polarization in the low and high frequency regions, respectively, and the presence of relaxation processes associated with structural dynamics of the solid-state ion–dipolar complexes. It has been found that the NSPE of relatively fast polymer chain segmental dynamics exhibits higher ionic conductivity. The room temperature ionic conductivity of the 13.3 wt% LiBF4 containing SPE is found more than two times higher as compared to that of the SPE film having 9.7 wt% LiBF4. When the MMT is incorporated, the ionic conductivity of 13.3 wt% LiBF4 containing NSPEs enhances by about one order of magnitude at room temperature. The dc ionic conductivity of the 13.3 wt% LiBF4 containing SPE film is found 1 × 10–5 S/cm at 55 °C, whereas it is 1.65 × 10–5 S/cm at 27 °C for the 5 wt% MMT incorporated NSPE film. The significantly enhanced ionic conductivity with ions transference number close to unity, high electrochemical stability voltage window and good reversibility of these NSPE materials confirm their potential applications as ion conductor/separator for the development of all-solid-state ion conducting devices and the lithium-ion batteries.