Study of time-ageing effect on the ionic conduction and structural dynamics in solid polymer electrolytes by dielectric relaxation spectroscopy

This research work demonstrates the effect of time-ageing on the dielectric and electrical properties, and also the structural dynamics of solid polymer electrolyte (SPE) and nanocomposite solid polymer electrolyte (NSPE) films over a period of one-year. The SPE and NSPE films based on polymer blend matrix of poly(ethylene oxide) (PEO) and poly(methyl methacrylate) (PMMA) (50/50 wt%) with lithium triflate (LiCF3SO3) as dopant ionic salt (22 wt%) and montmorillonite (MMT) clay (3 wt%) as inorganic nanofiller have been prepared by solution-cast method followed by melt-pressing technique. These films are characterized by employing scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, differential scanning calorimetry (DSC), dielectric relaxation spectroscopy (DRS) and electrochemical analysis (ECA) techniques. The influence of MMT filler on the polymer-ion interactions was confirmed from comparative analysis of the structural and electrochemical properties of the SPE and NSPE films. The XRD and DRS measurements on these films were repeated at various time intervals over one-year duration in order to explore the time-ageing effect on the structural properties, dielectric parameters, and ionic conduction mechanisms in the electrolyte samples. The XRD study reveals the irregular variation of PEO crystalline phase in these films and also the intercalated/exfoliated MMT phases in the NSPE film with time-ageing. The ionic conductivity of the SPE and NSPE films increases by about one order of magnitude over the time-ageing period of 2 to 3 months of these films, whereas it drops by more than one order of magnitude at the one-year ageing in comparison to that of the freshly prepared films measured on day first. It is found that the ionic conductivity of these materials has a correlation with the relaxation time of polymers cooperative chain segmental motion which validates the fact that the ions transport in the solid ion-dipolar complexes occurs through hopping mechanism coupled with polymers structural dynamics not only for the freshly prepared electrolyte films but also for the films with time-ageing. Further, these electrolyte films have good electrochemical stability, better reversibility and cyclability, and the ion transference number close to unity.