Effects of preparation methods on structure, ionic conductivity and dielectric relaxation of solid polymeric electrolytes

The solid polymer electrolytes (SPEs) consisted of poly(ethylene oxide) (PEO) and lithium perchlorate (LiClO4) (PEO20-LiClO4 and PEO8-LiClO4 electrolytes of composition stoichiometric ratios EO:Li+ = 20:1 and 8:1) have been prepared by various blending methods. The simple solution casting, solution-cast hot pressed, dry blended melt pressed, high intensity ultrasonic assisted, microwave irradiated, and both the ultrasonicated and microwave irradiated solution-cast followed by their remelt with hot pressed methods have been used for preparation of the SPEs films. The complex formation between etheric oxygen (EO) of PEO and cation (Li+) of LiClO4 is confirmed by relative changes in amorphous phase of these electrolytes which is investigated by X-ray diffraction measurements. It is found that the amount of amorphous phase of these SPEs is strongly influenced by their preparation methods and the salt concentration. The complex dielectric function, ac electric conductivity, electric modulus and impedance spectra of the electrolytes are studied over the frequency range of 20 Hz to 1 MHz by dielectric relaxation spectroscopy at ambient temperature. The dc ionic conductivity of PEO8-LiClO4 electrolytes is found two to three orders of magnitude higher than that of the PEO20-LiClO4 electrolytes, which is significantly affected by their preparation methods. The cations coupled PEO chain segmental dynamics and its correlation with the ionic conductivity of these electrolytes has been explored by considering the values of relaxation times and dielectric relaxation strength. Results reveal that the ionic conductivity of PEO8-LiClO4 electrolytes can be tuned over two orders of magnitude by adopting different blending methods with a state-of-the-art engineering.