Crystallization and melting of PEO:LiTFSI polymer electrolytes investigated simultaneously by impedance spectroscopy and polarizing microscopy

Influence of crystallization on dielectric properties of PEO:LiTFSI polymer electrolyte

“…2(b),(d)). Such behavior was reported in our earlier publications for electrolytes ranging from pure PEO to PEO:LiTFSI 3:1 [14,15,19]. The decrease of ionic conductivity was caused by blocking of conductivity pathways in the amorphous phase by the crystalline lamellae.…”

“…In the background of structure created by these spherulites, some brighter areas with slight granular pattern are visible. By comparison with our previous studies [15,19], the regular spherulites observed in PEO:LiTFSI 8:1 electrolyte can be identified as PEO 6 :LiT-FSI crystalline complex, whereas the structures visible in the background can be related to the pure PEO. This is confirmed by the X-ray study: the presence of two crystalline phases: PEO 6 :LiTFSI complex and pure PEO, was identified in the X-ray diffraction patterns of the semicrystalline PEO:LiTFSI 8:1 electrolyte (Fig.…”

“…To confirm the presence of the crystalline phase and determine its morphology, an additional series of impedance measurements was carried out in a cell with transparent electrodes made of glass covered with a conductive layer of indium tin oxide (ITO), which enabled observation of the sample with a polarizing microscope. The principles of simultaneous impedance measurement and microscope observation were described in our earlier publications [14,15]. Impedance measurements were made using Solartron 1260 Impedance Analyzer with Keithley 428 current amplifier [16] in the frequency range from 10 À2 to 10 7 Hz.…”

Conductivity and dielectric properties of polymer electrolytes PEO:LiN(CF3SO2)2 near glass transition

“…The holder was placed in a thermostat, driven by Peltier elements. To confirm the presence of crystalline phases, additional impedance measurements were carried out in a cell with transparent glass electrodes covered with conductive layer of indium tin oxide (ITO), which enabled observation of sample with polarizing microscope [19][20][21]. Impedance was measured in the frequency range of 10 7 to 10 À2 Hz using Novocontrol Alpha-N impedance/dielectric analyzer.…”

“…In this range we were able to obtain overcooled amorphous samples as well as samples in semicrystalline state. It should be noted, that detailed information on properties of some of specific electrolyte compositions can be found in our previous publications [9,[19][20][21]. Here we present trends which can be considered as general for PEO:LiTFSI system.…”