Electrical Spectroscopy Studies of Lithium and Magnesium Polymer Electrolytes Based on PEG400

Abstract

Four classes of solvent-free polymer electrolytes were prepared in order to study the mechanism of ionic motion and the interactions existing in polymer electrolytes. The following electrolytic complexes were studied PEG400/(MgCl2)x(0.00329 less than or equal to x less than or equal to 0.7000) (PEG400 = poly(ethylene glycol) 400); poly[PEG400-alt-DEOS]/ (MgCl2)x (6.28 x 10-2 less than or equal to x less than or equal to 13.16) (DEOS = diethoxydimethylsilane); [EDTA][PEG400]2/(LiCl)2.26; [EDTA][PEG400]2/(MgCl2)1.98; [EDTA][PEG400]/(LiCl)2.26(MgCl2)1.9; [EDTA]3[PEG400]7/(LiCl)6.39; [EDTA]3[PEG400]7/(MgCl2)8.23; and [EDTA]3[PEG400]7/(LiCl)6.39(MgCl2)6.16 (EDTA = ethylenediaminetetraacetic acid). The studies were carried out by impedance spectroscopy in the 20 Hz to 1 MHz range at different temperatures. Real and imaginary components of conductivity spectra in terms of equivalent circuit analysis and correlated ionic motion analysis based on a generalized universal power law were investigated. Results revealed that in the PEG400/(MgCl2), and poly[PEG400-alt-DEOS]/(MgCl2)x systems the ionic species formed in the bulk materials are, crucial for the overall conductivity. Indeed, in PEG400/(MgCl2)x, conductivity takes place through hopping of the cationic species Mg2+ and [MgCl]+ between the coordination sites present along the polyether chains. In poly [PEG400-alt-DEOS]/(MgCl2)x systems, two types of mechanisms were detected: (a) the migration of cationic species Mg2+ and [MgCl](+) at low salt concentrations and (b) the hopping of Cl- anions between magnesium species coordinated by the oxygen donor atoms of polyether chains at high salt concentrations. This latter phenomenon results in cation migration without any substantial geometric site relaxation. Studies of the lithium and magnesium polymer electrolytes based on [EDTA][PEG400]2 and [EDTA]3[PEG400]7 polymers revealed that the type and geometry of coordination sites present in the polymer host are of crucial importance in modulating the conductivity of the polymer electrolytes. In particular, the chelating EDTA sites, which are able to strongly coordinate cations such as Mg2+, are excluded from the overall conductivity mechanism

Broadband Dielectric Spectroscopy: A Powerful Tool for the Determination of Charge Transfer Mechanisms in Ion Conductors

“…where s * m ðoÞ is the complex measured conductivity spectrum. On the basis of Equations 5.18 and 5.21, the relationship between the real and imaginary components of s * m ðoÞ and e * m ðoÞ is: where r à (o) and Z à (o) are the complex resistivity and impedance spectra [2][3][4], respectively, and K is a geometric cell constant in cm (K ¼ A/d; A is the area of the electrode and d is the spacing), the following relationships are obtained [2][3][4][5]: Equations 5. 22 and 5.23 show that the electric response of a material can be studied by analyzing the complex permittivity, conductivity, or impedance spectra.…”

“…The electrode polarization exhibits similar behavior at higher values of permittivity in e 0 and e 00 , but displays different behavior in the conductivity spectra. The peak in the imaginary component of the permittivity corresponds to a peak in s 00 and a plateau in s 0 associated with the direct current (d.c.) conductivity [2][3][4][5]. Profiles of the real and imaginary components of the conductivity and permittivity are shown in Figure 5.14 for a conductive oil.…”

“…The predominant conductivity processes are attributed to: (a) the migration of ions between coordination sites in the host materials [2][3][4][5], and (b) the increase of conductivity due to relaxation phenomena involving the dynamics of the host materials [2][3][4][5]. Ions "hopping" to new chemical environments can lead to successful charge migration only if ion-occupying domains relax via reorganizational processes [2-5], which generally are coupled with relaxation events associated with the host matrix.…”

Dielectric relaxation studies in soft — matter like nanocomposite polymer electrolyte PPG4 — AgCF3SO3: MgO

“…In fact, the forward and backward displacements of ions with faster orientations are observed simultaneously at higher frequencies. A frequencyindependent ionic motion appearing at low frequency region may be attributed to the effect of electrode -electrolyte interface polarization [11]. Indeed, the displacement of ions performs two distinct relaxation phenomena each mobile ions having an effective definite potential, one can hop back to the original position resulting in no contribution to the conductivity and their potential remains unchanged, whereas the ionic displacement to another site may create an effective potential minimum thus contributing to the total ion transport [6].…”

Electrical conductivity relaxation in PVOH–LiClO4–Al2O3

“…This contribution therefore focus on ionic conduction behaviour of the PVOH-LiClO 4 polymer electrolyte system in which nanoporous Al 2 O 3 particles were dispersed with the objective of looking at their influence on the dynamics of the mobile ions. We used the impedance spectroscopy technique to study the ac electrical response of the studied SPE system in order to study the correlations of structure-conductivity mechanism [11][12][13][14][15]. As demonstrated previously [14][15][16], the complete characterization of the ac electrical response may be achieved by a detailed study of the real part of the conductivity, including the determination of the exact bulk dc conductivity without any use of equivalent circuit analysis.…”