Ionic Conductivity in Solutions of Poly(ethylene oxide) and Lithium Perchlorate

Abstract

Summary: Solution casting technique served to prepare solid solutions of lithium perchlorate and poly(ethylene oxide) (PEO) having different molecular masses. Salt concentrations of solutions were varied between around 2 and 13 wt%. Crystallinity and melting point depression served to determine composition and content of amorphous phase as well as thermodynamic behavior of the solutions. Conductivity as a function of salt concentration in the amorphous phase follows a power law at constant temperature (30 °C). It results that both exponent and mobility of charge carriers increase with ascending molecular mass of PEO. The mobility follows an increase with molecular mass proportional to M2.8 indicating dependence of mobility on interstitial volume between chain molecules. Deviation of solution from perfect behavior can be evaluated by melting point depression. Accordingly, increase in conductivity is preferably related to approach to perfect solution behavior. Determination of dielectric function allows some conclusion about ion pair formation in the systems under discussion. It turns out that probability of ion pair formation decreases with increasing molecular mass of PEO in agreement with thermodynamic behavior of the solutions.

On Thermal and Spectroscopic Studies of Poly(ethylene oxide)/Poly(methyl methacrylate) Blends with Lithium Perchlorate

“…On the other hand, no significant shifting of the 2u peaks is observed upon addition of LiClO 4 to the 75/25 blend except that the intensities of the peaks are reduced especially for the blend with W S ¼ 0.091 ( Figure 5 (b)). This observation reveals that the PEO crystal structure remains relatively unchanged with the addition of a small amount of salt as reported by Nasir et al [6] FTIR Analysis FTIR is a useful tool to study spectroscopically the intermolecular attractions between components of a blend. The characteristic v(CH 2 ) mode of PEO which appears as a sharp doublet at 1359 and 1341 cm À1 denotes the crystalline phase of PEO ( Figure 6 Figure), thus, confirms the heterogeneity of the PEO/PMMA 50/50 blend.…”

“…Meanwhile, addition of a small amount of salt (W S ¼ 0.048) causes only a slight dip in the X Ã of neat PEO. [6] Again, reduction in the X Ã of PEO similar to that of the saltfree PEO/PMMA blends is observed for the blends doped with salt concentration W S ¼ 0.048. In addition, the X Ã of the saltdoped PEO/PMMA blend with W S ¼ 0.048 as shown in Figure 3 are very close to, if not overlaps those of the salt-free blend indicates that the X Ã of PEO in the blend is not influenced by the presence of the salt.…”

“…Ion conductivity (s DC ) of PEO SPEs is mainly ruled by the ion mobility and ion concentration in the amorphous phase of these systems. [6][7][8][9] PEO consists of $ 60% of crystalline phase at room temperature. [10] Thus, PEO-based SPEs suffer low conductivity ($ 10…”

Ionic conductivity and diffusion coefficients of lithium salt polymer electrolytes measured with dielectric spectroscopy

“…We measure the ionic conductivity and the relaxation polarization due to mobile ionic charges. Also, we propose a method to estimate the values of cation and anion diffusion coefficients together with the free ion concentration assuming that the diffusion coefficient values for both the cation and anion of the dissolved salt are of the same order of magnitude, which is in agreement with reported measurements from other methods [16,17]. In this case, the tan δ data can be analyzed with the Trukhan model [4,5] and the diffusion coefficients and ionic concentration of free charge carriers can be estimated.…”

“…However, measurements reported in the literature [16,17] show that the difference between the anion and cation diffusion coefficients is at most less than one order of magnitude. For the case when the diffusion coefficients of the cations and anions are different, the Trukhan model must be solved numerically, and it will be reported in a future paper.…”