Investigating the effect of interaction behavior on the ionic conductivity of Polyester/LiClO4 blend systems

doi:10.1016/j.polymer.2011.06.055

Polymer

Volume 52, Issue 18, 18 August 2011, Pages 4106-4113

https://doi.org/10.1016/j.polymer.2011.06.055 Get rights and content

Abstract

We describe the interaction behavior between Polyester and Li⁺ that affects the ionic conductivity on binary electrolyte of lithium perchlorate (LiClO₄) blends with Poly(ethylene adipate), (PEA); Poly(1,4-butylene adipate), (PBA); Poly(1,6- hexamethylene adipate), (PHA); and Polycarprolatone (PCL), respectively. The individual four binary blend systems are similar and fully miscible, a different ionic conductivity exists in the binary Polyester electrolyte system corresponds to the result of the different interactions strength between lithium perchlorate (LiClO₄) and various Polyesters. The lithium ion is able to coordinate with more functional groups of PEA polymer chain than that in other three polyester chains. Both DSC and FTIR studies demonstrate that the ability of PEA to donate its electron to coordinate with Li⁺ is significantly stronger than that of PBA, PHA and PCL. Consequently, the maximum ionic conductivity (1.06 × 10⁻⁵ S cm⁻¹) at ambient temperature (30 °C) occurred at a composition of PEA/LiClO₄ (90/10).

It is further found that the ionic conductivity of Polyester electrolyte is not only dependent on the electron donation strength of carbonyl group, but also on the molecular structure of Polyester.

Graphical abstract

Polyester/LiClO₄ = 90/10 weight ratio, the PEA shows the highest Li⁺ concentration in this system.

Introduction

Solid polymer electrolytes (SPEs), which are complexes of solvent-free polymers and metal salts, are prepared by dissolving salts in high-molecular-weight polar polymer hosts. Polymer electrolytes have been studied extensively during the past two decades because of their potential applications, which include high energy density batteries and fuel cells [1], [2], [3], [4], [5]. The major motivation for this interest is the application in rechargeable and high energy density power sources. It is generally agreed that both of these qualities that achieved by the lithium-based electrochemical systems to configure the battery [6], [7], [8]. Ionic transport occurs in the polymer and very often is the result of a Li-salt dissolve and a coupling between the ions and segmental motions of the polymer chains. There are many methods have been applied to increase the ionic conductivity of the electrolyte, such as addition of a plasticizer to polymer matrix forming a gel polymer electrolyte [9], [10], [11]; addition of miner to polymer matrix forming a nanocomposites [12]; designing new polymeric matrices by synthetic processes or modifying existing polymer–salt complexes, and thus improve ionic conductivity [13], [14], [15], [16], [17], [18], [19].

It is an important challenge to develop practical methods for preparing the SPEs that have higher ionic conductivity and dimensional stability. In this regard, the preparation of polymeric electrolytes by choice an appropriate polymer structure is of interest. Polyester-based polymeric electrolytes are still among the most extensively studied polymer ionic conductors because their structures are beneficial for supporting fast ion transport. A strong electron donor within oxygen atom of carbonyl group in Polyester-based polymer electrolyte would tend to complex with lithium ion. The electron donation strength of carbonyl group would effect on the solubility of Li-salt and on the isolation of Li⁺ ion within the polymer matrix. However, the effect of electron donation strength of carbonyl group in Polyester on the ionic conductivity enhancement is not clearly understood.

There has been no previous study of the influence of the electron donation strength and its mechanism on the Polyester-based polymer electrolyte so far. A model system based on Adipate acidic Polyester doped with Lithium perchlorate (LiClO₄) examined in this work. The polyester of Polycarprolatone is added into this study to contrast the effect of polyester molecular structure on the ionic conductivity. The electron donation strength and isolation of Li⁺ ion within polymer electrolytes carbonyl group are detected by used differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR). Alternating current (AC) impedance investigates the electron donation strength and its related conductivity behavior of Polyester-based polymer electrolyte blend system. The rule to obtain is a higher ionic conductivity in Polyester-based polymer electrolyte blend system is presented.

Section snippets

Materials

Poly(ethylene adipate) (PEA) with Mw of 10,000 and m.p. = 58–62 °C;

Poly(1,4-butylene adipate) (PBA) with Mw of 12,000 and m.p. = 56–60 °C;

Poly(1,6-hexamethylene adipate) (PHA) with Mw of 3800 and m.p. = 55–65 °C;

Polycarprolatone (PCL) with Mw of 65,000 and m.p. = 60 °C;

was purchased from Aldrich. All polymers without purification before used.

The Lithium perchlorate (LiClO₄‧3H₂O) salt, obtained form Acros, will be treated in 190 °C for 24 h in vacuum for eliminating crystal water and then

DSC studies

The DSC analysis is one of the most convenient methods for determining the miscibility in polymer blends. Fig. 1a–d present the conventional second-run DSC thermograms of PEA, PBA, PHA and PCL blended with various LiClO₄ content ranging from 0 to 35 wt% contents, respectively. T_g of the pure polymers used in this study, PEA, PBA, PHA and PCL, are ca. −49, −60, −62 and −65 °C, respectively. The observed T_g is changed and identified with the increase of LiClO₄ content in all blends. A changed T_g

Conclusions

We have investigated the effect of interaction mechanism on ionic conductivity of Polyester/LiClO₄ binary blend-based electrolyte systems by the use of DSC, FTIR spectroscopy, and AC impedance measurements. Although each of the four individual binary pairs is fully miscible, a similar interaction behavior exists in four Polyester blend systems. Li⁺ ion more preferably coordinates with the carbonyl group atom of PEA rather than with that of the other three polyesters, it is because that the C double bond O

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Investigating the effect of interaction behavior on the ionic conductivity of Polyester/LiClO4 blend systems

Abstract

Graphical abstract

Introduction

Section snippets

Materials

DSC studies

Conclusions

Solid State Ionics

Electrochim Acta

J Power Sources

Electrochim Acta

J Power Sources

Polymer

Polymer

Polymer

Solid State Ionics

Spectrochim Acta Part A

Solid State Ionics

J Electrochem Soc

Investigating the effect of interaction behavior on the ionic conductivity of Polyester/LiClO₄ blend systems