Effect of zwitterions on electrochemical properties of oligoether-based electrolytes
Introduction
Polymer electrolytes have been investigated for their potential application in electrochemical devices, particularly in secondary lithium-ion batteries. Solid polymer electrolytes have several advantages, such as no leakage of electrolytes and no internal shorting. Poly(ethylene oxide) (PEO)/lithium salt complexes have been extensively studied as polymer electrolytes [1], [2], [3], [4], [5], [6], [7] because PEO has a high polarity, which promotes the dissociation of lithium salts, and high mobility, which can promote the transport of dissociated ions. However, the conductivity of these complexes is mainly due to the migration of anionic species; the lithium-ion transference number (tLi+) is generally low, with values below 0.4. These low values may result in a concentration polarization that limits the rate (power) of batteries [8]. In addition, the anodic limit of pristine PEO is about 4.0 V. It is difficult to use electrodes with high charge voltages, such as LiCoO2 and LiNi1/3Mn1/3Co1/3O2 (NMC), as cathode materials [9], [10]. In order to improve the electrochemical stability of these materials, many kinds of additives have been investigated. For example, PEO-based electrolytes exhibited an anodic stability of up to 4.5 V with addition of low molecular weight poly(ethylene glycol) dimethyl ether (PEGDME) [11], ceramic fillers [12], [13], or PEG-borate ester [14]. Although the electrochemical stability of PEO-based electrolytes was improved with these additives, the ionic conductivity values were below 10−4 S cm−1 at room temperature. It is still difficult to achieve high ionic conductivity and good electrochemical stability simultaneously because the additives cause an increase in the viscosity of matrices.
It has been reported that the addition of zwitterions promotes the dissociation of lithium salts and facilitates the transport of lithium ions in ionic-liquid-based electrolytes and polymer electrolytes [15]. In addition to enhancing the conduction of lithium ions, battery cycle performances were improved by the formation of a solid electrolyte interface (SEI) film on the surface of the electrodes [16], [17], [18]. We previously reported that an imidazolium-based zwitterion containing two oxyethylene units (ImZ2) can be synthesized as a colorless liquid at room temperature [19], and that lithium bis(fluorosulfonyl) amide (LiFSA) mixed with a small amount of the liquid zwitterion exhibited high ionic conductivity and tLi+ values [20].
In order to improve the lithium transference number and oxidation resistance at around 4.0 V for PEO, ImZ2 was added to poly(ethylene glycol) dimethyl ether (G5)/LiFSA electrolytes. In this study, we investigated the effects of ImZ2 on the ionic conductivity and electrochemical stability of G5/LiFSA electrolytes.
Section snippets
Materials
3-(1-(2-Methoxyethoxyethyl)-1H-imidazol-3-ium-3-yl) propane-1-sulfonate (ImZ2) was synthesized according to the published procedure [19]. LiFSA (Piotrek, 99.0%) was used as received. Poly(ethylene glycol) dimethyl ether (G5) (Aldrich, Mn = 250) was dried in vacuo before use. The chemical structures of G5, LiFSA, and ImZ2 are shown in Fig. 1. G5 was mixed with LiFSA in an argon filled glove box. The molar ratio of ethylene oxide (EO) units to Li+ was fixed at 20 for the G5/LiFSA electrolytes [21].
Thermal properties
TGA measurements were carried out for G5/LiFSA and G5/LiFSA/ImZ2(x). Watanabe and co-workers reported that complexes of glyme and lithium bis(trifluoromethylsulfonyl) amide (LiTFSA) are thermally stable up to 200 °C [24]. Although the onset thermal decomposition temperature (Td) values of G5/LiFSA and G5/LiFSA/ImZ2(x) were about 150 °C, G5/LiFSA and G5/LiFSA/ImZ2(x) exhibited sufficient thermal stability (> 100 °C) for use as electrolytes in lithium-ion batteries. These lower Td values could be
Conclusion
G5-based electrolytes (G5/LiFSA and G5/LiFSA/ImZ2(x)) were prepared and the effects of ImZ2 on the thermal and electrochemical properties were investigated. When the added amount of ImZ2 was below 5.5 wt%, the ionic conductivity values of the G5/LiFSA electrolytes were maintained above 10−3 S cm−1 at room temperature. The electrochemical stability of the G5-based electrolytes was improved by the incorporation of ImZ2. G5/LiFSA/ImZ2(5.5) showed an electrochemical window in the potential range of
Acknowledgement
This study was supported by a Grant-in-Aid for Scientific Research (C) (No. 26410140) from Japan Society for the Promotion of Science (JSPS).
References (37)
- et al.
Electrochim. Acta
(1995) - et al.
J. Power Sources
(1995) - et al.
Electrochim. Acta
(2000) - et al.
J. Power Sources
(2001) - et al.
Electrochim. Acta
(2011) - et al.
Electrochim. Acta
(2014) - et al.
J. Power Sources
(2001) - et al.
Eur. Polym. J.
(2001) - et al.
J. Power Sources
(2001) - et al.
Electrochim. Acta
(2004)
J. Power Sources
Solid State Ionics
Electrochem. Commun.
J. Power Sources
Electrochim. Acta
Int. J. Electrochem. Sci.
J. Power Sources
J. Power Sources
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