What can we learn from ionic conductivity measurements in polymer electrolytes? A case study on poly(ethylene oxide) (PEO)-NaI and PEO-LiTFSI.
What can we learn from ionic conductivity measurements in polymer electrolytes? A case study on poly(ethylene oxide) (PEO)-NaI and PEO-LiTFSI.
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DOI：
10.1021/jp2111956
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发表时间：
2012-02
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影响因子：
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通讯作者：
N. Stolwijk;M. Wiencierz;Christian Heddier;J. Kösters
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文献类型：
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作者：
N. Stolwijk;M. Wiencierz;Christian Heddier;J. Kösters
我们详细探讨了离子扩散率和离子配对的信息，可以完全从聚合物电解质中的准确的直流电导率数据与一种新的评价模型相结合。该研究是在两个原型系统的基础上聚（环氧乙烷）（PEO）与已知的不同的离子缔合特性，这是由于不同的盐成分是碘化钠（NaI）或锂双（三氟甲磺酰基）酰亚胺（LiN（CF（3）SO（2））（2）或LiTFSI）。电导率的温度依赖性可以通过扩展的Vogel-Tammann-Fulcher（VTF）方程来描述，该方程涉及包含成对形成焓ΔH（p）的Boltzmann因子。我们发现，随着盐浓度的降低，正ΔH（p）值明显增加，相关的VTF参数也有类似的明显趋势。分析进一步揭示了PEO-NaI结合了高的对分数与I（-）离子的高扩散率。相比之下，PEO-LiTFSI似乎以低离子配对趋势和相对低的大体积TFSI（-）离子迁移率为特征。观察到的显着差异之间的PEO-NaI和PEO-LiTFSI复合物的同源组合物在高温和低盐浓度是最明显的。
We explore in detail what information on ionic diffusivity and ion pairing can be exclusively gained from combining accurate direct-current conductivity data in polymer electrolytes with a novel evaluation model. The study was performed on two prototype systems based on poly(ethylene oxide) (PEO) with known disparate ion-association properties, which are due to the dissimilar salt components being either sodium iodide (NaI) or lithium bis(trifluoromethane-sulfonyl)imide (LiN(CF(3)SO(2))(2) or LiTFSI). The temperature dependence of the conductivity can be described by an extended Vogel-Tammann-Fulcher (VTF) equation, which involves a Boltzmann factor containing the pair-formation enthalpy ΔH(p). We find a distinct increase of the positive ΔH(p) values with decreasing salt concentration and similarly clear trends for the pertinent VTF parameters. The analysis further reveals that PEO-NaI combines a high pair fraction with a high diffusivity of the I(-) ion. By contrast, PEO-LiTFSI appears to be characterized by a low ion-pairing tendency and a relatively low mobility of the bulky TFSI(-) ion. The observed marked differences between PEO-NaI and PEO-LiTFSI complexes of homologous composition are most pronounced at high temperatures and low salt concentrations.