Systematics of ionic transport and pair formation in amorphous PEO-NaI polymer electrolytes

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• 作者：Manfred Wiencierz ; Nicolaas A. Stolwijk ; ^{stolwij@nwz.uni-muenster.de}
• 关键词：Poly(ethylene oxide) ; Radiotracer diffusion ; Charge diffusivity ; Nernst&ndash ; Einstein equation ; Ion pairing ; Free-ion fraction
• 刊名：Solid State Ionics
• 出版年：2012
• 期刊代码：96_01672738
• 类别：ch
• 出版时间：29 March, 2012
• 卷：212
• 期：Complete
• 页码：88-99
• 文件大小：1487 K

摘要

Mass and charge transport in the prototype polymer electrolyte system PEO_yNaI were investigated by radiotracer diffusion and conductivity measurements over wide ranges of composition (y = 20 to 1000) and temperature (T = 鈭?#xA0;60 to 200 掳C). All data were simultaneously fitted within a comprehensive ion-transport model which takes into account for each composition the glass transition temperature (T_g), the fraction of ion pairs, and the diffusivities of single ions and pairs. This approach yields the pertinent model parameters as a function of salt concentration (C_s), including the Vogel-Tammann-Fulcher parameters of individual species and the enthalpy () and entropy () of pair formation. We find that the mobility of cations and anions distinctly increase with increasing T and decreasing C_s, whereas the fraction of free ions shows an anomalous reverse T- and C_s-dependence. This special constellation explains the appearance of a maximum in plots of the isothermal charge diffusivity versus salt concentration. Quantitative results for transference numbers, Haven ratios, and relative pair contributions to the tracer diffusion coefficients are presented as well.