Relationship between Ion Dissociation, Melt Morphology, and Electrochemical Performance of Lithium and Magnesium Single-Ion Conducting Block Copolymers

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• 作者：Jacob L. Thelen ; Sebnem Inceoglu ; Naveen R. Venkatesan ; Nikolaus G. Mackay ; Nitash P. Balsara
• 刊名：Macromolecules
• 出版年：2016
• 出版时间：December 13, 2016
• 年：2016
• 卷：49
• 期：23
• 页码：9139-9147
• 全文大小：512K
• ISSN：1520-5835

文摘

Single-ion conducting block copolymers, such as poly(ethylene oxide)-b-poly[(styrene-4-sulfonyltrifluoromethylsulfonyl)imide lithium] (PEO–P[(STFSI)Li]), represent an exciting new class of materials capable of improving the performance of solid-state batteries with metal anodes. In this work, we report on the synthesis and characterization of a matched set of lithiated (PEO–P[(STFSI)Li]) and magnesiated (PEO–P[(STFSI)₂Mg]) single-ion conducting diblock copolymers. We measure the temperature dependence of ionic conductivity, and through analysis using the Vogel–Tamman–Fulcher (VTF) relation, demonstrate that ion dissociation is significantly lower for all PEO–P[(STFSI)₂Mg] samples when compared to their PEO–P[(STFSI)Li] counterparts. The VTF parameter characterizing the activation barrier to ion hopping was similar for both cations, but the VTF prefactor that reflects effective charge carrier concentration was higher in the lithiated samples by an order of magnitude. We study the melt morphology of the single-ion conducting block copolymers using temperature-dependent X-ray scattering and use the mean-field theory of Leibler to extract the effective Flory–Huggins interaction parameter (χ) for PEO/P[(STFSI)Li] and PEO/P[(STFSI)₂Mg] from the X-ray scattering data. We demonstrate a linear relationship between the charge-concentration-related VTF parameter and the parameter quantifying the enthalpic contribution to χ. It is evident that ion dissociation and block copolymer thermodynamics are intimately coupled; ion dissociation in these systems suppresses microphase separation.