Structure and Ionic Conductivity of Polystyrene-block-poly(ethylene oxide) Electrolytes in the High Salt Concentration Limit

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• 作者：Mahati Chintapalli ; Thao N. P. Le ; Naveen R. Venkatesan ; Nikolaus G. Mackay ; Adriana A. Rojas ; Jacob L. Thelen ; X. Chelsea Chen ; Didier Devaux ; Nitash P. Balsara
• 刊名：Macromolecules
• 出版年：2016
• 出版时间：March 8, 2016
• 年：2016
• 卷：49
• 期：5
• 页码：1770-1780
• 全文大小：705K
• ISSN：1520-5835

文摘

We explore the relationship between the morphology and ionic conductivity of block copolymer electrolytes over a wide range of salt concentrations for the system polystyrene-block-poly(ethylene oxide) (PS-b-PEO, SEO) mixed with lithium bis(trifluoromethanesulfonyl)imide salt (LiTFSI). Two SEO polymers were studied, SEO(16–16) and SEO(4.9–5.5), over the salt concentration range r = 0.03–0.55. The numbers x and y in SEO(x–y) are the molecular weights of the blocks in kg mol^–1, and the r value is the molar ratio of salt to ethylene oxide moieties. Small-angle X-ray scattering was used to characterize morphology and grain size at 120 °C, differential scanning calorimetry was used to study the crystallinity and the glass transition temperature of the PEO-rich microphase, and ac impedance spectroscopy was used to measure ionic conductivity as a function of temperature. The most surprising observation of our study is that ionic conductivity in the concentration regime 0.11 ≤ r ≤ 0.21 increases in SEO electrolytes but decreases in PEO electrolytes. The maximum in ionic conductivity with salt concentration occurs at about twice the salt concentration in SEO (r = 0.21) as in PEO (r = 0.11). We propose that these observations are due to the effect of salt concentration on the grain structure in SEO electrolytes.