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研究揭示环氧乙烷基均聚物和嵌段共聚物电解质中离子溶剂化和传输行为的分子水平差异
作者:小柯机器人 发布时间:2021/2/25 15:45:30

美国芝加哥大学Paul F. Nealey团队揭示了环氧乙烷基均聚物和嵌段共聚物电解质中离子溶剂化和输运行为的分子水平差异。 相关研究成果于2021年2月22日发表在国际知名学术期刊《美国化学会杂志》。

嵌段共聚物电解质(BCE),如聚苯乙烯嵌段聚氧乙烯(SEO)与锂双(三氟甲磺酰)酰亚胺(LiTFSI)共混,组成机械性能良好的绝缘和橡胶导电纳米畴,是很有前途的锂电池固体电解质。

该文中,研究人员比较了SEO-LiTFSI-BCEs及其均聚物PEO-LiTFSI类似物中的离子溶剂化、缔合、分布和导电性,以基本了解作为盐浓度函数的导电性和传输机制的最大值。离子电导率测量显示SEO-LiTFSI和PEO-LiTFSI表现出相似的行为,Li/EO比高达1/12,系统中大约一半的可用溶剂化位点被填充,电导率最大。当Li/EO比值增加到1/5时,PEO-LiTFSI的电导率下降近3倍,而SEO-LiTFSI的电导率保持不变。

FTIR光谱表明,当Li/EO比超过1/12时,均聚电解质中的锂离子被额外的EO单元络合,而在BCE中,复合和非复合EO单元的比例保持不变;相同浓度下的拉曼光谱数据表明,SEO-LiTFSI样品中的锂离子更倾向于与其反阴离子配位。原子尺度的分子动力学模拟证实了这些结果,并进一步表明相关离子倾向于分离到SEO-LiTFSI结构域界面。“多余”的盐在BCE界面被隔离,导致在BCE的导电纳米域的中间未完成和复杂的PEO溶剂化位点达到平衡,并在广泛的盐浓度范围内实现导电性最大化。

附:英文原文

Title: Molecular Level Differences in Ionic Solvation and Transport Behavior in Ethylene Oxide-Based Homopolymer and Block Copolymer Electrolytes

Author: Daniel Sharon, Peter Bennington, Michael A. Webb, Chuting Deng, Juan J. de Pablo, Shrayesh N. Patel, Paul F. Nealey

Issue&Volume: February 22, 2021

Abstract: Block copolymer electrolytes (BCE) such as polystyrene-block-poly(ethylene oxide) (SEO) blended with lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and composed of mechanically robust insulating and rubbery conducting nanodomains are promising solid-state electrolytes for Li batteries. Here, we compare ionic solvation, association, distribution, and conductivity in SEO-LiTFSI BCEs and their homopolymer PEO-LiTFSI analogs toward a fundamental understanding of the maximum in conductivity and transport mechanisms as a function of salt concentration. Ionic conductivity measurements reveal that SEO-LiTFSI and PEO-LiTFSI exhibit similar behaviors up to a Li/EO ratio of 1/12, where roughly half of the available solvation sites in the system are filled, and conductivity is maximized. As the Li/EO ratios increase to 1/5 the conductivity, of the PEO-LiTFSI drops nearly 3-fold, while the conductivity of SEO-LiTFSI remains constant. FTIR spectroscopy reveals that additional Li cations in the homopolymer electrolyte are complexed by additional EO units when the Li/EO ratio exceeds 1/12, while in the BCE, the proportion of complexed and uncomplexed EO units remains constant; Raman spectroscopy data at the same concentrations show that Li cations in the SEO-LiTFSI samples tend to coordinate more to their counteranions. Atomistic-scale molecular dynamics simulations corroborate these results and further show that associated ions tend to segregate to the SEO-LiTFSI domain interfaces. The opportunity for “excess” salt to be sequestered at BCE interfaces results in the retention of an optimum ratio of uncompleted and complexed PEO solvation sites in the middle of the conductive nanodomains of the BCE and maximized conductivity over a broad range of salt concentrations.

DOI: 10.1021/jacs.0c12538

Source: https://pubs.acs.org/doi/10.1021/jacs.0c12538

 

期刊信息

JACS:《美国化学会志》,创刊于1879年。隶属于美国化学会,最新IF:14.612
官方网址:https://pubs.acs.org/journal/jacsat
投稿链接:https://acsparagonplus.acs.org/psweb/loginForm?code=1000