Structural Dynamics of Strongly Segregated Block Copolymer Electrolytes
Structural Dynamics of Strongly Segregated Block Copolymer Electrolytes
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DOI：
10.1021/acs.macromol.7b01803
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发表时间：
2018-04-10
期刊：
影响因子：
5.5
通讯作者：
Hallinan, Daniel, Jr.
中科院分区：
文献类型：
--
作者：
Oparaji, Onyekachi;Narayanan, Suresh;Hallinan, Daniel, Jr.
聚合物电解质是高能量密度可充电电池的有前途的材料。然而，它们具有低离子传输速率，并且在循环期间逐渐失去电极粘附。这些效应取决于聚合物结构和动力学。这激发了二嵌段共聚物电解质动力学的研究。结构和应力松弛已被测量与X射线光子相关光谱（XPCS）和流变学，分别作为盐浓度和温度的函数。在这项工作中研究的聚合物电解质是聚（苯乙烯-b-环氧乙烷），SEO，和锂bistrifluoromethanesulfonimide（LiTFSI）的混合物。来自XPCS实验的结果示出了对于各种锂盐浓度和在不同温度下的超扩散运动，这指示软玻璃质材料。这种行为归因于合作动态。衰减时间是一个弱的，盐浓度的非单调函数，并随着温度的升高而降低，在Arrhenius的方式。相反，剪切模量随着盐浓度的增加和温度的升高而降低。从流变学测量的缠结松弛遵循Vogel-Fulcher-Tammann行为。在玻璃化转变温度以上的温度下，结构衰减时间比缠结弛豫时间慢，但它们在Tg下近似相等，而与盐浓度无关。这可能表明在这种材料中合作结构运动和聚合物链运动之间的基本联系。
Polymer electrolytes are promising materials for high energy density rechargeable batteries. However, they have low ion transport rates and gradually lose electrode adhesion during cycling. These effects are dependent on polymer structure and dynamics. This motivates an investigation of diblock copolymer electrolyte dynamics. Structural and stress relaxations have been measured with X-ray photon correlation spectroscopy (XPCS) and rheology, respectively, as a function of salt concentration and temperature. The polymer electrolyte studied in this work is a mixture of poly(styrene-b-ethylene oxide), SEO, and lithium bistrifluoromethanesulfonimide (LiTFSI). Results from XPCS experiments showed hyperdiffusive motion for various lithium salt concentrations and at varying temperatures, which is indicative of soft glassy materials. This behavior is attributed to cooperative dynamics. The decay time was a weak, nonmonotonic function of salt concentration and decreased with increasing temperature, in an Arrhenius fashion. In contrast, the shear modulus decreased with increasing salt concentration and increasing temperature. The entanglement relaxation from rheological measurements followed Vogel-Fulcher-Tammann behavior. The structural decay time was slower than the entanglement relaxation time at temperatures above the glass transition temperature, but they were approximately equal at Tg regardless of salt concentration. This may indicate a fundamental connection between cooperative structural motion and polymer chain motion in this material.