Orientation-Dependent Distortion of Lamellae in a Block Copolymer Electrolyte under DC Polarization,Macromolecules

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Orientation-Dependent Distortion of Lamellae in a Block Copolymer Electrolyte under DC Polarization
Macromolecules ( IF 5.1 ) Pub Date : 2021-08-27 , DOI: 10.1021/acs.macromol.1c01295
Michael D. Galluzzo _{1,

2} , Lorena S. Grundy _{1,

3} , Christopher J. Takacs _{4,

5} , Chuntian Cao _{4,

6} , Hans-Georg Steinrück _{4,

5,

7} , Sean Fu ₁ , Michael A. Rivas Valadez ₁ , Michael F. Toney ₆ , Nitash P. Balsara _{1,

2,

3,

8}

Affiliation

Lithium-salt-doped block copolymers have the potential to serve as solid electrolytes in rechargeable batteries with lithium metal anodes. In this work, we use small-angle X-ray scattering (SAXS) to study the structure of polystyrene-block-poly(ethylene oxide) (PS-b-PEO) doped with bis-(trifluoromethylsulfonyl)amine lithium salt (LiTFSI) during direct current (dc) polarization experiments in lithium–lithium symmetric cells. The block copolymer studied is nearly symmetric in composition, has a total molecular weight of 39 kg mol^–1, and exhibits a lamellar morphology at all studied salt concentrations. When ionic current is passed through the electrolyte, a salt concentration gradient forms that induces a spatial gradient in the domain spacing, d. The dependence of d on distance from the positive electrode, x, was determined experimentally by scanning the incident X-ray beam from one lithium electrode to the other. By studying the two-dimensional (2D) SAXS patterns as a function of azimuthal scattering angle, we find that lamellae with PS/PEO interfaces oriented perpendicular to the flow of ionic current (LAM_⊥) swell and contract to a greater degree than those with interfaces oriented parallel to the current direction (LAM_||). While domains with the LAM_⊥ do not provide direct conducting pathways between the electrodes, our analysis suggests that they play an important role in establishing the salt concentration gradient necessary for sustaining a large ionic current through greater expansion and contraction.

中文翻译：

直流极化下嵌段共聚物电解质中薄片的取向相关畸变

锂盐掺杂的嵌段共聚物有可能在具有锂金属阳极的可充电电池中用作固体电解质。在这项工作中，我们使用小角 X 射线散射 (SAXS) 来研究掺杂双（三氟甲基磺酰基）胺锂盐（LiTFSI）的聚苯乙烯-嵌段-聚（环氧乙烷）（PS- b - PEO）的结构在锂-锂对称电池的直流（dc）极化实验中。所研究的嵌段共聚物在组成上几乎是对称的，总分子量为 39 kg mol ^–1，并且在所有研究的盐浓度下都表现出层状形态。当离子电流通过电解质时，会形成盐浓度梯度，从而在域间距d中产生空间梯度. 通过从一个锂电极向另一个锂电极扫描入射 X 射线束，实验确定了d与距正极的距离x的关系。通过研究作为方位角散射角函数的二维 (2D) SAXS 模式，我们发现 PS/PEO 界面垂直于离子电流流动 (LAM _⊥ ) 的薄片膨胀和收缩的程度大于那些具有平行于当前方向的界面 (LAM _|| )。带有 LAM 的域_⊥ 不提供电极之间的直接导电通路，我们的分析表明，它们在建立通过更大的膨胀和收缩维持大离子电流所必需的盐浓度梯度方面发挥着重要作用。

更新日期：2021-09-14

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