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arXiv 2107.14722cond-mat.softphysics.chem-ph
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polymer电解质中离子对寿命的重要性

Importance of the ion-pair lifetime in polymer electrolytes

Harish Gudla, Yunqi Shao, Supho Phunnarungsi, Daniel Brandell, Chao Zhang

摘要:

离子配对通常被认为是聚合物电解质体系中离子电导率降低的罪魁祸首。然而,这个简单的热力学图像不应该从字面上理解,因为离子配对是一种动力学现象。通过调节溶剂极性,构建了不同离子配对程度的PEO-LiTFSI模型体系,并利用分子动力学模拟研究了正负离子电导率$σ^\rm{d}_{+-}$与离子对$τ_{+-}$寿命之间的关系.发现存在两种不同的制度,其中$σ^\rm{d}_{+-}$分别与$1/τ_{+-}$和$τ_{+-}$成比例,后者是对总离子电导率有负贡献的长寿命离子对的特征。这表明,离子对是动力学上不同的溶剂极性,这使得离子对寿命非常重要,当讨论其在聚合物电解质系统中的离子传输的影响。

英文摘要:

Ion-pairing is commonly considered as a culprit for the reduced ionic conductivity in polymer electrolyte systems. However, this simple thermodynamic picture should not be taken literally, as ion-pairing is a dynamical phenomenon. Here we construct model PEO-LiTFSI systems with different degree of ion-pairing by tuning solvent polarity, and examine the relation between the cation-anion distinct conductivity $σ^\rm{d}_{+-}$ and the lifetime of ion-pairs $τ_{+-}$ using molecular dynamics simulations. It is found that there exist two distinct regimes where $σ^\rm{d}_{+-}$ scales with $1/τ_{+-}$ and $τ_{+-}$ respectively, and the latter is a signature of longer-lived ion-pairs which contribute negatively to the total ionic conductivity. This suggests that ion-pairs are kinetically different depending on the solvent polarity, which renders the ion-pair lifetime highly important when discussing its effect on ion transport in polymer electrolyte systems.

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