Webb Michael A, Yamamoto Umi, Savoie Brett M, Wang Zhen-Gang, Miller Thomas F
Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91125, United States.
ACS Macro Lett. 2018 Jun 19;7(6):734-738. doi: 10.1021/acsmacrolett.8b00237. Epub 2018 Jun 6.
We investigate how ion-polymer complexation suppresses molecular motion in conventional polymer electrolytes using molecular dynamics (MD) simulations of lithium hexafluorophosphate in poly(ethylene oxide) and a modified Rouse model. The employed model utilizes an inhomogeneous friction distribution to describe ion-polymer interactions and provides an effective way to examine how ion-polymer interactions affect polymer motion. By characterizing the subdiffusive Li transport and polymer relaxation times at several salt concentrations, we observe that increases in local friction due to ion-polymer complexation are significantly smaller than previously assumed. We find that a Rouse-based model that only considers local increases in friction cannot simultaneously capture the magnitude of increased polymer relaxation times and the apparent power-law exponent for Li subdiffusion observed in MD simulations. This incompatibility is reconciled by augmenting the modified Rouse model with a term that increases the global friction with the square of the salt concentration; this significantly improves the agreement between the model and MD, indicating the importance of ion-ion interactions and distributions on ion/polymer mobility.
我们使用聚环氧乙烷中六氟磷酸锂的分子动力学（MD）模拟和修正的Rouse模型，研究离子-聚合物络合如何抑制传统聚合物电解质中的分子运动。所采用的模型利用非均匀摩擦分布来描述离子-聚合物相互作用，并提供了一种有效的方法来研究离子-聚合物相互作用如何影响聚合物运动。通过表征几种盐浓度下的亚扩散锂传输和聚合物弛豫时间，我们观察到，由于离子-聚合物络合导致的局部摩擦增加明显小于先前的假设。我们发现，仅考虑局部摩擦增加的基于Rouse的模型无法同时捕捉MD模拟中观察到的聚合物弛豫时间增加的幅度和锂亚扩散的表观幂律指数。通过在修正的Rouse模型中增加一个与盐浓度平方成正比增加全局摩擦的项，解决了这种不兼容性；这显著提高了模型与MD之间的一致性，表明离子-离子相互作用和分布对离子/聚合物迁移率的重要性。
