Bollinger Jonathan A, Stevens Mark J, Frischknecht Amalie L
Center for Integrated Nanotechnologies, Sandia National Laboratories, Albuquerque, New Mexico 87185, United States.
ACS Macro Lett. 2020 Apr 21;9(4):583-587. doi: 10.1021/acsmacrolett.0c00139. Epub 2020 Apr 2.
Single-ion conducting polymers such as ionomers are promising battery electrolyte materials, but it is critical to understand how rates and mechanisms of free cation transport depend on the nanoscale aggregation of cations and polymer-bound anions. We perform coarse-grained molecular dynamics simulations of ionomer melts to understand cation mobility as a function of polymer architecture, background relative permittivity, and corresponding ionic aggregate morphology. In systems exhibiting percolated ionic aggregates, cations diffuse via stepping motions along the ionic aggregates. These diffusivities can be quantitatively predicted by calculating the lifetimes of continuous association between oppositely charged ions, which equal the time scales of the stepping (diffusive) motions. In contrast, predicting cation diffusivity for systems with isolated ionic aggregates requires another time scale. Our results suggest that to improve conductivity the Coulombic interaction strength should be strong enough to favor percolated aggregates but weak enough to facilitate ion dissociation.
诸如离聚物之类的单离子导电聚合物是很有前景的电池电解质材料，但了解自由阳离子传输的速率和机制如何取决于阳离子与聚合物结合阴离子的纳米级聚集至关重要。我们对离聚物熔体进行粗粒度分子动力学模拟，以了解阳离子迁移率与聚合物结构、背景相对介电常数以及相应离子聚集体形态的函数关系。在呈现渗流离子聚集体的系统中，阳离子通过沿离子聚集体的步进运动进行扩散。这些扩散系数可以通过计算相反电荷离子之间连续缔合的寿命来定量预测，该寿命等于步进（扩散）运动的时间尺度。相比之下，预测具有孤立离子聚集体的系统的阳离子扩散系数需要另一个时间尺度。我们的结果表明，为了提高电导率，库仑相互作用强度应足够强以有利于渗流聚集体，但又足够弱以促进离子解离。
