Understanding Ionic Diffusion through SEI Components for Lithium-Ion and Sodium-Ion Batteries: Insights from First-Principles Calculations,Chemistry of Materials

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Understanding Ionic Diffusion through SEI Components for Lithium-Ion and Sodium-Ion Batteries: Insights from First-Principles Calculations
Chemistry of Materials ( IF 7.2 ) Pub Date : 2018-04-23 00:00:00 , DOI: 10.1021/acs.chemmater.8b00635
Fernando A. Soto ₁ , Asma Marzouk ₂ , Fedwa El-Mellouhi ₂ , Perla B. Balbuena ₁

Affiliation

The insufficient understanding of the physical and chemical phenomena taking place at the electrode–electrolyte interface is the main roadblock for improvement of current battery technologies and development of new ones. Of particular interest is the solid–electrolyte interphase (SEI) layer because many aspects of the battery performance depend on its quality. Recently we have shown that a stable SEI layer can be designed in specific Li- or Na-based electrolytes. In this paper, we continue exploring this concept by identifying the interactions that take place at the lithiated (or sodiated) carbon–electrolyte interface and discussing the transport mechanisms of Li and Na ions through the most commonly found SEI layer inorganic components. For the ab initio molecular dynamics (AIMD) simulations, we considered the case of the sodiated hard carbon structure. The simulations show the decomposition of ethylene carbonate on the edge of the graphite layers leading to products such as CO and other organic fragments. The decomposition of the PF₆^– anion is a precursor step for the formation of NaF layers. Regarding the Li- and Na-ion transport through the SEI, the results show that the energy to create defects is lowest when Li ions are guests at an interstitial position in NaF and lattice positions in Na₂CO₃. For the LiF and Li₂CO₃ crystals, the energy to create defects is lowest when Na ions substitute Li. This lower energy cost for Li-ion defects in Na-based components is due to the smaller size of the Li ion when compared to the Na ion. Regarding diffusion barriers, the Na ions in Li-based SEI components show a preference for the vacancy diffusion and knock-off mechanisms as the preferred pathways to migrate through the SEI while Li ions in Na-based SEI components prefer a mechanism involving the migration of the interstitial ion through the knock-off or direct hopping mechanism. This work also emphasizes the interplay between the crystallographic orientation of the SEI components and the direction dependent ion migration guiding the controlled design of efficient artificial SEI layers.

中文翻译：

通过SEI组件了解锂离子和钠离子电池的离子扩散：第一性原理计算的见解

对电极-电解质界面处发生的物理和化学现象的了解不足，是改进现有电池技术和开发新电池技术的主要障碍。特别令人感兴趣的是固态电解质相间（SEI）层，因为电池性能的许多方面都取决于其质量。最近，我们表明可以在特定的基于Li或Na的电解质中设计稳定的SEI层。在本文中，我们通过识别在锂化（或钠化）碳-电解质界面发生的相互作用，并讨论Li和Na离子通过最常见的SEI层无机组分的传输机理，来继续探索这一概念。对于从头分子动力学（AIMD）模拟中，我们考虑了硬质碳酸钠结构的情况。模拟显示碳酸亚乙酯在石墨层边缘上的分解，导致生成诸如CO和其他有机碎片的产物。所述PF的分解₆^-阴离子为氟化钠层的形成前体步骤。关于通过SEI的Li和Na离子传输，结果表明，当Li离子在NaF的间隙位置和Na ₂ CO _3的晶格位置作为客体时，产生缺陷的能量最低。对于LiF和Li ₂ CO ₃晶体中，当钠离子替代锂时，产生缺陷的能量最低。Na基组件中锂离子缺陷的较低能源成本是由于与Na离子相比，Li离子的尺寸较小。关于扩散障碍，Li基SEI组分中的Na离子显示出空位扩散和敲除机理的优先选择，因为它是通过SEI迁移的首选途径，而Na基SEI组分中的Li离子则更喜欢涉及迁移的机理。间隙离子通过敲除或直接跳跃机制产生。这项工作还强调了SEI组件的晶体学取向与方向相关的离子迁移之间的相互作用，指导了有效的人工SEI层的受控设计。

更新日期：2018-04-23

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