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Structural, Chemical, and Dynamical Frustration: Origins of Superionic Conductivity in closo-Borate Solid Electrolytes
Chemistry of Materials ( IF 8.6 ) Pub Date : 2017-10-31 00:00:00 , DOI: 10.1021/acs.chemmater.7b02902
Kyoung E. Kweon 1 , Joel B. Varley 1 , Patrick Shea 1 , Nicole Adelstein 2 , Prateek Mehta 3 , Tae Wook Heo 1 , Terrence J. Udovic 4 , Vitalie Stavila 5 , Brandon C. Wood 1
Affiliation  

Li2B12H12, Na2B12H12, and their closo-borate relatives exhibit unusually high ionic conductivity, making them attractive as a new class of candidate electrolytes in solid-state Li- and Na-ion batteries. However, further optimization of these materials requires a deeper understanding of the fundamental mechanisms underlying ultrafast ion conduction. To this end, we use ab initio molecular dynamics simulations and density-functional calculations to explore the motivations for cation diffusion. We find that superionic behavior in Li2B12H12 and Na2B12H12 results from a combination of key structural, chemical, and dynamical factors that introduce intrinsic frustration and disorder. A statistical metric is used to show that the structures exhibit a high density of accessible interstitial sites and site types, which correlates with the flatness of the energy landscape and the observed cation mobility. Furthermore, cations are found to dock to specific anion sites, leading to a competition between the geometric symmetry of the anion and the symmetry of the lattice itself, which can facilitate cation hopping. Finally, facile anion reorientations and other low-frequency thermal vibrations lead to fluctuations in the local potential that enhance cation mobility by creating a local driving force for hopping. We discuss the relevance of each factor for developing new ionic conductivity descriptors that can be used for discovery and optimization of closo-borate solid electrolytes, as well as superionic conductors more generally.

中文翻译:

结构,化学和动力学挫折:在超离子电导率的起源闭合碳硼酸盐固体电解质

212 ħ 12,钠212 ħ 12,和它们的闭合碳硼酸盐亲属表现出特别高的离子电导率,使得它们如在固态俪和Na离子电池一类新的候选电解质的吸引力。然而,对这些材料的进一步优化要求对超快离子传导的基本机理有更深入的了解。为此,我们使用从头算分子动力学模拟和密度泛函计算来探索阳离子扩散的动机。我们发现Li 2 B 12 H 12和Na中的超离子行为2 B 1212是由引入内在的挫败感和无序性的关键结构,化学和动力学因素共同导致的。使用统计量度来显示结构显示出高密度的可访问间隙位置和位置类型,这与能量景观的平坦度和观察到的阳离子迁移率相关。此外,发现阳离子停靠在特定的阴离子位点上,导致阴离子的几何对称性与晶格本身的对称性之间的竞争,这可以促进阳离子跳变。最后,容易的阴离子重新定向和其他低频热振动会导致局部电势波动,从而通过产生用于跳跃的局部驱动力来增强阳离子迁移率。闭合碳硼酸盐的固体电解质,以及超离子导体更普遍。
更新日期:2017-11-01
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