The Coupling between Stability and Ion Pair Formation in Magnesium Electrolytes from First-Principles Quantum Mechanics and Classical Molecular Dynamics
The Coupling between Stability and Ion Pair Formation in Magnesium Electrolytes from First-Principles Quantum Mechanics and Classical Molecular Dynamics
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DOI：
10.1021/jacs.5b01004
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发表时间：
2015-03-11
影响因子：
15
通讯作者：
Persson, Kristin A.
中科院分区：
文献类型：
--
作者：
Rajput, Nav Nidhi;Qu, Xiaohui;Persson, Kristin A.
在这项工作中，我们发现了浓度依赖离子对形成和阴离子稳定性之间的新效应在还原电位，例如，在金属阳极。通过综合计算，使用第一原理和经典分子动力学在电解质矩阵上，涵盖溶剂和盐阴离子具有广泛的化学范围，我们阐明了分子水平相互作用与复合电解质性能之间的系统相关性，如电化学稳定性，溶剂化结构和动力学。我们发现，即使在中等浓度下，对于具有不同介电常数的广泛溶剂，Mg电解质也很容易形成离子对，这对动力学和电荷转移有影响。具体来说，我们观察到，在Mg金属电位下，离子对在Mg阳离子中心（Mg2+ -> Mg+）发生部分还原，这与电荷转移机制竞争，并可以激活阴离子，使其易于分解。具体来说，TFSI在与瞬态部分还原的Mg+配对时表现出明显的键弱化。相反，BH4和BF4在还原离子对结构中表现出化学稳定性。此外，我们观察到，高阶glyme和DMSO提高了Mg盐的溶解度，但只有较长的glyme链降低了溶液中离子的动力学。这些信息为未来的电解质提供了关键的设计指标，因为它阐明了体溶剂化与阴极稳定性以及盐的动力学之间的密切联系。
In this work we uncover a novel effect between concentration dependent ion pair formation and anion stability at reducing potentials, e.g., at the metal anode. Through comprehensive calculations using both first-principles as well as well-benchmarked classical molecular dynamics over a matrix of electrolytes, covering solvents and salt anions with a broad range in chemistry, we elucidate systematic correlations between molecular level interactions and composite electrolyte properties, such as electrochemical stability, solvation structure, and dynamics. We find that Mg electrolytes are highly prone to ion pair formation, even at modest concentrations, for a wide range of solvents with different dielectric constants, which have implications for dynamics as well as charge transfer. Specifically, we observe that, at Mg metal potentials, the ion pair undergoes partial reduction at the Mg cation center (Mg2+ -> Mg+), which competes with the charge transfer mechanism and can activate the anion to render it susceptible to decomposition. Specifically, TFSI exhibits a significant bond weakening while paired with the transient, partially reduced Mg+. In contrast, BH4 and BF4 are shown to be chemically stable in a reduced ion pair configuration. Furthermore, we observe that higher order glymes as well as DMSO improve the solubility of Mg salts, but only the longer glyme chains reduce the dynamics of the ions in solution. This information provides critical design metrics for future electrolytes as it elucidates a close connection between bulk solvation and cathodic stability as well as the dynamics of the salt.