Ion Pairing and Diffusion in Magnesium Electrolytes Based on Magnesium Borohydride.
Ion Pairing and Diffusion in Magnesium Electrolytes Based on Magnesium Borohydride.
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基于硼氢化镁的镁电解质中的离子对和扩散。
DOI：
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发表时间：
2017
影响因子：
9.5
通讯作者：
Donald J. Siegel
中科院分区：
文献类型：
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作者：
D. Samuel;Carl Steinhauser;Jeffrey G. Smith;A. Kaufman;M. Radin;Junichi Naruse;Hidehiko Hiramatsu;Donald J. Siegel
实现实用的可充电镁离子电池的一个障碍是开发高效的镁电解质。基于简单 Mg(BH4)2 盐的电解质存在盐溶解度差和/或电导率低的问题，这可能是由于强离子对所致。了解这些电解质中发生的分子尺度过程将有助于克服这些性能限制。为了实现这一目标，本研究利用经典分子动力学研究了基于 Mg(BH4)2 盐的一系列镁电解质的溶剂化、团聚和传输特性。这些特性在五种不同的溶剂（四氢呋喃和甘醇二甲醚 G1-G4）和从稀释极限到 0.4 M 的四种盐浓度下进行了检查。在所有非稀释 Mg(BH4)2 浓度下，在所有溶剂中观察到显着且不可逆的盐聚集。在这些二价镁体系中观察到的聚集程度比报道的含有单价阳离子（例如锂）的电解质的聚集程度大得多。观察到盐团聚率和 Mg2+ 扩散率均与溶剂自扩散率相关：使用较长（较短）链溶剂的电解质具有最低（最高）的 Mg2+ 扩散率和团聚率。将 Mg2+ 掺入 Mg2+-BH4- 团簇中，通过将位移限制在基本上不移动的团聚体内的局部运动，显着降低了 Mg2+ 的扩散率。因此，随着 Mg(BH4)2 浓度的增加，扩散越来越受阻碍。这些数据与实验观察到的 Mg(BH4)2 基电解质的溶解度限制一致，并强调需要采取尽量减少含有二价阳离子的电解质中盐团聚的策略。
One obstacle to realizing a practical, rechargeable magnesium-ion battery is the development of efficient Mg electrolytes. Electrolytes based on simple Mg(BH4)2 salts suffer from poor salt solubility and/or low conductivity, presumably due to strong ion pairing. Understanding the molecular-scale processes occurring in these electrolytes would aid in overcoming these performance limitations. Toward this goal, the present study examines the solvation, agglomeration, and transport properties of a family of Mg electrolytes based on the Mg(BH4)2 salt using classical molecular dynamics. These properties were examined across five different solvents (tetrahydrofuran and the glymes G1-G4) and at four salt concentrations ranging from the dilute limit up to 0.4 M. Significant and irreversible salt agglomeration was observed in all solvents at all nondilute Mg(BH4)2 concentrations. The degree of clustering observed in these divalent Mg systems is much larger than that reported for electrolytes containing monovalent cations, such as Li. The salt agglomeration rate and diffusivity of Mg2+ were both observed to correlate with solvent self-diffusivity: electrolytes using longer- (shorter-) chain solvents had the lowest (highest) Mg2+ diffusivity and agglomeration rates. Incorporation of Mg2+ into Mg2+-BH4- clusters significantly reduces the diffusivity of Mg2+ by restricting displacements to localized motion within largely immobile agglomerates. Consequently, diffusion is increasingly impeded with increasing Mg(BH4)2 concentration. These data are consistent with the solubility limitations observed experimentally for Mg(BH4)2-based electrolytes and highlight the need for strategies that minimize salt agglomeration in electrolytes containing divalent cations.
影响因子：
3.9
作者：
Tang S;Zhao H
通讯作者：
Zhao H