Elucidating the structure of the magnesium aluminum chloride complex electrolyte for magnesium-ion batteries
Elucidating the structure of the magnesium aluminum chloride complex electrolyte for magnesium-ion batteries
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DOI：
10.1039/c5ee02340h
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发表时间：
2015-01-01
影响因子：
32.5
通讯作者：
Ceder, Gerbrand
中科院分区：
文献类型：
--
作者：
Canepa, Pieremanuele;Jayaraman, Saivenkataraman;Ceder, Gerbrand
非水镁离子电池提供了一种很有前途的方法，可以克服最先进的锂离子电池技术的安全性、成本和能量密度限制。我们对四氢呋喃（THF）中的氯化镁铝络合物（MACC）进行了严格的分析，四氢呋喃（THF）是少数几种可以可逆地板化和剥离Mg的电解质之一。我们使用从头计算和经典分子动力学模拟来询问MACC电解质组成，目的是解决困扰电池研究人员的两个紧迫问题：(i)电解质的功能种类，（ii）在长时间电化学循环后调节MACC物种形成的复杂平衡，这一过程称为条件作用，而在长时间不活动后，这一过程称为老化。提出了一种解决电解质、离子液体和其他液体介质复杂结构的通用计算策略。Mg-Al-Cl-THF的形成能和大电位相图分析表明，MACC电解质具有简单的化学结构，其简单成分较少，即电活性物质MgCl+和AlCl4-与MgCl2和AlCl3平衡。MACC电解质的稳定种类的知识使我们能够确定在电化学循环过程中发生的最重要的平衡。我们观察到Al沉积总是优于Mg沉积，这解释了为什么新合成的MACC不能运行，需要进行预备调理。同样，我们认为电解液静息时溶液中的铝位移和耗尽（以及连续的MgCl2再生）是电解液老化的原因之一。最后，我们计算了选定分子和离子的屏蔽张量的核磁共振位移，为指导未来的实验研究提供了指纹。
Non-aqueous Mg-ion batteries offer a promising way to overcome safety, costs, and energy density limitations of state-of-the-art Li-ion battery technology. We present a rigorous analysis of the magnesium aluminum chloride complex (MACC) in tetrahydrofuran (THF), one of the few electrolytes that can reversibly plate and strip Mg. We use ab initio calculations and classical molecular dynamics simulations to interrogate the MACC electrolyte composition with the goal of addressing two urgent questions that have puzzled battery researchers: (i) the functional species of the electrolyte, and (ii) the complex equilibria regulating the MACC speciation after prolonged electrochemical cycling, a process termed as conditioning, and after prolonged inactivity, a process called aging. A general computational strategy to untangle the complex structure of electrolytes, ionic liquids and other liquid media is presented. The analysis of formation energies and grand-potential phase diagrams of Mg-Al-Cl-THF suggests that the MACC electrolyte bears a simple chemical structure with few simple constituents, namely the electro-active species MgCl+ and AlCl4- in equilibrium with MgCl2 and AlCl3. Knowledge of the stable species of the MACC electrolyte allows us to determine the most important equilibria occurring during electrochemical cycling. We observe that Al deposition is always preferred to Mg deposition, explaining why freshly synthesized MACC cannot operate and needs to undergo preparatory conditioning. Similarly, we suggest that aluminum displacement and depletion from the solution upon electrolyte resting (along with continuous MgCl2 regeneration) represents one of the causes of electrolyte aging. Finally, we compute the NMR shifts from shielding tensors of selected molecules and ions providing fingerprints to guide future experimental investigations.