了解无机非水电解质中镁的可逆沉积和剥离的初始阶段
Understanding the Initial Stages of Reversible Mg Deposition and Stripping in Inorganic Non-Aqueous Electrolytes
摘要：
基于将Mg金属阳极与高电压（$\sim$ 3 V）嵌入阴极配对的多价（MV）电池体系结构提供了一种现实的设计途径，以显著超过传统的基于Li离子的电池的能量存储性能，但是目前只有很少的电解质系统支持可逆的Mg沉积。采用静态第一性原理计算和$ab\; initio$分子动力学方法，研究了几种盐和溶剂在Mg金属与电解质（Mg $^{2+}$和Cl $^-$溶解于液体四氢呋喃（THF）中）界面上的吸附行为.我们的研究结果不仅提供了界面处的稳定物种的图片，而且还解释了该系统如何支持可逆的Mg沉积，因此我们提供了如何设计用于Mg电镀和剥离的其他电解质的见解。活性沉积物种被确定为（MgCl）$^+$单体与THF配位，与可能的钝化物种（如THF溶剂或中性MgCl $_2$络合物）相比，其在Mg上表现出优先吸附。沉积后，能量去溶剂化这些吸附的复合物，并促进电荷转移被证明是小的（$\sim$ 61 $-$ 46.2 kJ mol $^{-1}$，以消除3 THF从最强的吸附复合物），和吸附，但去溶剂化（MgCl）$^+$复合物的稳定取向出现有利于电荷转移。最后，在非常低的THF配位（0和1）的Mg表面的Mg-Cl解离的观察表明，有害的Cl在阳极中的掺入可能会发生电镀。在汽提过程中，这通过进一步促进Mg去除反应而有益。
英文摘要：
Multi-valent (MV) battery architectures based on pairing a Mg metal anode with a high-voltage ($\sim$ 3 V) intercalation cathode offer a realistic design pathway toward significantly surpassing the energy storage performance of traditional Li-ion based batteries, but there are currently only few electrolyte systems that support reversible Mg deposition. Using both static first-principles calculations and $ab\; initio$ molecular dynamics, we perform a comprehensive adsorption study of several salt and solvent species at the interface of Mg metal with an electrolyte of Mg$^{2+}$ and Cl$^-$ dissolved in liquid tetrahydrofuran (THF). Our findings not only provide a picture of the stable species at the interface, but also explain how this system can support reversible Mg deposition and as such we provide insights in how to design other electrolytes for Mg plating and stripping. The active depositing species are identified to be (MgCl)$^+$ monomers coordinated by THF, which exhibit preferential adsorption on Mg compared to possible passivating species (such as THF solvent or neutral MgCl$_2$ complexes). Upon deposition, the energy to desolvate these adsorbed complexes and facilitate charge-transfer is shown to be small ($\sim$ 61 $-$ 46.2 kJ mol$^{-1}$ to remove 3 THF from the strongest adsorbing complex), and the stable orientations of the adsorbed but desolvated (MgCl)$^+$ complexes appear favorable for charge-transfer. Finally, observations of Mg-Cl dissociation at the Mg surface at very low THF coordinations (0 and 1) suggest that deleterious Cl incorporation in the anode may occur upon plating. In the stripping process, this is beneficial by further facilitating the Mg removal reaction.
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