用计算化学方法研究镁离子电池阳极表面钝化层的形成机理

Rechargeable magnesium batteries offer the opportunity to safely and cheaply store energy. Compared with lithium, magnesium batteries have double the theoretical volumetric capacity. However, there are several challenges which must be addressed with magnesium batteries before the technology can be commercialized. Presently, there are only a handful of electrolytes which allow for reversibly cycling the battery without loss of capacity. This is primarily due to the degradation of electrolyte to form solid electrolyte interphase(SEI) on the magnesium anode surface, which are not permeable to magnesium ions. To address this problem, we propose to use quantum chemistry calculations, and molecular simulations using both classical and reactive force fields to elucidate the adsorption of magnesium at the anode surface. The relationship between the structure and energy of passivation layers at the magnesium anode surface due to the interactions between the electrode and electrolyte will be studied. This study can provide useful insight to experimentalists to select appropriate electrolytes for magnesium batteries.

可充电镁离子电池是一种安全经济的储能方式。跟锂离子电池相比，镁离子电池理论上有两倍的单位体积电池容量。然而，镁离子电池的一些缺陷阻碍了其大规模的商业应用。目前，只有少数电解质能够在不影响镁离子电池容量的情况下循环充放电。这是因为电解质溶液降解在阳极（镁金属）表面上形成固体-电解质界面，形成钝化层阻断镁离子与镁金属的相互接触。针对这些问题，我们结合量子化学计算、经典力场及反应力场模拟研究不同电解质环境下镁离子在阳极表面的吸附，电解液和电极的相互作用所形成的钝化层的结构和能量关系，揭示其形成机理。为实际应用中选择合适的电解质提供理论指导。

本项目使用量子化学方法和分子动力学对于镁离子电池体系进行了研究，主要分以下三个部分：1.镁离子电池的镁-硼氢化物电解质系统，阐明镁-硼氢化物电解液的液体结构。我们使用了密度泛函理论（DFT）计算了镁离子与四氢化硼体系的构型变化、自由能改变以及相应的溶剂分子配位情况等; 2. 镁离子电池的复合电解液体系，通过在Mg(BH4)2 中加入LiBH4 和NaBH4，经过DFT计算详细研究了LiBH4 和NaBH4的液体结构并且阐明了Li和Na作为镁离子电解液的添加剂所产生的协同效应; 3. 开发了一种方法从反应力场模拟数据中构建反应动力学以及反应机理。这一方法为使用反应力场模拟计算电化学反应作了技术上的铺垫。本项目从量子化学计算水平出发，详细计算了镁离子电池电解液体系的热力学和液体结构性质，阐明了Li和Na作为镁离子电解液的添加剂所产生的协同效应。三年项目进行期间发表论文4篇，达到项目计划书的设定目标。