Using density functional calculations, we examine insertion/extraction of Mg ions in Mg3Bi2, an interesting Mg-ion battery anode. We found that a (1 1 0) facet is the most stable termination. Vacating a Mg2+ ion from the octahedral site is more favourable for both surface and bulk regions of the material. However, the diffusion barriers among the tetrahedral sites are around 3 times smaller than those among octahedral sites. Consequently, during the magnesiation/demagnesiation process, Mg ions first vacate the octahedral sites and then diffuse through the tetrahedral sites. The spin-orbit interaction lowers Mg's vacancy formation energy but has a minor effect on diffusion barriers.

中文翻译：

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镁离子电池 Mg3Bi2 阳极的充放电机制；自旋轨道耦合的作用

使用密度泛函计算，我们检查了 Mg 离子在 Mg3Bi2（一种有趣的 Mg 离子电池阳极）中的插入/提取。我们发现 (1 1 0) 面是最稳定的终止。从八面体位置腾出 Mg2+ 离子对材料的表面和本体区域都更有利。然而，四面体位点之间的扩散势垒比八面体位点之间的扩散势垒小约 3 倍。因此，在镁化/去镁化过程中，Mg 离子首先腾出八面体位点，然后通过四面体位点扩散。自旋轨道相互作用降低了 Mg 的空位形成能，但对扩散势垒的影响很小。