The atomistic mechanisms during lithiation and delithiation of amorphous Si nanowires ($a$-SiNW) have been investigated over cycles by molecular dynamics simulations. First, the modified embedded atom method potential from Cui et al. [J. Power Sources 207, 150 (2012).] has been further optimized on static (${\mathrm{Li}}_x\mathrm{Si}$ alloy phases and point-defect energies) and on dynamic properties (Li diffusion) to reproduce the lithiation of small crystalline Si nanowires calculated at the ab initio level. The lithiation of $a$-SiNW reveals a two-phase process of lithiation with a larger diffusion interface compared to crystalline Si lithiation. Compressive axial stresses are observed in the amorphous ${\mathrm{Si}}_x\mathrm{Li}$ alloy outer shell. They are easily released thanks to the soft glassy behavior of the amorphous alloy. Conversely, in crystalline SiNW, the larger stress in the narrow crystalline lithiated interface is hardly released and requires a phase transformation to amorphous to operate, which delays the lithiation. The history of the charge-discharge cycles as well as the temperature appear as driving forces for phase transformation from amorphous ${\mathrm{Li}}_x\mathrm{Si}$ alloy to the more stable crystalline phase counterpart. Our work suggests that a SiNW anode with an enhanced plastic behavior could help release the internal stress, while a full delithiation could heal the cracks that appear with time and thus increase the life cycles of Li-ion batteries using such anode materials.

中文翻译：

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非晶硅纳米线的锂化-脱锂循环研究的经验电势优化

非晶硅纳米线锂化和脱锂过程中的原子机理$\mathrm{一种}$-SiNW）已通过分子动力学模拟在整个循环中进行了研究。首先，Cui等人的改进的嵌入原子方法的潜力。[ J. Power Sources 207，150（2012）。]在静态（${里}_X硅$合金相和点缺陷能量）和动态特性（Li扩散）来重现从头算级计算出的小晶体Si纳米线的锂化。的锂化$\mathrm{一种}$-SiNW揭示了与结晶硅锂化相比具有更大扩散界面的锂化两相过程。在非晶态中观察到轴向压缩应力${硅}_X里$合金外壳。由于非晶态合金的柔软玻璃态，它们很容易释放。相反，在结晶SiNW中，几乎不释放窄结晶锂化界面中的较大应力，并且需要相变为非晶态才能工作，这会延迟锂化作用。充放电循环的历史以及温度是非晶态相变的驱动力${里}_X硅$合金到更稳定的结晶相对应物。我们的工作表明，具有增强的塑性行为的SiNW阳极可以帮助释放内部应力，而完全脱锂可以修复随时间推移出现的裂纹，从而增加使用此类阳极材料的锂离子电池的使用寿命。