Alloying-type anode materials provide high capacity for lithium-ion batteries; however, they suffer pulverization problems resulting from the volume change during cycling. Realizing the cycling reversibility of these anodes is therefore critical for sustaining their electrochemical performance. Here, we investigate the structural reversibility of Sn NPs during cycling at atomic-level resolution utilizing in situ high-resolution TEM. We observed a surprisingly near-perfect structural reversibility after a complete cycle. A three-step phase transition happens during lithiation, accompanied by the generation of a significant number of defects, grain boundaries, and up to 202% volume expansion. In subsequent delithiation, the volume, morphology, and crystallinity of the Sn NPs were restored to their initial state. Theoretical calculations show that compressive stress drives the removal of vacancies generated within the NPs during delithiation, therefore maintaining their intact morphology. This work demonstrates that removing vacancies during cycling can efficiently improve the structural reversibility of high-capacity anode materials.

中文翻译：

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纳米锡阳极的结构可逆性

合金型负极材料为锂离子电池提供高容量；然而，它们由于循环过程中的体积变化而遭受粉化问题。因此，实现这些阳极的循环可逆性对于维持其电化学性能至关重要。在这里，我们利用原位高分辨率 TEM以原子级分辨率研究了 Sn NP 在循环过程中的结构可逆性。我们在一个完整的循环后观察到令人惊讶的近乎完美的结构可逆性。锂化过程中会发生三步相变，伴随着大量缺陷、晶界和高达 202% 的体积膨胀的产生。在随后的脱锂过程中，Sn NPs 的体积、形态和结晶度恢复到初始状态。理论计算表明，压应力驱动去除脱锂过程中纳米颗粒内产生的空位，从而保持其完整的形态。这项工作表明，在循环过程中去除空位可以有效提高高容量负极材料的结构可逆性。