Nanoparticulate electrodes, such as Li _x FePO₄, have unique advantages over their microparticulate counterparts for the applications in Li-ion batteries because of the shortened diffusion path and access to nonequilibrium routes for fast Li incorporation, thus radically boosting power density of the electrodes. However, how Li intercalation occurs locally in a single nanoparticle of such materials remains unresolved because real-time observation at such a fine scale is still lacking. We report visualization of local Li intercalation via solid-solution transformation in individual Li _x FePO₄ nanoparticles, enabled by probing sub-angstrom changes in the lattice spacing in situ. The real-time observation reveals inhomogeneous intercalation, accompanied with an unexpected reversal of Li concentration at the nanometer scale. The origin of the reversal phenomenon is elucidated through phase-field simulations, and it is attributed to the presence of structurally different regions that have distinct chemical potential functions. The findings from this study provide a new perspective on the local intercalation dynamics in battery electrodes.

中文翻译：

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嵌入纳米颗粒过程中锂的局部浓度逆转。

纳米粒子电极（例如Li _x FePO _4）在锂离子电池中的应用比其微粒对手具有独特的优势，这是因为缩短了扩散路径并可以通过非平衡途径快速掺入锂，从而从根本上提高了电极的功率密度。然而，由于仍缺乏如此精细规模的实时观察，尚未解决如何在这种材料的单个纳米颗粒中局部发生Li嵌入的问题。我们报告了通过单个Li _x FePO _4中的固溶体转化实现的局部Li嵌入的可视化 通过探测原位晶格间距的亚埃变化而实现的纳米颗粒。实时观察显示不均匀的插层，并伴随着纳米级Li浓度的意外反转。反转现象的起源通过相场模拟得以阐明，并且归因于存在具有不同化学势功能的结构不同区域。这项研究的发现为电池电极中的局部嵌入动力学提供了新的视角。