Potassium-ion batteries (PIBs) have great potential in energy storage due to their high abundance and low cost of potassium resources. Tellurium (Te) is a promising PIB cathode due to its high volumetric capacity and good electronic conductivity. However, the electrochemical (de)potassiation mechanism of Te remains elusive due to the lack of an effective method of directly observing the dynamic reaction at atomic resolution. Here, the phase transformations of single crystal Te on (de)potassiation are clearly revealed by in situ high-resolution transmission electron microscopy and electron diffraction. Te undergoes a consecutive phase transformation during potassiation: from Te to K₂Te₃ in the initial potassiation, and then part of the K₂Te₃ to K₅Te₃ on further potassiation. The reaction has extremely high reversibility in the following depotassiation. By atomic-scale observation, an anisotropic reaction mechanism where K⁺ intercalates into Te crystalline lattice preferentially through the (001) plane (having a large d-spacing) is established during potassiation. While in the depotassiation process, K ions extract from the polycrystalline K_xTe along the same diffusion path to form single crystal Te, indicating the potassium storage is highly reversible. The strong orientation-dependent (de)potassiation mechanism revealed by this work provides implications for the future design of nanostructured cathodes for high-performance PIBs.

中文翻译：

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Te 纳米线中电化学（去）钾化的原位原子尺度观察

钾离子电池（PIBs）由于钾资源丰度高、成本低，在储能方面具有巨大潜力。碲 (Te) 是一种很有前途的 PIB 阴极，因为它具有高体积容量和良好的电子导电性。然而，由于缺乏以原子分辨率直接观察动态反应的有效方法，Te 的电化学（去）钾化机制仍然难以捉摸。在这里，通过原位高分辨率透射电子显微镜和电子衍射清楚地揭示了单晶 Te 在（去）钾化过程中的相变。Te 在钾化过程中经历了一个连续的相变：在初始钾化过程中从 Te 转变为 K ₂ Te ₃，然后是部分 K ₂ Te ₃进一步钾化至 K ₅ Te ₃。该反应在随后的去钾中具有极高的可逆性。通过原子尺度观察，钾化过程中建立了K ^{+优先通过（001）平面（具有大的}d-间距）插入Te晶格的各向异性反应机制。而在去钾过程中，K离子沿相同的扩散路径从多晶K _x Te中提取出来，形成单晶Te，表明钾的储存是高度可逆的。这项工作揭示的强取向依赖性（去）钾化机制为未来高性能 PIB 的纳米结构阴极设计提供了启示。