Transmission electron microscopy investigation of the LiMn2O4/NaxMnO2 interface as a model study of a Na-ion battery electrode
Transmission electron microscopy investigation of the LiMn2O4/NaxMnO2 interface as a model study of a Na-ion battery electrode
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DOI：
10.1063/1.4968605
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发表时间：
2016-11-01
期刊：
影响因子：
1.6
通讯作者：
Kohyama, Masanori
中科院分区：
文献类型：
--
作者：
Kitta, Mitsunori;Akita, Tomoki;Kohyama, Masanori
通过钠插入-脱出循环从尖晶石 LiMn2O4 到层状岩盐 NaxMnO2 的相变对于钠离子电池中的 LiMn2O4 正极至关重要。为了揭示结构转换的原子尺度机制，我们将先进的分析电子显微镜技术应用于含钠的 LiMn2O4 样品，该样品是通过对含有 Na 杂质的薄 MnO 晶片进行锂化而形成的。扫描透射电子显微镜(STEM)-能量色散X射线能谱(EDX)和电子能量损失能谱(EELS)分析表明，Na和Li分别分布在样品的两相中，环形明场(ABF)-STEM观察证实它们是层状NaxMnO2和尖晶石LiMn2O4相。 Na和Li离子半径的巨大差异被认为是没有原子级混合的清晰相分离的原因。 EDX分析表明，具有P3结构的层状NaxMnO2相的Na成分表现出局部变化，最大值x=0.6。高分辨率透射电子显微镜（HRTEM）和ABF-STEM成像清楚地表明，外延LiMn2O4/NaxMnO2界面的形成没有任何晶格位错，然而，由于晶格失配，该界面具有较低的倾角，并且在NaxMnO2相中引起局部畸变。外延晶格转变表明尖晶石LiMn2O4晶体中具有层状结构的钠插入相的顺利生成，这应该有助于LiMn2O4电极在钠离子电池中的优越性。 (C) 2016 年作者。
The phase transformation from spinel LiMn2O4 to layered rock-salt NaxMnO2 via Na insertion-extraction cycles is crucial for a LiMn2O4 positive electrode in a Na-ion battery. To reveal the atomic-scale mechanism of the structural conversion, we applied advanced techniques of analytical electron microscopy to a Na-containing LiMn2O4 specimen, formed by lithiation of a thin MnO wafer containing Na impurity. Scanning transmission electron microscopy (STEM)-energy dispersive X-ray spectroscopy (EDX) and electron energy loss spectroscopy (EELS) analyses revealed that Na and Li are separately distributed in the two phases of the specimen, which are layered NaxMnO2 and spinel LiMn2O4 phases confirmed by annular bright field (ABF)-STEM observation. The large difference in the ionic radii of Na and Li is considered to be the reason for the clear phase separation without atomic-scale mixture. EDX analysis showed that the layered NaxMnO2 phase with P3 structure exhibits local variations in Na composition, with the maximum value of x = 0.6. High-resolution transmission electron microscopy (HRTEM) and ABF-STEM imaging clearly showed that an epitaxial LiMn2O4/NaxMnO2 interface is formed without any lattice dislocations, however, the interface has a low inclination angle due to the lattice mismatch, and local distortions are induced in the NaxMnO2 phase. The epitaxial lattice transition suggests smooth generation of a Na-inserted phase with a layered structure in a spinel LiMn2O4 crystal, which should contribute to the superiority of the LiMn2O4 electrode in a Na-ion battery. (C) 2016 Author(s).