Characterization of two phase distribution in electrochemically-lithiated spinel Li4Ti5O12 secondary particles by electron energy-loss spectroscopy
Characterization of two phase distribution in electrochemically-lithiated spinel Li4Ti5O12 secondary particles by electron energy-loss spectroscopy
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DOI：
10.1016/j.jpowsour.2013.03.022
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发表时间：
2013-09
影响因子：
9.2
通讯作者：
M. Kitta;T. Akita;Shingo Tanaka;M. Kohyama
中科院分区：
文献类型：
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作者：
M. Kitta;T. Akita;Shingo Tanaka;M. Kohyama
尖晶石钛酸锂，Li4Ti5O12（LTO）作为锂离子电池中碳基阳极的替代材料，由于其高倍率性能以及耐用性和安全性而备受关注。尖晶石li4ti5o12和岩盐Li7Ti5O12两相在充放电反应中的共存是理解反应机理和开发性能更高的LTO电极的关键问题。然而，由于难以以高分辨率识别插入li的li7ti5o12相，实际LTO电极中的两相分布形貌尚未报道。因此，我们采用最新的高能量和空间分辨率的扫描透射电子显微镜与电子能量损失光谱（STEM-EELS）。与li4ti5o12相相比，通过EELS分析Li组成、Ti氧化态和氧原子周围的局部构型，我们成功地确定了li7ti5o12相在Li插入LTO二次粒子中的存在。我们还获得了50% li -insert LTO二次粒子的两相分布图像，其中两相的分离存在被清楚地揭示出来。这表明了粒子间的反应机理，其中速率决定过程存在于初级粒子之间的边界。
Spinel lithium titanate, Li4Ti5O12(LTO) is attracting much attention as an alternative material replacing carbon based anodes in lithium ion batteries, due to its high rate properties as well as its durability and safety. The coexistence of the two phases, spinel Li4Ti5O12and rock salt Li7Ti5O12, during the charge–discharge reactions is the key issue for the understanding of reaction mechanism and the development of LTO electrodes with improved performance. However, the two-phase distribution morphology in real LTO electrodes has not yet been reported, due to the difficulty in identifying the Li-inserted Li7Ti5O12phase with high resolutions. Thus we apply the scanning transmission electron microscopy with electron energy loss spectroscopy (STEM–EELS) using the latest equipment with high energy and spatial resolutions. We have successfully identified the presence of the Li7Ti5O12phase in Li-inserted LTO secondary particles, by the EELS analysis of Li composition, Ti oxidation state, and local configurations around oxygen atoms, compared to the Li4Ti5O12phase. We have also obtained the two-phase distribution image in 50% Li-inserted LTO secondary particles, where separate presence of both the phases is clearly revealed. This indicates the particle-by-particle reaction mechanism, where the rate determining process exists in the boundary between primary particles.