Characterization of two phase distribution in electrochemically-lithiated spinel Li₄Ti₅O₁₂ secondary particles by electron energy-loss spectroscopy

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• 作者：Mitsunori Kitta ; ^{m-kitta@aist.go.jp} ; Tomoki Akita ; Shingo Tanaka ; Masanori Kohyama
• 关键词：Li ion battery ; Li4Ti5O12 ; Two-phase reaction mechanism ; Electron energy loss spectroscopy
• 刊名：Journal of Power Sources
• 出版年：2013
• 出版时间：1 September, 2013
• 年：2013
• 卷：237
• 期：Complete
• 页码：26-32
• 全文大小：1737 K

文摘

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 Li₄Ti₅O₁₂ and 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 Li₇Ti₅O₁₂ phase 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 Li₇Ti₅O₁₂ phase 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 Li₄Ti₅O₁₂ phase. 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.