Delithiation/Lithiation Behavior of LiNi0.5Mn1.5O4 Studied by In Situ and Ex Situ 6,7Li NMR Spectroscopy

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• 作者：Keiji Shimoda ; Miwa Murakami ; Hideyuki Komatsu ; Hajime Arai ; Yoshiharu Uchimoto ; Zempachi Ogumi
• 刊名：Journal of Physical Chemistry C
• 出版年：2015
• 出版时间：June 18, 2015
• 年：2015
• 卷：119
• 期：24
• 页码：13472-13480
• 全文大小：555K
• ISSN：1932-7455

文摘

Delithiation and lithiation behaviors of ordered spinel LiNi_0.5Mn_1.5O₄ and disordered spinel LiNi_0.4Mn_1.6O₄ were investigated by using in situ (in operando) ⁷Li NMR and ex situ ⁶Li MAS NMR spectroscopy. The in situ ⁷Li monitoring of the ordered spinel revealed a clear appearance and subsequent disappearance of a new signal from the well-defined phase Li_0.5Ni_0.5Mn_1.5O₄, suggesting the two-phase reaction processes among Li_1.0Ni_0.5Mn_1.5O₄, Li_0.5Ni_0.5Mn_1.5O₄, and Li_0.0Ni_0.5Mn_1.5O₄. Also, for the disordered spinel, Li_0.5Ni_0.4Mn_1.6O₄ was identified with a broad distribution in Li environment. High-resolution ⁶Li MAS NMR spectra were also acquired for the delithiated and lithiated samples to understand the detailed local structure around Li ions. We suggested that the nominal Li-free phase Li_0.0Ni_0.5Mn_1.5O₄ can accommodate a small amount of Li ions in its structure. The tetragonal phases Li_2.0Ni_0.5Mn_1.5O₄ and Li_2.0Ni_0.4Mn_1.6O₄, which occurred when the cell was discharged down to 2.0 V, were very different in the Li environment from each other. It is found that ^6,7Li NMR is highly sensitive not only to the Ni/Mn ordering in LiNi_0.5Mn_1.5O₄ but also to the valence changes of Ni and Mn on charge鈥揹ischarge process.