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–discharge process.

中文翻译：

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原位和异位^6,7 Li NMR光谱研究LiNi _0.5 Mn _1.5 O _4的去锂/锂化行为

通过使用原位（操作中）⁷ Li NMR和非原位⁶ Li MAS NMR光谱研究了有序尖晶石LiNi _0.5 Mn _1.5 O ₄和无序尖晶石LiNi _0.4 Mn _1.6 O _4的去锂和锂化行为。对有序尖晶石的原位⁷ Li监测显示出清晰的外观并随后从明确定义的相Li _0.5 Ni _0.5 Mn _1.5 O _4中消失了新信号，表明Li _1.0 Ni _0.5 Mn _1.5之间的两相反应过程O ₄，Li _0.5 Ni _0.5 Mn _1.5 O ₄和Li _0.0 Ni _0.5 Mn _1.5 O ₄。另外，对于无序尖晶石，发现在Li环境中分布广泛的Li _0.5 Ni _0.4 Mn _1.6 O ₄。还获得了去锂化和锂化样品的高分辨率⁶ Li MAS NMR光谱，以了解Li离子周围的详细局部结构。我们建议标称无锂相Li _0.0 Ni _0.5 Mn _1.5 O ₄可以在其结构中容纳少量的锂离子。当电池放电至2.0V时发生的四方相Li _2.0 Ni _0.5 Mn _1.5 O ₄和Li _2.0 Ni _0.4 Mn _1.6 O ₄在Li环境中彼此非常不同。发现^6,7 Li NMR不仅对LiNi _0.5 Mn _1.5 O _4中的Ni / Mn有序，而且对充放电过程中Ni和Mn的价态变化高度敏感。