High-temperature X-ray diffraction study of crystallization and phase segregation on spinel-type lithium manganese oxides
High-temperature X-ray diffraction study of crystallization and phase segregation on spinel-type lithium manganese oxides
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DOI：
10.1016/j.jssc.2009.11.008
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发表时间：
2010
影响因子：
3.3
通讯作者：
S. Komaba;N. Yabuuchi;S. Ikemoto
中科院分区：
文献类型：
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作者：
S. Komaba;N. Yabuuchi;S. Ikemoto
为研究尖晶石型Li 1 + xMn 2 − xO 4的晶化过程，以Li 2CO 3和Mn 2 O3为原料，在25-700°C温度范围内，利用原位高温X射线衍射技术（HT-XRD）研究了Li 1 + xMn 2 − xO 4的晶化过程。原位HT-XRD分析直接揭示了Li 1 + xMn 2 − xO 4的晶化过程受到前驱体中Li/Mn摩尔比的差异的显著影响。在700°C时形成了化学计量比的单相LiMn 2 O 4。随着前驱体中Li/Mn摩尔比的增加，在比化学计量样品更低的温度下实现了尖晶石的单相形成。化学计量LiMn 2 O 4在25°C时的晶格参数为8.24 Å，在700°C时扩展到8.31 Å，这对应于晶胞体积的约3%扩展。根据晶格参数随温度变化的斜率，计算出化学计量LiMn 2 O 4在该温度范围内的线性热膨胀系数为1.2×10−5°C− 1。当Li/Mn摩尔比增加（x > 0.1）时，尖晶石相在加热过程中发生分凝，形成Li 1 + yMn 2 − yO 4（x > y）和Li 2 MnO 3，这与材料中的氧损失有关。在从700°C冷却的过程中，分离的相合并成Li 1 + xMn 2 − xO 4并掺入氧。通过原位HT-XRD直接观察到的这种趋势通过热重分析作为在较高温度（500-700°C）下的可逆重量（氧）损失/增加而得到支持。
To study crystallization process of spinel-type Li1+xMn2−xO4, in-situ high-temperature X-ray diffraction technique (HT-XRD) was utilized for the mixture consisting of Li2CO3and Mn2O3as starting material in the temperature range of 25–700°C. In-situ HT-XRD analysis directly revealed that crystallization process of Li1+xMn2−xO4was significantly affected by the difference in the Li/Mn molar ratio in the precursor. Single phase of stoichiometric LiMn2O4formed at 700°C. The formation of single phase of spinel was achieved at the lower temperature than the stoichiometric sample as Li/Mn molar ratio in the precursor increased. Lattice parameter of the stoichiometric LiMn2O4at 25°C was 8.24Å and expanded to 8.31Å at 700°C, which corresponds to the approximately 3% expansion in the unit cell volume. From the slope of the lattice parameter change as a function of temperatures, linear thermal expansion coefficient of the stoichiometric LiMn2O4was calculated to be 1.2×10−5°C−1in this temperature range. When the Li/Mn molar ratio in Li1+xMn2−xO4increased (x > 0.1), the spinel phase segregated into the Li1+yMn2−yO4(x > y) and Li2MnO3during heating, which involved the oxygen loss from the materials. During the cooling process from 700°C, and the segregated phase merged into Li1+xMn2−xO4with oxygen incorporation. Such trend directly observed by in-situ HT-XRD was supported by thermal gravimetric analysis as reversible weight (oxygen) loss/gain at higher temperature (500–700°C).