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An in situ structural study on the synthesis and decomposition of LiNiO2†
Journal of Materials Chemistry A ( IF 10.7 ) Pub Date : 2019-12-24 , DOI: 10.1039/c9ta12073d
Matteo Bianchini 1, 2, 3, 4, 5 , François Fauth 6, 7, 8 , Pascal Hartmann 1, 2, 3, 4, 5 , Torsten Brezesinski 1, 2, 3, 4, 5 , Jürgen Janek 1, 2, 3, 4, 5
Affiliation  

The electrification trend in the automotive industry is fueling research on positive electrode materials with high specific capacities. The nickel content in such layered oxide systems is continuously increasing, and so is the importance of LiNiO2 (LNO). Despite decades of research, LNO still exhibits properties, closely related to its instability, that require better understanding. One of these is the difficult solid-state synthesis that never seems to yield LNO samples of perfect stoichiometry. At present, improved experimental capabilities allow for investigating the synthesis process in unprecedented detail. Here, we leverage synchrotron X-ray diffraction, carried out in situ during calcination and decomposition of LNO at high temperature, to reveal the evolution of precursor materials during solid-state synthesis. We evaluate the effect of pre-annealing the hydroxide precursors’ mixture at low temperature, prior to the actual calcination at 700 °C. We then show that LNO formation is a structurally complex process, beginning from LNO seeds with a compressed rhombohedral unit cell (c/a < 4.9) within the rock salt framework. We identify a key aspect in the presence of Ni vacancies in Ni slabs, creating space for cation migration and allowing for the material's layering. We also investigate the decomposition of LNO, since it can be seen as the reverse process of synthesis. In fact, beginning already at 700 °C, it is in a way a byproduct of the synthesis. We correlate the change in stoichiometry with the unit cell volume of LNO and show how permanent damage is done to it by even a short time at too low O2 chemical potential. Taken together, this work aims at providing insights that may be of help in optimizing the synthesis of LNO while minimizing decomposition effects. Moreover, the same information can be seen as a starting point to further studies on Ni-rich (doped) compositions of practical interest.

中文翻译:

一个原位上的LiNiO的合成和分解的结构研究2

汽车工业的电气化趋势推动了高比容量正极材料的研究。在这种层状氧化物体系中,镍含量不断增加,因此,LiNiO 2(LNO)的重要性也不断提高。尽管进行了数十年的研究,但LNO仍具有与其不稳定性密切相关的特性,需要更好地了解。其中之一是困难的固态合成,似乎从未产生出理想化学计量的LNO样品。目前,改进的实验能力允许对合成过程进行前所未有的详细研究。在这里,我们利用原位进行的同步加速器X射线衍射在高温下煅烧和分解LNO的过程中,揭示了固态合成过程中前驱物材料的演化。我们评估了在700°C实际煅烧之前,在低温下对氢氧化物前体混合物进行预退火的效果。然后,我们表明,LNO的形成是一个结构复杂的过程,从带有压缩菱形六面体晶胞(c / a<4.9)。我们确定了镍平板中存在镍空位的关键方面,为阳离子迁移创造了空间并允许了材料的分层。我们还研究了LNO的分解,因为它可以看作是合成的逆过程。实际上,它已经从700°C开始,在某种程度上是合成的副产物。我们将化学计量的变化与LNO的晶胞体积相关联,并显示即使在太低的O 2下短时间对它的永久性损害化学势。综上所述,这项工作旨在提供一些见解,这些见解可能有助于优化LNO的合成,同时最大程度地降低分解效果。此外,相同的信息可以看作是对具有实际意义的富镍(掺杂)成分进行进一步研究的起点。
更新日期:2020-01-04
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