Structural stability of Na-inserted spinel-type sodium titanium oxide
Structural stability of Na-inserted spinel-type sodium titanium oxide
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插钠尖晶石型钠钛氧化物的结构稳定性
DOI：
10.1016/j.jallcom.2020.157211
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发表时间：
2021
影响因子：
6.2
通讯作者：
Shingo Tanaka
中科院分区：
文献类型：
--
作者：
M. Kitta;R. Kataoka;T. kojima;K. Tada;Shingo Tanaka
尖晶石型钠钛氧化物（Na 3LiTi 5 O 12，NTO）具有与Li 4 Ti 5 O 12（LTO）类似的结构，可作为钠离子电池负极的单相材料。基于其与LTO反应机理的相似性，可实现上级Na插入和提取循环性能。然而，NTO材料在Na插入状态下的详细结构仍然不清楚。因此，Na插入机制的晶体学特征尚未得到充分阐明。在这项研究中，NTO和钠插入NTO（Na-NTO）电极的结构分析进行了通过X射线衍射和Rietveld精修。通过电化学钠插入反应，NTO尖晶石晶格的钠占据位置从氧四面体变为八面体。NTO和Na-NTO的晶格常数分别为aNTO = 8.73 Ω和aNa-NTO = 8.84 Ω，Na的插入证实了NTO和Na-NTO的晶格膨胀约为1%，这是由于NTO中Ti-O原子间距的局部压缩和Na-NTO中Ti-O原子间距的弛豫引起的.值得注意的是，NTO中的Ti-O原子距离非常不均匀，值为1.8 μ m和2.2 μ m，而Na-NTO晶格中的Ti-O原子距离均匀化为2.0 μ m、2.1 μ m和2.2 μ m。此外，NTO晶格中的氧位置被修改以通过Na插入来增强晶格对称性，类似于LTO晶格的Li插入反应。因此，Na-NTO晶格结构比NTO晶格稳定得多，这保证了NTO材料对于Na离子电池利用的稳定的Na插入和提取循环性能。
Spinel-type sodium titanium oxide (Na3LiTi5O12, NTO), which has an analogous structure to Li4Ti5O12(LTO), is prepared as a single-phase material for the negative electrode of Na-ion batteries. A superior Na insertion and extraction cycle performance is achievable based on its similarity with the LTO reaction mechanism. However, the detailed structure of the NTO material in the Na insertion state remains obscure. Consequently, the crystallographic features of the Na insertion mechanism have not been sufficiently elucidated. In this study, the structural analyses of NTO and Na-inserted NTO (Na-NTO) electrodes were performed via X-ray diffraction and Rietveld refinement. The Na occupation site of the NTO spinel lattice was altered from the oxygen tetrahedral to the octahedral site by the electrochemical Na insertion reaction. The lattice constants of NTO and Na-NTO were refined foraNTO= 8.73 Å andaNa-NTO= 8.84 Å; approximately 1% lattice expansion, which was caused by the local compressions of the Ti–O atomic distance existing in the NTO and their relaxation in the Na-NTO, was confirmed by Na insertion. Notably, Ti–O atomic distances in NTO are quite heterogeneous with values of 1.8 Å and 2.2 Å, while they are homogenized to 2.0 Å, 2.1 Å, and 2.2 Å in the Na-NTO lattice. Furthermore, the oxygen position in the NTO lattice is modified to enhance lattice symmetry by Na insertion, similar to the Li insertion reaction of the LTO lattice. Thus, the Na-NTO lattice structure is considerably more stable than the NTO lattice, which promises stable Na insertion and extraction cycle performances for NTO materials toward Na-ion battery utilization.