Structural and Electronic State Changes of Spinel Oxides During Lithium Insertion and Extraction

用x射线衍射和电子自旋共振方法分析了尖晶石LiMn_2O_4中锂的插入和萃取过程。从这些分析可以看出，随着锂含量的降低，LiMn_2O_4变得不稳定。为了防止这种行为，本研究开发了一种新的尖晶石化合物。一般来说，尖晶石化合物有时在其结构中具有阳离子有序。这种阳离子的排序为晶体结构提供了一种稳定性。因此，锂萃取引起的LiMn_2O_4的不稳定性可以通过阳离子有序效应产生的稳定能来克服。在本研究中，我们制备了Li_<4/3>Mn_<5/3>O_4，它在16d位点具有正离子有序。在该化合物中，Li和Mn离子以规则的方式占据了16d个位点，这一点通过x射线衍射方法得到了证实。用x射线衍射和电化学方法分析了该锰化合物的结构和电子态变化。不同锂含量下的x射线衍射图无法区分，表明该超结构尖晶石的结构变化是无穷小的。这种结构行为就像一个理想的锂插入和提取材料。在恒流条件下，研究了电化学电位的变化。在插入和提取锂的过程中，电位没有变化。通常，电极电位随锂含量的变化而逐渐变化。所以，这种超结构尖晶石的电化学行为非常有趣。超结构尖晶石Ti （Li_<4/3>Ti_<5/3>O_4）也有相同的行为。因此，上层结构提供了一种从未在任何地方报道过的非常独特的特征。

An insertion and extraction of lithium into/from spinel LiMn_2O_4 were analyzed by X-ray diffraction and electron spin resonance methods. From these analyzes, it can be seen that LiMn_2O_4 become unstable with decreasing lithium content. In order to prevent such a behavior, a new spinel compound was developed in this study. In general, spinel compounds sometimes have a cation ordering in their structure. This cation ordering provides a stabilization to a crystal structure. Therefore, the unstableness of LiMn_2O_4 caused by a lithium extraction may be overcome by such a stabilization energy from the cation ordering effect. In this study, we prepared Li_<4/3>Mn_<5/3>O_4 which has a cation ordering at 16d sites. In this compound, Li and Mn ions occupied 16d sites in a regular manner, that was confirmed by X-ray diffraction method. The structural and electronic state changes of this Mn compound were analyzed by X-ray diffraction and electrochemical methods. The X-ray diffraction patterns at various lithium contents could not be distinguished, indicating that the structural change of this super structure spinel is infinitesimal. This structural behavior is like an ideal one for lithium insertion and extraction materials. The electrochemical potential change was also investigated under a galvanostatic condition. The potential did not change during the lithium insertion and extraction. Usually, the electrode potential changes gradually with changing lithium content. So, the electrochemical behavior of this super structure spinel is extremely interesting. The same behaviors were also observed for super structure spinel of Ti (Li_<4/3>Ti_<5/3>O_4) . Thus, the super structure provides a very unique characteristics which has never been reported anywhere.