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

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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.