Structural variation of Li2MnO3 during charge-discharge cycling

The structural variation of Li2MnO3 during charge-discharge cycling as a lithium-battery cathode was investigated. The Rietveld refinement of neutron diffraction data revealed that the Li2MnO3 synthesized at 900 degrees C was assigned to the monoclinic symmetry corresponding to the C2/m space group (z = 4). The transmission electron microscopy (TEM) and high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) measurements were carried out using the samples after cycling in the potential ranges of 2.0-4.6, 2.0-4.8, and 2.0-5.0V. As a result, it was observed that structures based on the cubic (Fd (3) over barm) and rhombohedral (R (3) over barm) symmetries, having the compositions of LiMn2O4 and LiMnO2, respectively, are locally generated on the surface of the particles, depending on the upper voltage for the charge process. It was also found that the voltage at which the R (3) over barm rhombohedral structure is generated tended to be higher than the voltage at which the Fd (3) over barm cubic structure is formed. Such a structural variation of Li2MnO3 is anticipated to be related to the extraction of oxygen molecules which is induced during the charge processes. Furthermore, the generation of the R (3) over barm LiMnO2 could be understood by the introduction of oxygen vacancies into the material. (C) 2015 The Ceramic Society of Japan. All rights reserved.