期刊
ACS APPLIED MATERIALS & INTERFACES
卷 6, 期 2, 页码 1219-1227出版社
AMER CHEMICAL SOC
DOI: 10.1021/am404963u
关键词
phase transition; lithium manganese oxide; monoclinic; domain; oxygen vacancy; transmission electron microscopy; lithium-ion batteries
资金
- 973 Program [2011CB933300]
- National Natural Science Foundation of China [51071110, 51271134, 40972044, J1210061]
- China MOE NCET Program [NCET-07-0640]
- MOE Doctoral Fund [20090141110059]
- Fundamental Research Funds for the Central Universities
- China Postdoctoral Science Foundation [2013M540602]
- U.S. Department of Energy, the Assistant Secretary for Energy Efficiency and Renewable Energy, Office of Vehicle Technologies [DEACO298CH10886]
The powdered crystalline samples of nominal composition Li1.07Mn1.93O4-delta have been investigated by transmission electron microscopy (TEM) combined with X-ray powder diffraction (XRD) at room temperature. As suggested by the TEM observation, the dominant phase of the particles is a cubic spinel Li1+aMn2-alpha O4-delta with space group Fd3m. A monoclinic Li2MnO3 phase with C2/m space group was also identified. Furthermore, the occurrence of nanoscale rotational twinning domains in Li2MnO3 with 120 degrees rotation angles, stacked along the [103](m)/[111](c) (m and c represent the monoclinic and cubic descriptions, respectively) axis was also observed. These nanoscale rotational twining domains are responsible for the pseudo-3-fold axis and their formation is supported by the superstructure reflections in selected-area electron-diffraction (SAED) patterns. Similar patterns were reported in the literature but may have been misinterpreted without the consideration of such domains. Consistent with the TEM observation, the XRD results reveal the increasing percentage of monoclinic Li2MnO3 with increasing annealing time, associated with more oxygen vacancies. In addition, the electron beam irradiation during TEM studies may cause the nucleation of nanoscale cubic spinel Li-Mn-O crystallites on the monoclinic Li2MnO3 grains. These results provide the detailed structural information about the Li1.07Mn1.93O4-delta samples and advance the understanding of corresponding electrochemical properties of this material as well as other layer structured cathode materials for lithium-ion batteries.
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