Atomic Structure of Li2MnO3 after Partial Delithiation and Re-Lithiation.

Li₂MnO₃ is the parent compound of the well-studied Li-rich Mn-based cathode materials xLi₂MnO₃·(1- x)LiMO₂ for high-energy-density Li-ion batteries. Li₂MnO₃ has a very high theoretical capacity of 458 mA h g⁻¹ for extracting 2 Li. However, the delithiation and lithiation behaviors and the corresponding structure evolution mechanism in both Li₂MnO₃ and Li-rich Mn-based cathode materials are still not very clear. In this research, the atomic structures of Li₂MnO₃ before and after partial delithiation and re-lithiation are observed with spherical aberration-corrected scanning transmission electron microscopy (STEM). All atoms in Li₂MnO₃ can be visualized directly in annular bright-field images. It is confirmed accordingly that the lithium can be extracted from the LiMn₂ planes and some manganese atoms can migrate into the Li layer after electrochemical delithiation. In addition, the manganese atoms can move reversibly in the (001) plane when ca. 18.6% lithium is extracted and 12.4% lithium is re-inserted. LiMnO₂ domains are also observed in some areas in Li_1.63MnO₃ at the first cycle. As for the position and occupancy of oxygen, no significant difference is found between Li_1.63MnO₃ and Li₂MnO₃. [ABSTRACT FROM AUTHOR]