Atomic Structure of Li 2 MnO 3 after Partial Delithiation and Re‐Lithiation

Li 2 MnO 3 is the parent compound of the well‐studied Li‐rich Mn‐based cathode materials x Li 2 MnO 3 ·(1‐ x )LiMO 2 for high‐energy‐density Li‐ion batteries. Li 2 MnO 3 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 Li 2 MnO 3 and Li‐rich Mn‐based cathode materials are still not very clear. In this research, the atomic structures of Li 2 MnO 3 before and after partial delithiation and re‐lithiation are observed with spherical aberration‐corrected scanning transmission electron microscopy (STEM). All atoms in Li 2 MnO 3 can be visualized directly in annular bright‐field images. It is confirmed accordingly that the lithium can be extracted from the LiMn 2 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. LiMnO 2 domains are also observed in some areas in Li 1.63 MnO 3 at the first cycle. As for the position and occupancy of oxygen, no significant difference is found between Li 1.63 MnO 3 and Li 2 MnO 3 .