Local structure and composition studies of Li1.2Ni0.2Mn0.6O2 by analytical electron microscopy

Local Structure of Layered Oxide Electrode Materials for Lithium‐Ion Batteries

“…This arrangement results in a pile of thin platelets, each belonging to a different space group dictated by the local plane stacking sequence, which is revealed by low-magnification bright-field images (see Supporting Information) perpendicular to the bonds in the hexagonal planes (A 1 zone axis), but absent when the sample is viewed parallel to the bonds (A 2 zone axis). [9] Complementary information provided by SAED also points to a quasi-random stack of monoclinic unit cells. Figure 3b shows a SAED pattern corresponding to the HAADF image in Figure 3a.…”

“…The vertical spacing between two consecutive rows in the images corresponds Figure 1a and 1c consists of a periodic sequence of two bright spots and one dark spot, corresponding to the projection of LiMn 2 onto a sequence of two Mn-and one Li-atomic column with a spacing corresponding to the projected interatomic distance within hexagonal planes in Li 2 MnO 3 . Additionally, the overall geometry of the spot patterns, R or P, is indicative of the LiMn 2 plane stacking sequence, [9,20,27,28] as will be explained below.…”

“…[14] This fact, together with the cation configuration [LiMn 6 ] being the building block for Li 2 MnO 3 , poses the question of whether these compounds form homogeneous solid solutions or composite structures of intergrown Li 2 MnO 3 and LiTM Ã O 2 domains. [18] Since a LiTM Ã O 2 -like region in a Li 1þd (TM x Mn 1-x ) 1-d O 2 sample is not expected to show Li-ordering at TM-planes and therefore should not show a significant Z contrast, knowledge of the appearance of Li 2 MnO 3 can be used to scan HAADF images of Li 1þd (TM x Mn 1-x ) 1 Figure 3a-c. [9] Figure 3a is an aberration-corrected HAADF image of a Li 1 O 2 presents both R and P patterns within the field of view, indicating a high density of stacking faults within the a-sublattice, each of which represents a rotation of the local monoclinic sub-unit by AE1208 around the hexagonal plane normal. The small vertical size of these R and P meshes and the irregularity of the mesh sizes preclude the assignment of a single stacking sequence (i.e., overall crystal structure) throughout the field of view, but seem to indicate a quasi-random stacking of the (LiNiMn) planes based on an a-NaFeO 2 structure with a high density of stacking faults.…”

“…[2][3][4][5][6][7][8][9] These batteries typically contain several cells that are connected in series and/or in parallel to achieve the energy and power densities required by the applications. Both high-energy and highpower lithium-ion cells are being studied at Argonne as part of the U.S. Department of Energy's FreedomCar and Vehicle Technologies (FCVT) program.…”

“…[17] This electroactivity is probably associated with the material's defect chemistry, which is not well understood. Moreover, there is an ongoing debate in the literature on whether the Li 1þd (TM x Mn 1-x ) 1-d O 2 compounds form homogeneous solid solutions [18] [9] samples. The combination of selected area electron diffraction (SAED) and 0.1 nm STEM mode provided structural information down to the nanometer length scale, thus bridging the gap between other complementary techniques such as X-ray absorption spectroscopy (XAS) and nuclear magnetic resonance (NMR), which provide information on the few nearest neighbor environments of selected atoms, and X-ray diffraction (XRD), which reveals the long-range ordering of the atomic arrangement for all orientations present within a sample volume.…”