Electron diffraction and high-resolution electron microscopy studies on layered Li2-δ(Mn1-xCox)1+δO3

The structure of Li2MnO3-LiCoO2 solid solutions or Li2-delta(Mn1-xCo5)(1+delta)O-3 (LMCO) which are promising lithium-battery cathodes was studied by high-resolution electron microscopy (HREM). X-ray diffraction (XRD) analyses indicate that Li1.6Mn0.2Co1.2O3 and Li1.7Mn0.4Co0.9O3 take a rhombohedral (R (3) over barm space group) structure, whereas Li1.85Mn0.7Co0.45O3 and Li1.95Mn0.9Co0.15O3 take a monoclinic (C2/m) super-structure. HREM studies on those samples reveal that all of the observed crystallites in sample Li1.95Mn0.9Co0.15O3 contain sharp stripe structures due to the planar defects along the c(h)-axis (stacking direction of the hexagonal close-packed planes) of parent rhombohedral Rim cell. Such stripe structures become faint with increasing x, Co content. The origin of the planar defects is mainly attributed not to the different structures but to the different local orientations of the monoclinic LMCO. Local disordering of Li and (Mn,Co) in (Li,Mn,Co) planes is developed with increasing x and the structures are transformed from C2/m to R (3) over barm. The alternative (Li,Mn,Co)-plane stacking structure, trigonal P3(1)12 LMCO, was occasionally observed. However, only P3(1)12 LMCO platelets with a thickness of a single unit cell were detected. (C) 2013 Elsevier Inc. All rights reserved.