A long and irreversible plateau is observed for Li-1.12(Ni0.425Mn0.425Co0.15)(0.88)O-2. The layered Li-y(Ni0.425Mn0.425Co0.15)(0.88)O-2 (y=0.93 and 0.73) materials were prepared by discharging to 3.2 V Li//Li-y(Ni0.425Mn0.425Co0.15)(0.88)O-2 cells charged up to 4.4 V (beginning of the plateau) and 4.8 V (end of the plateau), respectively. The structure was investigated using the combination of X-ray and electron diffraction experiments to study a possible structural evolution upon cycling of the superstructure observed for the pristine material. The disappearance of the superlattice lines in the 19.5-34 degrees (2 theta(Cu)) range in the X-ray diffraction pattern as well as that of the diffuse disorder scattering lines (or the extra spots) in the electron diffraction patterns were clearly observed for Li-0.73(Ni0.425Mn0.425Co0.15)(0.88)O-2. These results revealed the loss of the root 3 center dot a(hex.)x root 3 center dot a(hex.) superstructure and thus of the cation ordering within the slabs when the Li//Li-1.12(Ni0.425Mn0.425Co0.15)(0.88)O-2 cells are charged to the end of the plateau. Moreover, other new diffuse disorder scattering lines were observed along the c(*) axis itself for the Li-0.73(Ni0.425Mn0.425Co0.15)(0.88)O-2 material that has seen the plateau, which were attributed to local interslab space thickness variations.