Layered metastable lithium manganese oxides, Li-2/3[Ni-1/3-Mn2/3-yMx+y]O-2 (x=y=1/36 for M=Al, Co. and Fe and x=2/36, y=O for M=Mg) were prepared by the ion exchange of Li for Na in P2-Na-2/3[Ni1/3-xMn2/3-yMx+y]O-2 precursors. The Al and Co doping produced the T(#)2 structure with the space group Cmca. On the other hand, the Fe and Mg doped samples had the 06 structure with space group R-3m. Electron diffraction revealed the 1:2 type ordering within the Ni1/3-xMn2/3-yMx+y O-2 slab. It was found that the stacking sequence and electrochemical performance of the Li cells containing T(#)2-Li-2/3[Ni1/3Mn2/3]O-2 were affected by the doping with small amounts of Al, Co, Fe, and Mg. The discharge capacity of the Al doped sample was around 200mAh g(-1) in the voltage range between 2.0 and 4.7V at the current density of 14.4 mAg(-1) along with a good capacity retention. Moreover, for the Al and Co doped and undoped oxides, the irreversible phase transition of the T(#)2 into the O-2 structure was observed during the initial lithium deintercalation. (C) 2008 Elsevier Ltd. All rights reserved.