Layered sodium manganese bronzes having the P2 structure (Nau(2/3)[Li1/6Mn5/6]O-2), were used to prepare layered lithium manganese oxides by ion exchange of Na by Li using LiBr in hexanol. X-ray diffraction and chemical analysis show that layered Li-2/3[Li1/6Mn5/6]O-2 has an O2 type structure. The arrangement of manganese and oxygen atoms in this phase differs fundamentally from that found in layered LiMnO2 (O3 structure), in orthorhombic LiMnO2, and in spinel Li2Mn2O4 so that conversion to spinel during electrochemical cycling is not expected. Li-2/3[Li1/6Mn5/6]O-2 as well as the related Li-2/3[Li1/18Mn17/18]O-2 and Li-2/3[Mn0.85Co0.15]O-2 have a reversible charge capacity of about 150 mAh/g. During cycling the new cathode materials do not convert to spinel, in contrast to the behavior of layered and orthorhombic LiMnO2.