Layered Li-Mn-oxide with the O2 structure : A cathode material for Li-ion cells which does not convert to spinel

Layered sodium manganese bronzes having the P2 structure (Na{sub 2/3}[Li{sub 5/6}]O{sub 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{sub 2/3}[Li{sub 1/6}Mn{sub 5/6}]O{sub 2} has an O2 type structure. The arrangement of manganese and oxygen atoms in this phase differs fundamentally from that found in layered LiMnO{sub 2}(O3 structure), in orthorhombic LiMnO{sub 2}, and in spinel Li{sub 2}Mn{sub 2}O{sub 4} so that conversion to spinel during electrochemical cycling is not expected. Li{sub 2/3}[Li{sub 1/6}Mn{sub 5/6}]O{sub 2} as well as the related Li{sub 2/3}[Li{sub 1/18}Mn{sub 17/18}]O{sub 2} and Li{sub 2/3}[Mn{sub 0.85}Co{sub 0.15}]O{sub 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 LiMnO{sub 2}.