O 2‐Type Li2 / 3 [ Ni1 / 3Mn2 / 3 ] O 2: A New Layered Cathode Material for Rechargeable Lithium Batteries II. Structure, Composition, and Properties

Li 2/3 [Ni 1/3 Mn 2/3 ]O 2 is prepared from the corresponding P2-Na 2/3 [Ni 1/3 Mn 2/3 ]O 2 by ion exchange. This work investigates the correlation between structure, composition, and electrochemical properties. Crystalline Li 2/3 [Ni 1/3 Mn 2/3 ]O 2 is a layered oxide with the T2 structure. Small deviations from the Ni 1/3 Mn 2/3 stoichiometry cause less ordered samples showing T2-02 intergrowth structures. Larger deviations (Ni 0.25 Mn 0.75 ) or doping with 15% Co lead to stacking-faulted 02 structures instead of T2. Best electrochemical results are obtained if the sample has a slightly disordered T2 structure. The electrochemical properties of O2-Li 2/3 [Ni 1/3 Mn 2/3 ]O 2 are compared to those of related phases with the alternative 03 structure. Only 02-type Li x [Ni 1/3 Mn 2/3 ]O 2 can be cycled with little loss of capacity as a function of cycle number.