O[sub 2]-Type Li[sub 2/3][Ni[sub 1/3]Mn[sub 2/3]]O[sub 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 P 2 ‐ 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‐O2 intergrowth structures. Larger deviations ( Ni 0.25 Mn 0.75 ) or doping with 15% Co lead to stacking‐faulted O2 structures instead of T2. Best electrochemical results are obtained if the sample has a slightly disordered T2 structure. The electrochemical properties of O 2 ‐ Li 2 / 3 [ Ni 1 / 3 Mn 2 / 3 ] O 2 are compared to those of related phases with the alternative O3 structure. Only O2‐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. © 2000 The Electrochemical Society. All rights reserved.