Layered Manganese Oxide Intergrowth Electrodes for Rechargeable Lithium Batteries. 1. Substitution with Co or Ni

Lithium manganese oxides substituted with nickel or cobalt were characterized electrochemically in lithium cell configurations. The compounds studied were either single-phase layered structures with either primarily O2 or O3 stacking arrangements, or O2/O3 intergrowths, prepared from P2, P3, and P2/P3 sodium-containing precursors, respectively. The stacking arrangements are extremely sensitive to the Na/TM (TM = transition metal) ratios and the level of substitution. Phase diagrams showing the stability regions of the various arrangements for the Na−Ni−Mn−O system are presented. A possible correlation between vacancies in the transition metal layers and electrochemical performance is suggested. For high levels of substitution with Ni, fewer defects are possible for materials containing more O3 component and higher discharge capacities can be achieved, but spinel conversion upon cycling also occurs more rapidly as the O3 content increases. Intergrowths show intermediate behavior and represent a potential route toward designing stable, high-capacity electrodes.