Set forth herein are positive electrode active material compositions, e.g., lithium-rich nickel manganese cobalt oxides. The lithium-rich nickel manganese cobalt oxides set forth herein are characterized, in some examples, by an expanded unit cell which maximizes the uniform distribution of transition metals in the crystalline oxide. Also set forth herein are positive electrode thin films including lithium-rich nickel manganese cobalt oxide materials. Disclosed herein are novel and inventive methods of making and using lithium-rich nickel manganese cobalt oxide materials for lithium rechargeable batteries. Also disclosed herein are novel electrochemical devices which incorporate these materials.