Two series of Mg substituted and F substituted nickelates were prepared, among them Li1-zNi1+zFyO2-y (y = 0.015, z = 0.06) and Li1-z(MgxNi1-x)(1+z)O-2 (x = 0.05, z = 0.08) have shown improved cycling performance compared to un-substituted LiNiO2. Cyclic voltametry (CV), quasi open circuit voltage (QOCV) measurements, and X-ray. diffraction all indicate that phase transitions in the charge and discharge reactions are partially suppressed after F or Mg substitution. Excessive substitution, however, results in reduced capacity acid the lack of electrochemical activity. For Li1-zNi1+zFyO2-y this is explained by the increasing presence of divalent nickel ions at the lithium 3b sites. For Li1-z(MgxNi1-x)(1+z)O-2, the presence of Mg ions at the lithium sites is more likely the reason.