LiMn2-y-zLiyNizO4 (0 less than or equal to y less than or equal to 0.075 and 0 less than or equal to z less than or equal to 0.075) cathodes have been synthesized by two procedures at 800degreesC in air: (1) standard solid state reactions of Li2CO3, Mn2O3 and NiO (oxide method) and (2) reaction of a Lisimilar to0.5MnO2 precursor supplied by a commercial firm with lithium and nickel hydroxides (precursor method). The samples have been characterized by X-ray diffraction, surface area, manganese dissolution, scanning electron microscopy, and electrochemical charge-discharge measurements. The co-substituted LiMn2-y-zLiyNizO4 (0.04 less than or equal to y less than or equal to 0.075 and 0.05 less than or equal to z less than or equal to 0.075) samples obtained by both the oxide and precursor methods exhibit superior capacity retention, rate capability, and storage characteristics compared to both LiMn2O4 and LiMn1.97Li0.03O4. While the rate capability and storage characteristics of the LiMn2-y-zLiyNizO4 samples do not differ significantly between the two synthesis procedures, the samples obtained by the precursor method exhibit slightly better capacity retention despite a higher amount of manganese dissolution than the samples obtained by the oxide method. The differences are attributed to the larger and more uniform size of the secondary particles and smaller primary particles of the former compared to those of the latter. (C) 2003 Elsevier B.V. All rights reserved.