LiMn2-2yLiyNiyO4 ( 0.05 less than or equal to y less than or equal to 0.1) cathodes synthesized by solid-state reactions at 800 degreesC exhibit superior capacity retention and rate capability both at room temperature and 60 degreesC compared to the LiMn2O4 cathodes. For example, the y = 0.05, 0.075, and 0.1 samples exhibit little capacity fades of, respectively, 3.2, 0.9, and 0.5% at room temperature and 7.4, 2.6, and 2.4% at 60 degreesC in 50 cycles with initial capacities of around 90-115 mAh/g compared to around 40-50% fade for LiMn2O4. The y = 0.075 and 0.1 samples retain 98% of their capacity on going from C/10 to 4C rate with excellent cycling performance at 4C rate as well. The superior performances of these cathodes are attributed to the smaller lattice parameter differences between the two cubic phases formed during the discharge/charge process. The low cost and environmentally benign nature of these cathodes coupled with the high rate capability may make them attractive for electric vehicles despite slightly lower capacity values. (C) 2002 The Electrochemical Society.