A new series of cathode materials Li2+xMn0.91Cr1.09O4 (x = 0.7, 0.9, 1.1, and 1.3) was prepared from the reaction of Mn0.91Cr1.09O4 and LiOH . H2O by heat-treatment at 700 degrees C for 3, 6, and 12 h. The length of the heat-treatment significantly influenced the capacity, with longer heat-treatment times resulting in smaller capacities. Li3.1Mn0.91Cr1.09O4 phases heat-treated for 3 h showed the highest discharge capacity of 220 mAh/g at the 0.1 C rate (18 mA/g) cycled between 4.5 and 2 V. Tests of Li2+xMn0.91Cr1.09O4 in Li-ion cells (C/Li3.1Mn0.91Cr1.09O4) showed an initial capacity of 220 mAh/g at the 0.1 C rate, and relatively good rate capability from the 0.2 C to the 2 C rate between 4.5 and 2 V.