The first discharge capacities of LiFeyMn2-yO4 (y = 0.0, 0.1, 0.25, 0.38 and 0.5) in a voltage range 3.5 V-4.3 V decrease as the value y increases, but the cycling performance improves. LiFe0.25Mn1.75O4 has the largest discharge capacity after 30 cycles and the best cycling performance. In the cyclic voltammograms the peaks for oxidation and reduction processes shift to the higher voltage side as the amount of substitution y increases. The samples with higher first discharge capacity ina voltage range 3.5 V-4.3 V have lower first discharge capacity in a voltage range 4.3 V-5.2 V. These two results show that the voltage range for intercalation and deintercalation shifts to the higher voltage side as the amount of substitution y increases.