To investigate the electrochemical properties of LiMn2O4−x F x (0< x <1) as a cathode material for 4-V class lithium secondary batteries, spinel phases synthesized at 800°C are examined. Although the initial discharge capacity of LiMn2O4 is improved by substitution of F− for O2− in the single-phase region, the cycle performance is reduced considerably compared with that of parent LiMn2O4. X-ray diffraction (XRD) data show that the single-phase region of x in LiMn2O4−x F x is 0< x <0.2. A secondary phase (Mn2O3) is observed in the region 0.4< x <1.0. Voltammetric peaks between 3 and 4.5V region and XRD data suggest that the oxidation state of Mn in the parent LiMn2O4 increases at the expense of creating second phase (Mn2O3). These results also imply that a second phase spinel can improve the cycling performance of LiMn2O4 by suppressing the Jahn–Teller instability. The oxidation state of Mn in the single-phase spinel and the second-phase coexisting spinel is compared by means of XPS measurements. The electronic conductivity and activation energy of LiMn2O4 is also discussed.