The capacity loss behaviors of $LiMn_2O_4$ and $LiMn_{1.9}Zn_{0.1}O_4$ prepared by solid state reaction were investigated by cycling experiment with giving various cut-off discharge voltage in 1M $LiClO_4$ propylene carbonate(PC) solution. $LiMn_2O_4$ prepared by emulsion drying method was also investigated by same method. These powder specimens were identified as cubic spinel structure with space group Fd3m by X-ray diffractometry. From the Rietveld refinement result of $LiMn_{1.9}Zn_{0.1}O_4$, it was concluded that the substituted Zn locates in 16d octahedral site of $LiMn_2O_4$ lattice. Composite cathode was charge/discharge cycled in the potential range of cut-off discharge voltage to 4.5V (vs. Li/$Li^+$). Cut-off discharge voltages were 4.0, 3.85 and 3.2V. $LiMn_2O_4$ and $LiMn_{1.9}Zn_{0.1}O_4$ prepared by solid state reaction showed largest capacity loss in low-voltage region of 4V plateau. $LiMn_2O_4$ prepared by emulsion drying method showed largest capacity loss in high-voltage region of 4V plateau. From these results, it could be concluded that the capacity loss behavior of cathode material is related to making process. All XRD pattern of cathode taken after experiment showed no tetragonal spinel phase and it could be concluded that Jahn-Teller distortion doesn't affect the capacity loss in 4V plateau. Small initial capacity of $LiMn_2O_4$ and $LiMn_{1.9}Zn_{0.1}O_4$ prepared by solid state reaction were thought to have relation to severe XRD pattern change.
