This paper reports a spinel-type LiMn2O4/carbon nanotube (CNT) composite cathode material with high electrochemical performance for energy storage applications. The composite material is prepared by hydrothermal reaction between birnessite MnO2/multiwalled carbon nanotube (MWCNT) composite and LiOH solution, followed by heat treatment at 700 °C in air atmosphere, where the MnO2/MWCNT precursor is obtained by in situ redox reaction between KMnO4 solution and MWCNTs. The heat treated LiMn2O4/CNT composite material consists of well-crystallized spinel LiMn2O4 with small amount of enwrapped segmented carbon nanotubes, which is confirmed by X-ray diffraction and transmission electron microscopy. Electrochemical experimental results demonstrate that the LiMn2O4/CNT composite material heat treated for 8 h exhibits high specific capacity and excellent high-rate capability in 5 M LiNO3 aqueous electrolyte. The (LiMn2O4/CNT)/5 M LiNO3/activated carbon hybrid supercapacitor with this LiMn2O4-based composite material as the cathode presents excellent high-power capability and good charge/discharge cyclability.