Well-defined o-LiMnO2 cathode materials were synthesized by quenching method at 1050°C in an argon flow. The synthesized LiMnO2 particle was characterized by X-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM). LiMnO2/solid polymer electrolyte (SPE)/Li batteries were characterized electrochemically by charge/discharge experiments, cyclic voltammetry (CV) and ac impedance spectroscopy. The charge/discharge results show that the discharge capacities of LiMnO2 are 62mAhg−1 at the first cycle and 124mAhg−1 after 70 cycles, respectively. Moreover, we evaluated batteries using liquid electrolyte and SPE. From the charge/discharge results, the discharge capacity of LiMnO2/SPE/Li battery is greater than that of LiMnO2/Li battery with liquid electrolyte.