Spinel LiMn2O4 was synthesized by a solid-state method. A 204468-size battery was fabricated and stored at 55℃. The structure and mor-phology of the LiMn2O4 cathode were analyzed by X-ray diffraction (XRD) and scanning electron microscopy (gEM) technique. Energy dispersive spectroscopy (EDS) was used to analyze the surface component of the carbon anode. The discharge capacities of LiMn2O4 stored for 0, 24, 48, and 96 h are 106, 98, 96, and 92 mAh-g-1, respectively. The cyclic performance is improved after storage. The capacity reten-tions of LiMn2O4 stored for 0, 24, 48, and 96 h are 83.8%, 85.8%, 86.9%, and 88.6% after 180 cycles. The intensity of all the LiMn2O4 dif-fraction peaks is weakened. Mn is detected from the carbon electrode when the battery is stored for 96 h. Cyclic voltammograms and elec-trochemical impedance spectroscopy (EIS) were used to examine the surface state of the electrode after storage. The results show that the re-sistance and polarization of LiMn2O4/electrolyte is increased after storage, which is responsible for the fading of capacity.