The 5V spinel LiNi0.5Mn1.5O4 cathodes have been surface-modified with ZnAl2O4 by a sol–gel method and characterized by X-ray diffraction, high-resolution transmission electron microscopy, and electrochemical measurements. Although the pristine electrode experienced the prominent degradation after the storage test at 60°C in the intervals of cycling test at room temperature, the ZnAl2O4-coated LiNi0.5Mn1.5O4 cathode exhibited the significant capacity retention even after storing at elevated temperatures. The X-ray photoelectron spectroscopy data reveals that the improved electrochemical performances of surface-coated cathode are mostly due to the suppressed side reaction between the cathode and the electrolyte especially at the high-temperature environment. Differential scanning calorimetry showed that the decreased heat evolution could be found with the surface-modified cathode. Our experimental findings suggest a direction to the further development of cathode materials which are endurable to the highly oxidized state and high-temperature environment.