Surface modification of LiNi_0.5Mn_1.5O₄ cathodes with ZnAl₂O₄ by a sol-gel method for lithium ion batteries

The 5 V spinel LiNi_0.5Mn_1.5O₄ 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 ZnAl₂O ₄-coated LiNi_0.5Mn_1.5O₄ 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.