Electrochemical and In Situ Synchrotron XRD Studies on Al[sub 2]O[sub 3]-Coated LiCoO[sub 2] Cathode Material

Using a commercial available as starting material, surface-modified cathode material was obtained by coating its surface with a nanosize layer of amorphous Electrochemical performances and structural evolutions of the modified cathode material were characterized and compared with that of pristine Specific capacity of 190 mAh/g was obtained in -coated experimental cells when charged to 4.5 V. The relationship between the structural evolution and the electrochemical performances at overcharged state was investigated using in situ synchrotron X-ray diffraction (XRD). After charging the half-cell using uncoated as cathode, the variation of the c value in hexagonal structure is significantly reduced during subsequent cycles. This reduction in c variation range is concurrently related to the capacity fading. In contrast, the variation range of c is preserved in the -coated cathodes, and so is capacity. Based on these results, a capacity fading mechanism of -type cathode materials after overcharge is proposed, and an explanation of the surface coating effects is given.