Surface chemistry study of LiCoO2 coated with alumina

The surface chemistry of the Al2O3-coated LiCoO2 prepared under heat treatment at 80-800 degrees C was studied by SEM, XRD, IR, XPS and NMR spectroscopy combined with electrochemical testing. It is shown that the particle bulk is free from dopant. XPS Al2s core-level spectrum of the coated LiCoO2 differs from that of alpha-Al2O3 and is associated with Al oxyhydroxide. Al-27 NMR spectra of the samples prepared at 80-600 degrees C consist of intensive asymmetric peak with maximum at 4.8-6.2 ppm (Al in an octahedral coordination free from Co in the second coordination sphere) and two less intensive ones at similar to 55-56 and similar to 61-62 ppm. On the other hand, the spectrum of the 800 T sample has no peak near 0 ppm, but has a series of peaks in the range of 26-62 ppm with an interval of about 7 ppm, characteristic of Al octahedral environment with neighboring Al number ranging from 6 to 0. This indicates that the shell consists mostly of amorphous oxyhydroxide in the first case and of LiCo1-yAlyO2 solid solution in the second. Electrochemical testing shows a significant increase in discharge capacity (> 150 mAh/g) and improved cyclability of the coated samples heated below 600 degrees C, while after heat treatment at 800 degrees C the capacity of composite cathode fades quickly. (C) 2008 Elsevier B.V. All rights reserved.