Influence of aluminum doping on the properties of LiCoO2 and LiNi0.5Co0.5O2 oxides

We have prepared LiCo1-yAlyO2 and LiNi0.5-yAlyCo0.5O2 (0 less than or equal to y less than or equal to 0.3) powder samples by a low temperature sol-gel method using succinic acid as chelating agent. We have studied the details of their crystallographic and local structure by X-ray diffraction (XRD) and FTIR spectroscopy, respectively; we have analyzed their chemical composition by ICP and obtained information about the morphology of the polycrystalline particles by SEM. Also, we have studied the electrochemical performance of the as-prepared materials in the Li//LiNi0.5-yAlyCo0.5O2 cells cycled in the potential range 2.5-4.2 V finding that the overall capacity of the oxides has been reduced due to the metal substitution. For example, at 4.2 V cut-off, the charge capacity of the Li//LiNi0.35Al0.15Co0.5O2 cell is ca. 115 mA h/g. However, more stable charge-discharge cycling performances have been obtained as compared to those displayed by the native oxides. Finally, we have characterized the kinetics of Li-diffusion by the galvanostatic intermittent titration technique and, according to our results, Al substitution provides an increase in the chemical diffusion coefficients of Li ions in the LiNi0.5-yAlyCo0.5O2 matrix. (C) 2003 Elsevier Science B.V. All rights reserved.