LiAl yCo 1− yO 2 (0.0≤ y≤0.3) intercalation compounds synthesized from the citrate precursors

Abstract

We present the synthesis, characterization and electrode behaviour of LiAl y Co 1− y O 2 (0.0≤ y≤0.3) oxides prepared by the citrate route. The phase evolution was studied as a function of the aluminium substitution and the modification on the intercalation and deintercalation of Li ions. Characterization methods include X-ray powder diffraction (XRD), thermogravimetry analysis (TG–DTA), scanning electron microscopy (SEM), Raman scattering (RS) and Fourier transform infrared (FTIR) spectroscopy. Samples belong to the LiCoO 2–LiAlO 2 solid solution and have the layered α-NaFeO 2 structure ( R 3 ̄ m space group). Raman scattering and FT-infrared vibrational spectroscopies indicate that the vibrational mode frequencies and relative intensities of the bands are sensitive to the covalency of the (Co, Al)O 2 slabs. SEM micrographs show that the particle size of the LiAl y Co 1− y O 2 powders ranges in the submicronic domain with a narrow grain-size distribution. The overall electrochemical capacity of the LiAl y Co 1− y O 2 oxides have been reduced due to the sp metal substitution, however, a more stable charge–discharge cycling performances have been observed when electrodes are charged up to 4.3 V as compared to the performance of the native oxide. For such a cut-off voltage, the charge capacity of the Li//LiAl 0.2Co 0.8O 2 cell is ca. 118 mAh g −1. Kinetics were characterized by the galvanostatic intermittent titration technique (GITT). Aluminium substitution provides an increase of the chemical diffusion coefficients of Li + ions in the LiAl y Co 1− y O 2 matrix. Differences and similarities between LiCoO 2 and Al-substituted oxides are discussed therefrom.