LiAlyCo1−yO2 (0.0≤y≤0.3) intercalation compounds synthesized from the citrate precursors

We present the synthesis, characterization and electrode behaviour of LiAlyCo1−yO2 (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 LiCoO2–LiAlO2 solid solution and have the layered α-NaFeO2 structure (R3̄m 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)O2 slabs. SEM micrographs show that the particle size of the LiAlyCo1−yO2 powders ranges in the submicronic domain with a narrow grain-size distribution. The overall electrochemical capacity of the LiAlyCo1−yO2 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//LiAl0.2Co0.8O2 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 LiAlyCo1−yO2 matrix. Differences and similarities between LiCoO2 and Al-substituted oxides are discussed therefrom.