LiCo1-yMyO2 positive electrodes for rechargeable lithium batteries.: II.: Nickel substituted materials grown by the citrate method

The layered LiCo1-yNiyO2 microcrystalline powders were synthesized by a sol-gel method using citric acid as a chelating agent in the range 0.2 <= y <= 0.8. Submicron-sized particles of the precursor were obtained at temperature below 400 degrees C and microcrystalline powders were grown by thermal treatment at 700 degrees C for 5 h in air. The carboxylic-based acid functioned such as a fuel, decomposed the homogeneous precipitate of metal complexes at low temperature, and yielded the free impurity LiCo1-yNiyO2 single-phases suitable for electrochemical applications. The synthesized products were characterized by structural, spectroscopic and thermal analyses. FT-IR measurements provide information on the growth process and the final local environment in the cationic sublattice of LiCo1-yNiyO2 solid solution. The electrochemical performance of the synthesized products in rechargeable Li cells was evaluated using non-aqueous solution I M LiPF6 in EC-DMC as electrolyte. The electrochemical features of a series of LiCo1-yNiyO2 compounds (0.2 <= y <= 1.0) are discussed in relation with their synthesis procedure and substitutive amount. The substitution of Ni3+ for Co3+ in LiCo1-yNiyO2 for y = 0.75 shows improvement of the specific capacity at ca. 187 mAh/g upon 32 cycles. (c) 2005 Elsevier B.V. All rights reserved.