Synthesis, Characterization, and Electrochemical Performances of Substituted Layered Transition Metal Oxides. LiM1-yM'yO2. (M=Ni and Co. M'= B and AI)

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Abstract
The synthesis, characterization and electrochemical performances of lithiated nickelate and cobaltate doped with Al and B are reported. The synthesis involves solid state reaction between lithium hydroxide, nickel or cobalt oxides and several sources of aluminum and boron. Careful selection of precursors and heat treatment conditions are required to prepare single phase impurity free samples. X-ray diffraction and Rietveld refinement analysis indicate that the layered structure is preserved upon considerable substitution of aluminum and boron. X-ray diffraction line intensities and positions remained in good agreement with the space group. The IR spectra of the samples indicate formation of compressed CoO6 and NiO6, and elongated LiO6 octahedra. The IR vibrational mode of the LiO6 remains in the 200–300 cm-1 and the vibrational modes of the MO6 expand over 400–650 cm-1. Results of long charge-discharge cycling of the samples as cathode materials in lithium cells showed long cycle life. The capacity of the electrodes upon substitution were reduced almost linearly as the concentration of substitution was increased. The solubility limit for the formation of solid solutions upon substitution of Al and B in LiNiO2 and LiCoO2 was found to be around 25%. Specific capacities of the samples were between 120 to 160 mAh/g depending on the amount of substitution.