Optimization of the Composition of the Li1 − z Ni1 + z O 2 Electrode Materials: Structural, Magnetic, and Electrochemical Studies

TLDR: In this paper, a quasi-2D LiNiO{sub 2}O and NiO was submitted to several thermal treatments, in order to determine the influence of the temperature on the composition.

Abstract: Lithium nickel oxide, used as the positive electrode in lithium batteries, crystallizes in the rhombohedral system (SG:R{bar 3}m) with a layered structure. In fact, stoichiometric LiNiO{sub 2} has never been reported. The true formula is Li{sub 1{minus}z}Ni{sub 1+z}O{sub 2} (0.00 < z < 0.20); z is dependent on the experimental conditions. This nonstoichiometry leads to a strong decrease of the battery performance. Therefore, several methods of preparation were investigated to synthesize stoichiometric LiNiO{sub 2}. The Li{sub 0.98}Ni{sub 1.02}O{sub 2} composition, which is very close to the ideal one, was obtained from a mixture of Li{sub 2}O and NiO heated at 700 C. This quasi-2D LiNiO{sub 2} was submitted to several thermal treatments, in order to determine the influence of the temperature on the composition. Purposely lithium deficient phases were also prepared. Correlations between the composition of each material (deduced from the Rietveld refinement of the X-ray diffraction pattern) and the magnetic and electrochemical behavior are discussed.