The Syntheses and Characterization of Layered LiNi_1-y-zMn_yCo_zO₂ Compounds

The layered compounds of formula LiNi0.4Mn0.6-yCoyO2, for y=0.2, 0.3, and 0.4 and LiNi0.7-yMn0.3CoyO2 for y=0.3, and 0.1 were synthesized at 800°C. X-ray powder diffraction indicates layered structure of R 3m symmetry similar to a-NaFeO2. Rietveld refinement data shows that Mn and Ni increase the tendency of transition metal ions to migrate into the interlayer sites relative to LiCoO2. Both magnetic susceptibility and XPS data support a 2+ oxidation state for Ni and 4+ and 3+ for Mn and Co, respectively. The layered compound LiNi0.4Mn0.4Co0.2O2 shows a high initial capacity of about 200mAh/g when cycled between 2.5V and 4.3 V at 20°C.