The synthesis, characterization and electrochemical behavior of the layered LiNi0.4Mn0.4Co0.2O2 compound

The mixed transition metal layered compound, LiNi0.4Mn0.4Co0.2O2, with the alpha-NaFeO2 layer structure has been synthesized and characterized. The optimum temperature of synthesis was found to be 800 - 900 degreesC. Rietveld refinement showed that cobalt suppresses transition metal ion migration into the Li sites whereas nickel promotes the migration. XPS analysis shows that the Co and about 20% of the Ni and Mn are in the 31 oxidation state, while 80% of the Ni and Mn are in the 21 and 41 oxidation states, respectively. LiNi0.4Mn0.4Co0.2O2 shows Curie - Weiss paramagnetic behavior above 150 K, and the value of the Curie constant is consistent with the above oxidation states. In lithium electrochemical cells the composition LiNi0.4Mn0.4Co0.2O2 gave the highest reversible capacity among the studied compositions. It shows excellent rate capability, giving reversible capacities ranging from 180 to 155 mA h g(-1) at current densities from 0.1 to 2.0 mA cm(-2).