Nickel-based positive electrode active material, method of preparing the same, and lithium battery using the nickel-based positive electrode active material

A secondary lithium battery comprising:

• a positive electrode comprising a positive electrode active material comprising lithium nickel complex oxide material having a surface portion and a core portion, in which lithium ions are distributed in a concentration gradient decreasing from the surface portion to the core portion of the lithium nickel complex oxide material;
• a negative electrode;
• and
• an electrolyte;
• and
• wherein the surface portion of the lithium nickel complex oxide is represented by Formula 2 below, and the core portion of the lithium nickel complex oxide is represented by Formula 3 below:
• Lia[NixCoyMnz]O2 <Formula 2>
• Lia[NixCoyMnz]O2 <Formula 3>
• wherein in Formula 2, 1.1≦a≦1.2, 0.5≦x≦0.6, 0.2≦y≦0.3, 0.2≦z≦0.3, and x+y+z=1,
• and wherein in Formula 3, 0.8≦a≦0.9 0.5≦x≦0.6, 0.2≦y≦0.3, 0.2≦z≦0.3, and x+y+z=1, and
• wherein, in the lithium nickel complex oxide, a mole ratio of lithium to nickel of the surface portion of the lithium nickel complex oxide is from 1.22 to 1.5 times a mole ratio of lithium to nickel of the core portion of the lithium nickel complex oxide.

A method of manufacturing a positive electrode active material comprising a lithium nickel complex oxide for a lithium battery comprising:

• mixing a nickel salt solution, a cobalt salt solution, and a manganese salt solution to form a mixture;
• adding a base to the mixture to form a nickel complex oxide precursor;
• adding a lithium-containing material to the nickel complex oxide precursor;
• subjecting the nickel complex oxide precursor to thermal treatment for about 1 hour or less, wherein lithium ions are distributed in a concentration gradient decreasing from a surface portion of the lithium nickel complex oxide to a core portion of the lithium nickel complex oxide, and
• wherein the surface portion of the lithium nickel complex oxide is represented by Formula 2 below, and wherein the core portion of the lithium nickel complex oxide is represented by Formula 3 below:
• Lia[NixCoyMnz]O2 <Formula 2>
• Lia[NixCoyMnz]O2 <Formula 3>
• wherein in Formula 2, 1.1≦a≦1.2, 0.5≦x≦0.6, 0.2≦y≦0.3, 0.2≦z≦0.3, and x+y+z=1, and
• wherein in Formula 3, 0.8≦a≦0.9 0.5≦x≦0.6, 0.2≦y≦0.3, 0.2≦z≦0.3, and x+y+z=1, and
• wherein, in the lithium nickel complex oxide, a mole ratio of lithium to nickel of the surface portion of the lithium nickel complex oxide is from 1.22 to 1.5 times a mole ratio of lithium to nickel of the core portion of the lithium nickel complex oxide.