Layered lithium nickel oxide, process for producing the same and lithium secondary cell employing it

1. A metal oxide for a cathode active material of a lithium secondary battery, the metal oxide represented by the following Chemical Formula 1:

Li a Ni x Co y M z O 2   [Chemical Formula 1]

wherein, in Chemical Formula 1, M is any one selected from aluminum, magnesium, titanium, gallium and indium, and a, x, y and z satisfy 1.01≦a≦1.05, 0.7≦x≦0.9, 0≦y≦0.17, 0.02≦z≦0.16, and x+y+z=1, respectively, and wherein a concentration of M has a gradient at which the concentration is decreased from a surface of the metal oxide to a center thereof.

2. The metal oxide for a cathode active material of a lithium secondary battery of claim 1 , wherein z of Chemical Formula 1 satisfies 0.02≦z≦0.09.

3. The metal oxide for a cathode active material of a lithium secondary battery of claim 1 , wherein the cathode active material has a rhombohedral structure.

4. A method for preparing a metal oxide for a cathode active material of a lithium secondary battery, the method comprising:

preparing an aqueous solution by dissolving acetate containing at least any one metal selected from aluminum, magnesium, titanium, indium, and gallium in an organic solvent;

preparing a metal oxide precursor mixed solution by adding a metal salt containing nickel and cobalt to the aqueous solution;

obtaining a solid dried material by removing a solvent of the mixed solution; and

mixing and pulverizing the solid dried material and lithium precursor and performing a heat treatment, wherein the metal oxide obtained by the method is represented by the following Chemical Formula 1:

Li a Ni x CO y M z O 2   [Chemical Formula 1]

wherein, in Chemical Formula 1, M is any one selected from aluminum, magnesium, titanium, gallium and indium, and a, x, y, and z satisfy 1.01≦a≦1.05, 0.7≦x≦0.9, 0≦y≦0.17, 0.02≦z≦0.16, and x+y+z=1, respectively, and wherein a concentration of M has a gradient at which the concentration is decreased from a surface of the metal oxide to a center thereof.

5. The method of claim 4 , wherein the acetate containing at least any one metal selected from aluminum, magnesium, titanium, indium, and gallium is any one or two or more mixtures selected from aluminum acetate, indium acetate hydrate, and gallium acetate.

6. The method of claim 4 , wherein the metal oxide finally obtained by the method includes a composition represented by the following Chemical Formula 1:

Li a NixCo y M z O 2   [Chemical Formula 1]

(in Chemical Formula 1, M is any one selected from aluminum, magnesium, titanium, gallium and indium, and a, x, y and z satisfy 1.01≦a≦1.05, 0.7≦x≦0.9, 0≦y≦0.17, 0.02≦z≦0.16, and x+y+z=1, respectively).

7. The method of claim 4 , wherein the solvent of the mixed solution is removed by any one process of a drying process and a solvent extracting process.

8. The method of claim 7 , wherein the drying process is performed at room temperature to 200° C. under a condition of vacuum or a normal pressure.

9. The method of claim 7 , wherein the solid dried material has a particle size of 3 to 10 μm.

10. A lithium secondary battery comprising the metal oxide for a cathode active material of a lithium secondary battery of claim 1 .

11. A lithium secondary battery comprising the oxide for a cathode active material of a lithium secondary battery of claim 2 .

12. A lithium secondary battery comprising the oxide for a cathode active material of a lithium secondary battery of claim 3 .