Positive electrode for rechargeable lithium battery, preparing same, and rechargeable lithium battery

1. A positive active material that includes a lithium nickel composite oxide represented by the following Chemical Formula 1, wherein a full width at half maximum (FWHM 003 ) at a (003) plane in X-ray diffraction ranges from about 0.12 to about 0.155,

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

wherein, M is one or more kinds of metal element selected from Al, Mn, Cr, Fe, V, Mg, Ti, Zr, Nb, Mo, W, Cu, Zn, Ga, In, Sn, La, and Ce, 0.20≦a≦1.20, 0.80≦x<1.00, 0<y≦0.20, 0≦z≦10, and x+y+z=1.

2. The positive active material of claim 1 , wherein the positive active material has a (I 003 )/(I 104 ) ratio of a diffraction peak intensity (I 003 ) at a (003) plane and a diffraction peak intensity (I 104 ) at a (104) plane in X-ray diffraction ranges from about 1.05 to about 1.25.

3. The positive active material of claim 1 , wherein the lithium nickel composite oxide particle has an average secondary particle diameter (D50) of about 3μm to about 9 μm.

4. The positive active material of claim 1 , wherein the lithium nickel composite oxide particle has a specific surface area of about 0.38 m 2 /g to about 1.05 m 2 /g.

5. The positive active material of claim 1 , wherein M is Al or Mn,

0.80≦x<1.00,

0<y≦0.15,

0<z≦0.05, and x+y+z=1.

6. A method of preparing a positive active material, comprising;

adding a saturated NaOH aqueous solution to a mixed aqueous solution including a hydrate of Co and Ni and an M-containing compound in a dropwise fashion so as to maintaining pH to be 8 to 12;

agitating the resulting mixture to prepare a hydroxide salt precursor of a transition metal; and

mixing the hydroxide salt precursor of the transition metal with a Li compound, and firing the resultant under an oxygen atmosphere at about 700° C. to about 800 ° C. for about 1 hour to about 10 hours to prepare a lithium nickel composite oxide,

wherein the M-containing compound is a sulfate, a nitrate, an oxide, or a hydroxide of the metal element M, and

the M is one or more kinds of metal element selected from Al, Mn, Cr, Fe, V, Mg, Ti, Zr, Nb, Mo, W, Cu, Zn, Ga, In, Sn, La, and Ce.

7. The method of claim 6 , wherein the mixing mole ratio of the hydrate of Co and Ni and the M-containing compound is Ni:Co:Al=(80 to 84) :15: (1 to 5).

8. A rechargeable lithium battery comprising;

the positive electrode including a positive active material of claim 1 ;

a negative electrode; and

an electrolyte.