Cathode active material, method of preparing the same, and cathode and lithium battery containing the material

1. A composite cathode active material comprising:

at least one large diameter active material selected from the group consisting of LiNi 0.8 Co 0.1 Mn 0.1 O 2 , LiNiO 2 , LiNi 0.9 Co 0.1 O 2 , LiNi 0.8 Co 0.1 Al 0.1 O 2 and mixtures thereof; and

at least one small diameter active material comprising a carbon-based material selected from the group consisting of graphite, hard carbon, carbon black, carbon fiber, carbon nanotubes (CNT) and mixtures thereof,

wherein a ratio of an average particle diameter of the large diameter active material to an average particle diameter of the small diameter active material ranges from about 6:1 to about 100:1.

2. The composite cathode active material according to claim 1 , wherein the ratio of the average particle diameter of the large diameter active material to the average particle diameter of the small diameter active material ranges from about 6:1 to about 20:1.

3. The composite cathode active material according to claim 1 , wherein a weight ratio of the large diameter active material to the small diameter active material ranges from about 60:40 to about 90:10.

4. The composite cathode active material according to claim 1 , wherein a weight ratio of the large diameter active material to the small diameter active material ranges from about 70:30 to about 80:20.

5. The composite cathode active material according to claim 1 , wherein a mole ratio of the large diameter active material to the small diameter active material ranges from about 60/M w1 :40/M w2 to about 90/M w1 :10/M w2 ,

wherein:

M w1 is a molecular weight of the large diameter active material,

M w2 is a molecular weight of the small diameter active material, and each of w1 and w2 is an integer other than 0.

6. The composite cathode active material according to claim 1 , wherein a mole ratio of the large diameter active material to the small diameter active material ranges from about 70/M w1 :30/M w2 to about 80/M w1 :20/M w2 ,

wherein:

M 1 is a molecular weight of the large diameter active material,

M 2 is a molecular weight of the small diameter active material, and each of w1 and w2 is an integer other than 0.

7. The composite cathode active material according to claim 1 , wherein the average particle diameter of the large diameter active material ranges from about1 to about 25 μm.

8. The composite cathode active material according to claim 1 , wherein the average particle diameter of the small diameter active material ranges from about 0.05 to about 5 μm.

9. A cathode comprising the composite cathode active material of claim 1 .

10. A lithium battery comprising the cathode of claim 9 .

11. The composite cathode active material of claim 1 , wherein the at least one small diameter active material further comprises a material selected from the group consisting of compounds represented by Formula 2, compounds represented by Formula 3, and compounds represented by Formula 4

Li x Co 1-y-z Ni y M z O 2-α X α   Formula 2

Li x Mn 2-y M y O 4-α X α   Formula 3

Li x Co 2-y M y O 4-α X α   Formula 4

wherein 0.90≦x≦1.1, 0≦y≦0.9, 0≦z≦0.5, 0≦α≦2, M is selected from the group consisting of Al, Ni, Mn, Cr, Fe, Mg, Sr, V, rare earth elements and mixtures thereof, and X is selected from the group consisting of O, F, S, P and combinations thereof

12. A composite cathode active material comprising:

at least one large diameter active material selected from the group consisting of compounds represented by Formula 1 and compounds represented by Formula 2; and

at least one small diameter active material comprising a carbon-based material selected from the group consisting of graphite, hard carbon, carbon black, carbon fiber, carbon nanotubes (CNT) and mixtures thereof, the at least one small diameter active material further comprising a material selected from the group consisting of LiNi 1/3 Co 1/3 Mn 1/3 O 2 , LiMn 2 O 4 , LiNi 0.5 Mn 0.5 O 2 , LiC 0.95 Mg 0.05 O 2 , LiNi 1/2 Mn 3/2 O 4 and mixtures thereof;

wherein a ratio of an average particle diameter of the large diameter active material to an average particle diameter of the small diameter active material ranges from about 6:1 to about 100:1;

Li x Co 1-y M y O 2-α X α   Formula 1

Li x Co 1-y-z Ni y M z O 2-α X α   Formula 2

wherein 0.90≦x≦1.1, 0≦y≦0.9, 0≦z≦0.5, 0≦α≦2, M is selected from the group consisting of Al, Ni, Mn, Cr, Fe, Mg, Sr, V, rare earth elements and mixtures thereof, and X is selected from the group consisting of O, F, S, P and combinations thereof.

13. A composite cathode active material comprising:

at least one large diameter active material selected from the group consisting of compounds represented by Formula 1 and compounds represented by Formula 2, wherein a pressed density of the large diameter active material ranges from about 2.5 to about 4.0 g/cm 3 ; and

at least one small diameter active material comprising a carbon-based material selected from the group consisting of graphite, hard carbon, carbon black, carbon fiber, carbon nanotubes (CNT) and mixtures thereof, wherein a pressed density of the small diameter active material ranges from about 1.0 to about 4.0 g/cm 3 ;

wherein a ratio of an average particle diameter of the large diameter active material to an average particle diameter of the small diameter active material ranges from about 6:1 to about 100:1

Li x Co 1-y M y O 2-α X α   Formula 1

Li x Co 1-y-z Ni y M z O 2-α X α   Formula 2

wherein 0.90≦x≦1.1, 0≦y≦0.9, 0≦z≦0.5, 0≦α≦2, M is selected from the group consisting of Al, Ni, Mn, Cr, Fe, Mg, Sr, V, rare earth elements and mixtures thereof, and X is selected from the group consisting of O, F, S, P and combinations thereof.