Cathode materials having high energy density and lithium secondary battery containing the same

1. A cathode material comprising a mixture of an oxide powder (a) defined below and an oxide powder (b2) defined below and a combination thereof wherein a mix ratio of the two oxide powders (oxide powder (a):oxide powder (b2)) is 50:50 to 90:10;

[oxide powder (a)]

an oxide powder represented by Formula I below:

Li x (Co y A m D z )O t   (1)

wherein 0.8≦x≦1.2, 0≦z≦0.3, 1.8≦t≦4.2, (0.8-m-z)≦y≦(2.2-m-z), 0≦m≦0.3, A is at least one selected from Mg and Ca, and D is at least one selected from the group consisting of Ti, Zr, Hf, V, Nb, Ta; Cr, Mo, W, Mn, Tc, Re, Fe, Ru, Os, Co, Rh, Ir, Ni, Pd, Pt, Cu, Au, Ag, Zn, Cd, Hg, B, Al, Ga, In, TI, C, Si, Ge, Sn, Pb, N, P, As, Sb and Bi;

[oxide powder (b2)]

an oxide powder which contains a transition metal mixture of Ni, Mn and Co, has an average oxidation number of all transition metals except for lithium, larger than +3 and satisfies Equations 3 and 4 below:

1.1<m(Ni)/m(Mn)<1.5  (3)

0.4<m(Ni 2+ )/m(Mn 4+ )<1  (4)

wherein m(Ni)/m(Mn) is a molar ratio of nickel to manganese and m(Ni 2+ )/m(Mn 4+ ) is a molar ratio of Ni 2+ to Mn 4+ .

2. The cathode material according to claim 1 , wherein a mix ratio of the oxide powders is 50:50 to 70:30.

3. The cathode material according to claim 1 , wherein the oxide powder (a) is LiCoO 2 .

4. The cathode material according to claim 1 , wherein, in the oxide powder (b2), m(Ni)/m(Mn) satisfies 1.2≦m(Ni)/m(Mn)≦1.4.

5. The cathode material according to claim 1 , wherein, in the oxide powder (b2), the average oxidation number of transition metals other than lithium is higher than 3.0 and is lower than or equal to 3.5.

6. The cathode material according to claim 1 , wherein the nickel in the oxide powder (b2) is composed of nickel (1) present in an excessive amount, as compared to the manganese content, and nickel (2) present in an amount corresponding to the manganese content.

7. The cathode material according to claim 1 , wherein the nickel in the oxide powder (b2) has an average oxidation number higher than 2+.

8. The cathode material according to claim 6 , wherein the nickel (1) is Ni 3+ .

9. The cathode material according to claim 6 , wherein an average oxidation number of the nickel (2) is higher than 3.0 and is lower than or equal to 3.5.

10. Ile cathode material according to claim 6 , wherein the nickel (2) contains Ni 2+ and Ni 3+ .

11. The cathode material according to claim 6 , wherein a ratio of Ni 3+ in the nickel (2) is 11 to 60%.

12. The cathode material according to claim 1 , wherein the content of Ni(Ni 2+ ) sites in the total lithium site in the oxide powder (b2) is lower than 5 mol %.

13. The cathode material according to claim 1 , wherein the oxide powder (a) is a monolithic particle and the oxide powder (b2) is an agglomerated particle composed of an agglomerate of micro particles.

14. The cathode material according to claim 1 , wherein the oxide powder (a) has a D50 of 15 μm or more and the oxide powder (b2) has a D50 of 8 μm or less.

15. The cathode material according to claim 14 , wherein the oxide powder (a) has a D50 of 20 to 30 μm and the oxide powder (b2) has a D50 of 4 to 7 μm.

16. The cathode material according to claim 15 , wherein 90% or more of the oxide powder (b2) is an agglomerate of micro particles having a size of 1 to 4 μm.

17. A lithium secondary battery comprising the cathode material according to claim 1 .

18. The lithium secondary battery according to claim 17 , wherein the lithium secondary battery is a pouch battery in which an electrode assembly is sealed in a pouch-type case made of a laminate sheet including a resin layer and a metal layer.