Cathode active material for lithium secondary battery

1. A cathode active material for a lithium secondary battery containing a lithium transition metal oxide capable of lithium ion intercalation/deintercalation, which further comprises a lithium nickel oxide represented by the following formula 1 that is surface-coated with an oxide other than lithium nickel oxides, as an additive in an amount of 0.1 to 9 parts by weight based on 100 parts by weight of the total cathode active material, and wherein the oxide other than lithium nickel oxides is an oxide or composite oxide of at least one element selected from the group consisting of P, C, Sc, Cr, Mn, Fe, Cu, Zn, Mo, and Nb:

Li 2+x Ni 1−y M y O 2+a

wherein, x is a number satisfying −0.5≦x≦0.5, y is a number satisfying 0<y<1, a is a number satisfying 0≦a<0.3, and M is at least one element selected from the group consisting of P, C, Nb, Mo and Cd.

2. The cathode active material according to claim 1 , wherein the lithium nickel oxide represented by formula 1 belongs to a space group Immm.

3. The cathode active material according to claim 2 , wherein the lithium nickel oxide represented by formula 1 forms a tetra-coordinated planar structure, (Ni,M)O 4 and two tetra-coordinated planar structures facing to each other share one side formed by O—O so as to form a primary chain.

4. The cathode active material according to claim 2 , wherein the compound represented by formula 1 has the following lattice constants: a=3.7±0.5 Å, b=2.8±0.5 Å, c=9.2±0.5 Å, α=90°, β=90° and γ=90.

5. The cathode active material according to claim 1 , wherein the lithium transition metal oxide is at least one selected from the group consisting of LiCoO 2 , LiNiO 2 , LiMnO 2 , LiMn 2 O 4 , Li(Ni a Co b Mn c )O 2 , LiNi 1−d Co d O 2 , LiCo 1−d Mn d O 2 , LiNi 1−d Mn d O 2 , Li(Ni x Co y Mn z )O 4 , LiMn 2−n Ni n O 4 , LiMn 2−n Co n O 4 , LiCoPO 4 and LiFePO 4 , wherein 0<a<1, 0<b<1, 0<c<1, a+b+c=1, 0≦d<1, 0<x<2, 0<y<2, 0<z<2, x+y+z=2, and 0<n<2.

6. The cathode active material according to claim 1 , wherein the additive is in an amount of 0.1 to 5 parts by weight based on 100 parts by weight of the total cathode active material.

7. A lithium secondary battery comprising a cathode, an anode, a separator and a non-aqueous electrolyte containing a lithium salt and an electrolyte compound,

wherein the cathode comprises the cathode active material containing a lithium transition metal oxide capable of lithium ion intercalation/deintercalation, which further comprises a lithium nickel oxide represented by the following formula 1 that is surface-coated with an oxide other than lithium nickel oxides, as an additive in an amount of 0.1 to 9 parts by weight based on 100 parts by weight of the total cathode active material, and wherein the oxide other than lithium nickel oxides is an oxide or composite oxide of at least one element selected from the group consisting of P, C, Sc, Cr, Mn, Fe, Cu, Zn, Mo, and Nb:

Li 2+x Ni 1−y MyO 2+a

wherein, x is a number satisfying −0.5≦x≦0.5, y is a number satisfying 0<y<1, a is a number satisfying 0≦a<0.3, and M is at least one element selected from the group consisting of P, C, Nb, Mo and Cd.

8. The lithium secondary battery according to claim 7 , wherein the lithium nickel oxide represented by formula 1 belongs to a space group Immm.

9. The cathode active material according to claim 8 , wherein the lithium nickel oxide represented by formula 1 forms a tetra-coordinated planar structure, (Ni,M)O 4 and two tetra-coordinated planar structures facing to each other share one side formed by O—O so as to form a primary chain.

10. The lithium secondary battery according to claim 8 , wherein the compound represented by formula 1 has the following lattice constants: a=3.7±0.5 Å, b=2.8±0.5 Å, c=9.2±0.5 Å, α=90°, β=90° and γ=90.

11. The lithium secondary battery according to claim 7 , wherein the lithium transition metal oxide is at least one selected from the group consisting of LiCoO 2 , LiNiO 2 , LiMnO 2 , LiMn 2 O 4 , Li(Ni a Co b Mn c )O 2 , LiNi 1−d Co d O 2 , LiCo 1−d Mn d O 2 , LiNi 1−d Mn d O 2 , Li(Ni x Co y Mn z )O 4 , LiMn 2−n Ni n O 4 , LiMn 2−n Co n O 4 , LiCoPO 4 and LiFePO 4 , wherein 0<a<1, 0<b<1, 0<c<1, a+b+c=1, 0≦d<1, 0<x<2, 0<y<2, 0<z<2, x+y+z=2, and 0<n<2.

12. The lithium secondary battery according to claim 7 , wherein the additive is in an amount of 0.1 to 5 parts by weight based on 100 parts by weight of the total cathode active material.

13. The lithium secondary battery according to claim 7 , wherein the lithium salt is at least one selected from the group consisting of LiClO 4 , LiCF 3 SO 3 , LiPF 6 , LiBF 4 , LiAsF 6 and LiN(CF 3 SO 2 ) 2 , and the electrolyte compound is at least one carbonate selected from the group consisting of ethylene carbonate, propylene carbonate, gamma-butyrolactone, diethyl carbonate, dimethyl carbonate, ethylmethyl carbonate and methylpropyl carbonate.