Nonaqueous electrolyte secondary battery

1. A nonaqueous electrolyte secondary battery which has a positive electrode containing a positive active material, a negative electrode containing a negative active material and a nonaqueous electrolyte, said secondary battery being characterized in that said positive active material consists of a mixture of a lithium transition metal complex oxide A obtained by incorporating at least Zr and Mg into LiCoO z and a lithium transition metal complex oxide B having a layered structure and containing at least Ni and Mn as the transition metal.

2. The nonaqueous electrolyte secondary battery as recited in claim 1 , characterized in that said lithium transition metal complex oxide A is represented by the chemical formula: Li a Co 1-x-y-z- Zr x Mg y M z O 2 (in the formula, M is at least one element selected from Al, Ti and Sn, and a, x, y and z satisfy 0 ≦a ≦1.1, x >0, y >0, z ≧0 and 0<x+y+z≦0.03).

3. The nonaqueous electrolyte secondary battery as recited in claim 1 , characterized in that Zr contained in said lithium transition metal complex oxide A exists in the form of a compound adhered onto a surface of the lithium transition metal complex oxide A.

4. The nonaqueous electrolyte secondary battery as recited in claim 3 , characterized in that said Zr compound contained in said lithium transition metal complex oxide A exists in the form of particles adhered onto said surface of the lithium transition metal complex oxide A.

5. The nonaqueous electrolyte secondary battery as recited in claim 4 , characterized in that said lithium transition metal complex oxide B is represented by the chemical formula: Li b Mn s Ni t Co u O 2 (in the formula, b, s, t and u satisfy 0≦b≦1.2, s+t+u=1, 0<s≦0.5, 0<t≦0.5 and u≦0).

6. The nonaqueous electrolyte secondary battery as recited in claim 4 , characterized in that said lithium transition metal complex oxide B contains substantially the same amount by mole of Mn and Ni.

7. The nonaqueous electrolyte secondary battery as recited in claim 4 , characterized in that said positive active material contains 51-90% by weight of the lithium transition metal complex oxide A.

8. The nonaqueous electrolyte secondary battery as recited in claim 4 , characterized in that said positive and negative active materials are contained such that when a prescribed end-of-charge voltage is 4.3 V, a ratio in charge capacity of the negative to positive electrode is 1.0-1.2.

9. The nonaqueous electrolyte secondary battery as recited in claim 4 , characterized in that said positive and negative active materials are contained such that, when a prescribed end-of-charge voltage is 4.4 V, a ratio in charge capacity of the negative to positive electrode is 1.0-1.2.

10. The nonaqueous electrolyte secondary battery as recited in claim 1 , characterized in that said lithium transition metal complex oxide B is represented by the chemical formula: Li b MN s Ni t Co U O 2 (in the formula, b, s, t and u satisfy 0≦b≦1.2, s+t+u=1, 0<s≦0.5, 0<t≦0.5 and u≧0).

11. The nonaqueous electrolyte secondary battery as recited in claim 10 , characterized in that said lithium transition metal complex oxide B contains substantially the same amount by mole of Mn and Ni.

12. The nonaqueous electrolyte secondary battery as recited in claim 10 , characterized in that said positive active material contains 51-90% by weight of the lithium transition metal complex oxide A.

13. The nonaqueous electrolyte secondary battery as recited in claim 10 , characterized in that said positive and negative active materials are contained such that, when a prescribed end-of-charge voltage is 4.3 V, a ratio in charge capacity of the negative to positive electrode is 1.0-1.2.

14. The nonaqueous electrolyte secondary battery as recited in claim 10 , characterized in that said positive and negative active materials are contained such that, when a prescribed end-of-charge voltage is 4.4 V, a ratio in charge capacity of the negative to positive electrode is 1.0-1.2.

15. The nonaqueous electrolyte secondary battery as recited in claim 1 , characterized in that said lithium transition metal complex oxide B contains substantially the same amount by mole of Mn and Ni.

16. The nonaqueous electrolyte secondary battery as recited in claim 1 , characterized in that said positive active material contains 51-90% by weight of the lithium transition metal complex oxide A.

17. The nonaqueous electrolyte secondary battery as recited in claim 1 , characterized in that said positive and negative active materials are contained such that, when a prescribed end-of-charge voltage is 4.3 V, a ratio in charge capacity of the negative to positive electrode is 1.0-1.2.

18. The nonaqueous electrolyte secondary battery as recited in claim 1 , characterized in that said positive and negative active materials are contained such that, when a prescribed end-of-charge voltage is 4.4 V, a ratio in charge capacity of the negative to positive electrode is 1.0-1.2.

19. A nonaqueous electrolyte secondary battery which has a positive electrode containing a positive active material, a negative electrode containing a negative active material and a nonaqueous electrolyte, said secondary battery being characterized in that said positive active material consists of a mixture of a lithium transition metal complex oxide A obtained by incorporating at least Zr and Mg into LiCoO 2 and a lithium transition metal complex oxide B having a layered structure and containing at least Ni and Mn as the transition metal, the Zr contained in said lithium transition metal complex oxide A existing in the form of a compound adhered onto a surface of the lithium transition metal complex oxide A with at least 80% of the surface of said lithium transition metal complex oxide A being left exposed without being covered with said Zr compound.

20. A nonaqueous electrolyte secondary battery which has a positive electrode containing a positive active material, a negative electrode containing a negative active material and a nonaqueous electrolyte, said secondary battery being characterized in that said positive active material consists of a mixture of a lithium transition metal complex oxide A obtained by incorporating at least Zr and Mg into LiCoO 2 and a lithium transition metal complex oxide B having a layered structure and containing at least Ni and Mn as the transition metal, the Zr compound contained in said lithium transition metal complex oxide A existing in the form of particles adhered onto said surface of the lithium transition metal complex oxide A with at least 80% of the surface of said lithium transition metal complex oxide A being left exposed without being covered with said Zr compound.