Electrode active material, method for producing same, electrode for nonaqueous secondary battery, and nonaqueous secondary battery

1. An electrode active material comprising particles of a lithium-containing composite oxide represented by the general compositional formula:

Li 1+x MO 2 ,

where x is within a range of −0.05≦x≦0.15, and M represents an element group of three or more elements including at least Ni, Co and Mn,

wherein the ratios of Ni, Co and Mn to the total elements constituting M satisfy 45≦a≦60, 5≦b≦30, 5≦c≦30 and 10≦b+c≦55, where the ratios of Ni, Co and Mn are represented by a, b and c, respectively, in units of mol%,

the average valence A of Ni in the whole particles is 2.2 to 3.2, the valence B of Ni on the surface of the particles has the relationship: B<A,

the average valence C of Co in the whole particles is 2.5 to 3.2, the valence D of Co on the surface of the particles has the relationship: D≦C, and

the average valence of Mn in the whole particles is 3.5 to 4.2.

2. The electrode active material according to claim 1 ,

wherein the average valence A of Ni in the whole particles is 2.2 to 2.9, and the valence B of Ni on the surface of the particles has the relationship: B≦A.

3. The electrode active material according to claim 1 ,

wherein the ratio b of Co and the ratio c of Mn have the relationship: b>c.

4. The electrode active material according to claim 1 ,

wherein the ratio b of Co and the ratio c of Mn have the relationship: b≦c.

5. The electrode active material according to claim 1 ,

wherein the lithium-containing composite oxide is represented by the general compositional formula: Li 1+x Ni 1 −d−e CO d Mn e O 2 , where −0.15≦x≦0.15, 0.05≦d≦0.3, 0.05≦e≦0.3, and 0.1≦d+e≦0.55.

6. The electrode active material according to claim 1 ,

wherein the lithium-containing composite oxide is formed by washing a composite oxide of Li and the element group M with water or an organic solvent, heat treating the washed composite oxide at a temperature of 600 to 1000° C. in an atmosphere containing 18 vol% or more of oxygen, and pulverizing the composite oxide.

7. The electrode active material according to claim 1 ,

wherein the particles of the lithium-containing composite oxide have a true density of 4.55 to 4.95 g/cm 3 .

8. The electrode active material according to claim 1 ,

wherein in the particles of the lithium-containing composite oxide, the ratio of primary particles having a particle size of 1 μm or less to the total primary particles of the lithium-containing composite oxide particles is 30 vol% or less.

9. The electrode active material according to claim 1 ,

wherein the lithium-containing composite oxide has a BET specific surface area of 0.1 to 0.3 m 2 /g.

10. The electrode active material according to claim 1 ,

wherein the particles of the lithium-containing composite oxide has a spherical shape.

11. An electrode for a non-aqueous secondary battery comprising an electrode material mixture layer containing the electrode active material according to claim 1 , wherein the electrode material mixture layer has a density of 3.2 to 3.8 g/cm 3 .

12. The electrode for a non-aqueous secondary battery according to claim 11 ,

wherein the electrode material mixture layer has a density of 3.5 to 3.8 g/cm 3 .

13. A non-aqueous secondary battery comprising a positive electrode, a negative electrode and a non-aqueous electrolyte,

wherein the positive electrode is the electrode for a non-aqueous secondary battery according to claim 11 .

14. The electrode active material according to claim 1 ,

wherein the valence D of Co on the surface of the particles is 2.65 or less.