Positive electrode active material and non-aqueous electrolyte secondary cell comprising the same

1. A positive electrode active material comprising crystal particles of an oxide having a layered single-phase crystal structure and a composition represented by the formula (1):

LiNi 2/3 Mn 1/3 O 2 ,

wherein the arrangement of oxygen atoms constituting the oxide is a cubic close-packed structure, the nickel and manganese are incorporated in said crystal particles at the atomic level,

wherein the arrangement of nickel element and manganese element is a superlattice arrangement of a [√3×√3] R30° in the layer, of said crystal particles, in which nickel element and manganese element exist in a ratio of 2:1, and

the crystal particles are doped with a different element,

wherein the concentration of said different element is higher at the surface of said crystal particles than inside said crystal particles.

2. The positive electrode active material in accordance with claim 1 , wherein the crystal structure of said oxide is a layered structure belonging to R-3m.

3. The positive electrode active material in accordance with claim 1 , wherein the volume of the unit lattice of said crystal particles does not increase by an oxidation.

4. The positive electrode active material in accordance with claim 1 , wherein the error range of the ratio of said Ni and Mn is within 10 atom %.

5. The positive electrode active material in accordance with claim 1 , wherein said different element is at least one selected from the group consisting of aluminum, magnesium, calcium, strontium, yttrium and ytterbium.

6. The positive electrode active material in accordance with claim 1 , wherein the added amount of said different element is 0.05 to 20 atom % of the total amount of the Ni and Mn.

7. The positive electrode active material in accordance with claim 1 , wherein said crystal particles comprise a mixture of crystal particles of the oxide with a particle size of 0.1 to 2 μm and secondary particles of the crystal particles with a particle size of 2 to 20 μm.

8. A non-aqueous electrolyte secondary battery comprising a negative electrode containing, as a negative electrode active material, a material capable of absorbing and desorbing lithium ions and/or lithium metal, a positive electrode containing a positive electrode active material comprising crystal particles of an oxide having a layered single-phase crystal structure and a composition represented by the formula (1):

LiNi 2/3 Mn 1/3 O 2 ,

characterized in that the arrangement of oxygen atoms constituting the oxide is a cubic close-packed structure, and an electrolyte, the nickel and manganese are incorporated in said crystal particles at the atomic level, and

the crystal particles are doped with a different element,

wherein the concentration of said different element is higher at the surface of said crystal particles than inside said crystal particles, and

the arrangement of nickel element and manganese element is a superlattice arrangement of a [√3×√3] R30° in the layer, of said crystal particles, in which nickel element and manganese element exist in a ratio of 2:1.

9. A non-aqueous electrolyte secondary battery in accordance with claim 8 , wherein, when said battery is continuously overcharged at a constant current value corresponding to a ⅓ hour rate (3C) for an hour, a highest surface temperature of the battery is 125° C. or lower.

10. The non-aqueous electrolyte secondary battery in accordance with claim 8 , wherein said crystal particles comprise a mixture of crystal particles of the oxide with a particle size of 0.1 to 2 pm and secondary particles of the crystal particles with a particle size of 2 to 20 μm.

11. A positive electrode active material comprising crystal particles of an oxide having a layered single-phase crystal structure and a composition represented by the formula (1):

LiNi 2/3 Mn 1/3 O 2 ,

wherein the arrangement of oxygen atoms constituting the oxide is a cubic close-packed structure, the nickel and manganese are incorporated in said crystal particles at the atomic level, said crystal particles comprise a mixture of crystal particles of the oxide with a particle size of 0.1 to 2 μm and secondary particles of the crystal particles with a particle size of 2 to 20 μm, and

the arrangement of nickel element and manganese element is a superlattice arrangement of a [√3×√3] R30° in the layer, of said crystal particles, in which nickel element and manganese element exist in a ratio of 2:1.

12. The positive electrode active material in accordance with claim 11 , wherein the crystal structure of said oxide is a layered structure belonging to R-3m.

13. The positive electrode active material in accordance with claim 11 , wherein the volume of the unit lattice of said crystal particles does not increase by an oxidation.

14. The positive electrode active material in accordance with claim 11 , wherein the error range of the ratio of said Ni and Mn is within 10 atom %.

15. The positive electrode active material in accordance with claim 11 , wherein the surface of said crystal particles is doped with a different element.

16. The positive electrode active material in accordance with claim 15 , wherein said different element is at least one selected from the group consisting of aluminum, magnesium, calcium, strontium, yttrium and ytterbium.

17. The positive electrode active material in accordance with claim 15 , wherein the added amount of said different element is 0.05 to 20 atom % of the total amount of the Ni and Mn.