Process for producing lithium-containing composite oxide for positive electrode for lithium secondary battery

1. A process for producing a lithium-containing composite oxide for a lithium secondary battery comprising:

impregnating an N element source powder with an aqueous solution comprising a carboxylic acid having two or more carboxylic acid groups or carboxylic acid groups and hydroxyl groups and an M element or its salt;

drying a slurry of the N element source powder impregnated with the aqueous solution comprising a carboxylic acid having two or more carboxylic acid groups or carboxylic acid groups and hydroxyl groups and an M element or its salt;

mixing a lithium source, the dried slurry of the N element impregnated with the carboxylic acid and M element and optionally, a fluorine source; and

firing the mixture at from 950° C. to 1050° C.;

wherein

the lithium-containing composite oxide is represented by the formula:

Li p N x M y O z F a

wherein

N is at least one element selected from the group consisting of Co, Mn and Ni,

M is at least one element selected from the group consisting of Sn, Zn, Al, alkaline earth metal elements, and transition metal elements other than N,

0.9≦p≦1.1,

0.97≦x<1.00,

0<y≦0.03,

1.9≦z≦2.1,

x+y=1,

0≦a≦0.02,

the N element source powder has an average particle size (D 50 ) of from 2 to 20 μm, and

the M element and optionally fluorine are present on the surface of particles of the lithium-containing composite oxide.

2. The process according to claim 1 , wherein the carboxylic acid is a carboxylic acid having from 2 to 8 carbon atoms.

3. The process according to claim 2 , wherein the carboxylic acid is at least one member selected from the group consisting of citric acid, lactic acid, oxalic acid and tartaric acid.

4. The process according to claim 1 , wherein the aqueous solution comprising a carboxylic acid or its salt has a pH of from 2 to 12.

5. The process according to claim 1 , wherein

the N element source powder is impregnated with an aqueous solution of M element salt of the carboxylic acid,

dried to remove water,

then dryly mixed with a lithium source powder, and optionally, the fluorine source, and

the obtained powder mixture is fired at from 950 to 1050° C. in an oxygen- containing atmosphere.

6. The process according to claim 1 , wherein

the N element source powder is impregnated with an aqueous solution of M element salt of the carboxylic acid in the presence of a lithium source powder, and optionally, the fluorine source,

dried to remove water, and

the powder mixture thus obtained is fired at from 950 to 1050° C. in an oxygen-containing atmosphere.

7. The process according to claim 1 , wherein the M element is at least one member selected from the group consisting of Ti, Zr, Hf, Nb, Ta, Mg, Sn, Zn and Al.

8. The process according to claim 7 , wherein

the M element comprises Al and Mg,

an Al/Mg atomic ratio is from 1/3 to3/1, and 0.005≦y≦0.025.

9. The process according to claim 7 , wherein

the M element comprises Mg and M2 wherein M2 is at least one element selected from the group consisting of Ti, Zr, Ta and Nb, the M 2 /Mg atomic ratio is from 1/40 to 2/1, and 0.005≦y≦0.025.

10. The process according to claim 1 , wherein the lithium-containing composite oxide powder comprises,

an integral breadth of a diffraction peak on ( 110 ) plane in the vicinity of 2θ=66.5±1° from 0.08 to 0.14° as measured by means of X-ray diffraction in which CuKα is used as a radiation source,

a surface area from 0.2 to 0.6m 2 /g, and

a heat generation starting temperature is at least 160° C.

11. A process for producing a lithium-containing composite oxide for a lithium secondary battery according to claim 1 , wherein

a solid/liquid ratio of the slurry obtained by impregnating the N element source powder with the aqueous solution of the M element salt of the carboxylic acid is from 50/50to 90/10.