Process for producing positive electrode active material for lithium secondary battery
To provide a process for producing a lithium-cobalt composite oxide for a positive electrode of a lithium secondary battery, which has a large volume capacity density, high safety, high charge and discharge cycle durability, high press density and high productivity. A process for producing a lithium-cobalt composite oxide represented by the formula Li p Co x M y O z F a (wherein M is a transition metal element other than Co, or an alkaline earth metal element, 0.9≦p≦1.1, 0.980≦x≦1.000, 0≦y≦0.02, 1.9≦z≦2.1, x+y=1, and 0≦a≦0.02), characterized in that as a cobalt source, a mixture is used which comprises cobalt hydroxide in the form of substantially spherical secondary particles with an average particle size of from 8 to 20 μm formed by agglomeration of primary particles and tricobalt tetroxide in the form of secondary particles with an average particle size of from 2 to 10 μm formed by agglomeration of primary particles, in a cobalt atomic ratio of from 5:1 to 1:5, and firing is carried out at from 700 to 1,050° C.
1. A process for producing a lithium-cobalt composite oxide for a positive electrode of a lithium secondary battery, said lithium-cobalt composite oxide being represented by the formula Li p Co x M y O z F a (wherein M is a transition metal element other than Co, or an alkaline earth metal element, 0.9≦p≦1.1, 0.980≦x≦1.000, 0≦y≦0.02, 1.9≦z≦2.1, x+y=1, and 0≦a≦0.02), which comprises firing a mixture comprising a cobalt source and a lithium source in an oxygen-containing atmosphere, characterized in that as the cobalt source, a mixture is used which comprises cobalt hydroxide in the form of substantially spherical secondary particles with an average particle size of from 8 to 20 μm formed by agglomeration of primary particles and tricobalt tetroxide in the form of secondary particles with an average particle size of from 2 to 10 μm formed by agglomeration of primary particles, in a cobalt atomic ratio of from 5:1 to 1:5, and the firing is carried out at from 700 to 1,050° C.
2. The process according to claim 1 , wherein the average particle size D50 after dispersing the secondary particles of cobalt hydroxide in pure water, is at most ¼ of the initial average particle size D50.
3. The process according to claim 1 , wherein in the X-ray diffraction spectrum using Cu-Kα-ray, of cobalt hydroxide, the half value width of the diffraction peak on (001) plane at 2θ=19±1° is from 0.18 to 0.35°, and the half value width of the diffraction peak on (101) plane at 2θ=38±1° is from 0.15 to 0.35°, and the specific surface area is from 5 to 50 m 2 /g.
4. The process according to claim 1 , wherein the cobalt hydroxide has a press density of from 1.0 to 2.5 g/cm 3 .
5. The process according to claim 1 , wherein in the X-ray diffraction spectrum using Cu-Kα-ray, of tricobalt tetroxide, the half value width of the diffraction peak on (220) plane at 2θ=31±1° is at most 0.5°, and the half value width of the diffraction peak on (311) plane at 2θ=37±1° is at most 0.5°, and the specific surface area is from 0.5 to 20 m 2 /g.
6. The process according to claim 1 , wherein the lithium-cobalt composite oxide has a half value width of the diffraction peak on its (110) plane of from 0.07 to 0.14°, a specific surface area of from 0.3 to 0.7 m 2 /g, a heat generation initiation temperature of at least 160° C. and a press density of from 3.15 to 3.8 g/cm 3 .
7. A positive electrode for a lithium secondary battery containing the lithium-cobalt composite oxide produced by the process as defined in claim 1 .
8. A lithium secondary battery employing the positive electrode as defined in claim 7 .