Positive electrode active material for lithium secondary battery and process for producing the same

Abstract

A positive electrode active material for a lithium secondary battery containing a lithium-cobalt composite oxide, which has a large volume capacity density, has a high safety and is excellent in charge and discharge cyclic durability, and its production process, are provided. 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) and comprising a mixture containing substantially spherical hard first particles of lithium-cobalt composite oxide having such a sharp particle size distribution that the volume basis cumulative size D10 is at least 50% of the average particle size D50, and the volume basis cumulative size D90 is at most 150% of the average particle size D50, and second particles of lithium-cobalt composite oxide filling the space among the first particles, in a mass ratio of first particles/second particles of from 1/2 to 9/1, and process for producing the same.

1 . A positive electrode active material which comprises 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) and comprising a mixture comprising substantially spherical first particles of lithium-cobalt composite oxide having such a sharp particle size distribution that the volume basis cumulative size D10 is at least 50% of the average particle size D50, and the volume basis cumulative size D90 is at most 150% of the average particle size D50, and second particles of lithium-cobalt composite oxide filling the space among the above lithium-cobalt composite oxide particles, in a mass ratio of first particles/first particles of from 1/2 to 9/1.  
     
     
         2 . The positive electrode active material according to  claim 1 , wherein in the formula, M is at least one member selected from the group consisting of Ti, Zr, Hf, V, Nb, Ta, Mn, Mg, Ca, Sr, Ba and Al.  
     
     
         3 . The positive electrode active material according to  claim 1 , wherein the average particle size D50 is from 5 to 15 μm, the specific surface area is from 0.3 to 0.7 m 2 /g, the half value width of the diffraction peak on (110) plane at 2θ=66.5±1° is from 0.07 to 0.14° as measured by X-ray diffraction using CuKα as a radiation source, and the press density is from 3.1 to 3.4 g/cm 3 .  
     
     
         4 . The positive electrode active material according to  claim 1 , wherein the first particles are large particles having an average particle size D50 of from 7 to 20 μm, and the second particles are small particles having an average particle size of from 10 to 30% of D50 of the first particles.  
     
     
         5 . The positive electrode active material according to  claim 1 , wherein the first particles have a press density of from 2.9 to 3.2 g/cm 3 , and the second particles have a press density of from 2.7 to 3.1 g/cm 3 .  
     
     
         6 . A process for producing the positive electrode active material as claimed in  claim 1 , which comprises firing, as a cobalt source, a mixture of substantially spherical large particle size cobalt hydroxide or tricobalt tetraoxide having such a sharp particle size distribution that the average particle size D50 is from 7 to 20 μm, the average particle size D10 is at least 50% of the average particle size D50 and the average particle size D90 is at most 150% of the average particle size D50, and small particle size cobalt hydroxide or tricobalt tetraoxide having an average particle size D50 of from 10 to 30% of the average particle size D50 of the large particles, in a proportion of from 9:1 to 1:2 as the cobalt atomic ratio, at a temperature of from 700° C. to 1050° C. in an oxygen-comprising atmosphere.  
     
     
         7 . The production process according to  claim 6 , wherein the large particle size cobalt hydroxide or tricobalt tetraoxide has a press density of from 1.7 to 3.0 g/cm 3 , and the small particle size cobalt hydroxide or tricobalt tetraoxide has a press density of from 1.7 to 3.0 g/cm 3 .  
     
     
         8 . The production process according to  claim 6 , wherein each of the large particle size cobalt hydroxide or tricobalt tetraoxide and the small particle size cobalt hydroxide or tricobalt tetraoxide has a specific surface area of from 2 to 20 m 2 /g.  
     
     
         9 . The production process according to  claim 6 , wherein the large particle size or small particle size cobalt hydroxide has a half value width of the diffraction peak on (001) plane at 2θ=19±1° of from 0.18 to 0.35° and a half value width of the diffraction peak on (101) plane at 2θ=38±1° of from 0.15 to 0.35°, in an X-ray diffraction spectrum using CuKα-ray.  
     
     
         10 . A process for producing the positive electrode active material as claimed in  claim 1 , which comprises firing, as a cobalt source, a mixture of substantially spherical cobalt hydroxide or tricobalt tetraoxide having such a sharp particle size distribution that the average particle size D50 is from 7 to 20 μm, the average particle size D10 is at least 50% of the average particle size D50, the average particle size D90 is at most 150% of the average particle size D50, and the average particle size of secondary particles formed by agglomeration of primary particles is from 8 to 20 μm, and cobalt oxyhydroxide having an average particle size of secondary particles formed by agglomeration of primary particles of from 7 to 20 μm, in a proportion of from 5:1 to 1:5 as the cobalt atomic ratio, at a temperature of from 700° C. to 1050° C. in an oxygen-comprising atmosphere.  
     
     
         11 . The production process according to  claim 10 , wherein the cobalt oxyhydroxide has a half value width of the diffraction peak on (220) plane at 2θ=31±1° of at least 0.8° and a half value width of the diffraction peak on (311) plane at 2θ=37±1° of at least 0.8°, in an X-ray diffraction spectrum using CuKα-ray, and has a specific surface area of from 10 to 80 m 2 /g.  
     
     
         12 . The production process according to  claim 10 , wherein as the cobalt hydroxide, substantially spherical cobalt hydroxide having a half value width of the diffraction peak on (001) plane at 2θ=19±1° of at least 0.15° and a half value width of the diffraction peak on (101) plane at 2θ=38±1° of at least 0.15°, in an X-ray diffraction spectrum using CuKα-ray, and having a specific surface area of from 2 to 30 m 2 /g, is used.  
     
     
         13 . The production process according to  claim 10 , wherein the tricobalt tetraoxide has a half value width of the diffraction peak on (220) plane at 2θ=31±1° of at least 0.08° and a half value width of the diffraction peak on (311) plane at 2θ=37±1° of at least 0.10°, in an X-ray diffraction spectrum using CuKα-ray, and has a specific surface area of from 2 to 10 m 2 /g.  
     
     
         14 . The production process according to  claim 10 , wherein the cobalt hydroxide or the tricobalt tetraoxide has a press density of from 1.2 to 2.5 g/cm 3 .  
     
     
         15 . The production process according to  claim 10 , wherein the lithium-cobalt composite oxide has a half value width of the diffraction peak on (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 starting temperature of at least 160° C., and a press density of from 3.1 to 3.4 g/cm 3 .  
     
     
         16 . A positive electrode which comprises the positive electrode active material as claimed in  claim 1 .  
     
     
         17 . A positive electrode which comprises a positive electrode active material obtained by the production process as claimed in  claim 6 .  
     
     
         18 . A lithium secondary battery comprising the positive electrode active material as claimed in  claim 16 .  
     
     
         19 . A positive electrode which comprises a positive electrode active material obtained by the production process as claimed in  claim 10 .  
     
     
         20 . A lithium secondary battery comprising the positive electrode active material as claimed in  claim 17 .  
     
     
         21 . A lithium secondary battery comprising the positive electrode active material as claimed in  claim 19.