Positive electrode active material for nonaqueous electrolyte secondary battery, positive electrode for nonaqueous electrolyte secondary battery, and nonaqueous electrolyte secondary battery

Abstract

The positive electrode active material with lithium composite oxide A containing W and Ni and W-free lithium composite oxide B containing Ni. Regarding the lithium composite oxide A, the proportion of Ni relative to the total moles of metal elements except for lithium is 30 to 60 mol %, 50% particle size D50 is 2 to 6 μm, 10% particle size D10 is 1.0 μm or more, and 90% particle size D90 is 6.8 μm or less. Regarding the lithium composite oxide B, the proportion of Ni relative to the total moles of metal elements except for lithium is 50 to 95 mol %, 50% particle size D50 is 10 to 22 μm, 10% particle size D10 is 7.0 μm or more, and 90% particle size D90 is 22.5 μm or less. The mass ratio of the lithium composite oxide B to the lithium composite oxide A is 1:1 to 5.7:1.

Claims

1. A positive electrode active material for a nonaqueous electrolyte secondary battery, the positive electrode active material comprising lithium composite oxide A containing W and Ni and W-free lithium composite oxide B containing Ni, wherein, regarding the lithium composite oxide A, the proportion of Ni relative to the total moles of metal elements except for lithium is 30 to 60 mol %, 50% particle size D50 in a cumulative particle size distribution on a volume basis is 2 to 6 μm, 10% particle size D10 in a cumulative particle size distribution on a volume basis is 1.0 μm or more, and 90% particle size D90 in a cumulative particle size distribution on a volume basis is 6.8 μm or less, regarding the lithium composite oxide B, the proportion of Ni relative to the total moles of metal elements except for lithium is 50 to 95 mol %, 50% particle size D50 in a cumulative particle size distribution on a volume basis is 10 to 22 μm, 10% particle size D10 in a cumulative particle size distribution on a volume basis is 7.0 μm or more, and 90% particle size D90 in a cumulative particle size distribution on a volume basis is 22.5 μm or less, and a mass ratio of the lithium composite oxide B to the lithium composite oxide A is 1:1 to 5.7:1.

2. The positive electrode active material for a nonaqueous electrolyte secondary battery, according to claim 1, wherein regarding the lithium composite oxide A, the 50% particle size D50 is 2.5 to 4.5 μm, the 10% particle size D10 is 1.5 to 2.5 μm, and the 90% particle size D90 is 4.5 to 6.0 μm.

3. The positive electrode active material for a nonaqueous electrolyte secondary battery, according to claim 1, wherein regarding the lithium composite oxide B, the 50% particle size D50 is 11.0 to 21.5 μm, the 10% particle size D10 is 7.0 to 10.5 μm, and the 90% particle size D90 is 21.0 to 22.5 μm.

4. The positive electrode active material for a nonaqueous electrolyte secondary battery, according to claim 1, wherein at least one of the lithium composite oxide A and the lithium composite oxide B contains Zr.

5. A positive electrode for a nonaqueous electrolyte secondary battery, the positive electrode comprising the positive electrode active material for a nonaqueous electrolyte secondary battery according to claim 1.

6. A nonaqueous electrolyte secondary battery comprising the positive electrode for a nonaqueous electrolyte secondary battery according to claim 5.

Description

EXAMPLES

(1) Hereinafter, with reference to Examples, the present disclosure will be further described. The present disclosure is not limited to such Examples.

Example 1

(2) [Production of Lithium Composite Oxide A]

(3) A transition metal precursor represented by Ni.sub.0.35Co.sub.0.30Mn.sub.0.35(OH).sub.2 obtained by a coprecipitation method was fired at 350° C. for 12 hours to obtain a composite oxide containing Ni, Co, and Mn. The composite oxide containing Ni, Co and Mn, a tungsten salt, a zirconium salt, and LiOH were mixed together such that the molar ratio of Li/total amount of Ni, Co and Mn/W/Zr was 1.11:1.00:0.005:0.005. The mixture was fired at 875° C. for 15 hours in an oxygen atmosphere to produce lithium composite oxide A containing Ni, Co, Mn, W, and Zr.

(4) Regarding lithium composite oxide A, the proportion of Ni was 35 mol %, the proportion of Zr was 0.5 mol %, the proportion of W was 0.5 mol %, 50% particle size D50 was 4.2 μm, 10% particle size D10 was 2.3 μm, and 90% particle size D90 was 5.8 μm or less.

(5) [Production of Lithium Composite Oxide B]

(6) A transition metal precursor represented by Ni.sub.0.55Co.sub.0.20Mn.sub.0.25(OH).sub.2 obtained by a coprecipitation method was fired at 350° C. for 9 hours to obtain a composite oxide containing Ni, Co, and Mn. The composite oxide containing Ni, Co and Mn, LiOH, and a zirconium salt were mixed together such that the molar ratio of Li/total amount of Ni, Co and Mn/Zr was 1.08:1.00:0.005. The mixture was fired at 900° C. for 20 hours in an oxygen atmosphere to produce W-free lithium composite oxide B containing Ni, Co, Mn, and Zr.

(7) Regarding lithium composite oxide B, the proportion of Ni was 55 mol %, the proportion of Zr was 0.5 mol %, 50% particle size D50 was 12.1 μm, 10% particle size D10 was 7.3 μm, and 90% particle size D90 was 21.2 μm or less.

(8) [Production of Positive Electrode]

(9) W-free lithium composite oxide B containing Ni, Co, Mn, and Zr and lithium composite oxide A containing Ni, Co, Mn, W, and Zr were mixed together at a mass ratio of 7:3. The mixture was used as the positive electrode active material. Then, mixing was performed such that the resultant mixture contained 95.8 mass % of the positive electrode active material, 3 mass % of carbon powder, and 1.2 mass % of polyvinylidene fluoride powder serving as the binder. Thereafter, an appropriate amount of N-methyl-2-pyrrolidon was added to the mixture to prepare a positive electrode mixture slurry. Next, the positive electrode mixture slurry was applied by a doctor blade method to each surface of a positive electrode current collector made of an aluminum foil, dried, and thereafter, rolled by using a roller at a pressure of 500 MPa to produce a positive electrode including a positive electrode active material layer formed on each surface of the positive electrode current collector. A portion on which the positive electrode active material layer was not formed was provided in the center area of the positive electrode current collector in the longitudinal direction. A positive electrode tab was attached to such a portion. The thickness of the positive electrode mixture layer was about 140 μm. The total thickness of the positive electrode current collector and the positive electrode mixture layers on both surfaces of the positive electrode current collector was about 300 μm.

(10) [Production of Negative Electrode]

(11) Mixing was performed such that the resultant mixture contained 98.2 mass % of graphite serving as the negative electrode active material, 0.7 mass % of styrene-butadiene rubber, and 1.1 mass % of sodium carboxymethyl cellulose. Thereafter, an appropriate amount of water was added to the mixture to prepare a negative electrode mixture slurry. Next, the negative electrode mixture slurry was applied by a doctor blade method to each surface of a negative electrode current collector made of a copper foil, dried, and thereafter, rolled by using a roller to produce a negative electrode including a negative electrode active material layer formed on each surface of the negative electrode current collector. A portion on which the mixture layer was not formed was provided at each end of the negative electrode current collector in the longitudinal direction. A negative electrode tab was attached to each portion. The thickness of the negative electrode mixture layer was about 120 μm. The total thickness of the negative electrode current collector and the negative electrode mixture layers on both surfaces of the negative electrode current collector was about 250 μm.

(12) [Preparation of Nonaqueous Electrolyte Solution]

(13) In a nonaqueous solvent in which equal volumes of ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed together, lithium hexafluorophosphate (LiPF.sub.6) was dissolved at a concentration of 1.6 mol/L to prepare a nonaqueous electrolyte.

(14) [Production of Battery]

(15) A nonaqueous electrolyte secondary battery was produced by using the positive electrode, the negative electrode, the nonaqueous electrolyte solution, and a separator in accordance with the following procedure. (1) The positive electrode and the negative electrode were wound together with a separator disposed therebetween to produce an electrode body having a winding structure. (2) An insulating plate was disposed at each of the upper and lower ends of the electrode body. The wound electrode body was accommodated in a cylindrical battery outer can with a diameter of 18 mm and a height of 65 mm. (3) The current collector tab of the negative electrode was welded to the inner surface of the bottom portion of the battery outer can, and the current collector tab of the positive electrode was welded to the bottom plate of the sealing body. (4) A nonaqueous electrolyte solution was poured from the opening of the battery outer can, and thereafter, the battery outer can was sealed with the sealing body.

Example 2

(16) A nonaqueous electrolyte secondary battery was produced in the same manner as that in Example 1, except that W-free lithium composite oxide B containing Ni, Co, Mn, and Zr in Example 1 and lithium composite oxide A containing Ni, Co, Mn, W, and Zr in Example 1 were mixed together at a mass ratio of 8:2 and that the mixture was used as the positive electrode active material.

Example 3

(17) A nonaqueous electrolyte secondary battery was produced in the same manner as that in Example 1, except that W-free lithium composite oxide B containing Ni, Co, Mn, and Zr in Example 1 and lithium composite oxide A containing Ni, Co, Mn, W, and Zr in Example 1 were mixed together at a mass ratio of 5:5 and that the mixture was used as the positive electrode active material.

Example 4

(18) W-free lithium composite oxide B containing Ni, Co, Mn, and Zr was produced under the same conditions as that in Example 1, except that the precursor in Example 1 was changed to a precursor having a larger particle size in the production of the lithium composite oxide B. Regarding such a lithium composite oxide B, the proportion of Ni was 55 mol %, the proportion of Zr was 0.5 mol %, 50% particle size D50 was 17.0 μm, 10% particle size D10 was 8.6 μm, and 90% particle size D90 was 21.7 μm or less.

(19) A nonaqueous electrolyte secondary battery was produced in the same manner as that in Example 1, except that the above-produced W-free lithium composite oxide B containing Ni, Co, Mn, and Zr and lithium composite oxide A containing Ni, Co, Mn, W, and Zr in Example 1 were mixed together at a mass ratio of 7:3 and that the mixture was used as the positive electrode active material.

Example 5

(20) W-free lithium composite oxide B containing Ni, Co, Mn, and Zr was produced under the same conditions as that in Example 1, except that the precursor in Example 1 was changed to a precursor having a larger particle size than the precursor in Example 4 in the production of lithium composite oxide B. Regarding such a lithium composite oxide B, the proportion of Ni was 55 mol %, the proportion of Zr was 0.5 mol %, 50% particle size D50 was 21.0 μm, 10% particle size D10 was 10.2 μm, and 90% particle size D90 was 22.4 μm or less.

(21) A nonaqueous electrolyte secondary battery was produced in the same manner as that in Example 1, except that the above-produced W-free lithium composite oxide B containing Ni, Co, Mn, and Zr and lithium composite oxide A containing Ni, Co, Mn, W, and Zr in Example 1 were mixed together at a mass ratio of 7:3 and that the mixture was used as the positive electrode active material.

Example 6

(22) W-free lithium composite oxide B containing Ni, Co, Mn, and Zr was produced under the same conditions as that in Example 1, except that the precursor in Example 1 was changed to a precursor having a smaller particle size in the production of lithium composite oxide B. Regarding such a lithium composite oxide B, the proportion of Ni was 55 mol %, the proportion of Zr was 0.5 mol %, 50% particle size D50 was 10.0 μm, 10% particle size D10 was 7.0 μm, and 90% particle size D90 was 20.9 μm or less.

(23) A nonaqueous electrolyte secondary battery was produced in the same manner as that in Example 1, except that the above-produced W-free lithium composite oxide B containing Ni, Co, Mn, and Zr and lithium composite oxide A containing Ni, Co, Mn, W, and Zr in Example 1 were mixed together at a mass ratio of 7:3 and that the mixture was used as the positive electrode active material.

Example 7

(24) Lithium composite oxide A containing Ni, Co, Mn, W, and Zr was produced under the same conditions as that in Example 1, except that the precursor in Example 1 was changed to a precursor having a larger particle size in the production of lithium composite oxide A. Regarding such a lithium composite oxide A, the proportion of Ni was 35 mol %, the proportion of Zr was 0.5 mol %, the proportion of W was 0.5 mol %, 50% particle size D50 was 5.9 μm, 10% particle size D10 was 2.7 μm, and 90% particle size D90 was 6.8 μm or less.

(25) A nonaqueous electrolyte secondary battery was produced in the same manner as that in Example 1, except that W-free lithium composite oxide B containing Ni, Co, Mn, and Zr in Example 1 and the above-produced lithium composite oxide A containing Ni, Co, Mn, W, and Zr were mixed together at a mass ratio of 7:3 and that the mixture was used as the positive electrode active material.

Example 8

(26) Lithium composite oxide A containing Ni, Co, Mn, W, and Zr was produced under the same conditions as that in Example 1, except that the precursor in Example 1 was changed to a precursor having a smaller particle size in the production of lithium composite oxide A. Regarding such a lithium composite oxide A, the proportion of Ni was 35 mol %, the proportion of Zr was 0.5 mol %, the proportion of W was 0.5 mol %, 50% particle size D50 was 2.7 μm, 10% particle size D10 was 1.3 μm, and 90% particle size D90 was 4.4 μm or less.

(27) A nonaqueous electrolyte secondary battery was produced in the same manner as that in Example 1, except that W-free lithium composite oxide B containing Ni, Co, Mn, and Zr in Example 1 and the above-produced lithium composite oxide A containing Ni, Co, Mn, W, and Zr were mixed together at a mass ratio of 7:3 and that the mixture was used as the positive electrode active material.

Example 9

(28) W-free lithium composite oxide B containing Ni, Co, Mn, and Zr was produced under the same conditions as that in Example 1, except that the amount of Zr added in Example 1 was changed to 0.3 mol % in the production of lithium composite oxide B. Regarding such a lithium composite oxide B, the proportion of Ni was 55 mol %, the proportion of Zr was 0.3 mol %, 50% particle size D50 was 12.2 μm, 10% particle size D10 was 7.5 μm, and 90% particle size D90 was 21.3 μm or less.

(29) A nonaqueous electrolyte secondary battery was produced in the same manner as that in Example 1, except that the above-produced W-free lithium composite oxide B containing Ni, Co, Mn, and Zr and lithium composite oxide A containing Ni, Co, Mn, W, and Zr in Example 1 were mixed together at a mass ratio of 7:3 and that the mixture was used as the positive electrode active material.

Example 10

(30) Lithium composite oxide A containing Ni, Co, Mn, W, and Zr was produced under the same conditions as that in Example 1, except that the amount of Zr added in Example 1 was changed to 0.3 mol % in the production of lithium composite oxide A. Regarding such a lithium composite oxide A, the proportion of Ni was 35 mol %, the proportion of Zr was 0.3 mol %, the proportion of W was 0.5 mol %, 50% particle size D50 was 4.0 μm, 10% particle size D10 was 2.0 μm, and 90% particle size D90 was 5.6 μm or less.

(31) A nonaqueous electrolyte secondary battery was produced in the same manner as that in Example 1, except that W-free lithium composite oxide B containing Ni, Co, Mn, and Zr in Example 1 and the above-produced lithium composite oxide A containing Ni, Co, Mn, W, and Zr were mixed together at a mass ratio of 7:3 and that the mixture was used as the positive electrode active material.

Example 11

(32) Lithium composite oxide A containing Ni, Co, Mn, W, and Zr was produced under the same conditions as that in Example 1, except that the amount of W added in Example 1 was changed to 0.3 mol % in the production of lithium composite oxide A. Regarding such a lithium composite oxide A, the proportion of Ni was 35 mol %, the proportion of Zr was 0.5 mol %, the proportion of W was 0.3 mol %, 50% particle size D50 was 3.9 μm, 10% particle size D10 was 1.9 μm, and 90% particle size D90 was 5.6 μm or less.

(33) A nonaqueous electrolyte secondary battery was produced in the same manner as that in Example 1, except that W-free lithium composite oxide B containing Ni, Co, Mn, and Zr in Example 1 and the above-produced lithium composite oxide A containing Ni, Co, Mn, W, and Zr were mixed together at a mass ratio of 7:3 and that the mixture was used as the positive electrode active material.

Example 12

(34) W-free and Zr-free Lithium composite oxide B containing Ni, Co, and Mn was produced under the same conditions as that in Example 1, except that the composite oxide containing Ni, Co, and Mn and LiOH were mixed together such that the molar ratio of Li to the total amount of Ni, Co, and Mn was 1.10:1.00 in the production of lithium composite oxide B. Regarding lithium composite oxide B, the proportion of Ni and the particle size were the same as those in Example 1.

(35) A nonaqueous electrolyte secondary battery was produced in the same manner as that in Example 1, except that the above-produced W-free and Zr-free lithium composite oxide B containing Ni, Co, and Mn and lithium composite oxide A containing Ni, Co, Mn, W, and Zr in Example 1 were mixed together at a mass ratio of 7:3 and that the mixture was used as the positive electrode active material.

Example 13

(36) Zr-free lithium composite oxide A containing Ni, Co, Mn, and W was produced under the same conditions as that in Example 1, except that the composite oxide containing Ni, Co and Mn, LiOH, and the tungsten salt were mixed together such that the molar ratio of Li/total amount of Ni, Co and Mn/W was 1.07:1.00:0.005 in the production of lithium composite oxide A. Regarding lithium composite oxide A, the proportion of Ni and the particle size were the same as those in Example 1.

(37) A nonaqueous electrolyte secondary battery was produced in the same manner as that in Example 1, except that W-free and Zr-free lithium composite oxide B containing Ni, Co, and Mn in Example 12 and the above-produced Zr-free lithium composite oxide A containing Ni, Co, Mn, and W were mixed together at a mass ratio of 7:3 and that the mixture was used as the positive electrode active material.

Example 14

(38) Zr-free lithium composite oxide A containing Ni, Co, Mn, and W was produced under the same conditions as that in Example 1, except that the composite oxide containing Ni, Co and Mn, the tungsten salt, and LiOH were mixed together such that the molar ratio of Li/total amount of Ni, Co and Mn/W was 1.07:1.00:0.005 in the production of lithium composite oxide A. Regarding such a lithium composite oxide A, the proportion of Ni was 55 mol %, the proportion of W was 0.5 mol %, 50% particle size D50 was 4.1 μm, 10% particle size D10 was 2.3 μm, and 90% particle size D90 was 5.7 μm or less.

(39) A nonaqueous electrolyte secondary battery was produced in the same manner as that in Example 1, except that W-free lithium composite oxide B containing Ni, Co, Mn, and Zr in Example 1 and the above-produced Zr-free lithium composite oxide A containing Ni, Co, Mn, and W were mixed together at a mass ratio of 7:3 and that the mixture was used as the positive electrode active material.

Comparative Example 1

(40) Lithium composite oxide B containing Ni, Co, Mn, W, and Zr was produced under the same conditions as that in Example 1, except that the composite oxide containing Ni, Co, and Mn, the tungsten salt, the zirconium salt, and LiOH were mixed together such that the molar ratio of Li/total amount of Ni, Co, and Mn/W/Zr was 1.08:1.00:0.005:0.005 in the production of lithium composite oxide B. Regarding such a lithium composite oxide B, the proportion of Ni was 55 mol %, the proportion of W was 0.5 mol %, the proportion of Zr was 0.3 mol %, 50% particle size D50 was 11.9 μm, 10% particle size D10 was 7.4 μm, and 90% particle size D90 was 21.1 μm or less.

(41) A nonaqueous electrolyte secondary battery was produced in the same manner as that in Example 1, except that the above-produced lithium composite oxide B containing Ni, Co, Mn, W, and Zr and lithium composite oxide A containing Ni, Co, Mn, W, and Zr in Example 1 were mixed together at a mass ratio of 7:3 and that the mixture was used as the positive electrode active material.

Comparative Example 2

(42) A nonaqueous electrolyte secondary battery was produced in the same manner as that in Example 1, except that lithium composite oxide B containing Ni, Co, Mn, W, and Zr in Comparative Example 1 and lithium composite oxide A containing Ni, Co, Mn, W, and Zr in Example 1 were mixed together at a mass ratio of 9:1 and that the mixture was used as the positive electrode active material.

Comparative Example 3

(43) A nonaqueous electrolyte secondary battery was produced in the same manner as that in Example 1, except that lithium composite oxide B containing Ni, Co, Mn, W, and Zr in Comparative Example 1 and lithium composite oxide A containing Ni, Co, Mn, W, and Zr in Example 1 were mixed together at a mass ratio of 4:6 and that the mixture was used as the positive electrode active material.

Comparative Example 4

(44) W-free lithium composite oxide B containing Ni, Co, Mn, and Zr was produced under the same conditions as that in Example 1, except that the precursor in Example 1 was changed to a precursor having a larger particle size in the production of the lithium composite oxide B. Regarding such a lithium composite oxide B, the proportion of Ni was 55 mol %, the proportion of Zr was 0.5 mol %, 50% particle size D50 was 25.3 μm, 10% particle size D10 was 12.0 μm, and 90% particle size D90 was 29.3 μm or less.

(45) A nonaqueous electrolyte secondary battery was produced in the same manner as that in Example 1, except that the above-produced W-free lithium composite oxide B containing Ni, Co, Mn, and Zr and lithium composite oxide A containing Ni, Co, Mn, W, and Zr in Example 1 were mixed together at a mass ratio of 7:3 and that the mixture was used as the positive electrode active material.

Comparative Example 5

(46) W-free lithium composite oxide B containing Ni, Co, Mn, and Zr was produced under the same conditions as that in Example 1, except that the precursor in Example 1 was changed to a precursor having a smaller particle size in the production of lithium composite oxide B. Regarding such a lithium composite oxide B, the proportion of Ni was 55 mol %, the proportion of Zr was 0.5 mol %, 50% particle size D50 was 7.0 μm, 10% particle size D10 was 5.1 μm, and 90% particle size D90 was 10.2 μm or less.

(47) A nonaqueous electrolyte secondary battery was produced in the same manner as that in Example 1, except that the above-produced W-free lithium composite oxide B containing Ni, Co, Mn, and Zr and lithium composite oxide A containing Ni, Co, Mn, W, and Zr in Example 1 were mixed together at a mass ratio of 7:3 and that the mixture was used as the positive electrode active material.

Comparative Example 6

(48) Lithium composite oxide A containing Ni, Co, Mn, W, and Zr was produced under the same conditions as that in Example 1, except that the precursor in Example 1 was changed to a precursor having a larger particle size in the production of lithium composite oxide A. Regarding such a lithium composite oxide A, the proportion of Ni was 35 mol %, the proportion of W was 0.5 mol %, the proportion of Zr was 0.5 mol %, 50% particle size D50 was 7.0 μm, 10% particle size D10 was 4.9 μm, and 90% particle size D90 was 9.9 μm or less.

(49) A nonaqueous electrolyte secondary battery was produced in the same manner as that in Example 1, except that W-free lithium composite oxide B containing Ni, Co, Mn, and Zr in Example 1 and the above-produced lithium composite oxide A containing Ni, Co, Mn, W, and Zr were mixed together at a mass ratio of 7:3 and that the mixture was used as the positive electrode active material.

Comparative Example 7

(50) Lithium composite oxide A containing Ni, Co, Mn, W, and Zr was produced under the same conditions as that in Example 1, except that the precursor in Example 1 was changed to a precursor having a smaller particle size in the production of lithium composite oxide A. Regarding such a lithium composite oxide A, the proportion of Ni was 35 mol %, the proportion of W was 0.5 mol %, the proportion of Zr was 0.5 mol %, 50% particle size D50 was 1.5 μm, 10% particle size D10 was 0.3 μm, and 90% particle size D90 was 2.6 μm or less.

(51) A nonaqueous electrolyte secondary battery was produced in the same manner as that in Example 1, except that W-free lithium composite oxide B containing Ni, Co, Mn, and Zr in Example 1 and the above-produced lithium composite oxide A containing Ni, Co, Mn, W, and Zr were mixed together at a mass ratio of 7:3 and that the mixture was used as the positive electrode active material.

Comparative Example 8

(52) Zr-free lithium composite oxide A containing Ni, Co, Mn, and W was produced under the same conditions as that in Example 1, except that the composite oxide containing Ni, Co and Mn, the tungsten salt, and LiOH were mixed together such that the molar ratio of Li/total amount of Ni, Co and Mn/W was 1.11:1.00:0.005 in the production of lithium composite oxide A. Regarding such a lithium composite oxide A, the proportion of Ni was 35 mol %, the proportion of W was 0.5 mol %, 50% particle size D50 was 4.0 μm, 10% particle size D10 was 2.2 μm, and 90% particle size D90 was 5.6 μm or less.

(53) A nonaqueous electrolyte secondary battery was produced in the same manner as that in Example 1, except that lithium composite oxide B containing Ni, Co, Mn, W, and Zr in Comparative Example 1 and the above-produced Zr-free lithium composite oxide A containing Ni, Co, Mn, and W were mixed together at a mass ratio of 7:3 and that the mixture was used as the positive electrode active material.

Comparative Example 9

(54) W-free lithium composite oxide A containing Ni, Co, Mn, and Zr was produced under the same conditions as that in Example 1, except that the composite oxide containing Ni, Co, and Mn, the zirconium salt, and LiOH were mixed together such that the molar ratio of Li/total amount of Ni, Co, and Mn/Zr was 1.11:1.00:0.005 in the production of lithium composite oxide A. Regarding such a lithium composite oxide A, the proportion of Ni was 35 mol %, the proportion of Zr was 0.5 mol %, 50% particle size D50 was 4.3 μm, 10% particle size D10 was 2.3 μm, and 90% particle size D90 was 5.9 μm or less.

(55) A nonaqueous electrolyte secondary battery was produced in the same manner as that in Example 1, except that lithium composite oxide B containing Ni, Co, Mn, W, and Zr in Comparative Example 1 and the above-produced W-free lithium composite oxide A containing Ni, Co, Mn, and Zr were mixed together at a mass ratio of 7:3 and that the mixture was used as the positive electrode active material.

Comparative Example 10

(56) Zr-free lithium composite oxide B containing Ni, Co, Mn, and W was produced under the same conditions as that in Example 1, except that the composite oxide containing Ni, Co, and Mn, the tungsten salt, and LiOH were mixed together such that the molar ratio of Li/total amount of Ni, Co, and Mn/W was 1.08:1.00:0.005 in the production of lithium composite oxide B. Regarding such a lithium composite oxide B, the proportion of Ni was 55 mol %, the proportion of W was 0.5 mol %, 50% particle size D50 was 11.9 μm, 10% particle size D10 was 7.1 μm, and 90% particle size D90 was 21.1 μm or less.

(57) A nonaqueous electrolyte secondary battery was produced in the same manner as that in Example 1, except that the above-produced Zr-free lithium composite oxide B containing Ni, Co, Mn, and W and lithium composite oxide A containing Ni, Co, Mn, W, and Zr in Example 1 were mixed together at a mass ratio of 7:3 and that the mixture was used as the positive electrode active material.

(58) [Measurement of Battery Capacity]

(59) At an environmental temperature of 25° C., each battery in Examples and Comparative Examples was charged at a constant current of 2000 mA, which equaled 1 It, until the battery voltage reached 4.2 V, and thereafter, charged at a constant voltage of 4.2 V. Then, each battery was discharged at a constant current of 2000 mA, which equaled 1 It, until the battery voltage reached 2.5 V. The discharge capacity at this time was regarded as the battery capacity (rated capacity).

(60) [Measurement of Battery Power]

(61) After each battery in Examples and Comparative Examples was charged to 50% of its rated capacity, the discharge cut-off voltage was set to 2 V, and the power at a state of charge (SOC) of 50% was determined from the following formula by using the largest current at which charging can be performed for 10 seconds at a battery temperature of 25° C.
power (SOC 50%)=(largest current)×(discharge cut-off voltage (2.0 V))
[Charging/Discharging Cycle Test]

(62) At an environmental temperature of 45° C., each battery in Examples and Comparative Examples was charged at a constant current of 2000 mA, which equaled 1 It, until the battery voltage reached 4.2 V, and thereafter, charged at a constant voltage of 4.2 V. Then, each battery was discharged at a constant current of 2000 mA, which equaled 1 It, to 2.5 V. Such a charging/discharging cycle was performed 500 cycles. Then, capacity retention was calculated from the following formula.
capacity retention (%)=discharge capacity at 500th cycle/discharge capacity at 1st cycle×100
[Measurement Test of Amount of Gas Generated]

(63) After each battery in Examples and Comparative Examples was subjected to 500 cycles of the above charging/discharging cycles, the amount of gas generated was measured by a buoyancy method. Specifically, the difference between the mass of the battery in water after 500 cycles and the mass of the battery in water before the test was regarded as the amount of gas generated.

(64) Table 1 shows the results of the battery capacity, the battery power, and the amount of gas generated in each of Examples and Comparative Examples.

(65) TABLE-US-00001 TABLE 1 Lithium composite oxide A Lithium composite oxide B Additive Additive element element Battery characteristics content content Mass Discharge Power Capacity Amount Particle size (μm) (mol %) Particle size (μm) (mol %) ratio capacity characteristics retention of gas D50 D10 D90 Zr W D50 D10 D90 Zr W B:A (mAh) (W) (%) (cm.sup.3) Example 1 4.2 2.3 5.8 0.5 0.5 12.1  7.3 21.2 0.5 0.0 7:3 2052 71.9 90 3.8 Example 2 4.2 2.3 5.8 0.5 0.5 12.1  7.3 21.2 0.5 0.0 8:2 2068 70.0 92 3.2 Example 3 4.2 2.3 5.8 0.5 0.5 12.1  7.3 21.2 0.5 0.0 5:5 2001 75.3 88 4.3 Example 4 4.2 2.3 5.8 0.5 0.5 17.0  8.6 21.7 0.5 0.0 7:3 2039 70.1 93 3.6 Example 5 4.2 2.3 5.8 0.5 0.5 21.0 10.2 22.4 0.5 0.0 7:3 2021 69.0 92 3.0 Example 6 4.2 2.3 5.8 0.5 0.5 10.0  7.0 20.9 0.5 0.0 7:3 2046 72.6 89 4.0 Example 7 5.9 2.7 6.8 0.5 0.5 12.1  7.3 21.2 0.5 0.0 7:3 2058 68.9 91 2.6 Example 8 2.7 1.3 4.4 0.5 0.5 12.1  7.3 21.2 0.5 0.0 7:3 2013 74.7 88 4.3 Example 9 4.2 2.3 5.8 0.5 0.5 12.2  7.5 12.3 0.3 0.0 7:3 2057 72.0 89 3.9 Example 10 4.0 2.0 5.6 0.3 0.5 12.1  7.3 21.2 0.5 0.0 7:3 2053 72.0 89 4.1 Example 11 3.9 1.9 5.6 0.5 0.3 12.1  7.3 21.2 0.5 0.0 7:3 2052 69.0 90 2.9 Example 12 4.2 2.3 5.8 0.5 0.5 12.1  7.3 21.2 0.0 0.0 7:3 2059 72.0 87 4.5 Example 13 4.2 2.3 5.8 0.0 0.5 12.1  7.3 21.2 0.0 0.0 7:3 2055 72.0 85 5.9 Example 14 4.1 2.3 5.7 0.0 0.5 12.1  7.3 21.2 0.5 0.0 7:3 2054 71.9 86 4.6 Comparative 4.2 2.3 5.8 0.5 0.5 11.9  7.4 21.1 0.5 0.5 7:3 2020 72.2 89 5.0 Example 1 Comparative 4.2 2.3 5.8 0.5 0.5 11.9  7.4 21.1 0.5 0.5 9:1 2069 67.3 91 5.1 Example 2 Comparative 4.2 2.3 5.8 0.5 0.5 11.9  7.4 21.1 0.5 0.5 4:6 1977 74.0 85 6.9 Example 3 Comparative 4.2 2.3 5.8 0.5 0.5 25.3 12.0 29.3 0.5 0.0 7:3 1996 66.2 92 2.9 Example 4 Comparative 4.2 2.3 5.8 0.5 0.5  7.0  5.1 10.2 0.5 0.0 7:3 2023 73.9 89 4.9 Example 5 Comparative 7.0 4.9 9.9 0.5 0.5 12.1  7.3 21.2 0.5 0.0 7:3 2050 67.1 93 3.0 Example 6 Comparative 1.5 0.3 2.6 0.5 0.5 12.1  7.3 21.2 0.5 0.0 7:3 1990 75.2 87 5.0 Example 7 Comparative 4.0 2.2 5.6 0.0 0.5 11.9  7.4 21.1 0.5 0.5 7:3 2021 72.0 91 6.1 Example 8 Comparative 4.3 2.3 5.9 0.5 0.0 11.9  7.4 21.1 0.5 0.5 7:3 2022 64.9 88 3.2 Example 9 Comparative 4.2 2.3 5.8 0.5 0.5 11.9  7.1 21.1 0.0 0.5 7:3 2031 72.2 87 5.8 Example 10

(66) The positive electrode active materials in Examples 1 to 14 contain lithium composite oxide A containing W and Ni and W-free lithium composite oxide B containing Ni. Regarding the lithium composite oxide A, the proportion of Ni relative to the total moles of metal elements except for lithium is 30 to 60 mol %, 50% particle size D50 in the cumulative particle size distribution on a volume basis is 2 to 6 μm, 10% particle size D10 in the cumulative particle size distribution on a volume basis is 1.0 μm or more, and 90% particle size D90 in the cumulative particle size distribution on a volume basis is 6.8 μm or less. Regarding the lithium composite oxide B, the proportion of Ni relative to the total moles of metal elements except for lithium is 50 to 95 mol %, 50% particle size D50 in the cumulative particle size distribution on a volume basis is 10 to 22 μm, 10% particle size D10 in the cumulative particle size distribution on a volume basis is 7.0 μm or more, and 90% particle size D90 in the cumulative particle size distribution on a volume basis is 22.5 μm or less. The mass ratio of the lithium composite oxide A to the lithium composite oxide B is 1:1 to 1:5.7. The batteries in Examples 1 to 14 using such a positive electrode active material had characteristics including high battery capacity, high power, and a small amount of gas generated, compared with those in Comparative Examples 1 to 12, in which at least one of, for example, the above additive element, the above particle size, and the above mixture ratio was out of the above-defined range.

(67) Among Examples 1 to 14, the capacity retention in the charging/discharging cycle characteristics was higher and the amount of gas generated was smaller in Examples 1 to 11, in which Zr was added to lithium composite oxide B, than in the other Examples. In Examples 4 and 5, in which lithium composite oxide B had a larger particle size, and in Example 7, in which lithium composite oxide A had a larger particle size, the capacity retention further increased, and the amount of gas generated decreased. In Examples 6 and 8, in which lithium composite oxide A or B had a smaller particle size, the power further increased. In Examples 1, 2, and 3, in which the mass ratios of lithium composite oxide A to lithium composite oxide B were different from each other, as the ratio of lithium composite oxide B increased, the capacity retention increased, and the amount of gas decreased. As the ratio of lithium composite oxide A increased, the power increased.