Positive electrode active material powder for lithium secondary battery
To provide a lithium-nickel-cobalt-manganese composite oxide powder for a positive electrode of a lithium secondary battery, which has a large volume capacity density and high safety and is excellent in the charge and discharge cyclic durability. A positive electrode active material powder for a lithium secondary battery characterized by comprising a first granular powder having a compression breaking strength of at least 50 MPa and a second granular powder having a compression breaking strength of less than 40 MPa, formed by agglomeration of many fine particles of a lithium composite oxide represented by the formula Li p Ni x Co y Mn z M q O 2-a F a (wherein M is a transition metal element other than Ni, Co and Mn, Al or an alkaline earth metal element, 0.9≦p≦1.1, 0.2≦x≦0.8, 0≦y≦0.4, 0≦z≦0.5, y+z>0, 0≦q≦0.05, 1.9≦2−a≦2.1, x+y+z+q=1 and 0≦a≦0.02) to have an average particle size D50 of from 3 to 15 μm, in a weight ratio of the first granular powder/the second granular powder being from 50/50 to 90/10.
1. A positive electrode active material powder for a lithium secondary battery characterized by comprising a first granular powder having a compression breaking strength of at least 50 MPa and a second granular powder having a compression breaking strength of less than 40 MPa, formed by agglomeration of many fine particles of a lithium composite oxide represented by the formula Li p Ni x Co y Mn z M q O 2-a F a (wherein M is Al, an alkaline earth metal element or a transition metal element other than Ni, Co and Mn, 0.9≦p≦1.1, 0.2≦x≦0.8, 0≦y≦0.4 0.10≦z≦0.42,y+z>0, 0≦q≦0.05, 1.9≦2-a≦2.1, x+y+z+q=1, and 0≦a≦0.02) to have an average particle size D50 of from 3 to 15 μm, in a weight ratio of the first granular powder/the second granular powder being from 50/50 to 90/10; wherein the ratio of the compression strength of the first granular powder/the compression strength of the second granular powder is from 65/30 to 200/10.
2. The positive electrode active material powder for a lithium secondary battery according to claim 1 , wherein M is at least one element selected from the group consisting of Ti, Zr, Hf, V, Nb, Ta, Mg, Ca, Sr, Ba and Al.
3. The positive electrode active material powder for a lithium secondary battery according to claim 1 , wherein M is at least one element selected from the group consisting of Ti, Zr, Hf, Mg and Al.
4. The positive electrode active material powder for a lithium secondary battery according to claim 1 , wherein the specific surface area of the positive electrode active material powder is from 0.3 to 2.0 m 2 /g, and the grain shape is substantially spherical.
5. The positive electrode active material powder for a lithium secondary battery according to claim 1 , wherein the press density of the positive electrode active material powder is from 3.1 to 3.4 g/cm 3 .
6. A positive electrode for a lithium secondary battery containing the positive electrode active material powder as defined in claim 1 .
7. A lithium secondary battery employing the positive electrode as defined in claim 6 .
8. A method of making a positive electrode active material powder, the method comprising
firing at a temperature in a range of from 700° C. to 1050° C. a mixture comprising a lithium source, a nickel source, at least one of a cobalt source and a manganese source, an optional element M source, and an optional fluorine source; and
producing the powder of claim 1 .
9. The positive electrode active material powder for a lithium secondary battery according to claim 1 , wherein the compression breaking strength of the first granular powder is from 80 to 300 MPa and the compression breaking strength of the second granular powder is from 10 to 30 MPa.