Positive electrode active material for lithium secondary battery and positive electrode including same
There is provided a positive electrode active material capable of achieving a high volume energy density and yet superior rate characteristics when configured as a positive electrode for lithium secondary batteries. This positive electrode active material comprises a plurality of secondary particles each comprising primary particles composed of a lithium-nickel based complex oxide having a layered rock-salt structure. The plurality of secondary particles have a volume-based average particle diameter D50 of 5 to 100 μm, and at least part of the plurality of secondary particles are coarse secondary particles having a particle diameter of 9 μm or greater. The coarse secondary particles have a voidage of 5 to 25%, and the ratio of through holes among all voids in the coarse secondary particles is 70% or greater.
1. A positive electrode active material for lithium secondary batteries, comprising a plurality of secondary particles each comprising primary particles composed of a lithium-nickel-based complex oxide having a layered rock-salt structure,
wherein the plurality of secondary particles have a volume-based average particle diameter D50 of 5 to 100 μm, wherein at least part of the plurality of secondary particles are coarse secondary particles having a particle diameter of 9 μm or greater,
wherein the coarse secondary particles have a voidage of 5 to 25%, and wherein a ratio of through holes among all voids in the coarse secondary particles is 70% or greater, and
wherein the through holes are open pores with both ends of each through hole being in communication with outside the coarse secondary particle.
2. The positive electrode active material according to claim 1 , wherein a proportion of the coarse secondary particles among all the secondary particles is 20 to 100% by mass.
3. The positive electrode active material according to claim 1 , wherein the through holes among all voids in the coarse secondary particles have an average through hole diameter of 0.5 to 5 μm.
4. The positive electrode active material according to claim 1 , wherein the primary particles have an average particle diameter of 0.5 to 5 μm.
5. The positive electrode active material according to claim 4 , wherein a value obtained by dividing the average particle diameter of the primary particles by an average through hole diameter is 0.2 to 2.
6. The positive electrode active material according to claim 1 , having a tap density of 2.5 to 3.1 g/cc.
7. The positive electrode active material according to claim 1 , having a press density of 3.0 to 3.5 g/cc when uniaxially pressed at a pressure of 1.0 kgf/cm 2 .
8. The positive electrode active material according to claim 1 , wherein the lithium-nickel-based complex oxide is represented by a general formula:
Li x Ni 1-z M z O 2
wherein 0.96≤x≤1.09, 0<z≤0.5, and M is at least one metal element selected from the group consisting of Co, Al, Mg, Mn, Ti, Fe, Cr, Zn, and Ga.
9. The positive electrode active material according to claim 1 , wherein at least part of the coarse secondary particles are uniaxially oriented, plate-like coarse secondary particles having an aspect ratio of 2.0 or greater, wherein each of the uniaxially oriented, plate-like coarse secondary particle is composed of the primary particles that are oriented in an uniaxial direction.
10. The positive electrode active material according to claim 9 , wherein (003) planes of the primary particles in the uniaxially oriented, plate-like coarse secondary particles are oriented in parallel to plate surfaces of the uniaxially oriented, plate-like coarse secondary particles, and wherein a peak intensity ratio [003]/[104] of the uniaxially oriented, plate-like coarse secondary particles, which is a ratio of diffraction intensity from (003) planes to diffraction intensity from (104) planes in X-ray diffraction, is 3.0 or greater.
11. The positive electrode active material according to claim 9 , wherein approximately all of the coarse secondary particles are uniaxially oriented, plate-like coarse secondary particles.
12. The positive electrode active material according to claim 9 , wherein the uniaxially oriented, plate-like coarse secondary particles have a thickness of 10 to 20 μm and a width of 30 to 100 μm.
13. The positive electrode active material according to claim 9 , wherein at least part of the plurality of secondary particles are approximately spherical, isometric secondary particles, and wherein the secondary particles comprises a mixture of the isometric secondary particles and the uniaxially oriented, plate-like coarse secondary particles.
14. The positive electrode active material according to claim 13 , wherein a proportion of the uniaxially oriented, plate-like coarse secondary particles among all the secondary particles is 20 to 70% by mass.
15. The positive electrode active material according to claim 1 , wherein approximately all of the secondary particles are uniaxially oriented, plate-like coarse secondary particles.
16. A positive electrode for lithium secondary batteries, comprising a positive electrode active material layer comprising the positive electrode active material according to claim 1 , a binder, and an electrically conductive additive.
17. The positive electrode according to claim 16 , wherein the positive electrode active material layer has a thickness of 50 μm or greater.
18. The positive electrode according to claim 16 , wherein the positive electrode active material layer has a density of 3.4 g/cc or greater.