Positive electrode active material and rechargeable battery including the same

1. A positive electrode active material comprising:

primary particles including a metal including at least one of Ni, Co, or Mn; and

a secondary particle in which the primary particles are agglomerated,

wherein the primary particles are formed by particles having different crystal structure, but made of the same material.

2. The positive electrode active material of claim 1 , wherein the primary particles comprise:

a first type particle having a hexagonal crystal structure; and

a second type particle having a cubic crystal structure.

3. The positive electrode active material of claim 2 , wherein a length of the first type particle is longer than a length of the second type particle.

4. The positive electrode active material of claim 3 , wherein the lengths of the first type particle and the second type particle are defined in a direction from a central portion of the secondary particle toward a surface portion of the secondary particle.

5. The positive electrode active material of claim 2 , wherein a content ratio of the first type particle is higher than a content ratio of the second type particle in the secondary particle.

6. The positive electrode active material of claim 2 , wherein a content ratio of the second type particle is higher than a content ratio of the first type particle in the secondary particle.

7. The positive electrode active material of claim 1 , wherein a concentration of the metal is varied in a direction from a central portion of the secondary particle toward a surface portion of the secondary particle.

8. The positive electrode active material of claim 1 , wherein the secondary particle comprises:

a concentration maintained portion in which a concentration of the metal is constant; and

a concentration gradient portion which surrounds the concentration maintained portion and in which a concentration of the metal is varied in a direction from a central portion of the secondary particle toward a surface portion of the secondary particle.

9. The positive electrode active material of claim 1 , wherein the secondary particle comprises:

a first concentration gradient portion in which a concentration of the metal is varied with a first gradient in a direction from a central portion of the secondary particle toward a surface portion of the secondary particle; and

a second concentration gradient portion in which a concentration of the metal is varied with a second gradient different from the first gradient in the direction from the central portion of the secondary particle toward the surface portion of the secondary particle.

10. A positive electrode active material comprising:

primary particles including a metal including at least one of Ni, Co, or Mn; and

a secondary particle in which the primary particles are agglomerated,

wherein the primary particles comprise:

first type particles extending in a direction from a central portion of the secondary particle toward a surface portion of the secondary particle; and

second type particles disposed between the first type particles and having a different crystal structure from the first type particles,

wherein the crystal structure of the first type particle includes an a-axis and a c-axis,

wherein a length of the first type particle in an a-axis direction is longer than a length of the first type particle in a c-axis direction, and

wherein the a-axis of the first type particle extends in the direction from the central portion of the secondary particle toward the surface portion of the secondary particle.

11. A lithium metal composite oxide comprising:

a secondary particle formed by gathering a plurality of primary particles,

wherein the lithium metal composite oxide includes a transition metal, and

wherein the primary particles comprise: a primary particle having a hexagonal crystal structure; and a primary particle having a cubic crystal structure,

wherein the primary particle having the cubic crystal structure has a radial crystalline texture of which a {1,1,1} plane, on which positive ions are stacked, is oriented in a radial direction from a central portion of the secondary particle toward a surface portion of the secondary particle.

12. The lithium metal composite oxide of claim 11 , wherein the primary particle has a crystalline texture that is oriented in a radial direction from a central portion of the secondary particle toward a surface portion of the secondary particle.

13. The lithium metal composite oxide of claim 11 , wherein the primary particle having the hexagonal crystal structure has a crystalline texture of which a direction of an (a,b) layer surface is oriented in a radial direction from a central portion of the secondary particle toward a surface portion of the secondary particle and of which a direction of a c-layer surface is oriented in a tangential direction of the secondary particle.

14. The lithium metal composite oxide of claim 11 , wherein a content ratio of the primary particle having the cubic crystal structure in an entire portion of the secondary particle increases as a content ratio of nickel in the entire portion of the secondary particle increases.

15. A rechargeable battery comprising:

a positive electrode including the positive electrode active material of claim 1 ;

a negative electrode; and

an electrolyte disposed between the positive electrode and the negative electrode.

16. A rechargeable battery comprising:

a positive electrode including the positive electrode active material of claim 10 ;

a negative electrode; and

an electrolyte disposed between the positive electrode and the negative electrode.

17. A rechargeable battery comprising:

a positive electrode including the lithium metal composite oxide of claim 11 ;

a negative electrode; and

an electrolyte disposed between the positive electrode and the negative electrode.