Method of preparing cathode active material precursor for lithium rechargeable battery, cathode active material precursor for lithium rechargeable battery prepared thereby, and cathode active material formed using the cathode active material precursor
The present invention relates to a method of preparing a cathode active material precursor for a lithium rechargeable battery, the cathode active material precursor for the lithium rechargeable battery prepared thereby, and a cathode active material formed using the cathode active material precursor. According to the present invention, the method of preparing a cathode active material precursor for a lithium secondary battery controls the concentration of a concentration gradient part and a shell part in a precursor to obtain a desired concentration of a transition metal in the shell part. As a result, a metal composition is distributed in a continuous concentration gradient from the interface between the core part and the shell part to the surface of the cathode active material, thereby a cathode active material with excellent thermal stability.
1. A method of preparing a cathode active material precursor for a lithium rechargeable battery, the method comprising:
preparing a metallic salt aqueous solution for formation of a core part and a metallic salt aqueous solution for formation of a shell part that include nickel, cobalt, and manganese as metallic salts;
providing a first chelating agent, a first alkaline aqueous solution, the metallic salt aqueous solution for the formation of the core part, and the metallic salt aqueous solution for the formation of the shell part into a reactor while changing a mixing ratio of the metallic salt aqueous solution for the formation of the core part and the metallic salt aqueous solution for the formation of the shell part, thereby forming a concentration gradient part of which concentrations of metallic salts are gradually changed;
providing a second chelating agent, a second alkaline aqueous solution, the metallic salt aqueous solution for the formation of the core part, and the metallic salt aqueous solution for the formation of the shell part into the reactor while mixing the metallic salt aqueous solution for the formation of the core part and the metallic salt aqueous solution for the formation of the shell part at a fixed ratio, thereby forming a shell part having a fixed concentration; and
drying and heating a formed precipitate to prepare an active material precursor,
wherein a concentration of a specific metallic salt of the concentration gradient part in a contact portion of the concentration gradient part and the shell part is denoted by “M C ”, and a concentration of the specific metallic salt of the shell part in the contact portion of the concentration gradient part and the shell part is denoted by “M S ”, and
wherein the M C and the M S satisfy a relation formula M C ≠M S .
2. The method of claim 1 , wherein a concentration of the specific metallic salt at a center of the concentration gradient part is denoted by “M CO ”,
wherein the M C and the M S satisfy a relation formula M C <M S when the M CO and the M C satisfy a relation formula M CO <M C .
3. The method of claim 1 , wherein a concentration of the specific metallic salt at a center of the concentration gradient part is denoted by “M CO ”,
wherein the M C and the M S satisfy a relation formula M C >M S when the M CO and the M C satisfy a relation formula M CO >M C .
4. The method of claim 2 , wherein a difference between the M S and the M C is in a range of 2 mol % to 40 mol %.
5. The method of claim 3 , wherein a difference between the M S and the M C is in a range of 2 mol % to 30 mol %.
6. The method of claim 2 , wherein a metal of the specific metallic salt satisfying the relation formula M CO <M C is nickel.
7. The method of claim 3 , wherein a metal of the specific metallic salt satisfying the relation formula M CO >M C is cobalt and manganese.
8. The method of claim 1 , further comprising:
providing a third chelating agent, a third alkaline aqueous solution, and the metallic salt aqueous solution for the formation of the core part to form a core part between preparing the metallic salt aqueous solution for the formation of the core part and the metallic salt aqueous solution for the formation of the shell part; and providing the chelating agent, the alkaline aqueous solution, the metallic salt aqueous solution for the formation of the core part, and the metallic salt aqueous solution for the formation of the shell part into the reactor while changing a mixing ratio of the metallic salt aqueous solution for the formation of the core part and the metallic salt aqueous solution for the formation of the shell part, thereby preparing the concentration gradient part.
9. The method of claim 1 , wherein the metallic salt aqueous solution for the formation of the shell part is used in plurality, and the plurality of the metallic salt aqueous solutions for the formation of the shell part have concentrations different from each other.
10. The method of claim 1 , wherein the concentration gradient part includes a metallic salt of which a concentration gradient is changed.
11. A cathode active material precursor for a lithium rechargeable battery prepared by the method of claim 1 .
12. A method of preparing a cathode active material for a lithium rechargeable battery, the method comprising:
mixing the cathode active material precursor prepared by claim 1 with lithium salt; and
firing the mixture of the cathode active material precursor and the lithium salt to obtain a lithium composite metal oxide.
13. A cathode active material for a lithium rechargeable battery prepared by claim 12 .