Positive electrode active material for lithium secondary battery
Embodiments of the inventive concepts described herein relate to a positive electrode active material for lithium secondary battery, and more particularly, relate to a positive electrode active material for a lithium secondary battery having a new structure which includes a core portion having gradients of concentrations of nickel, manganese, and cobalt in a direction from a center to a surface and in which each of the concentration gradients of nickel, manganese, and cobalt has at least one vertex in the core portion.
1. A positive electrode active material for lithium secondary battery, the positive electrode active material comprising:
a core portion having nickel, manganese, and cobalt, and concentration gradients of the nickel, manganese, and cobalt in a direction from a center to a surface,
wherein a profile of each concentration gradient of the nickel, manganese, and cobalt has at least one vertex in the core portion,
wherein the vertexes of the nickel, manganese and cobalt are provided at the same distance from the center,
wherein the concentration gradients of the nickel and manganese from the center to the vertexes are constant, wherein a concentration of nickel is increased from the center to the vertex, and a concentration of manganese is decreased from the center to the vertex,
wherein the concentration of nickel in the core portion is higher than the concentration of manganese in the core portion, and
wherein the concentration of nickel in the core portion is higher than the concentration of cobalt in the core portion.
2. The positive electrode active material of claim 1 , wherein the core portion comprises:
a first core portion having magnitudes of the concentration gradients of nickel, manganese, and cobalt which are represented by CS1-Ni, CS1-Mn, and CS1-Co, respectively; and
a second core portion having magnitudes of the concentration gradients of nickel, manganese, and cobalt which are represented by CS2-Ni, CS2-Mn, CS2-Co, respectively, and
wherein the magnitude CS1-Ni of the concentration gradient of nickel in the first core portion and the magnitude CS2-Ni of the concentration gradient of nickel in the second core portion satisfy the following Equation
(CS1-Ni)×(CS2-Ni)<0.
3. The positive electrode active material of claim 2 , wherein the magnitude CS1-Mn of the concentration gradient of manganese in the first core portion and the magnitude CS2-Mn of the concentration gradient of manganese in the second core portion satisfy the following Equation
(CS1-Mn)×(CS2-Mn)<0.
4. The positive electrode active material of claim 2 , wherein the magnitude CS1-Co of the concentration gradient of cobalt in the first core portion and the magnitude CS2-Co of the concentration gradient of cobalt in the second core portion satisfy the following Equation
(CS1-Co)×(CS2-Co)<0.
5. The positive electrode active material of claim 2 , wherein the core portion further comprises: a first concentration-maintained portion having constant concentrations of nickel, manganese, and cobalt between the first core portion and the second core portion.
6. The positive electrode active material of claim 2 , wherein the core portion further comprises: a second concentration-maintained portion having constant concentrations of nickel, manganese, and cobalt,
wherein the second concentration-maintained portion is surrounded by the first core portion.
7. The positive electrode active material of claim 1 , further comprising: a shell portion having constant concentrations of nickel, manganese, and cobalt on an outer peripheral surface of the core portion.
8. The positive electrode active material of claim 7 , wherein the shell portion comprises:
a first shell portion having constant concentrations of nickel, manganese, and cobalt which are represented by SC1-Ni, SC1-Mn, and SC1-Co, respectively; and
a second shell portion having constant concentrations of nickel, manganese, and cobalt which are represented by SC2-Ni, SC2-Mn, and SC2-Co, respectively.
9. The positive electrode active material of claim 7 , wherein a volume of the shell portion is 30% or less of a total volume of the shell portion and the core portion.
10. A lithium secondary battery comprising the positive electrode active material of claim 1 .
11. The positive electrode active material of claim 2 , wherein CS2-Ni is larger than CS1-Ni, CS2-Mn is larger than CS1-Mn, and CS2-Co is larger than CS1-Co, and wherein the second core portion is thicker than the first core portion.