Lithium composite oxide and lithium secondary battery comprising the same
The present invention relates to a lithium composite oxide capable of improving capacity and lifetime characteristics of a lithium secondary battery and a lithium secondary battery including the same. According to the present invention, since the atomic ratio of boron (B) and nickel (Ni) in the surface region of the lithium composite oxide including primary particles enabling lithium intercalation and deintercalation and secondary particles formed by aggregating the primary particles is in a specific range, the stability of the lithium composite oxide may be improved, and thus it is possible to improve the capacity and lifetime characteristics of the lithium secondary battery using the lithium composite oxide as a positive electrode active material.
1. A lithium composite oxide, comprising:
primary particles enabling lithium intercalation and deintercalation and secondary particles formed by aggregating the primary particles,
wherein the lithium composite oxide comprises i) nickel (Ni) and cobalt (Co), ii) at least one selected from manganese (Mn) and aluminum (Al) and iii) boron (B),
wherein the atomic ratio of boron (B) and nickel (Ni) in a surface region of the secondary particles satisfies Expression 1 below:
0.2≤B/Ni≤29.0, [Expression 1]
wherein the surface region is from the outermost surface of the secondary particles to a depth of 10 nm of the secondary particles, and
wherein a ratio of the atomic ratio of boron (B) and nickel (Ni) in the surface region of the secondary particles and the atomic ratio of boron (B) and nickel (Ni) in the total composition of the secondary particles is 160 to 1,500.
2. The lithium composite oxide of claim 1 , wherein the lithium composite oxide is represented by Formula 1 below:
Li w Ni 1−(x+y+z) Co x B y M 1 z M 2 z′ O 2 [Formula 1]
(Here,
M1 is at least one selected from Mn and Al,
M2 is at least one selected from Mn, Ba, Ce, Hf, Ta, Cr, F, Mg, Al, Cr, V, Ti, Fe, Zr, Zn, Si, Y, Nb, Ga, Sn, Mo, W, P, Sr, Ge, Nd, Gd and Cu,
M1 and M2 are different elements, and
0.5≤w≤1.5, 0<x≤0.50, 0<y≤0.20, 0≤z≤0.20, and 0≤z′≤0.20).
3. The lithium composite oxide of claim 1 , wherein the atomic ratio (B/Ni) of boron (B) and nickel (Ni) in the lithium composite oxide has a gradient that decreases from a surface region of the lithium composite oxide to a core region of the lithium composite oxide.
4. The lithium composite oxide of claim 1 , comprising:
a coating layer in which a boron (B)-containing oxide is present, which covers at least a part of an interface between the primary particles, or at least a part of the surface region of the secondary particles, or both at least the part of the interface between the primary particles and at least the part of the surface region of the secondary particles.
5. The lithium composite oxide of claim 4 , wherein the coating layer further comprises at least one oxide represented by Formula 2 below:
Li a M 3 b O c [Formula 2]
(Here, M3 is at least one selected from Ni, Mn, Co, Fe, Cu, Nb, Mo, Ti, Al, Cr, Zr, Zn, Na, K, Ca, Mg, Pt, Au, B, P, Eu, Sm, W, Ce, V, Ba, Ta, Sn, Hf, Ce, Gd and Nd, 0≤a≤6, 0≤b≤8, and 2≤c≤13).
6. The lithium composite oxide of claim 5 , wherein the coating layer comprises:
a first oxide layer covering a part of the surface region of the secondary particles; and
a second oxide layer covering another part of the surface region of the secondary particles, which is not covered by the first oxide layer, and covering the surface of the first oxide layer,
wherein the at least one oxide represented by Formula 2 is present in the first oxide layer, and the boron-containing oxide is present in the second oxide layer.
7. A lithium secondary battery using a positive electrode comprising the lithium composite oxide according to claim 1 .