Anode active material for secondary battery, secondary battery including the same, and method of preparing the same
An anode active material for a secondary battery according to an embodiment of the present invention includes first particles serving as a core active material and second particles attached on surfaces of the first particles. A weight of the second particles based on 100 weight parts of a total weight of the first particles and the second particles satisfies a predetermined relation. A secondary battery including the anode active material is provided.
1. An anode active material for secondary battery, comprising:
first particles serving as a core active material; and
second particles attached on surfaces of the first particles,
wherein a bulk density of the second particles is smaller than a bulk density of the first particles, and
the bulk density of the first particles is from 0.5 g/mL to 3 g/mL, and the bulk density of the second particles is from 0.01 g/mL to 1 g/mL,
wherein a weight of the second particles based on 100 weight parts of a total weight of the first particles and the second particles satisfies Equation 1 below:
4
0
0
(
D
+
d
)
2
d
D
3
×
γ
d
γ
D
×
0
.
5
≤
A
≤
4
0
0
(
D
+
d
)
2
d
D
3
×
γ
d
γ
D
×
1
.
5
[
Equation
1
]
wherein, in Equation 1, A is a weight part of the second particles, D is a particle diameter (μm) of the first particles, γ D is the bulk density (g/mL) of the first particles, d is a particle diameter (μm) of the second particles, and γd is the bulk density (g/mL) of the second particles.
2. The anode active material for a lithium secondary battery according to claim 1 , wherein the weight of the second particles based on 100 weight parts of the total weight of the first particles and the second particles satisfies Equation 2 below:
4
0
0
(
D
+
d
)
2
d
D
3
×
γ
d
γ
D
×
0
.
7
5
≤
A
≤
4
0
0
(
D
+
d
)
2
d
D
3
×
γ
d
γ
D
×
1
.
2
5
.
[
Equation
2
]
3. The anode active material for a secondary battery according to claim 1 , wherein a ratio of the particle diameter of the second particles relative to the particle diameter of the first particles is 0.1 or less.
4. The anode active material for a secondary battery according to claim 1 , wherein a ratio of the particle diameter of the second particles relative to the particle diameter of the first particles is in a range from 0.001 to 0.1.
5. A secondary battery, comprising:
an anode comprising the anode active material for a secondary battery according to claim 1 ; and
a cathode facing the anode and being physically separated from the anode.
6. The anode active material for a secondary battery according to claim 1 , wherein the second particles form a mono-layered coating on a surface of each of the first particles.
7. The anode active material for a secondary battery according to claim 1 , wherein the first particles comprise at least one of a carbon-based active material or a silicon-based active material.
8. The anode active material for a secondary battery according to claim 1 , wherein the second particles comprise at least one of a carbon-based material, a silicon-based material, a metal-based material or an oxide-based material.
9. The anode active material for a secondary battery according to claim 8 , wherein the carbon-based material comprises at least one selected from the group consisting of carbon nanotube, carbon fiber and carbon black.
10. The anode active material for a secondary battery according to claim 8 , wherein the oxide-based material comprises at least one selected from the group consisting of lithium titanate (LTO), TiO 2 , ZrO 2 , ZnO 2 , AlO 2 , Fe 2 O 3 , Li 2 O, and MgO.
11. A method of preparing an anode active material for a secondary battery, comprising:
preparing first particles as a core active material and second particles as a coating particle; and
mixing the first particles and the second particles by a dry rotation to attach the second particles on surfaces of the first particles;
wherein a bulk density of the second particles is smaller than a bulk density of the first particles, and
the bulk density of the first particles is from 0.5 g/mL to 3 g/mL, and the bulk density of the second particles is from 0.01 g/mL to 1 g/mL,
wherein a weight of the second particles based on 100 weight parts of a total weight of the first particles and the second particles satisfies Equation 1 below:
4
0
0
(
D
+
d
)
2
d
D
3
×
γ
d
γ
D
×
0
.
5
≤
A
≤
4
0
0
(
D
+
d
)
2
d
D
3
×
γ
d
γ
D
×
1
.
5
[
Equation
1
]
wherein, in Equation 1, A is a weight part of the second particles, D is a particle diameter (μm) of the first particles, γD is the bulk density (g/mL) of the first particles, d is a particle diameter (μm) of the second particles, and γd is the bulk density (g/mL) of the second particles.
12. The method of claim 11 , wherein the dry rotation is performed at a linear velocity from 650 cm/s to 2,700 cm/s.