Anode active material for lithium secondary battery and lithium secondary battery including the same
Anode active materials and secondary batteries including the anode active materials are disclosed. An anode active material for a secondary battery based on an embodiment of the present disclosure includes a silicon oxide particle. The silicon oxide particle has a core portion including silicon oxide and a surface portion formed on the core portion. An oxidation number ratio defined as O S /O C of the silicon oxide particle is 1.7 or more, and less than 2.2. O S is an oxidation number of silicon oxide of the surface portion obtained by an X-ray photoelectron spectroscopy (XPS) analysis, and O C is an oxidation number of the silicon oxide of the core portion obtained by the XPS analysis.
1 . An anode active material for a lithium secondary battery comprising a silicon oxide particle and a carbon coating formed on at least a portion of a surface of the silicon oxide particle, wherein the silicon oxide particle has a core portion and a surface portion formed on the core portion, and an oxidation number ratio defined by Equation 1 of the silicon oxide particle is 2.13 to 2.19,
Oxidation
number
ratio
=
O
S
/
O
C
[
Equation
1
]
wherein, in Equation 1, O S is an oxidation number of silicon oxide at the surface portion obtained by an X-ray photoelectron spectroscopy (XPS) analysis, and O C is an oxidation number of silicon oxide at the core portion obtained by the XPS analysis.
2 . The anode active material for a lithium secondary battery according to claim 1 , wherein O S is calculated by Equation 2:
O
S
=
(
B
+
2
C
+
3
D
+
4
E
)
/
(
5
A
+
4
B
+
3
C
+
2
D
+
E
)
[
Equation
2
]
wherein, in Equation 2, A represents a peak area in a region from 98 eV to 100 eV measured by deconvolution of an Si2p spectrum of the surface portion, B represents a peak area in a region from 100 eV to 101 eV measured by deconvolution of the Si2p spectrum of the surface portion, C represents a peak area in a region from 101 eV to 102 eV measured by deconvolution of the Si2p spectrum of the surface portion, D represents a peak area in a region from 102 eV to 103 eV measured by deconvolution of the Si2p spectrum, and E represents a peak area in a region from 103 eV to 106 eV measured by deconvolution of the Si2p spectrum of the surface portion, wherein the Si2p spectrum is obtained through the XPS analysis.
3 . The anode active material for a lithium secondary battery according to claim 1 , wherein O C is calculated by Equation 3:
O
C
=
(
G
+
2
H
+
3
I
+
4
J
)
/
(
5
F
+
4
G
+
3
H
+
2
I
+
J
)
[
Equation
3
]
wherein, in Equation 3, F represents a peak area in a region from 98 eV to 100 eV measured by deconvolution of an Si2p spectrum of the core portion, G represents a peak area in a region from 100 eV to 101 eV measured by deconvolution of the Si2p spectrum of the core portion, H represents a peak area in a region from 101 eV to 102 eV measured by deconvolution of the Si2p spectrum of the core portion, I represents a peak area in a region from 102 eV to 103 eV measured by deconvolution of the Si2p spectrum of the core portion, and J represents a peak area in a region from 103 eV to 106 eV measured by deconvolution of the Si2p spectrum of the core portion, wherein the Si2p spectrum is obtained through the XPS analysis.
4 . The anode active material for a lithium secondary battery according to claim 1 , wherein a shortest distance from a surface of the silicon oxide particle to an outer surface of the core portion is 300 nm or more.
5 . The anode active material for a lithium secondary battery according to claim 1 , wherein O C is 0.8 or more.
6 . The anode active material for a lithium secondary battery according to claim 1 , wherein O C is in a range from 0.8 to 1.0.
7 . The anode active material for a lithium secondary battery according to claim 1 , wherein the silicon oxide particle includes SiO X , wherein x is larger than 0 and equal to or smaller than 2.
8 . The anode active material for a lithium secondary battery according to claim 1 , wherein the silicon oxide particle is doped with a metal including at least one of Li, Mg, Al, Ca, Fe, Ti, or V.
9 . A lithium secondary battery, comprising:
an anode comprising an anode active material; and
a cathode facing the anode,
wherein the anode active material comprises a silicon oxide particle that includes a core portion including silicon oxide occupying at least a center of the silicon oxide particle and a surface portion including silicon oxide formed on the core portion,
wherein an oxidation number ratio of the silicon oxide particle defined by Equation 1 is 2.13 to 2.19,
Oxidation
number
ratio
=
O
S
/
O
C
[
Equation
1
]
wherein, in Equation 1, O S is an oxidation number of the silicon oxide of the surface portion obtained by an X-ray photoelectron spectroscopy (XPS) analysis, and O C is an oxidation number of the silicon oxide of the core portion obtained by the XPS analysis, and
wherein the anode active material comprises a carbon coating formed on at least a portion of a surface of the silicon oxide particle.
10 . The lithium secondary battery according to claim 9 , wherein the anode further comprises a graphite-based active material.
11 . The lithium secondary battery according to claim 10 , wherein the graphite-based active material comprises at least one selected from the group consisting of artificial graphite and natural graphite.
12 . The lithium secondary battery according to claim 9 , wherein O S is calculated by Equation 2:
O
S
=
(
B
+
2
C
+
3
D
+
4
E
)
/
(
5
A
+
4
B
+
3
C
+
2
D
+
E
)
[
Equation
2
]
wherein, in Equation 2, A represents a peak area in a region from 98 eV to 100 eV measured by deconvolution of an Si2p spectrum of the surface portion, B represents a peak area in a region from 100 eV to 101 eV measured by deconvolution of the Si2p spectrum of the surface portion, C represents a peak area in a region from 101 eV to 102 eV measured by deconvolution of the Si2p spectrum of the surface portion, D represents a peak area in a region from 102 eV to 103 eV measured by deconvolution of the Si2p spectrum, and E represents a peak area in a region from 103 eV to 106 eV measured by deconvolution of the Si2p spectrum of the surface portion, wherein the Si2p spectrum is obtained through the XPS analysis.
13 . The lithium secondary battery according to claim 9 , wherein O C is calculated by Equation 3:
O
C
=
(
G
+
2
H
+
3
I
+
4
J
)
/
(
5
F
+
4
G
+
3
H
+
2
I
+
J
)
[
Equation
3
]
wherein, in Equation 3, F represents a peak area in a region from 98 eV to 100 eV measured by deconvolution of an Si2p spectrum of the core portion, G represents a peak area in a region from 100 eV to 101 eV measured by deconvolution of the Si2p spectrum of the core portion, H represents a peak area in a region from 101 eV to 102 eV measured by deconvolution of the Si2p spectrum of the core portion, I represents a peak area in a region from 102 eV to 103 eV measured by deconvolution of the Si2p spectrum of the core portion, and J represents a peak area in a region from 103 eV to 106 eV measured by deconvolution of the Si2p spectrum of the core portion, wherein the Si2p spectrum is obtained through the XPS analysis.
14 . The lithium secondary battery according to claim 9 , wherein a shortest distance from a surface of the silicon oxide particle to an outer surface of the core portion is 300 nm or more.
15 . The lithium secondary battery according to claim 9 , wherein O C is 0.8 or more.
16 . The lithium secondary battery according to claim 9 , wherein O C is in a range from 0.8 to 1.0.
17 . The lithium secondary battery according to claim 9 , wherein the silicon oxide particle includes SiO X , wherein x is larger than 0 and equal to or smaller than 2.
18 . The lithium secondary battery according to claim 9 , wherein the silicon oxide particle is doped with a metal including at least one of Li, Mg, Al, Ca, Fe, Ti, or V.