Anode active material for lithium secondary battery and lithium secondary battery including the same
An anode active material for a secondary battery includes a plurality of composite particles. The composite particles include carbon-based particles containing pores therein. A silicon-containing coating layer is formed inside the pores or on a surface of the carbon-based particles. A surface oxide layer is formed on the silicon-containing coating layer. The surface oxide layer contains silicon oxide. A silicon oxidation number ratio of the composite particle is predefined.
1 . An anode active material for a lithium secondary battery comprising:
a plurality of composite particles, wherein at least one of the composite particles comprises:
a carbon-based particle containing pores therein, wherein the carbon-based particle comprises a carbon-containing core;
a silicon-containing coating layer formed inside the pores or on a surface of the carbon-based particle; and
a surface oxide layer formed on the silicon-containing coating layer, the surface oxide layer containing silicon oxide,
wherein a silicon oxidation number ratio defined by Equation 1 of the composite particle is 0.6 or less:
silicon oxidation number ratio= O B /O S [Equation 1]
where, in Equation 1, O B is an oxidation number of silicon included in the silicon-containing coating layer measured by an X-ray photoelectron spectroscopy (XPS) and defines a first charge state of the silicon in the silicon-containing coating layer on the carbon-based particle, and O S is an oxidation number of silicon included in the surface oxide layer measured by the XPS and defines a second charge state of the silicon in the surface oxide layer on the silicon-containing coating layer covering the carbon-containing core, and
wherein silicon included in the silicon-containing coating layer has an amorphous silicon structure or has a crystallite size measured by an X-ray diffraction (XRD) analysis of 7 nm or less,
wherein silicon included in the silicon-containing coating layer has a peak intensity ratio of 1.0 or less in a Raman spectrum defined by Equation 4:
peak intensity ratio of Raman spectrum= I (515)/ I (480) [Equation 4]
where, in Equation 4, I(515) is a peak intensity of silicon included in the silicon-containing coating layer in a region of 515 cm −1 wavenumber in the Raman spectrum, and I(480) is a peak intensity of silicon included in the silicon-containing coating layer in a region of 480 cm −1 wavenumber in the Raman spectrum.
2 . The anode active material for a lithium secondary battery of claim 1 , wherein
O B is obtained by substituting a first value, obtained by subtracting 99.6 eV from a binding energy of silicon included in the silicon-containing coating layer measured by the XPS, into a silicon oxidation number calibration curve, and
O S is obtained by substituting a second value, obtained by subtracting 99.6 eV from a binding energy of silicon included in the surface oxide layer measured by the XPS, into the silicon oxidation number calibration curve.
3 . The anode active material for a lithium secondary battery of claim 2 , wherein the silicon oxidation number calibration curve is obtained by connecting points corresponding to Si 0 , Si 1+ , Si 2+ , Si 3+ and Si 4+ with a shortest distance between neighboring points in a graph in which an x-axis represents oxidation numbers of silicon and a y-axis represents the first and second values obtained by subtracting 99.6 eV from the binding energies of silicon measured by the XPS.
4 . The anode active material for a lithium secondary battery of claim 1 , wherein a distance between a surface of the composite particle and the silicon-containing coating layer is 100 nm to 700 nm, and a distance between the surface of the composite particle and the surface oxide layer formed on the silicon-containing coating layer is 10 nm or less.
5 . The anode active material for a lithium secondary battery of claim 1 , wherein O B is in a range from 1.2 to 2.0, and O S is in a range from 3.0 to 3.6.
6 . The anode active material for a lithium secondary battery of claim 1 , wherein an oxygen content ratio defined by Equation 2 is 0.4 or less:
oxygen content ratio= C B /C S [Equation 2]
where, in Equation 2, C B is a percentage (at %) of the number of oxygen atoms included in the silicon-containing coating layer relative to a sum of the number of atoms included both in the silicon-containing coating layer and in the surface oxide layer measured by the XPS, C S is a percentage (at %) of the number of oxygen atoms included in the surface oxide layer relative to the sum of the number of atoms included both in the silicon-containing coating layer and in the surface oxide layer measured by the XPS.
7 . The anode active material for a lithium secondary battery of claim 6 , wherein C B is in a range from 8 at % to 15 at %, and C S is in a range from 15 at % to 34 at %.
8 . The anode active material for a lithium secondary battery of claim 1 , wherein the carbon-based particle includes at least one selected from the group consisting of an activated carbon, a carbon nanotube, a carbon nanowire, graphene, a carbon fiber, carbon black, graphite, a porous carbon, pyrolyzed cryogel, pyrolyzed xerogel and pyrolyzed aerogel.
9 . The anode active material for a lithium secondary battery of claim 1 , wherein the carbon-based particle has an amorphous carbon structure.
10 . The anode active material for a lithium secondary battery of claim 1 , wherein the crystallite size of silicon included in the silicon-containing coating layer is measured by Equation 3:
L
=
0
.
9
λ
β
cos
θ
[
Equation
3
]
where, in Equation 3, L represents the crystallite size (nm), λ represents an X-ray wavelength (nm), β represents a full width at half maximum (rad) of a peak corresponding to a (111) plane of silicon contained in the silicon-containing coating layer, and θ represents a diffraction angle (rad).
11 . The anode active material for a lithium secondary battery of claim 1 , wherein the composite particle further comprises a carbon coating layer formed on an outermost portion of the composite particle.
12 . A lithium secondary battery, comprising:
an anode comprising an anode active material layer that comprises the anode active material for a lithium secondary battery of claim 1 ; and
a cathode facing the anode.