Anode active material for lithium secondary battery and lithium secondary battery including the same
An anode active material for a lithium secondary battery according to an embodiment of the present invention includes a first anode active material and a second anode active material, each of which includes a carbon-based active material and has a crystallite size in a range from 50 nm to 60 nm. An XRD orientation ratio of the first anode active material is in a range from 0.9 to 1.2, and an XRD orientation ratio of the second anode active material is in a range from 1 to 5. High-temperature storage and life-span properties are improved while maintaining high capacity using the combination of the first and second anode active materials.
1 . An anode active material for a lithium secondary battery, comprising a first anode active material comprising natural graphite, and a second anode active material comprising artificial graphite, each of which comprises a carbon-based active material and has a crystallite size defined as Equation 1 in a range from 50 nm to 60 nm,
wherein an XRD orientation ratio of the first anode active material comprising the natural graphite is in a range from 0.9 to 1.2, an XRD orientation ratio of the second anode active material comprising the artificial graphite is in a range from 1 to 5, and the XRD orientation ratio of the second anode active material is greater than the XRD orientation ratio of the first anode active material, and
the XRD orientation ratio is defined as I(004)/I(110) which is a ratio of a peak intensity at a (004) plane relative to a peak intensity at a (110) plane:
L
=
1
.
8
4
λ
β
cos
θ
[
Equation
1
]
wherein, in Equation 1, L is the crystallite size, λ is an X-ray wavelength (nm) used in an XRD analysis, β is a full width at half maximum (rad) of the (110) plane, and θ is a diffraction angle (rad).
2 . The anode active material for a lithium secondary battery of claim 1 , wherein the first anode active material includes natural graphite having a sphericity of 0.9 or more.
3 . The anode active material for a lithium secondary battery of claim 1 , wherein the XRD orientation ratio of the first anode active material is in a range from 0.99 to 1.2.
4 . The anode active material for a lithium secondary battery of claim 1 , wherein the XRD orientation ratio of the second anode active material is in a range from 2 to 4.
5 . The anode active material for a lithium secondary battery of claim 1 , wherein a weight of the second anode active material is equal to or greater than a weight of the first anode active material in the anode active material.
6 . The anode active material for a lithium secondary battery of claim 5 , wherein a weight ratio of the first anode active material and the second anode active material is in a range from 50:50 to 5:95.
7 . A lithium secondary battery, comprising:
an anode comprising the anode active material for a lithium secondary battery of claim 1 ; and
a cathode facing the anode.
8 . The lithium secondary battery of claim 7 , wherein the cathode comprises a lithium-transition metal oxide containing nickel (Ni), cobalt (Co) and manganese (Mn) as a cathode active material, and
a molar ratio of Ni among Ni, Co and Mn in the lithium-transition metal oxide is 0.6 or more.