Anode including spherical natural graphite and lithium secondary battery including the anode
Provided are an anode including spherical natural graphite having a surface coated with an amorphous carbon layer, wherein a crystal orientation ratio is in a range of 0.06 to 0.08 at a compressed density of 1.40 g/cc to 1.85 g/cc, and a lithium secondary battery including the anode. Initial efficiency, electrode adhesion, and capacity characteristics of the lithium secondary battery may be improved by using the anode of the present invention in the lithium secondary battery.
1. An anode comprising spherical natural graphite having a surface coated with an amorphous carbon layer, wherein the amorphous carbon layer is included in an amount of from 2% to 4.1% based on the total weight of the spherical natural graphite; and
wherein a crystal orientation ratio is in a range of 0.061 to 0.078 at a compressed density of 1.40 g/cc to 1.85 g/cc.
2. The anode of claim 1 , wherein the crystal orientation ratio is an area ratio ((110)/(004)) obtained by measuring a (110) plane and a (004) plane of the spherical natural graphite included in the anode by X-ray diffraction (XRD) and integrating each measured XRD peak.
3. The anode of claim 1 , wherein a specific surface area (BET) of the spherical natural graphite having a surface coated with an amorphous carbon layer is in a range of 1.5 m 2 /g to 4.0 m 2 /g.
4. The anode of claim 1 , wherein the amorphous carbon layer is formed by coating with pyrolytic carbon using one or more vapor or liquid carbon sources selected from the group consisting of methane, ethane, ethylene, butane, acetylene, carbon monoxide, propane, polyvinyl alcohol, and propylene; or coating with liquid or solid pitch.
5. The anode of claim 4 , wherein the pitch is coal pitch or petroleum pitch.
6. The anode of claim 1 , wherein a thickness of the amorphous carbon layer is in a range of 50 nm to 700 nm.
7. The anode of claim 1 , further comprising a water-based binder.
8. The anode of claim 7 , wherein the water-based binder is any one selected from the group consisting of an acrylonitrile-butadiene rubber, a styrene-butadiene rubber (SBR), and an acrylic rubber, or a mixture of two or more thereof.
9. The anode of claim 1 , further comprising a thickener.
10. The anode of claim 9 , wherein the thickener is a cellulose-based compound.
11. The anode of claim 10 , wherein the cellulose-based compound is any one selected from the group consisting of carboxymethyl cellulose, hydroxy methyl cellulose, hydroxy ethyl cellulose, and hydroxy propyl cellulose, or a mixture of two or more thereof.
12. A lithium secondary battery comprising:
a cathode;
an anode;
a separator disposed between the cathode and the anode; and
an electrolyte having a lithium salt dissolved therein, wherein the anode is the anode of claim 1 .
13. The anode of claim 1 , wherein the average particle diameter (D 50 ) of the spherical natural graphite having a surface coated with an amorphous carbon layer is in a range of 12 μm to 18 μm.