Conductive material for secondary battery, and secondary battery containing same
The present invention provides a conductive material for a secondary battery, and a secondary battery containing the same, the conductive material comprising carbon nanotubes, having a secondary structure in which carbon nanotube units having a diameter of 20-150 nm are entangled, having a ratio of true density to bulk density (TD/BD) of 30-120, having a metal content of 50 ppm or less, and having both excellent dispersibility and high purity, thereby being capable of improving, by increasing the conductivity within an electrode, battery performance, particularly, battery performance at room temperature and low temperature when applied to a battery.
1. A conductive material for a secondary battery comprising: carbon nanotubes having a spherical secondary structure in which carbon nanotube units having a diameter of 20 to 150 nm, are entangled, have a bulk density of 30 to 70 kg/m 3 , exhibiting a ratio (TD/BD) of a true density (TD) and a bulk density (BD) of 30 to 120, and containing a metal in an amount greater than 0 ppm and 50 ppm or less.
2. The conductive material of claim 1 , wherein the carbon nanotubes have a true density of 2,100 to 2,500 kg/m 3 .
3. The conductive material of claim 1 , wherein the carbon nanotubes have a BET specific surface area of 30 to 120 m 2 /g.
4. The conductive material of claim 1 , wherein the carbon nanotubes have an average particle size (D 50 ) of 200 to 800 μm.
5. The conductive material of claim 1 , wherein the carbon nanotubes comprise at least one of the elements selected from the group consisting of Fe, Co, Mo, V and Cr, in an amount greater than 0 ppm and 5 ppm or less.
6. The conductive material of claim 1 , wherein the carbon nanotubes comprise a secondary structure have a packing volume resistivity of 0.01 to 0.02 ohm·cm at a packing density of 0.9 to 1.5 g/cc.
7. The conductive material of claim 1 , further comprising 50 to 200 parts by weight of a particulate carbon-based material with respect to 100 parts by weight of the carbon nanotubes.
8. The conductive material of claim 7 , wherein the particulate carbon-based material is carbon black.
9. The conductive material of claim, 1 wherein the ratio (TD/BD) of a true density (TD) and a bulk density (BD) is 30 to 83.
10. A method of preparing the conductive material for a secondary battery according to claim 1 , comprising:
preparing the carbon nanotubes by bringing a supported catalyst in which a metal catalyst is supported in an α-alumina support in contact with a carbon source at equal to or greater than 650° C. and less than 800° C.; and
removing metal impurities in the carbon nanotubes through chlorination.
11. The method of claim 10 , wherein the removal of metal impurities in the carbon nanotubes is performed by a process in which the carbon nanotubes are brought in contact with a chlorine source under a nitrogen or vacuum atmosphere at 450 to 900° C. to chlorinate a metal in the carbon nanotubes, and then the chlorinated metal is evaporated through heating to 800 to 1,500° C.
12. An electrode for a secondary battery comprising the conductive material according to claim 1 .
13. The electrode of claim 12 , wherein the electrode is a positive electrode.
14. A lithium secondary battery comprising the electrode according to claim 12 .