Cathode and lithium battery including the same
A cathode includes: a cathode active material comprising a lithium transition metal oxide; a conductive material; and a binder, wherein the lithium transition metal oxide includes nickel and a transition metal other than nickel, wherein the lithium transition metal oxide has a layered crystal structure, wherein a content of the nickel is 30 mole percent or greater, based on a total number of moles of transition metals of the lithium transition metal oxide, wherein the conductive material comprises a linear carbon conductive material, wherein the binder includes a first binder, wherein the first binder including fluorine and a polar functional group, and a second binder, which does not include fluorine, and wherein an amount of the linear carbon conductive material is 0.1 weight percent or greater, based on a total combined weight of the cathode active material, the conductive material, and the binder.
1. A cathode, the cathode comprising:
a cathode active material comprising a lithium transition metal oxide;
a conductive material; and
a binder,
wherein the lithium transition metal oxide comprises nickel and a transition metal other than nickel,
wherein the lithium transition metal oxide has a layered crystal structure,
wherein a content of the nickel is equal to or greater than 30 mole percent to less than 100 mole percent, based on a total number of moles of transition metals of the lithium transition metal oxide,
wherein the conductive material comprises a linear carbon conductive material,
wherein the binder comprises
a first binder comprising fluorine and a polar functional group consisting of a carboxylic acid group, a sulfonic acid group, a phosphoric acid group, a hydroxyl group, a salt thereof, or a combination thereof, and
a second binder, which does not comprise fluorine, and
wherein an amount of the linear carbon conductive material is 0.1 weight percent to 5 weight percent, and an amount of the first binder is 0.01 weight percent to 1 weight percent, each based on a total combined weight of the cathode active material, the conductive material, and the binder,.
wherein the amount of the second binder is greater than the amount of the first binder.
2. The cathode of claim 1 , wherein the linear carbon conductive material comprises carbon nanotube, carbon nanofiber, carbon nanorod, or a combination thereof.
3. The cathode of claim 1 , wherein the conductive material further comprises a particulate carbon conductive material in addition to the linear carbon conductive material,
wherein an aspect ratio of the linear carbon conductive material is 2 or greater, and
wherein an aspect ratio of the particulate carbon conductive material is less than 2.
4. The cathode of claim 3 , wherein the particulate carbon conductive material comprises carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, natural graphite, artificial graphite, or a combination thereof.
5. The cathode of claim 3 , wherein a weight ratio of the linear carbon conductive material to the particulate carbon conductive material is from about 90:10 to about 10:90.
6. The cathode of claim 1 , wherein an amount of the first binder is 0.01 to 0.5 weight percent, based on the total combined weight of the cathode active material, the conductive material, and the binder.
7. The cathode of claim 1 , wherein the first binder comprises:
a repeating unit comprising a polar functional group;
a repeating unit derived from vinylidene fluoride; and
optionally, a repeating unit derived from tetrafluoroethylene, hexafluoropropylene, chlorotrifluoroethylene, a fluorovinyl group-containing monomer, a perfluoroalkyl vinyl ether, or a combination thereof,
wherein a weight average molecular weight of the first binder is 1,000,000 Daltons or greater.
8. The cathode of claim 1 , further comprising a third binder comprising fluorine, wherein the third binder does not comprise a polar functional group.
9. The cathode of claim 8 , wherein the third binder comprises a repeating unit derived from vinylidene fluoride and the third binder has a weight average molecular weight of 1,000,000 Daltons or less.
10. The cathode of claim 8 , wherein a weight ratio of the first binder to the third binder is from about 90:10 to about 10:90.
11. The cathode of claim 1 , wherein the second binder comprises a cyano group.
12. The cathode of claim 1 , wherein the second binder comprises a repeating unit derived from an acrylonitrile-containing monomer and a repeating unit derived from an olefin-containing monomer.
13. The cathode of claim 1 , wherein the lithium transition metal oxide is a compound represented by Formula 1:
Li a Ni x Co y M z O 2-b A b Formula 2
wherein, in Formula 2,
1≤a≤1.2, 0≤b≤0.2, 0.3≤x<1, 0<y≤0.4, 0<z≤0.4, x+y+z=1, M comprises manganese, vanadium, magnesium, gallium, silicon, tungsten, molybdenum, iron, chromium, copper, zinc, titanium, aluminum, boron, or a combination thereof, and
A is F, S, Cl, Br, or a combination thereof.
14. The cathode of claim 1 , wherein the lithium transition metal oxide is a compound represented by Formula 3 or 4:
LiNi x Co y Mn z O 2 Formula 3
LiNi x Co y Al z′ O 2 Formula 4
wherein, in Formula 2, 0.3≤x<1, 0<y≤0.4, and 0<z≤0.4, and
wherein in Formula 3, 0.3≤x′<1, 0<y′≤0.4, and 0<z′≤0.4.
15. The cathode of claim 1 , wherein an amount of the cathode active material is from about 95 weight percent to about 98.9 weight percent, an amount of the conductive material is from about 1 weight percent to 4 weight percent, and an amount of the binder is from about 0.01 weight percent to about 2 weight percent, based on the total combined weight of the cathode active material, the conductive material, and the binder, and
wherein a loading of the cathode is 3 milliampere hours per square centimeter or greater.
16. The cathode of claim 15 , wherein the loading of the cathode is 5 milliampere hours per square centimeter or greater.
17. The cathode of claim 1 , wherein the cathode has a bending range of motion of 90 degrees or greater during a flexural property test performed in accordance with ASTM D790.
18. The cathode of claim 1 , wherein a maximum bending strength of the cathode obtained from a flexural property test performed in accordance with ASTM D790 is 1 Newton or less.
19. The cathode of claim 1 , wherein a peel strength of the cathode obtained from a 180-degree peel strength test performed in accordance with ASTM D3330 is 0.3 gram-force per millimeter or greater.
20. The cathode of claim 1 ,
wherein the first binder comprises:
a repeating unit comprising the polar functional group;
a repeating unit derived from vinylidene fluoride; and
optionally, a repeating unit derived from tetrafluoroethylene, hexafluoropropylene, chlorotrifluoroethylene, a fluorovinyl group-containing monomer, a perfluoroalkyl vinyl ether, or a combination thereof, and
the second binder comprises a repeating unit derived from an acrylonitrile-containing monomer and a repeating unit derived from an olefin-containing monomer, and the second binder is present in an amount of 0.1 to 0.5 wt %, based on a total combined weight of the cathode active material, the conductive material, and the binder.
21. The cathode of claim 20 , wherein
the binder further comprises 0.01 to 1.5 wt % of a third binder based on a total combined weight of the cathode active material, the conductive material, and the binder, and
the third binder comprises a repeating unit derived from vinylidene fluoride.
22. A lithium battery comprising:
a cathode according to claim 1 ;
an anode; and
an electrolyte located between the cathode and the anode.