Positive electrode for secondary batteries and secondary battery including the same
View Patent ↗Disclosed is a positive electrode for secondary batteries manufactured by coating and rolling a slurry for a positive electrode mix including positive electrode active material particles on a current collector, wherein the positive electrode active material particles include one or more selected from the group consisting of lithium iron phosphate particles having an olivine crystal structure and lithium nickel-manganese-cobalt composite oxide particles according to Formula 1, the lithium nickel-manganese-cobalt composite oxide particles existing as secondary particles formed by agglomeration of primary particles, in an amount of greater than 50% and less than 90% based on the total volume of lithium nickel-manganese-cobalt composite oxide, and the lithium iron phosphate particles existing as primary particles in an amount of greater than 50% and less than 100% based on the total volume of lithium iron phosphate (Formula 1 is the same as defined in Claim 1 ).
1. A positive electrode for secondary batteries manufactured by coating and rolling a slurry for a positive electrode mix comprising positive electrode active material particles on a current collector,
wherein the positive electrode active material particles comprise lithium iron phosphate particles having an olivine crystal structure and lithium nickel-manganese-cobalt composite oxide particles according to Formula 1,
a ratio of the lithium iron phosphate particles to the lithium nickel-manganese-cobalt composite oxide particles is 30:70 to 70:30 based on a total weight of positive electrode active material,
the lithium nickel-manganese-cobalt composite oxide particles in an amount of greater than 50% and less than 90% based on the total volume of lithium nickel-manganese-cobalt composite oxide exist as secondary particles formed by agglomeration of primary particles, and
the lithium iron phosphate particles in an amount of greater than 50% and less than 100% based on the total volume of lithium iron phosphate exist as primary particles:
Li 1+z Ni b Mn c Co 1−(b+c+d) M d O (2−e) A e (1),
wherein −0.5≤z≤0.5, 0.1≤b≤0.8, 0.1≤c≤0.8, 0≤d≤0.2, 0≤e≤0.2, b+c+d<1, M is Al, Mg, Cr, Ti, Si or Y, and A is F, P or Cl.
2. The positive electrode according to claim 1 , wherein the lithium nickel-manganese-cobalt composite oxide particles in an amount of 80% or more and less than 90% based on a total volume of lithium nickel-manganese-cobalt composite oxide exist as secondary particles formed by agglomeration of primary particles.
3. The positive electrode according to claim 1 , wherein the lithium iron phosphate particles in an amount of 70% or more and less than 100% based on a total volume of lithium iron phosphate exist as primary particles.
4. The positive electrode according to claim 1 , wherein a particle change ratio based on volume when positive electrode active material particles in a secondary particle state are changed into primary particles by the rolling is 70% or more in the lithium iron phosphate particles and 20% or less in the lithium nickel-manganese-cobalt composite oxide particles.
5. The positive electrode according to claim 4 , wherein the particle change ratio of the lithium iron phosphate particles is 80% or more.
6. The positive electrode according to claim 4 , wherein the particle change ratio of the lithium nickel-manganese-cobalt composite oxide is 10% or less.
7. The positive electrode according to claim 4 , wherein, in the secondary particles, primary particles are agglomerated through physical bonding.
8. The positive electrode according to claim 4 , wherein an average particle diameter of the primary particles of the lithium iron phosphate particles and the lithium nickel-manganese-cobalt composite oxide particles is 50 nanometers to 550 nanometers and an average particle diameter of the secondary particles of the lithium iron phosphate particles and the lithium nickel-manganese-cobalt composite oxide particles is 5 micrometers to 100 micrometers.
9. The positive electrode according to claim 4 , wherein the secondary particles of the lithium iron phosphate particles and the lithium nickel-manganese-cobalt composite oxide particles have a globular shape.
10. The positive electrode according to claim 1 , wherein the lithium iron phosphate particles are coated with a conductive material.
11. The positive electrode according to claim 10 , wherein the conductive material is coated to a thickness of 1 nanometer or more and 10 nanometers or less.
12. The positive electrode according to claim 10 , wherein a content of the conductive material is 1% to 4% by weight based on a total weight of lithium iron phosphate.
13. The positive electrode according to claim 1 , wherein the lithium iron phosphate particles have a composition of Formula 2 below:
Li 1+a Fe 1−x M x (PO 4−b′ )X b′ (2),
wherein M is one or more selected from Al, Mg and Ti,
X is one or more selected from F, S and N, and
0.5≤a≤+0.5, 0≤x≤0.5, and 0≤b′≤0.1.
14. The positive electrode according to claim 1 , wherein the lithium nickel-manganese-cobalt composite oxide of Formula 1 is composed of a layered lithium nickel-manganese-cobalt oxide according to Formula 1a below:
Li 1+z Ni b Mn c CO 1−(b+c) O 2 (1a)
wherein b, c, and z are the same as defined in claim 1 .
15. The positive electrode according to claim 14 , wherein a content (b) of the nickel is 0.3≤b≤0.65.
16. A secondary battery comprising the positive electrode according to claim 1 .
17. A battery pack comprising one or more secondary batteries as claimed in claim 16 .
18. A device comprising the battery pack according to claim 17 .
19. The device according to claim 18 , wherein the device is an electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle or a system for storing power.