Cathode active material for secondary battery and lithium secondary battery including the same
View Patent ↗Disclosed is lithium iron phosphate having an olivine crystal structure, wherein the length in the direction [001] is greater than the length in the direction [010] when the Li+ diffusion direction is the direction [010] in the lattice structure of the crystal.
1. Secondary lithium iron phosphate particles which are comprised of aggregated primary lithium iron phosphate particles, wherein the primary lithium iron phosphate particles have an olivine crystal structure, wherein a length of the primary lithium iron phosphate particles in a direction [001] is greater than a length in a direction [010] such that a Li + diffusion direction is in the direction [010] in the lattice structure of the crystal,
wherein the macro-morphology of a majority of the primary particles is a rod structure and is bent at a predetermined angle in the direction [001].
2. The secondary lithium iron phosphate particles according to claim 1 , wherein the direction [001] is a direction in which the primary particles are grown.
3. The secondary lithium iron phosphate particles according to claim 1 , wherein the length of the primary particles in the direction [001] is two or more times the length of the primary particles in the direction [010].
4. The secondary lithium iron phosphate particles according to claim 3 , wherein the length of the primary particles in the direction [001] is within 2 to 50 times the length of the primary particles in the direction [010].
5. The secondary lithium iron phosphate particles according to claim 1 , wherein the plane (001) of the crystal has a circular or oval shape.
6. The secondary lithium iron phosphate particles according to claim 1 , wherein the primary particles are bent at an angle of 20 to 50 degrees.
7. The secondary lithium iron phosphate particles according to claim 1 , wherein the primary particles comprise lithium iron phosphate having a structure of the following formula 1:
Li 1+a Fe 1−b M b (PO 4−c )X c (1)
wherein
M represents at least one selected from Al, Mg and Ti,
X represents at least one selected from F, S and N, and
−0.5≦a≦+0.5, 0≦b≦0.5, 0≦c≦0.1.
8. The secondary lithium iron phosphate particles according to claim 1 , wherein the primary particles are prepared by rapid reaction for a short reaction time.
9. The secondary lithium iron phosphate particles according to claim 8 , wherein a reaction time of the rapid reaction is 0.5 seconds to 1 minute.
10. The secondary lithium iron phosphate particles according to claim 8 , wherein the rapid reaction is carried out by a continuous supercritical hydrothermal method.
11. An olivine-type secondary lithium iron phosphate particles, in which primary lithium iron phosphate particles according to claim 1 are aggregated to form secondary particles having an average particle diameter of 5 to 100 μm and a porosity of 15 to 40%.
12. The olivine-type secondary lithium iron phosphate particles according to claim 11 , wherein a size of pores present in the secondary particles is 300 to 600 nm.
13. The olivine-type secondary lithium iron phosphate particles according to claim 11 , wherein the primary particles are aggregated by physical bonding to form secondary particles.
14. The olivine-type secondary lithium iron phosphate particles according to claim 11 , wherein a mean particle diameter of the primary particles is 100 to 300 nm, and a mean particle diameter of the secondary particles is 5 to 40 μn.
15. The olivine-type secondary lithium iron phosphate particles according to claim 12 , wherein the secondary particles have a spherical shape.
16. A cathode mix for secondary batteries comprising the secondary lithium iron phosphate particles according to claim 1 as a cathode active material.
17. A cathode for secondary batteries in which the cathode mix for secondary batteries according to claim 16 is applied to a current collector.
18. A lithium secondary battery comprising the cathode for secondary batteries according to claim 17 .
19. A battery pack comprising the lithium secondary battery according to claim 18 as a unit battery.
20. The battery pack according to claim 19 , wherein the battery pack is suitable for use as a power source of a power tool, an electric vehicle, an electric two-wheeled vehicle, or an electric golf cart.