Positive active material for secondary battery of improved rate capability
Disclosed is a novel cathode active material for secondary batteries. More specifically, disclosed is a cathode active material for secondary batteries that reduces deintercalation of oxygen from a crystal structure of Li2MnO3 at a high voltage of 4.3V to 4.6V through incorporation of excess lithium in a transition metal cation layer.
1. A cathode active material for secondary batteries for reducing deintercalation of oxygen from a crystal structure at a high voltage of 4.3V to 4.6V through incorporation of excessive lithium in a cation layer composed of Ni and in a cation layer composed of Mn, the cathode active material being represented by Formula 1:
(1− x )Li(Li a M′ b M 1−a−b )O 2 *x Li 2 M″O 3 (1)
wherein
0<x<0.3;
0<a<0.2;
0≦b≦0.2;
M is at least one element selected from Ni and Mn;
M′ is a transition metal excluding Ni and Mn; and
M″ is at least one element selected from Mn, Sn and Ti,
wherein the compound of Formula 1 is a composite or solid solution with a layered structure.
2. The cathode active material according to claim 1 , wherein at least one of M, M′ and M″ are substituted by a metal or non-metal element which has a 6-coodination structure in an amount of 1 to 10%, based on molar ratio.
3. The cathode active material according to claim 1 , wherein M is Ni (1−a−b)/2 .Mn (1−a−b)/2 .
4. The cathode active material according to claim 1 , wherein M is Ni 0.5 Mn 0.5 .
5. The cathode active material according to claim 1 , wherein M′ is Co.
6. The cathode active material according to claim 1 , wherein oxygen of Formula 1 is substituted in a predetermined amount by other anion.
7. The cathode active material according to claim 6 , wherein the anion is at least one selected from the group consisting of fluorine (F), sulfur (S) and nitrogen (N).
8. A cathode mix for secondary batteries comprising the cathode active material according to claim 1 .
9. A cathode for secondary batteries in which the cathode mix according to claim 8 is applied to a current collector.
10. A lithium secondary battery comprising the cathode for secondary batteries according to claim 9 .
11. The lithium secondary battery according to claim 10 , wherein the lithium secondary battery has a ratio of 1 C to 0.06 C of 80% or higher.
12. A battery module comprising the lithium secondary battery according to claim 10 as a unit battery.
13. A battery pack comprising the battery module according to claim 12 as a power source of a device.
14. The battery pack according to claim 13 , wherein the device is an electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle or a power storage device.
15. The cathode active material according to claim 1 , wherein the compound of Formula 1 is a composite with a layered structure.
16. The cathode active material according to claim 1 , wherein the compound of Formula 1 is a solid solution with a layered structure.