Cathode active material for lithium secondary battery
View Patent ↗Provided is a cathode active material which is lithium transition metal oxide having an α-NaFeO 2 layered crystal structure, wherein the transition metal is a blend of Ni and Mn, an average oxidation number of the transition metals except lithium is more than +3, and lithium transition metal oxide satisfies the Equation m(Ni)≧m(Mn) (in which m (Ni) and m (Mn) represent an molar number of manganese and nickel, respectively). The lithium transition metal oxide has a uniform and stable layered structure through control of oxidation number of transition metals to a level higher than +3, thus advantageously exerting improved overall electrochemical properties including electric capacity, in particular, superior high-rate charge/discharge characteristics.
1. A cathode active material for lithium secondary batteries,
wherein the cathode active material is lithium transition metal oxide having a layered crystal structure,
wherein the transition metal is a blended transition metal of Ni and Mn, and an average oxidation number of transition metals except lithium is more than +3, and specific conditions represented by the following Formulae (1) and (2) are satisfied:
m (Ni)≧ m (Mn) (1)
0.4< m (Ni 2+ )/ m (Mn 4+ )<1 (2)
wherein m(Ni) and m(Mn) represent a molar number of nickel and manganese, respectively, and m(Ni 2+ )/m(Mn 4+ ) is a molar ratio of Ni 2+ to Mn 4+ .
2. The cathode active material according to claim 1 , wherein the layered crystal structure is an α-NaFeO 2 layered crystal structure.
3. The cathode active material according to claim 1 , wherein the average oxidation number of the transition metals except lithium is 3.0 to 3.5.
4. The cathode active material according to claim 3 , wherein the average oxidation number of the transition metals except lithium is 3.01 to 3.3.
5. The cathode active material according to claim 1 , wherein the lithium transition metal oxide further comprises cobalt.
6. The active material according to claim 1 , wherein the nickel portion has an average oxidation number of more than +2.
7. The cathode active material according to claim 1 , wherein the nickel portion comprises nickel (a) in an excess content relative to a content of manganese, as well as nickel (b) with a content corresponding to the content of manganese.
8. The active material according to claim 7 , wherein the nickel (a) in the excess content relative to the content of manganese is Ni 3+ .
9. The active material according to claim 7 , wherein an overall average oxidation number of the nickel (b) with a content corresponding to the content of manganese is more than 3.0 to not more than 3.5.
10. The active material according to claim 7 , wherein the nickel (b) with the content corresponding to the content of manganese comprises Ni 2+ and Ni 3+ .
11. The active material according to claim 7 , wherein Ni 3+ content ranges from 11 to 60% of the nickel (b) with the content corresponding to the content of manganese.
12. The active material according to claim 5 , wherein a content of Co is less than 10 mol % relative to a total amount of transition metals.
13. The active material according to claim 1 , wherein a content of nickel (Ni 2+ ) intercalated into lithium sites is lower than 5 mol %.
14. A cathode comprising the cathode active material according to claim 1 .
15. A lithium secondary battery comprising the cathode according to claim 14 .
16. A medium-large battery pack comprising the lithium secondary battery according to claim 15 as a unit.