Positive active material including lithium nickel-based metal oxide, method of preparing the same, and rechargeable lithium battery including the same
A positive active material for a rechargeable lithium battery includes a lithium nickel-based metal oxide represented by Li x Ni 1-y M y O 2 and a lithium-containing oxide on a surface of the lithium nickel-based metal oxide. In the formula Li x Ni 1-y M y O 2 , M is one or more of Co, Mn, Al, Mg, Ti, Zr, or a combination thereof, 0<x<1.1, and 0≤y<0.5.
1. A positive active material for a rechargeable lithium battery, the positive active material comprising:
a lithium nickel-based metal oxide represented by Chemical Formula 1 and a lithium-containing oxide on a surface of the lithium nickel-based metal oxide:
Li x Ni 1-y M y O 2 (1)
wherein:
in Chemical Formula 1, M is one or more of Co, Mn, Al, Mg, Ti, Zr, or a combination thereof, 0 <x <1.1, and 0≤y< 0 . 5 ,
the lithium-containing oxide is included in an amount of about 0.01 to about 10 parts by weight based on 100 parts by weight of the lithium nickel-based metal oxide,
the lithium-containing oxide is a coating layer that coats a part or a whole of the surface of the lithium nickel-based metal oxide,
the coating layer of the lithium-containing oxide has a rod shape or scale shape, and
the lithium-containing oxide includes Li 2 O.
2. The positive active material as claimed in claim 1 , wherein the coating layer consists of the lithium-containing oxide.
3. The positive active material as claimed in claim 1 , wherein the lithium-containing oxide further includes at least one of LiOH and Li 2 CO 3 .
4. The positive active material as claimed in claim 1 , wherein the coating layer has the rod shape, and has an aspect ratio of greater than or equal to about 1.
5. The positive active material as claimed in claim 1 , wherein the lithium-containing oxide is included in an amount of 1 to 10 parts by weight based on 100 parts by weight of the lithium nickel-based metal oxide.
6. The positive active material as claimed in claim 1 , wherein the lithium nickel-based metal oxide represented by Chemical Formula 1 with the lithium-containing oxide on the surface of the lithium nickel-based metal oxide is prepared by:
mixing a lithium raw material and a nickel-containing metal oxide precursor to prepare a mixture,
performing a first heat treatment on the mixture to prepare the lithium nickel-based metal oxide represented by Chemical Formula 1,
dry-mixing the lithium nickel-based metal oxide with the lithium-containing oxide, and
performing a second heat treatment on the dry-mixed lithium nickel-based metal oxide and lithium-containing oxide,
wherein the lithium-containing oxide includes Li 2 O.
7. The positive active material as claimed in claim 1 , wherein 0.1 ≤y≤0.4 in Chemical Formula 1.
8. The positive active material as claimed in claim 1 , wherein Chemical Formula 1 is represented by Chemical Formula 2 or Chemical Formula 3:
Li x Ni 1-a-b Co a Al b O 2 (2)
Li x Ni 1-a-b Co a Mn b O 2 (3)
where 0<x<1.1, 0<a<0.5, 0<b<0.5, and 0<a+b<0.5 in Chemical Formula 2 and Chemical Formula 3.
9. A rechargeable lithium battery, comprising:
a positive electrode including a positive active material as claimed in claim 1 ,
a negative electrode, and
an electrolyte solution.
10. A method of preparing the positive active material for a rechargeable lithium battery as claimed in claim 1 , the method comprising:
mixing a lithium raw material and a nickel-containing metal oxide precursor to prepare a mixture, and heat-treating the mixture to prepare the lithium nickel-based metal oxide represented by Chemical Formula 1, and
dry-mixing the lithium nickel-based metal oxide with the lithium-containing oxide followed by heat treatment,
wherein the lithium-containing oxide includes Li 2 O.
11. The method as claimed in claim 10 , wherein the lithium-containing oxide further includes at least one of LiOH and Li 2 CO 3 .
12. The method as claimed in claim 10 , wherein the mixture of the lithium raw material and nickel-containing metal oxide precursor is heat-treated at about 600° C. to about 1,000° C.
13. The method as claimed in claim 10 , wherein the heat treatment of the dry-mixture of the lithium nickel-based metal oxide with the lithium-containing oxide is performed at about 400° C. to about 700° C.
14. The method as claimed in claim 10 , wherein y is within a range of 0.1≤y≤0.4 in Chemical Formula 1.
15. The method as claimed in claim 10 , wherein the nickel-containing metal oxide precursor is represented by Chemical Formula 4:
Me(OH) 2 (4)
where Me is represented by Chemical Formula 5,
Ni k M 1-k (5)
where M is one or more of Co, Mn, Al, Mg, Ti, Zr, or a combination thereof and where 0.5<k≤1.0.