Positive active material for rechargeable lithium battery, preparing method thereof and rechargeable lithium battery including the same
A positive active material for a rechargeable lithium battery includes a lithium nickel-based metal composite oxide, wherein the positive active material includes secondary particles in which a plurality of primary particles are aggregated, a first boron coating portion present on the outer surfaces of the secondary particles, and a second boron coating portion present on surfaces of the primary particles inside the secondary particles, and a weight of the first boron coating portion is greater than a weight of the second boron coating portion.
1. A positive active material for a rechargeable lithium battery, the positive active material comprising:
a lithium nickel-based metal composite oxide;
a secondary particle, in which a plurality of primary particles are aggregated;
a first boron coating portion on an outer surface of the secondary particle; and
a second boron coating portion on surfaces of the primary particles inside the secondary particle,
wherein a weight of the first boron coating portion is greater than a weight of the second boron coating portion, and
wherein a content of the second boron coating portion is about 10 ppm to about 500 ppm based on the positive active material.
2. The positive active material of claim 1 , wherein the first boron coating portion and the second boron coating portion each comprise boron oxide, lithium boron oxide, or a combination thereof.
3. The positive active material of claim 1 , wherein the first boron coating portion is comprised in an amount of about 70 wt. % to about 98 wt. % and the second boron coating portion is comprised in an amount of about 2 wt. % to about 30 wt. %, each based on a total amount of the first boron coating portion and the second boron coating portion.
4. The positive active material of claim 1 , wherein the first boron coating portion is comprised in an amount of about 80 wt. % to about 95 wt. % and the second boron coating portion is comprised in an amount of about 5 wt. % to about 20 wt. %, each based on a total amount of the first boron coating portion and the second boron coating portion.
5. The positive active material of claim 1 , wherein a content of the first boron coating portion is about 200 ppm to about 5000 ppm based on the positive active material.
6. The positive active material of claim 1 , wherein a total amount of the first boron coating portion and the second boron coating portion is about 0.1 mol % to about 5 mol % based on 100 mol % of the positive active material.
7. The positive active material of claim 6 , wherein a total amount of the first boron coating portion and the second boron coating portion is about 0.1 mol % to about 1.3 mol % based on 100 mol % of the positive active material.
8. The positive active material of claim 1 , wherein in the lithium nickel-based metal composite oxide, a content of nickel is greater than or equal to about 60 mol % based on 100 mol % of the lithium nickel-based metal composite oxide.
9. The positive active material of claim 1 , wherein the lithium nickel-based metal composite oxide is represented by Chemical Formula 1:
Li a1 Ni x1 M 1 y1 M 2 1-x1-y1 O 2 , and Chemical Formula 1
wherein, in Chemical Formula 1, 0.9≤a1≤1.8, 0.6≤x1≤1, 0≤y1≤0.4, and M 1 and M 2 are each independently selected from Al, B, Ba, Ca, Ce, Co, Cr, Cu, F, Fe, Mg, Mn, Mo, Nb, P, S, Si, Sr, Ti, V, W, Zr, and combinations thereof.
10. The positive active material of claim 9 , wherein
M 1 is Co and M 2 is Al.
11. The positive active material of claim 1 , wherein the lithium nickel-based metal composite oxide is represented by Chemical Formula 2 or Chemical Formula 3:
Li a2 Ni x2 CO y2 Al z2 M 3 1-x2-y2-z2 O 2 , Chemical Formula 2
wherein, in Chemical Formula 2, 0.9≤a2≤1.8, 0.6≤x2<1, 0<y2<0.4, 0<z2<0.4, and M 3 is selected from B, Ba, Ca, Ce, Co, Cr, Cu, F, Fe, Mg, Mn, Mo, Nb, P, S, Si, Sr, Ti, V, W, Zr, and combinations thereof,
Li a3 Ni x3 CO y3 M 4 1-x3-y3 O 2 , and Chemical Formula 3
wherein, in Chemical Formula 3, 0.9≤a3≤1.8, 0.6≤x3<1, 0<y3≤0.4, and M 4 is selected from B, Ba, Ca, Ce, Co, Cr, Cu, F, Fe, Mg, Mn, Mo, Nb, P, S, Si, Sr, Ti, V, W, Zr, and a combination thereof.
12. The positive active material of claim 1 , wherein the lithium nickel-based metal composite oxide is represented by Chemical Formula 1:
Li a1 Ni x1 M 1 y1 M 2 1-x1-y1 O 2 , and Chemical Formula 1
wherein, in Chemical Formula 1, 0.9≤a1≤1.8, 0.92≤x1<1, 0≤y1≤0.04,
M 1 is selected from Al, B, Ba, Ca, Ce, Co, Cr, Cu, F, Fe, Mg, Mn, Mo, Nb, P, S, Si, Sr, Ti, V, W, Zr, and combinations thereof, and
M 2 is selected from Al, B, Ba, Ca, Ce, Cr, Cu, F, Fe, Mg, Mn, Mo, Nb, P, S, Si, Sr, Ti, V, W, Zr, and combinations thereof.
13. The positive active material of claim 12 , wherein
M 1 is Co and M 2 is Al.
14. The positive active material of claim 1 , wherein a weight ratio of the first boron coating portion to the second boron coating portion is about 70:30 to about 98:2.
15. A rechargeable lithium battery, comprising:
a positive electrode comprising the positive active material of claim 1 ,
a negative electrode, and
an electrolyte.
16. A method of preparing the positive active material of claim 1 , the method comprising:
mixing a nickel-based metal composite hydroxide, a lithium raw material and a boron raw material to obtain a mixture, and
heat-treating the mixture at a temperature of about 690° C. to about 725° C.
17. The method of claim 16 , wherein a content of the boron raw material is about 0.1 mol % to about 5 mol % based on 100 mol % of the nickel-based metal composite hydroxide.
18. The method of claim 16 , wherein the heat-treating of the mixture is performed for about 5 hours to about 15 hours.