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, a preparing method thereof, and a rechargeable lithium battery including the same are provided. The positive active material for a rechargeable lithium battery includes a first positive active material including a first lithium nickel-based composite oxide and including secondary particles formed by aggregation of a plurality of primary particles and a cobalt coating portion on the surface of the secondary particles; and a second positive active material including a second lithium nickel-based composite oxide and including individual particles and a cobalt coating portion on the surface of the individual particles, wherein the second positive active material has an uneven surface having concavo-convex features and an even surface that is substantially flat.
1 . A positive active material for a rechargeable lithium battery, the positive active material comprising:
a first positive active material comprising a first lithium nickel-based composite oxide, and comprising secondary particles formed by aggregation of a plurality of primary particles and a cobalt coating portion on a surface of the secondary particles, and
a second positive active material comprising a second lithium nickel-based composite oxide and comprising individual particles and a cobalt coating portion on a surface of the individual particles,
wherein the second positive active material has:
an uneven surface comprising concavo-convex features and having a maximum roughness (R max ; peak to peak height) of greater than or equal to about 18 nm; and
an even surface that is substantially flat and having a maximum roughness (R max ) of less than or equal to about 15 nm.
2 . The positive active material for a rechargeable lithium battery of claim 1 , wherein the maximum roughness of the uneven surface is greater than or equal to about 20 nm.
3 . The positive active material for a rechargeable lithium battery of claim 1 , wherein
the uneven surface of the second positive active material has an average roughness (R a ) of greater than or equal to about 1.9 nm and a root mean square roughness (R q ) of greater than or equal to about 2.3 nm.
4 . The positive active material for a rechargeable lithium battery of claim 1 , wherein the maximum roughness of the even surface is less than or equal to about 14 nm.
5 . The positive active material for a rechargeable lithium battery of claim 1 , wherein
the even surface of the second positive active material has an average roughness (R a ) of less than or equal to about 1.8 nm and a root mean square roughness (R q ) of less than or equal to about 2.2 nm.
6 . The positive active material for a rechargeable lithium battery of claim 1 , wherein
a ratio of area of the uneven surface to total surface area of the second positive active material is about 40% to about 80%.
7 . The positive active material for a rechargeable lithium battery of claim 1 , wherein the positive active material comprising the first positive active material and the second positive active material has a Brunauer, Emmett and Teller (BET) specific surface area of about 0.2 m 2 /g to about 0.6 m 2 /g.
8 . The positive active material for a rechargeable lithium battery of claim 1 , wherein
the first positive active material has an average particle diameter of about 7 μm to about 25 μm, and
the second positive active material has an average particle diameter of about 0.05 μm to about 10 μm.
9 . The positive active material for a rechargeable lithium battery of claim 1 , wherein
the first positive active material is included in an amount of about 50 wt % to about 90 wt % and the second positive active material is included in an amount of about 10 wt % to about 50 wt % based on total amount of the first positive active material and the second positive active material.
10 . The positive active material for a rechargeable lithium battery of claim 1 , wherein
the first positive active material comprises the first lithium nickel-based composite oxide represented by Chemical Formula 1, and
the second positive active material comprises the second lithium nickel-based composite oxide represented by Chemical Formula 11:
Li a1 Ni x1 M 1 y1 M 2 1-x1-y1 O 2 Chemical Formula 1
wherein, in Chemical Formula 1, 0.9≤a1≤1.8, 0.3≤x1≤1, 0≤y1≤0.7, and M 1 and M 2 are each independently Al, B, Ba, Ca, Ce, Co, Cr, Cu, F, Fe, Mg, Mn, Mo, Nb, P, S, Si, Sr, Ti, V, W, Zr, or a combination thereof,
Li a11 Ni x11 M 11 y11 M 12 1-x11-y11 O 2 Chemical Formula 11
wherein, in Chemical Formula 11, 0.9≤a11≤1.8, 0.3≤x11≤1, 0≤y11≤0.7, and M 11 and M 12 are each independently Al, B, Ba, Ca, Ce, Co, Cr, Cu, F, Fe, Mg, Mn, Mo, Nb, P, S, Si, Sr, Ti, V, W, Zr, or a combination thereof.
11 . A rechargeable lithium battery comprising
a positive electrode comprising the positive active material of claim 1 , a negative electrode, and an electrolyte.