COMPOSITE CATHODE ACTIVE MATERIAL, CATHODE AND LITHIUM BATTERY INCLUDING THE SAME, AND METHOD OF PREPARING THE COMPOSITE CATHODE ACTIVE MATERIAL
A composite cathode active material includes: a secondary including a core including a plurality of primary particles; and a shell on the core, wherein the plurality of primary particles include a nickel-containing lithium transition metal oxide doped with a first metal, and wherein at least one grain boundary between the plurality of primary particles includes a first composition including the first metal.
1 . A composite cathode active material, comprising:
a secondary particle comprising
a core comprising a plurality of primary particles; and
a shell on the core,
wherein the plurality of primary particles comprise a nickel-containing lithium transition metal oxide doped with a first metal, and
wherein at least one grain boundary between the plurality of primary particles comprises a first composition comprising the first metal.
2 . The composite cathode active material of claim 1 , wherein the nickel-containing lithium transition metal oxide comprises a first phase and the first composition comprises a second phase which is different from the first phase.
3 . The composite cathode active material of claim 2 , wherein the second phase has a monoclinic crystalline structure.
4 . The composite cathode active material of claim 3 , wherein the monoclinic crystalline structure belongs to a C2/m, C12/c1, or C2/c space group.
5 . The composite cathode active material of claim 1 , wherein the first metal comprises Zr, Mn, Si, Mo, Pd, Co, Ni, Ti, Sn, Mo, Ir, Pt, Ru, or a combination thereof.
6 . The composite cathode active material of claim 1 , wherein the first composition comprises lithium, the first metal, and oxygen, and,
the first composition comprises about 1.7 moles to about 2.3 moles of lithium, about 0.7 moles to about 1.3 moles of the first metal, and about 2.7 moles to about 3.3 moles of oxygen, per mole of the first composition.
7 . The composite cathode active material of claim 1 , wherein the first composition is represented by Formula 1:
Li a M1 b O c <Formula 1>
wherein, in Formula 1, M1 comprises Zr, Mn, Si, Mo, Pd, Co, Ni, Ti, Sn, Mo, Ir, Pt, Ru, or a combination thereof, 1.9≤a≤2.1, 0.9≤b≤1.1, and 2.9≤c≤3.1.
8 . The composite cathode active material of claim 1 , wherein the core comprises a first inner region and a second inner region,
wherein the first inner region extends from a center of the core to halfway between the center of the core and a surface of the core, and the second inner region extends from halfway between the center of the core and the surface of the core to the surface of the core, and
about 50% or greater of the grain boundaries in the first inner region comprise the first composition, and about 50% or greater of the grain boundaries in the second inner region comprise the first composition.
9 . The composite cathode active material of claim 1 , wherein at least one grain boundary between the plurality of primary particles has a substantially rectilinear form.
10 . The composite cathode active material of claim 1 , wherein at least one grain boundary between adjacent primary particles among the plurality of primary particles, extends in a direction parallel to adjacent surfaces of the adjacent primary particles, and
at least one grain boundary extends in a direction different from a tangential direction of an outer surface of the core of the secondary particle.
11 . The composite cathode active material of claim 1 , wherein the core comprises a first grain boundary and a second grain boundary, and each of the first grain boundary and the second grain boundary are adjacent to a same primary particle, and
wherein the first grain boundary and the second grain boundary intersect at an angle determined by a shape of the primary particle.
12 . The composite cathode active material of claim 1 , wherein the core comprises a plurality of grain boundaries amongst the plurality of primary particles, wherein each grain boundary of the plurality of grain boundaries extends in a direction parallel to a surface of an adjacent primary particle, and
wherein each grain boundary of the plurality of grain boundaries extends in a different direction from each other.
13 . The composite cathode active material of claim 1 , wherein an average grain boundary length is in a range of about 50 nanometers to about 1000 nanometers and an average grain boundary thickness is in a range of about 1 nanometer to about 50 nanometers, and
wherein a length direction of the grain boundary is parallel to adjacent surfaces of adjacent primary particles, and thickness direction of the grain boundary is perpendicular to adjacent surfaces of adjacent primary particles.
14 . The composite cathode active material of claim 1 , wherein the shell comprises the first composition comprising the first metal.
15 . The composite cathode active material of claim 1 , wherein the shell comprises a second composition comprising a second metal.
16 . The composite cathode active material of claim 15 , wherein the second metal comprises Zr, Co, Mg, Mn, Si, Mo, Pd, Co, Ni, Ti, Sn, Mo, Ir, Pt, Ru, or a combination thereof.
17 . The composite cathode active material of claim 1 , wherein the shell has a thickness of about 300 nanometers or less.
18 . The composite cathode active material of claim 1 , wherein an amount of the first metal in the secondary particle is about 1 mole percent or less with respect to total moles of the transition metal and the first metal in the nickel-containing lithium transition metal oxide.
19 . The composite cathode active material of claim 1 , wherein the nickel-containing lithium transition metal oxide comprises lithium, nickel, the first metal, a third metal, and oxygen,
wherein, the nickel-containing lithium transition metal oxide comprises about 0.1 mole to about 1.3 moles of lithium, about 0.7 moles to about 0.99 moles of nickel, about 0.001 moles to about 0.01 moles of the first metal, about 0.01 mole to about 0.3 moles of the third metal, and about 1.7 moles to about 2.3 moles of oxygen, per mole of the nickel-containing lithium transition metal oxide.
20 . The composite cathode active material of claim 1 , wherein the nickel-containing lithium transition metal oxide is represented by Formula 2:
Li a MO 2 Formula 2
wherein, in Formula 2, 0.9≤a≤1.1, M comprises nickel, the first metal, and an element comprising a Group 2 to Group 13 element which is different from the first metal, and an amount of nickel in M is about 70 mole percent to less than 100 mole percent based on total moles of M in the lithium transition metal oxide.
21 . The composite cathode active material of claim 1 , wherein the nickel-containing lithium transition metal oxide is represented by Formula 3:
Li a Ni b M1 c M2 d M3 e O 2 Formula 3
wherein, in Formula 3, 0.9≤a≤1.1, 0.7<b<1.0, 0<c<0.3, 0<d<0.3, 0≤e<0.1, b+c+d+e=1, and M1, M2, and M3 differ from one another and are each independently an element selected from Mn, V, Cr, Fe, Co, Zr, Re, Al, B, Ru, Ti, Nb, Mo, Mg, and Pt.
22 . The composite cathode active material of claim 1 , wherein the nickel-containing lithium transition metal oxide is represented by Formula 4:
Li a Ni b CO c Mn d M3 e O 2 Formula 4
wherein, in Formula 4, 0.9≤a≤1.1, 0.7<b<1.0, 0<c<0.1, 0<d<0.1, 0≤e<0.01, b+c+d+e=1, and
M3 comprises Zr, V, Cr, Fe, Re, Al, B, Ru, Ti, Nb, Mo, Mg, Pt, or a combination thereof.
23 . The composite cathode active material of claim 1 , wherein the nickel-containing lithium transition metal oxide is represented by Formula 5:
a Li 2 MnO 3- (1− a )LiMO 2 Formula 5
wherein, in Formula 5, 0<a<1, and
M comprises at least two elements selected from Ni, Co, Mn, V, Cr, Fe, Zr, Re, Al, B, Ru, Ti, Nb, Mo, Mg, and Pt.
24 . The composite cathode active material of claim 1 , wherein an area of pores in a cross-section of the composite cathode active material is about 1% or less with respect to the total area of the cross-section.
25 . A cathode comprising the composite cathode active material according to claim 1 .
26 . A lithium battery comprising,
the cathode according to claim 25 ,
an anode, and
an electrolyte between the cathode and the anode.
27 . A method of preparing a composite cathode active material, the method comprising:
providing a first solution comprising a first metal precursor;
combining the first solution with a nickel-containing lithium transition metal oxide precursor to prepare a second solution comprising a precipitate;
separating the precipitate from the second solution and drying the precipitate to prepare a dried product;
mixing the dried product and a lithium precursor compound to prepare a mixture; and
thermally treating the mixture to thereby prepare the composite cathode active material.
28 . The method of claim 28 , wherein a porosity of the composite cathode active material is less than a porosity of the nickel-containing lithium transition metal oxide precursor.
29 . The method of claim 27 , wherein the nickel-containing lithium transition metal oxide precursor comprises primary particles having a needle shape.
30 . The method of claim 27 , wherein the composite cathode active material comprises:
a secondary particle comprising
a core comprising a plurality of particles, and
a shell on the core,
wherein the plurality of primary particles comprise the nickel-containing lithium transition metal oxide doped with the first metal, and
wherein at least one grain boundary between the plurality of primary particles comprises the first metal.