Positive active material, method of preparing the same, and lithium secondary battery including the same
A positive active material includes a secondary particle in which a plurality of primary particles is agglomerated. The positive active material is composed of, in which a compound containing nickel, lithium, and oxygen. An average angle between a reference line connecting a center portion of the secondary particle and a center portion of the primary particle provided at the outermost portion of the secondary particle and a particle orientation line penetrating the center portion of the primary particle provided at the outermost portion of the secondary particle and extending in parallel to an orientation direction of the primary particles is 12.2° or less. A concentration of the nickel in the compound is 59 mol % or more. The compound further includes an added metal composed of a different element from the nickel and the lithium. The added metal includes one or more of boron (B) and tungsten (W).
1. A positive active material comprising:
a secondary particle in which a plurality of primary particles is agglomerated, wherein:
the positive active material is composed of a compound containing nickel, lithium, and oxygen, and
an average angle between a reference line that is a line connecting a center portion of the secondary particle and a center portion of the primary particle provided at the outermost portion of the secondary particle and a particle orientation line that is a line penetrating the center portion of the primary particle provided at the outermost portion of the secondary particle and extending in parallel to an orientation direction of the primary particles is 12.2° or less,
wherein a concentration of the nickel in the compound is 59 mol % or more,
wherein the compound further includes an added metal composed of a different element from the nickel and the lithium, and
wherein the added metal includes tungsten (W).
2. The positive active material of claim 1 , wherein when the concentration of the nickel is 79 mol % or more, the average angle is 5.6° or less and a standard deviation is 4.5 or less.
3. The positive active material of claim 1 , wherein:
the compound further includes an added metal composed of a different element from the nickel and the lithium, and
an aspect ratio of the primary particle increases by the added metal.
4. The positive active material of claim 1 , wherein compound further includes at least one of aluminum, cobalt, and manganese.
5. The positive active material of claim 1 , wherein:
the compound further includes an added metal composed of a different element from the nickel and the lithium, and
the added metal is included in the primary particle by doping of the added metal, and the added metal is provided on a surface portion of the primary particle in at least a part of the primary particle.
6. The positive active material of claim 1 , wherein:
the compound further includes an added metal composed of a different element from the nickel and the lithium, and
the compound is expressed by Li a M1 x M2 y M3 z O 2 , in which:
1≤a≤1.1,
0.59≤x<1,
0≤y≤0.2,
0<z≤0.02,
M1 is nickel,
M2 includes at least one of aluminum, cobalt, and manganese, and
M3 includes Tungsten (W).
7. The positive active material of claim 6 , wherein the (003) surface of the primary particle is arranged to be parallel to a direction from the center portion to a surface portion of the secondary particle.
8. The positive active material of claim 1 , wherein:
a concentration of the added metal is 2 mol % or less.
9. A lithium secondary battery comprising:
a positive electrode including the positive active material of claim 1 ,
a negative electrode spaced apart from the positive electrode; and
an electrolyte between the positive electrode and the negative electrode.