Nickel-based active material, positive electrode including the same, and lithium secondary battery employing the positive electrode
A nickel-based active material, a positive electrode including the same, and a lithium secondary battery including the positive electrode, a negative electrode, and an electrolyte between the positive electrode and the negative electrode are provided. The nickel-based active material includes 80 mol % or more of nickel with respect to the metal elements excluding lithium, and the nickel-based active material includes: i) large secondary particles having a size in a range of 10 μm to 20 μm and including aggregates of primary particles having a size of 1 μm or less; ii) large crystal particles including primary particles having a size in a range of 1 μm to 5 μm; and iii) small secondary particles having a size in a range of 1 μm to 7 μm and including aggregates of primary particles having a size of 1 μm or less.
1 . A positive electrode comprising a positive active material layer comprising a nickel-based active material having 80 mol % or more of nickel with respect to 100 mol % of total metal elements of the nickel-based active material excluding lithium,
the nickel-based active material comprising:
i) large secondary particles having a size in a range of 10 μm to 20 μm and each comprising an aggregate of primary particles having a size of 1 μm or less;
ii) large crystal particles comprising primary particles having a size in a range of 1 μm to 5 μm; and
iii) small secondary particles having a size in a range of 1 μm to 7 μm and each comprising an aggregate of primary particles having a size of 1 μm or less,
wherein the large secondary particles have a higher percentage of nickel compared to a percentage of nickel in the large crystal particles and compared to a percentage of nickel in the small secondary particles,
wherein an amount of the large secondary particles is higher than an amount of the small secondary particles,
wherein an amount of the large crystal particles is at most the amount of the small secondary particles, and
wherein a mixture density of the positive active material layer is 4.0 g/cm 3 or greater.
2 . The positive electrode of claim 1 , wherein the large crystal particles are each a one body particle or each have a monolithic structure.
3 . The positive electrode of claim 1 , wherein the large crystal particles are secondary particles that are aggregates of primary particles, and the secondary particles have a size of 1 μm to 9 μm.
4 . The positive electrode of claim 1 , wherein an amount of nickel in the large crystal particles is greater than an amount of nickel in the small secondary particles.
5 . The positive electrode of claim 1 , wherein an amount of nickel in the large secondary particles is 90 mol % to 99 mol % based on 100 mol % of the total metal elements of the nickel-based active material excluding lithium.
6 . The positive electrode of claim 1 , wherein an amount of nickel in the large crystal particles is 80 mol % to 95 mol % based on 100 mol % of the total metal elements of the nickel-based active material excluding lithium.
7 . The positive electrode of claim 1 , wherein an amount of nickel in the small secondary particles is 80 mol % to 95 mol % based on 100 mol % of the total metal elements of the nickel-based active material excluding lithium.
8 . A nickel-based active material having 80 mol % or more of nickel with respect to 100 mol % of total metal elements of the nickel-based active material excluding lithium, the nickel-based active material comprising:
i) large secondary particles having a size in a range of 10 μm to 20 μm and each comprising an aggregate of primary particles having a size of 1 μm or less;
ii) large crystal particles comprising primary particles having a size in a range of 1 μm to 5 μm; and
iii) small secondary particles having a size in a range of 1 μm to 7 μm and each comprising an aggregate of primary particles having a size of 1 μm or less,
wherein an amount of the large crystal particles is 5 wt % to 25 wt % based on a total amount of 100 wt % of the large secondary particles, the large crystal particles, and the small secondary particles,
an amount of the small secondary particles is 5 wt % to 25 wt % based on the total amount of 100 wt % of the large secondary particles, the large crystal particles, and the small secondary particles, and
an amount of the large secondary particles is higher than the amount of the large crystal particles and the amount of the small secondary particles.
9 . The positive electrode of claim 1 , wherein:
the nickel-based active material is a compound represented by Formula 1, a compound represented by Formula 2, or a combination thereof:
Li x Ni 1-y CO y O 2-z X z , Formula 1
wherein, in Formula 1, 0.9≤x≤1.2, 0<y≤0.2, 0≤z≤0.5, and 0.8≤1-y<1 are satisfied, and
X is F, S, P, or a combination thereof, and
Li x Ni 1-y-z CO y M z O 2-a X a , Formula 2
wherein, in Formula 2, 0.9≤x≤1.2, 0<y<0.5, 0.8≤1-y-z<1, 0≤z≤0.5, 0<y+z≤0.2, and 0≤a<2 are satisfied,
M is Ni, Co, Mn, Mg, Ca, Sr, Ba, Ti, Zr, Nb, Mo, W, Zn, Al, Si, Cr, Fe, V, a rare earth element, or a combination thereof, and
X is F, S, P, or a combination thereof.
10 . The positive electrode of claim 1 , wherein:
the nickel-based active material is a compound represented by Formula 3, a compound represented by Formula 4, or a combination thereof:
Li x Co a Ni b Mn c O 2 , Formula 3
wherein, in Formula 3, 0.9<x<1.2, 0<a<0.5, 0.8≤b<1, 0<c<0.5, and a+b+c=1 are satisfied, and
Li x Co a Ni b Al c O 2 , Formula 4
wherein, in Formula 4, 0.9<x<1.2, 0<a<0.5, 0.8≤b<1, 0<c<0.5, and a+b+c=1 are satisfied.
11 . The positive electrode of claim 1 , wherein:
in an X-ray diffraction analysis of the nickel-based active material, a full width at half maximum (FWHM) of a (003) plane peak is 0.120 degrees (°) to 0.270°, a FWHM of a (104) plane peak is 0.120° to 0.270°, and a distance between a (108) plane peak and a (110) plane peak is 0.1° to 0.5°.
12 . A lithium secondary battery comprising the positive electrode of claim 1 , a negative electrode, and an electrolyte therebetween.
13 . The positive electrode of claim 1 , wherein:
an amount of nickel in the large secondary particles is 90 mol % to 99 mol % based on 100 mol % of the total metal elements of the nickel-based active material excluding lithium, and
an amount of nickel in the large crystal particles is 80 mol % to 95 mol % based on 100 mol % of the total metal elements of the nickel-based active material excluding lithium.
14 . The positive electrode of claim 1 , wherein, in an X-ray diffraction analysis of the nickel-based active material, a full width at half maximum (FWHM) for a (003) plane peak is 0.120 degrees (°) to 0.270°.
15 . The positive electrode of claim 14 , wherein, in the X-ray diffraction analysis of the nickel-based active material, the full width at half maximum (FWHM) for the (003) plane peak is 0.120° to 0.150°.
16 . The positive electrode of claim 1 , wherein a difference in the percentage of nickel between the large secondary particles and the large crystal particles and a difference in the percentage of nickel between the large secondary particles and the small secondary particles are each 19 mol % or less.
17 . The nickel-based active material of claim 8 , wherein the amount of the large crystal particles is at most the amount of the small secondary particles.