This application claims the benefit of Korean Patent
Application Nos. 10-2022-0140776, filed on October 27, 2022,
and 10-2023-0143340, filed on October 24, 2023, the disclosures
10 of which are incorporated by reference herein.
[0003] Technical Field
[0004] The present invention relates to a lithium secondary
battery.
BACKGROUND ART
15 [0005] Demand for batteries as an energy source has been
significantly increased as technology development and demand
with respect to power tools, electric vehicles, and energy
storage systems (ESSs) have recently increased, and thus a
variety of researches on batteries capable of meeting various
20 needs have been carried out. As needs of the market for the
lithium secondary batteries, having high capacity, as a power
source of such a device have been increased, researches for
increasing cell energy density have been actively carried out.
In addition, as batteries which can be applied to devices,
25 requiring a high output, such as power tools, the demand for
3
batteries having excellent capacity characteristics as well as
excellent rate characteristics has been increasing.
[0006] However, when the secondary battery embedded in the
power tool is discharged with a high output, the system
5 operation of the power tool is terminated due to the voltage
drop of the secondary battery. That is, since the potential
value of the secondary battery is greatly reduced during the
high-rate discharge, the system determines that the battery
capacity is insufficient even though the battery capacity
10 remains, thereby causing the power of the power tool to be
turned off.
[0007] In addition, a cylindrical-type battery is generally
used as a battery for a power tool. In the case of a
cylindrical-type battery, since the battery can is heavy in
15 weight, the total weight of the power tool is increased when
the cylindrical-type battery is used, and thus there is a
limitation in that work convenience is reduced.
A lithium secondary battery comprising:
a battery case; and
5 an electrode assembly and an electrolyte accommodated in
the battery case,
wherein the electrode assembly comprises a positive
electrode,
the positive electrode comprises a first positive
10 electrode active material, a second positive electrode active
material, and a conductive agent,
the second positive electrode active material is a single
particle composed of one primary particle, a quasi-single
particle which is an aggregate of 2 to 30 primary particles,
15 or a combination thereof,
the weight ratio of the first positive electrode active
material and the second positive electrode active material is
7.5:2.5 to 9.5:0.5, and
the conductive agent comprises a point-type conductive
20 agent and a linear conductive agent at a weight ratio of 10:1
to 50:1.
2. The lithium secondary battery of claim 1, wherein the
first positive electrode active material comprises a compound
25 represented by Formula 1 below:
53
[Formula 1]
Li1+x[NiaCobM1cM2d]1-xO2-yX1y
wherein, in Formula 1 above, 0.8≤a≤0.95, 0≤b≤0.2, 0≤c≤0.2,
0≤d≤0.1, a+b+c+d=1, 0≤x≤0.3, 0≤y≤0.2, M1 is Mn, Al, or a
5 combination thereof, M2 is at least one metal element selected
from the group consisting of W, Cu, Fe, V, Cr, Ti, Zr, Zn, In,
Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo, and
X1 is at least one element selected from the group consisting
of F, Cl, Br, I, At, P, and S.
10
3. The lithium secondary battery of claim 1, wherein the
second positive electrode active material comprises a compound
represented by Formula 2 below:
[Formula 2]
15 Li1+z[NigCohM3iM4j]1-zO2-wX2w
wherein, in Formula 2 above, 0.85≤g≤0.95, 0≤h≤0.15,
0≤i≤0.15, 0≤j≤0.1, g+h+i+j=1, 0≤z≤0.3, 0≤w≤0.2, M3 is Mn, Al,
or a combination thereof, M4 is at least one metal element
selected from the group consisting of W, Cu, Fe, V, Cr, Ti,
20 Zr, Zn, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B,
and Mo, and X2 is at least one element selected from the group
consisting of F, Cl, Br, I, At, P, and S.
4. The lithium secondary battery of claim 1, wherein the
25 first positive electrode active material comprises a lithium
54
nickel-based oxide containing at least 80 mol% of nickel with
respect to the total number of moles of transition metals
excluding lithium.
5 5. The lithium secondary battery of claim 1, wherein the
first positive electrode active material comprises a lithium
nickel-based oxide containing 80-85 mol% of nickel with respect
to the total number of moles of transition metals excluding
lithium.
10
6. The lithium secondary battery of claim 1, wherein the
second positive electrode active material comprises a lithium
nickel-based oxide containing at least 85 mol% of nickel with
respect to the total number of moles of transition metals
15 excluding lithium.
7. The lithium secondary battery of claim 1, wherein the
first positive electrode active material is a secondary
particle in which at least 50 primary particles are aggregated
20 with each other.
8. The lithium secondary battery of claim 1, wherein the
second positive electrode active material has an average
particle diameter D50 smaller than the first positive electrode
25 active material.