This application claims the benefit of Korean Patent
Application Nos. 10-2022-0140773, filed on October 27, 2022,
10-2022-0140774, filed on October 27, 2022, and 10-2023-
10 0143338, filed on October 24, 2023, in the Korean Intellectual
Property Office, the disclosures of which are incorporated
herein in their entirety.
Technical Field
[0002] The present invention relates to a lithium secondary
15 battery.
BACKGROUND ART
[0003] 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
20 storage systems (ESSs) have recently increased, and thus a
variety of researches on batteries capable of meeting various
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
25 increasing cell energy density have been actively carried out.
2
In addition, as batteries which can be applied to devices,
requiring a high output, such as power tools, the demand for
batteries having excellent capacity characteristics as well as
excellent rate characteristics has been increasing.
5 [0004] However, when the secondary battery embedded in the
power tool is discharged with a high output, the system
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
10 high-rate discharge, the system determines that the battery
capacity is insufficient even though the battery capacity
remains, thereby causing the power of the power tool to be
turned off.
[0005] In addition, a cylindrical-type battery is generally
15 used as a battery for a power tool. In the case of a
cylindrical-type battery, since the battery can is heavy in
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.
20 DISCLOSURE OF THE INVENTION
TECHNICAL PROBLEM
[0006] In order to solve the above-described problems, the
present invention provides a lithium secondary battery having
a low degree of voltage drop in the battery during high-rate
25 discharge, thereby being capable of preventing the power-off
3
phenomenon of a power tool.
[0007] In addition, the present invention provides a pouchtype lithium secondary battery having a low degree of voltage
drop in the battery during high-rate discharge while having
5 excellent work convenience due to a relatively light weight
thereof, and having low resistance and excellent output
properties.
TECHNICAL SOLUTION
[0008] According to an aspect of the present invention, there
10 is provided a lithium secondary battery which includes a
battery case, and an electrode assembly and an electrolyte
received in the battery case, and has a Vd-40, which is a voltage
retention rate during 40 C discharge represented by Equation
1 below, of 74% or greater, specifically, 74% to 85%.
15 [0009] [Equation 1]
Vd-40 (%) = (Vf-40 / Vi-40) × 100
[0010] In Equation 1 above, Vf-40 is a voltage of the lithium
secondary battery after applying a discharge pulse at a rate
of 40 C, and Vi-40 is a voltage of the lithium secondary battery
20 before applying a discharge pulse at a rate of 40 C.
[0011] Meanwhile, the lithium secondary battery according to
the present invention may have a V'd,5, which is a voltage
retention rate during continuous discharge represented by
Equation 2 below, of 72% or greater, preferably 72% to 82%.
25 [0012] [Equation 2]
4
V'd,5 (%) = (V'f,5 / V'i) × 100
[0013] In Equation 2 above, V'f,5 is a voltage of the lithium
secondary battery after applying a discharge pulse 5 times
while increasing a rate by 40 C, and V'i is an initial voltage
5 of the lithium secondary battery fully charged before applying
a discharge pulse. At this time, the first discharge pulse is
applied at a rate of 24 C, and the fifth discharge pulse is
applied at a rate of 40 C.
[0014] According to the present invention, the electrode
10 assembly includes a positive electrode, a separator, and a
negative electrode, wherein the positive electrode may include,
as a positive electrode active material, a lithium nickelbased oxide containing 80 mol% or greater, preferably 85 mol%
to 90 mol% of nickel, based on the total number of moles of
15 transition metals except for lithium.
[0015] Preferably, the lithium nickel-based oxide may be a
compound represented by Formula 1 below.
[0016] [Formula 1]
Li1+x[NiaCobM1cM2d]1-xO2-yXy
20 [0017] 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, and 0≤y≤0.2, M1 is Mn, Al, or a
combination thereof, M2 is 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 X is
25 one or more elements selected from the group consisting of F,
5
Cl, Br, I, At, P, and S.
[0018] Meanwhile, in the present invention, the positive
electrode may include a positive electrode active material
layer having a porosity of greater than 30%, specifically 32%
5 to 38%.
[0019] According to the present invention, the electrolyte
may include ethyl propionate (EP), and at this time, the ethyl
propionate may be included in an amount of 80 wt% or less,
specifically 40 wt% to 70 wt%, based on the total weight of
10 the electrolyte.
[0020] In addition, the negative electrode may include
artificial graphite as a negative electrode active material.
[0021] Meanwhile, in the present invention, the battery case
may be a pouch-type battery case.
15 ADVANTAGEOUS EFFECTS
[0022] A lithium secondary battery according to the present
invention is characterized by having a voltage retention rate
Vd-40 of 75% or greater before and after discharge pulse
application when a discharge pulse is applied at a rate of 40
20 C. As a result, even when the lithium secondary battery of
the present invention is discharged at a high rate, the degree
of a voltage drop in the battery is not large, so that it is
possible to prevent a power shutdown phenomenon of a power
tool due to high-rate discharge when the battery according to
25 the present invention is used as a power source of the power
6
tool.
[0023] In addition, when the lithium secondary battery
according to the present invention is a pouch-type lithium
secondary battery, due to a relatively light weight thereof,
5 work convenience is excellent.
A lithium secondary battery comprising:
a battery case; and
5 an electrode assembly and an electrolyte received in the
battery case, wherein Vd-40, which is a voltage retention rate
during 40 C discharge represented by [Equation 1] below, is
74% or greater:
[Equation 1]
10 Vd-40 (%) = (Vf-40 / Vi-40) × 100
wherein in [Equation 1] above, Vf-40 is a voltage of the
lithium secondary battery after applying a discharge pulse at
a rate of 40 C, and Vi-40 is a voltage of the lithium secondary
battery before applying a discharge pulse at a rate of 40 C.
15
2. The lithium secondary battery of claim 1, wherein the Vd40, which is a voltage retention rate during 40 C discharge,
is 74% to 85%.
20 3. The lithium secondary battery of claim 1, whereinV'd,5,
which is a voltage retention rate during continuous discharge
represented by [Equation 2] below, is 72% or greater:
[Equation 2]
V'd,5 (%) = (V'f,5 / V'i) × 100
25 wherein in [Equation 2] above, V'f,5 is a voltage of the
48
lithium secondary battery after applying a discharge pulse 5
times while increasing a rate by 40 C, and V'i is an initial
voltage of the lithium secondary battery fully charged before
applying a discharge pulse.
5
4. The lithium secondary battery of claim 3, wherein the
V'd,5, which is a voltage retention rate during continuous
discharge, is 72% to 82%.
10 5. The lithium secondary battery of claim 1, wherein the
electrode assembly comprises a positive electrode, a separator,
and a negative electrode, wherein the positive electrode
includes, as a positive electrode active material, a lithium
nickel-based oxide containing 80 mol% or greater of nickel
15 based on the total number of moles of transition metals except
for lithium.
6. The lithium secondary battery of claim 5, wherein the
positive electrode active material comprises a lithium nickel20 based oxide containing 85 mol% to 90 mol% of nickel based on
the total number of moles of transition metals except for
lithium.
7. The lithium secondary battery of claim 5, wherein the
25 lithium nickel-based oxide is a compound represented by Formula
49
1 below:
[Formula 1]
Li1+x[NiaCobM1cM2d]1-xO2-yXy
(wherein in Formula 1 above, 0.8≤a≤0.95, 0≤b≤0.2, 0≤c≤0.2,
5 0≤d≤0.1, a+b+c+d=1, 0≤x≤0.3, and 0≤y≤0.2, M1 is Mn, Al, or a
combination thereof, M2 is 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 X is
one or more elements selected from the group consisting of F,
10 Cl, Br, I, At, P, and S).
8. The lithium secondary battery of claim 5, wherein the
positive electrode comprises a positive electrode active
material layer with a porosity of greater than 30%.
15
9. The lithium secondary battery of claim 8, wherein the
positive electrode active material layer has a porosity of 32%
to 38%.
20 10. The lithium secondary battery of claim 1, wherein the
electrolyte comprises ethyl propionate (EP).
11. The lithium secondary battery of claim 10, wherein the
ethyl propionate is included in an amount of 80 wt% or less
25 based on the total weight of the electrolyte.
50
12. The lithium secondary battery of claim 10, wherein the
ethyl propionate is included in an amount of 40 wt% to 70 wt%
based on the total weight of the electrolyte.
5
13. The lithium secondary battery of claim 5, wherein the
negative electrode comprises artificial graphite as a negative
electrode active material.
10 14. The lithium secondary battery of claim 1, wherein the
battery case is a pouch-type battery case.