TECHNICAL FIELD
Cross-reference to Related Applications
[0001] This application claims the benefit of Korean Patent
10 Application No. 10-2020-0055339, filed on May 8, 2020, in the
Korean Intellectual Property Office, the disclosure of which
is incorporated herein in its entirety by reference.
Technical Field
[0002] The present invention relates to a negative electrode,
15 a method for manufacturing the same, a secondary battery
related to the same, and a method for manufacturing the
secondary battery, wherein the negative electrode has a first
negative electrode active material layer and a second
negative electrode active material layer, and the first
20 negative electrode active material layer close to a current
collector includes ethylene carbonate.
BACKGROUND ART
[0003] As technology development and demand for mobile
devices have increased in recent years, the demand for
25 secondary batteries as an energy source has been rapidly
2
increased. Accordingly, various studies have been conducted
on batteries which may meet various needs. Particularly,
research has been actively conducted on a lithium secondary
battery having high energy density and excellent lifespan and
5 cycle properties as a power source for such devices.
[0004] A lithium secondary battery means a battery in which
an electrolyte solution containing lithium ions is included
in an electrode assembly including a positive electrode
containing a positive electrode active material capable of
10 intercalation/deintercalation of lithium ions, a negative
electrode containing a negative electrode active material
capable of intercalation/deintercalation of lithium ions, and
a microporous separator interposed between the positive
electrode and the negative electrode.
15 [0005] When the electrode assembly is formed, the electrode
assembly is put into a case, and then the electrolyte
solution is injected into the case to impregnate the
electrode assembly in the electrolyte solution. At this time,
the electrolyte solution wets the negative electrode, thereby
20 serving to increase the mobility of lithium ions in the
negative electrode.
[0006] However, when the loading amount of a negative
electrode active material layer in the negative electrode is
set to be high in order to increase the energy density of the
25 negative electrode, it is difficult for the electrolyte
3
solution to easily move into the negative electrode, so that
the electrolyte solution wetting of the negative electrode is
significantly lowered. When the electrolyte solution wetting
is lowered, an SEI layer is not uniformly generated on the
5 surface of the negative electrode, causing non-uniformity of
performance in the negative electrode, so that the lifespan
and stability of the secondary battery are deteriorated. In
addition, low electrolyte solution wetting lowers the
efficiency of a production process.
10 [0007] Typically, a negative electrode active material layer
is formed into two layers in order to improve electrolyte
solution wetting. However, with this method alone, there is
a limitation in improving the electrolyte solution wetting of
a negative electrode active material layer close to a current
15 collector.
[0008] Therefore, in the present specification, a negative
electrode capable of dramatically increasing electrolyte
solution wetting, a method for manufacturing the negative
electrode, a secondary battery, and a method for
20 manufacturing the secondary battery will be described.
DISCLOSURE OF THE INVENTION
TECHNICAL PROBLEM
[0009] An aspect of the present invention provides a
negative electrode capable of improving electrolyte solution
25 wetting, and a method for manufacturing the same.
4
[0010] Another aspect of the present invention provides a
secondary battery with improved electrolyte solution wetting,
and a method for manufacturing the same.
TECHNICAL SOLUTION
5 [0011] According to an embodiment of the present invention,
there is provided a negative electrode including a current
collector, and a negative electrode active material layer
having a first negative electrode active material layer
disposed on the negative electrode current collector and a
10 second negative electrode active material layer disposed on
the first negative electrode active material layer, wherein
the first negative electrode active material layer includes
ethylene carbonate.
[0012] According to another embodiment of the present
15 invention, there is provided a method for manufacturing a
negative electrode, the method including forming a first
negative electrode active material layer on a negative
electrode current collector through a first negative
electrode slurry including ethylene carbonate, and forming a
20 second negative electrode active material layer though a
second negative electrode slurry, wherein the second negative
electrode active material layer is disposed on the first
negative electrode active material layer.
[0013] According to another embodiment of the present
25 invention, there is provided a secondary battery including a
5
negative electrode, a positive electrode, a separator, and an
electrolyte solution, wherein the negative electrode includes
a negative electrode current collector, a first negative
electrode active material layer disposed on the negative
5 electrode current collector, and a second negative electrode
active material layer disposed on the first negative
electrode active material layer, wherein the first negative
electrode active material layer includes ethylene carbonate.
[0014] According to another embodiment of the present
10 invention, there is provided a method for manufacturing a
secondary battery, the method including manufacturing an
electrode assembly having the negative electrode of the above
embodiment, a positive electrode, and a separator, and
impregnating the electrode assembly in an electrolyte
15 solution.
ADVANTAGEOUS EFFECTS
[0015] A negative electrode according to the present
invention includes a first negative electrode active material
layer and a second negative electrode active material layer,
20 wherein the first negative electrode active material layer
close to a current collector includes ethylene carbonate.
Accordingly, when an electrolyte solution penetrates into the
negative electrode in a secondary battery, the ethylene
carbonate is changed into a liquid phase, and the ethylene
25 carbonate changed into a liquid phase also changes adjacent
6
ethylene carbonate around into a liquid phase. Due to the
successive changes of the ethylene carbonate, a path of
wetting which may allow the electrolyte solution to easily
penetrate into the negative electrode may be formed, so that
5 electrolyte solution wetting may be dramatically improved.
In addition, the ethylene carbonate has high ion conductivity,
so that the mobility of lithium ions in the negative
electrode may be increased, and an SEI layer may be uniformly
formed on the surface of the negative electrode.
10 BRIEF DESCRIPTION OF THE DRAWINGS
[0016] FIG. 1 is a schematic view of a negative electrode
according to an embodiment of the present invention.
MODE FOR CARRYING OUT THE INVENTION
[0017] It will be understood that words or terms used in the
15 specification and claims of the present invention shall not
be construed as being limited to having the meaning defined
in commonly used dictionaries. It will be further understood
that the words or terms should be interpreted as having
meanings that are consistent with their meanings in the
20 context of the relevant art and the technical idea of the
invention, based on the principle that an inventor may
properly define the meaning of the words or terms to best
explain the invention.
[0018] The terminology used herein is for the purpose of
25 describing particular exemplary embodiments only and is not
7
intended to be limiting of the present invention. The terms
of a singular form may include plural forms unless the
context clearly indicates otherwise.
[0019] It will be further understood that the terms
5 “include,” “comprise,” or "have" when used in this
specification, specify the presence of stated features,
numbers, steps, elements, or combinations thereof, but do not
preclude the presence or addition of one or more other
features, numbers, steps, elements, or combinations thereof.
10 [0020] In the present specification, “%” means wt% unless
otherwise noted.
[0021] In the present specification, a “specific surface
area” is measured by a BET method, and specifically, may be
calculated from the adsorption amount of nitrogen gas under a
15 liquid nitrogen temperature (77K) using Belsorp-mini II of
BEL Japan Co., Ltd.
[0022] In the present specification, an average particle
diameter (D50) may be defined as a particle diameter
corresponding to 50% of the volume accumulation in a particle
20 diameter distribution curve of a particle. The average
particle diameter (D50) may be measured by, for example, a
laser diffraction method. The laser diffraction method
generally enables measurement of a particle diameter from a
sub-micron region to several millimeters, so that results of
25 high reproducibility and high resolution may be obtained.
8
[0023] In the present specification, porosity may be
identified by the following method. A manufactured secondary
battery is decomposed, dissembled, and then ion-milling is
applied to a negative electrode to identify the cross5 sectional thickness of each of a first negative electrode
active material layer and a second negative electrode active
material layer with an SEM, and the bulk volume of each of
the first negative electrode active material layer and the
second negative electrode active material layer are derived
10 from the thickness. Thereafter, the second negative
electrode active material layer is scraped off and removed to
measure the weight of the first negative electrode active
material layer and the weight of the second negative
electrode active material layer, and then the loading amount
15 (mass/area) of each thereof are calculated. Thereafter, the
weight of each layer is divided by the negative electrode
active material density of each layer to obtain a true volume.
Thereafter, the porosity of each layer is calculated through
[(Bulk volume - true volume) / Bulk volume]×100.
20
[0024] Hereinafter, the present invention will be described
in detail.
[0025] 1. Negative electrode
25
9
[0026] A negative electrode according to an embodiment of
the present invention includes a negative electrode current
collector, and a negative electrode active material layer
having a first negative electrode active material layer
5 disposed on the negative electrode current collector and a
second negative electrode active material layer disposed on
the first negative electrode active material layer, wherein
the first negative electrode active material layer may
include ethylene carbonate.
10
[0027] The negative electrode current collector is not
particularly limited as long as it has conductivity without
causing a chemical change in the battery. For example, as
the negative electrode current collector, copper, stainless
15 steel, aluminum, nickel, titanium, fired carbon, or aluminum
or stainless steel that is surface-treated with one of carbon,
nickel, titanium, silver, and the like may be used.
Specifically, a transition metal which well adsorbs carbon
such as copper and nickel may be used as the negative
20 electrode current collector.
[0028] The negative electrode may include a negative
electrode active material layer. The negative electrode
active material layer may be disposed on one surface or on
25 both surfaces of the negative electrode current collector.
10
The loading amount of the negative electrode active material
layer may be 50 mg/25 m2 to 600 mg/25 m2, specifically 400
mg/25 cm2 to 600 mg/25 cm2. The above loading amount is
higher than the loading amount of a typical negative
5 electrode active material layer.
[0029] Referring to FIG. 1, the negative electrode active
material layer may include a first negative electrode active
material layer 210 and a second negative electrode active
10 material layer 220. The first negative electrode active
material layer 210 may be disposed on a negative electrode
current collector 100, and specifically, may be in contact
with the negative electrode current collector 100. The
second negative electrode active material layer 220 may be
15 disposed on the first negative electrode active material
layer 210, and the first negative electrode active material
layer 210 may be disposed between the second negative
electrode active material layer 220 and the negative
electrode current collector 100. Since the first negative
20 electrode active material layer 210 and the second negative
electrode active material layer 220 are formed through a
respectively prepared slurry, there may be a boundary surface
between the first negative electrode active material layer
210 and the second negative electrode active material layer
25 220.
11
[0030] Each of the first negative electrode active material
layer and the second negative electrode active material layer
may include a negative electrode active material. The
5 negative electrode active material may be a negative
electrode active material commonly used in the art, and the
type thereof is not particularly limited. The negative
electrode active material of the first negative electrode
active material layer and the negative electrode active
10 material of the second negative electrode active material
layer may be the same, or different.
[0031] The negative electrode active material may be at
least one of a carbon-based active material and a siliconbased active material. As the carbon-based active material
15 particle, one or more selected from the groups consisting of
artificial graphite, natural graphite, a graphitized carbon
fiber, and a graphitized mesocarbon microbead may be used.
Particularly, when artificial graphite is used, it is
possible to improve rate properties. As the silicon-based
20 active material, one or more selected from the group
consisting of SiOX(0≤X<2), an Si-C composite, and an Si-Y
alloy (wherein Y is an element selected from the group
consisting of an alkali metal, an alkaline earth metal, a
transition metal, a Group 13 element, a Group 14 element, a
25 rare earth element, and a combination thereof) may be used.
12
[0032] Each of the first negative electrode active material
layer and the second negative electrode active material layer
may further include a binder. The binder of the first
5 negative electrode active material layer and the binder of
the second negative electrode active material layer may be
the same, or different. The binder is to ensure the adhesion
force between the negative electrode active materials or
between the negative electrode active material and the
10 current collector. Any binder commonly used in the art may
be used, and the type thereof is not particularly limited.
[0033] The binder may be, for example, polyvinylidene
fluoride, a polyvinylidene fluoride-hexafluoropropylene
copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile,
15 starch, hydroxypropyl cellulose, regenerated cellulose,
polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene,
polypropylene, an ethylene-propylene-diene polymer(EPDM), a
sulfonated-EPDM, carboxymethyl cellulose (CMC), styrenebutadiene rubber (SBR), fluorine rubber, or various
20 copolymers thereof, and the like, and any one thereof or a
mixture of two or more thereof may be used.
[0034] Each of the first negative electrode active material
layer and the second negative electrode active material layer
25 may further include a conductive material. The conductive
13
material may be a conductive material commonly used in the
art, and the type thereof is not particularly limited. The
conductive material of the first negative electrode active
material layer and the conductive material of the second
5 negative electrode active material layer may be the same, or
different.
[0035] The conductive material is not particularly limited
as long as it has conductivity without causing a chemical
change in the battery. For example, graphite such as natural
10 graphite or artificial graphite; carbon black such as
acetylene black, Ketjen black, channel black, furnace black,
lamp black, and thermal black; conductive fiber such as
carbon fiber and metal fiber; a conductive tube such as a
carbon nanotube; fluorocarbon powder ; metal powder such as
15 aluminum powder, and nickel powder; a conductive whisker such
as a zinc oxide and potassium titanate; a conductive metal
oxide such as a titanium oxide; a conductive material such as
a polyphenylene derivative, and the like may be used.
20 [0036] The loading amount of the first negative electrode
active material layer may be 50 mg/25 cm2 to 400 mg/25 cm2,
specifically 100 mg/25 cm2 to 300 mg/25 cm2, more
specifically 150 mg/25 cm2 to 250 mg/25 cm2. The above
loading amount is similar to the loading amount of a typical
25 negative electrode active material, and when the second
14
negative electrode active material layer is added, a negative
electrode active material layer with a higher loading amount
than the typical negative electrode active material layer is
formed. In the present invention, since the first negative
5 electrode active material layer includes ethylene carbonate,
the electrolyte solution wetting degradation problem is
solved, so that the loading amount of the entire negative
electrode active material may be high.
10 [0037] The first negative electrode active material layer
may include ethylene carbonate. The ethylene carbonate is in
a solid phase at room temperature, so that it is advantageous
to include the same in the first negative electrode active
material layer . In addition, the ethylene carbonate in a
15 solid phase is changed into a liquid phase when the negative
electrode is impregnated in the electrolyte solution. The
liquid-phase ethylene carbonate serves as a path of wetting
of the electrolyte solution, and forms pores in the first
negative electrode active material layer, thereby
20 dramatically improving the electrolyte solution wetting of
the negative electrode. In addition, the ethylene carbonate
has high ion conductivity, so that the mobility of lithium
ions in the negative electrode may be increased, and an SEI
layer may be uniformly formed on the surface of the negative
25 electrode. This leads to an improvement in the lifespan and
15
stability of a secondary battery.
[0038] The ethylene carbonate may be included in the first
negative electrode active material layer in an amount of 0.5
wt% to 15 wt%, specifically 2 wt% to 10 wt%, more
5 specifically 3 wt% to 6 wt%. When the above range is
satisfied, the effect of improving electrolyte solution
wetting may be maximized.
[0039] The second negative electrode active material layer
10 may not include ethylene carbonate. In that case, the ratio
of the negative electrode active material in the second
negative electrode active material layer may be increased,
and the thickness of the second negative electrode active
material layer may be reduced, so that energy density may be
15 improved.
[0040] 2. Method for manufacturing negative electrode
[0041] A method for manufacturing a negative electrode
20 according to another embodiment of the present invention
includes forming a first negative electrode active material
layer on a negative electrode current collector through a
first negative electrode slurry including ethylene carbonate,
and forming a second negative electrode active material layer
25 though a second negative electrode slurry, wherein the second
16
negative electrode active material layer may be disposed on
the first negative electrode active material layer. A
negative electrode manufactured accordingly may be the same
as the negative electrode of the above-described negative
5 electrode. The ethylene carbonate, the negative electrode
current collector, the first negative electrode active
material layer, and the second negative electrode active
material layer are the same as the ethylene carbonate, the
negative electrode current collector, the first negative
10 electrode active material layer, and the second negative
electrode active material layer described in the embodiment
described above with reference to a negative electrode, and
thus, descriptions thereof will be omitted.
15 [0042] Each of the first negative electrode slurry and the
second negative electrode slurry may include a negative
electrode active material and a solvent. In addition, each
of the first negative electrode slurry and the second
negative electrode slurry may further include a binder and a
20 conductive material. The negative electrode active material,
the binder, and the conductive material are the same as the
negative electrode active material, the binder, and the
conductive material described in the above-described
embodiment, and thus, descriptions thereof will be omitted.
25 [0043] The solvent may be, for example, water ; an amide-
17
based polar organic solvent such as dimethylformamide (DMF),
diethylformamide, dimethylacetamide (DMAc), and Nmethylpyrrolidone (NMP); an alcohol such as methanol, ethanol,
1-propanol, 2-propanol (isopropyl alcohol), 1-butanol (n5 butanol), 2-methyl-1-propanol (isobutanol), 2-butanol (secbutanol), 1-methyl-2-propanol (tert-butanol), pentanol,
hexanol, heptanol, and octanol; a glycol such as ethylene
glycol, diethylene glycol, triethylene glycol, propylene
glycol, 1,3-propanediol, 1,3-butanediol, 1,5-pentanediol, and
10 hexylene glycol; a polyhydric alcohol such as glycerin,
trimethylol propane, pentaerythritol, and sorbitol; a glycol
ether such as ethylene glycol monomethyl ether, diethylene
glycol monomethyl ether, triethylene glycol monomethyl ether,
tetraethylene glycol monomethyl ether, ethylene glycol
15 monoethyl ether, diethylene glycol monoethyl ether,
triethylene glycol monoethyl ether, tetraethylene glycol
monoethyl ether, ethylene glycol monobutyl ether, diethylene
glycol monobutyl ether, triethylene glycol monobutyl ether,
and tetraethylene glycol monobutyl ether; a ketone such
20 acetone, methyl ethyl ketone, methyl propyl ketone, and
cyclopentanone; and an ester such as ethyl acetate, γ-butyl
lactone, and ε-propiolactone . Any one thereof and a mixture
of two or more thereof may be used.
25 [0044] The first negative electrode slurry may include
18
ethylene carbonate. The first negative electrode slurry may
be formed by mixing and stirring a negative electrode active
material and ethylene carbonate in a solvent. In some cases,
a binder and/or a conductive material may be additionally
5 mixed and stirred in addition to the negative electrode
active material and the ethylene carbonate. Meanwhile, the
second negative electrode slurry may not include ethylene
carbonate. Specifically, the second negative electrode
slurry may be formed by mixing and stirring the negative
10 electrode active material in a solvent. In some cases, a
binder and/or a conductive material may be additionally mixed
and stirred in addition to the negative electrode active
material.
15 [0045] When preparing the first negative electrode slurry,
ethylene carbonate is included, and the ethylene carbonate
may be in a solid phase. Since ethylene carbonate is
included in a solid phase, not in a liquid phase, in the
first negative electrode slurry, a process may be simplified.
20 Specifically, when the ethylene carbonate is in a liquid
phase, it is difficult to weigh the ethylene carbonate and to
prepare a slurry. Therefore, it is preferable to use
ethylene carbonate present in a solid phase when preparing
the slurry.
25 [0046] The ethylene carbonate may be included in a solid of
19
the first negative electrode slurry in an amount of 0.5 wt%
to 15 wt%, specifically 2 wt% to 10 wt%, more specifically 3
wt% to 6 wt%. When the above range is satisfied, the effect
of improving electrolyte solution wetting may be maximized.
5
[0047] The first negative electrode active material layer
and the second negative electrode active material layer may
be manufactured by the following method, but are not limited
thereto.
10 [0048] As a first method, the first negative electrode
slurry may be applied on the negative electrode current
collector and dried to form the first negative electrode
active material layer, and then the second negative electrode
slurry may be applied on the first negative electrode active
15 material layer and dried to form the second negative
electrode active material layer. A roll-pressing process may
be performed immediately after the first negative electrode
slurry is dried and immediately after the second negative
electrode slurry is dried, or may be performed only after the
20 second negative electrode slurry is dried.
[0049] As a second method, the first negative electrode
slurry and the second negative electrode slurry may be
sequentially applied on the negative electrode current
collector, dried, and then roll-pressed to form the first
25 negative electrode active material layer and the second
20
negative electrode active material layer.
[0050] 3. Secondary battery
5 [0051] A secondary battery according to another embodiment
of the present invention includes a negative electrode and an
electrolyte solution, wherein the negative electrode may
include a negative electrode current collector, a first
negative electrode active material layer disposed on the
10 negative electrode current collector, and a second negative
electrode active material layer disposed on the first
negative electrode active material layer, wherein the first
negative electrode active material layer may include ethylene
carbonate.

CLAIMS
1. A negative electrode comprising:
a negative electrode current collector; and
5 a negative electrode active material layer including a
first negative electrode active material layer disposed on
the negative electrode current collector and a second
negative electrode active material layer disposed on the
first negative electrode active material layer,
10 wherein the first negative electrode active material
layer includes ethylene carbonate.
2. The negative electrode of claim 1, wherein the ethylene
carbonate is included in the first negative electrode active
15 material layer in an amount of 0.5 wt% to 15 wt%.
3. The negative electrode of claim 1, wherein the ethylene
carbonate is included in the first negative electrode active
material layer in an amount of 3 wt% to 6 wt%.
20
4. The negative electrode of claim 1, wherein the loading
amount of the first negative electrode active material layer
is 50 mg/25 m2 to 400 mg/25m2.
25 5. The negative electrode of claim 1, wherein the loading
35
amount of the negative electrode active material layer is 50
mg/25 m2 to 600 mg/25 m2.
6. A method for manufacturing a negative electrode, the
5 method comprising:
forming a first negative electrode active material
layer on a negative electrode current collector through a
first negative electrode slurry including ethylene carbonate;
and
10 forming a second negative electrode active material
layer though a second negative electrode slurry,
wherein the second negative electrode active material
layer is disposed on the first negative electrode active
material layer.
15
7. The method of claim 6, wherein the ethylene carbonate
is included in a solid of the first negative electrode slurry
in an amount of 0.5 wt% to 15 wt%.
20 8. The method of claim 6, wherein the ethylene carbonate
is in a solid phase.
9. A secondary battery comprising:
a negative electrode; a positive electrode; a separator;
25 and an electrolyte solution,
36
wherein the negative electrode includes:
a negative electrode current collector;
a first negative electrode active material layer
disposed on the negative electrode current collector; and
5 a second negative electrode active material layer
disposed on the first negative electrode active material
layer,
wherein the first negative electrode active material
layer includes ethylene carbonate.
10
10. The secondary battery of claim 9, wherein the first
negative electrode active material layer includes pores, and
the porosity of the first negative electrode active material
layer is greater than the porosity of the second negative
15 electrode active material layer by 1% to 5%.
11. The secondary battery of claim 9, wherein the ethylene
carbonate is in a liquid phase.
20 12. The secondary battery of claim 9, wherein the
electrolyte solution includes an organic solvent, and the
organic solvent includes ethylene carbonate.
13. A method for manufacturing a secondary battery, the
25 method comprising:
37
manufacturing an electrode assembly including the
negative electrode of claim 1, a positive electrode, and a
separator; and
impregnating the electrode assembly in an electrolyte
5 solution.
14. The method of claim 13, wherein the electrolyte
solution includes an organic solvent, and the organic solvent
includes ethylene carbonate.