U.S. patent application number 16/323696 was filed with the patent office on 2019-06-06 for electrode drying method.
This patent application is currently assigned to LG Chem, Ltd.. The applicant listed for this patent is LG Chem, Ltd.. Invention is credited to Ji-Hee Ahn, Hee-Seok Jeong, Myung-Ki Lee, Joo-Yong Song.
Application Number | 20190173075 16/323696 |
Document ID | / |
Family ID | 62626748 |
Filed Date | 2019-06-06 |
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United States Patent
Application |
20190173075 |
Kind Code |
A1 |
Jeong; Hee-Seok ; et
al. |
June 6, 2019 |
Electrode Drying Method
Abstract
Disclosed herein is an electrode drying method for drying a
plurality of electrodes in the state in which the electrodes are
stacked, the electrode drying method including interposing a
hygroscopic film between adjacent ones of the electrodes and drying
the electrodes in the state in which the hygroscopic film is
interposed between the electrodes, wherein at least one of the
surfaces of the hygroscopic film that faces the electrodes has an
uneven structure, or an electrode drying method for drying an
electrode sheet in the state in which the electrode sheet is wound,
the electrode drying method including winding the electrode sheet
with a hygroscopic film and drying the electrode sheet in the state
in which the hygroscopic film is interposed between overlapping
portions of the electrode sheet, wherein at least one of the
surfaces of the hygroscopic film that is disposed opposite the
electrode sheet has an uneven structure.
Inventors: |
Jeong; Hee-Seok; (Daejeon,
KR) ; Lee; Myung-Ki; (Daejeon, KR) ; Song;
Joo-Yong; (Daejeon, KR) ; Ahn; Ji-Hee;
(Daejeon, KR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
LG Chem, Ltd. |
Seoul |
|
KR |
|
|
Assignee: |
LG Chem, Ltd.
Seoul
KR
|
Family ID: |
62626748 |
Appl. No.: |
16/323696 |
Filed: |
November 6, 2017 |
PCT Filed: |
November 6, 2017 |
PCT NO: |
PCT/KR2017/012492 |
371 Date: |
February 6, 2019 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01M 4/621 20130101;
H01M 4/1391 20130101; H01M 4/0404 20130101; H01M 4/139 20130101;
H01M 4/04 20130101 |
International
Class: |
H01M 4/04 20060101
H01M004/04; H01M 4/1391 20060101 H01M004/1391; H01M 4/62 20060101
H01M004/62 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 21, 2016 |
KR |
10-2016-0175265 |
Claims
1. An electrode drying method for drying a plurality of electrodes
in a state in which the plurality of electrodes is stacked, the
electrode drying method comprising: interposing a hygroscopic film
between adjacent ones of the plurality of electrodes; and drying
the plurality of electrodes in a state in which the hygroscopic
film is interposed between the adjacent ones of the plurality of
electrodes, wherein at least one surface of the hygroscopic film
that faces one of the adjacent ones of the plurality of electrodes
has an uneven structure.
2. An electrode drying method for drying an electrode sheet in a
state in which the electrode sheet is wound, the electrode drying
method comprising: winding the electrode sheet with a hygroscopic
film; and drying the electrode sheet in a state in which the
hygroscopic film is interposed between overlapping portions of the
electrode sheet, wherein at least one of surfaces of the
hygroscopic film that is disposed opposite the electrode sheet has
an uneven structure.
3. The electrode drying method according to claim 1, wherein the
uneven structure is a convex structure or a concave and convex
combination structure.
4. The electrode drying method according to claim 3, wherein the
uneven structure is any one selected from a group consisting of: a
structure having embossed curved domes, a structure having embossed
polygonal domes, a round tile structure having curved valleys and
curved ridges, and a polygonal tile structure having polygonal
valleys and polygonal ridges.
5. (canceled)
6. (canceled)
7. The electrode drying method according to claim 1, wherein the
uneven structures formed on the opposite surfaces of the
hygroscopic film are complementary concave and convex combination
structures or corresponding convex structures.
8. The electrode drying method according to claim 1, wherein the
hygroscopic film is a film made of ester fiber, cellulose fiber, or
alcohol fiber.
9. The electrode drying method according to claim 8, wherein the
alcohol fiber is made of a polyvinyl alcohol (PVA) resin.
10. The electrode drying method according to claim 1, wherein a
thickness of the hygroscopic film is equal to or smaller than a
thickness of each of the plurality of electrodes.
11. (canceled)
12. The electrode drying method according to claim 1, wherein an
adsorptive material that is capable of adsorbing moisture (H2O) is
coated on at least one surface of the hygroscopic film.
13-16. (canceled)
17. An electrode manufactured through an electrode drying method
according to claim 1.
18. The electrode drying method according to claim 2, wherein the
uneven structure is a convex structure or a concave and convex
combination structure.
19. The electrode drying method according to claim 18, wherein the
uneven structure is any one selected from a group consisting of: a
structure having embossed curved domes, a structure having embossed
polygonal domes, a round tile structure having curved valleys and
curved ridges, and a polygonal tile structure having polygonal
valleys and polygonal ridges.
20. The electrode drying method according to claim 2, wherein the
uneven structures formed on the opposite surfaces of the
hygroscopic film are complementary concave and convex combination
structures or corresponding convex structures.
21. The electrode drying method according to claim 2, wherein the
hygroscopic film is a film made of ester fiber, cellulose fiber, or
alcohol fiber.
22. The electrode drying method according to claim 21, wherein the
alcohol fiber is made of a polyvinyl alcohol (PVA) resin.
23. The electrode drying method according to claim 2, wherein a
thickness of the hygroscopic film is equal to or smaller than a
thickness of each of the plurality of electrodes.
24. The electrode drying method according to claim 2, wherein an
adsorptive material that is capable of adsorbing moisture (H2O) is
coated on at least one surface of the hygroscopic film.
25. An electrode manufactured through an electrode drying method
according to claim 2.
Description
TECHNICAL FIELD
[0001] The present invention relates to an electrode drying method,
and more particularly to an electrode drying method for drying a
plurality of electrodes in the state in which a hygroscopic film is
interposed between the electrodes.
BACKGROUND ART
[0002] As mobile devices have been increasingly developed and the
demand for such mobile devices has increased, the demand for
secondary batteries as energy sources for such mobile devices has
also sharply increased. Among such secondary batteries is a lithium
secondary battery having a high energy density, a high voltage, a
long cycle lifespan, and a low self discharge rate, which is now
commercialized and widely used.
[0003] In general, a secondary battery is manufactured by placing
an electrode assembly, configured to have a structure in which a
positive electrode and a negative electrode are stacked in the
state in which a separator is interposed between the positive
electrode and the negative electrode, in a battery case and
injecting an electrolytic solution into the battery case such that
the electrode assembly is impregnated with the electrolytic
solution.
[0004] Each of the positive electrode and the negative electrode,
i.e. each electrode, is manufactured by applying a mixture of an
electrode active material, a conductive agent, and a binder to an
electrode current collector and drying the mixture. As needed, a
filler may be added to the mixture.
[0005] When the electrode is manufactured, as described above, a
plurality of unit electrodes is dried at the same time in the state
in which the unit electrodes are stacked, rather than drying the
unit electrodes individually. Alternatively, an electrode sheet is
dried in the state in which the electrode sheet is wound in the
form of a roll.
[0006] In this case, however, each of the electrodes that are
located in the middle of the electrode stack or the portion of the
electrode sheet that is located at the core side of the electrode
sheet wound in the form of a roll may not be sufficiently dried. As
a result, the moisture content of the electrodes that are located
in the middle of the electrode stack is different from the moisture
content of the electrodes that are located at the outer side of the
electrode stack, or the moisture content of the portion of the
electrode sheet that is located at the core side of the wound
electrode sheet is different from the moisture content of the
portion of the electrode sheet that is located at the outer side of
the wound electrode sheet. If a difference in the moisture content
of the electrodes or different portions of the electrode sheet
occurs when each of the electrodes or the electrode sheet is dried,
secondary batteries manufactured using the electrodes or the
electrode sheet dried as described above may perform differently.
Particularly, in the case in which each of the electrodes that are
located in the middle of the electrode stack, which may not be
completely dried, or the portion of the electrode sheet that is
located at the core side of the wound electrode sheet, which may
not be completely dried, is used, the performance of a battery cell
manufactured using the same may be greatly affected.
[0007] Furthermore, in order to completely dry each of the
electrodes that are located in the middle of the electrode stack or
the portion of the electrode sheet that is located at the core side
of the wound electrode sheet, it is necessary to dry the electrodes
or the electrode sheet in a vacuum drying furnace under a
decompression condition for 10 hours or more. As a result, the
drying time is lengthened. Consequently, the total electrode
manufacturing time is increased, whereby manufacturing efficiency
is lowered.
[0008] Alternatively, the drying temperature may be increased in
order to dry the electrodes or the electrode sheet. If the drying
temperature is too high, however, the electrodes or the electrode
sheet may crack. In addition, the active material may be
affected.
[0009] Therefore, there is an urgent necessity for technology that
is capable of easily drying the electrodes that are located in the
middle of the electrode stack or the portion of the electrode sheet
that is located at the core side of the wound electrode sheet
within a short time in order to reduce a difference in the moisture
content of the electrodes or different portions of the electrode
sheet.
DISCLOSURE
Technical Problem
[0010] The present invention has been made to solve the above
problems and other technical problems that have yet to be
resolved.
[0011] As a result of a variety of extensive and intensive studies
and experiments to solve the problems as described above, the
inventors of the present application have found that in the case in
which a plurality of stacked electrodes is dried in the state in
which a hygroscopic film having an uneven structure is interposed
between the electrodes or in the case in which an electrode sheet
is dried in the state in which the electrode sheet is wound with a
hygroscopic film having an uneven structure, it is possible to
reduce the drying time and to sufficiently dry the electrodes
located in the middle of the stacked electrodes or the portion of
the electrode sheet located at the core of the wound electrode
sheet, whereby it is possible to achieve a desired effect. The
present invention has been completed based on these findings.
Technical Solution
[0012] In accordance with one aspect of the present invention, the
above and other objects can be accomplished by the provision of an
electrode drying method for drying a plurality of electrodes in the
state in which the electrodes are stacked, the electrode drying
method including interposing a hygroscopic film between the
electrodes and drying the electrodes in the state in which the
hygroscopic film is interposed between the electrodes, wherein at
least one of the surfaces of the hygroscopic film that face the
electrodes has an uneven structure.
[0013] Alternatively, there is provided an electrode drying method
for drying an electrode sheet in the state in which the electrode
sheet is wound, the electrode drying method including winding the
electrode sheet with a hygroscopic film and drying the electrode
sheet in the state in which the hygroscopic film is interposed
between overlapping portions of the electrode sheet, wherein at
least one of the surfaces of the hygroscopic film that are opposite
the electrode sheet has an uneven structure.
[0014] In general, an electrode manufacturing process includes an
active material application process, a press process, an inspection
process, and a drying process. Specifically, at the active material
application process, electrode slurry is applied to at least one
surface of metal foil (as an electrode current collector), and then
the electrode slurry is dried in order to remove a solvent from the
electrode slurry, whereby an active material layer is formed. In
the press process, the active material layer is pressed in order to
improve the density of the active material layer. Subsequently, the
inspection process is performed. In the inspection process, the
surface of an electrode, particularly the active material layer, is
inspected. Subsequently, the drying process is performed. In the
drying process, the electrode is placed in a vacuum drying furnace
and is then dried under a decompression condition. In the active
material application process, drying is performed merely to remove
the solvent from the active material layer to the extent that the
subsequent process, i.e. the press process, can be performed and to
the extent that active material particles are settled on the
surface of the electrode current collector by a binder. In the
drying process, however, the solvent is completely removed from the
active material layer.
[0015] Meanwhile, in the drying process, a plurality of electrodes
is not individually dried, but a plurality of stacked electrodes is
dried in a vacuum drying furnace under a decompression condition,
or an electrode sheet wound in the form of a roll is dried in a
vacuum drying furnace under a decompression condition. At this
time, it is difficult to evaporate moisture from the electrodes
that are located in the middle of the stacked electrodes or from
the portion of the electrode sheet that is located at the core side
of the wound electrode sheet, since the electrodes are stacked or
the wound electrode sheet has overlapping portions. In order to
completely evaporate the moisture from the electrodes that are
located in the middle of the stacked electrodes or from the portion
of the electrode sheet that is located at the core side of the
wound electrode sheet, therefore, a long drying time is required.
If the drying time is short, a difference between the moisture
content of the electrodes that are located in the middle of the
electrode stack and the moisture content of the electrodes that are
located at the outer side of the electrode stack, or a difference
between the moisture content of the portion of the electrode sheet
that is located at the core side of the wound electrode sheet and
the moisture content of the portion of the electrode sheet that is
located at the outer side of the wound electrode sheet, occurs,
whereby the performance of cells may be reduced. In the present
invention, therefore, the electrodes are dried in the state in
which a hygroscopic film is interposed between the electrodes, or
the electrode sheet is dried in the state in which a hygroscopic
film is interposed between overlapping portions of the electrode
sheet. In addition, the hygroscopic film is configured such that
the surface of the hygroscopic film has an uneven structure,
whereby air flow paths are entirely formed over the electrodes or
the electrode sheet in order to solve the above problems.
[0016] Here, the uneven structure is not particularly restricted,
as long as the uneven structure defines air flow paths, through
which air can smoothly flow, between the electrodes or between the
overlapping portions of the electrode sheet. Specifically, the
uneven structure may be a convex structure or a concave and convex
combination structure. For example, the uneven structure may be any
one selected from the group consisting of a structure having
embossed curved domes, a structure having embossed polygonal domes,
a round tile structure having curved valleys and curved ridges, and
a polygonal tile structure having polygonal valleys and polygonal
ridges. In this case, the uneven structure may be configured such
that unit structures constituting the uneven structure, such as
curved domes, polygonal domes, round tiles, or polygonal tiles, are
regularly repeatedly arranged or randomly arranged. Specifically,
the unit structures constituting the uneven structure may be
regularly arranged in order to completely uniformly dry the
electrodes or the electrode sheet.
[0017] In addition, in the case in which an active material is
applied to opposite surfaces of each of the electrodes or to
opposite surfaces of the electrode sheet, each of the opposite
surfaces of the hygroscopic film that face the electrodes or that
are opposite the electrode sheet may have an uneven structure such
that the opposite surfaces of each of the electrodes or the
opposite surfaces of the electrode sheet are uniformly dried at
similar drying speeds, for a reason similar to the above
reason.
[0018] The uneven structures formed on the opposite surfaces of the
hygroscopic film may be the same as each other, or may be different
from each other. In consideration of convenience in manufacture,
the uneven structures formed on the opposite surfaces of the
hygroscopic film may be the same as each other. Specifically, the
uneven structures formed on the opposite surfaces of the
hygroscopic film may be complementary concave and convex
combination structures or corresponding convex structures.
[0019] Here, the complementary concave and convex combination
structures are configured such that when concave and convex
combination structures are formed on one surface and the other
surface of the hygroscopic film, a convex structure on one surface
of the hygroscopic film and a concave structure on the other
surface of the hygroscopic film are located so as to correspond to
each other, whereby the hygroscopic film is generally formed in the
shape of waves. The corresponding convex structures are configured
such that when convex structures are formed on one surface and the
other surface of the hygroscopic film, a convex structure on one
surface of the hygroscopic film and a convex structure on the other
surface of the hygroscopic film are located so as to correspond to
each other, whereby the hygroscopic film is formed in an embossed
shape.
[0020] In the case in which the hygroscopic film has an uneven
structure, as described above, air flows to the electrodes that are
located in the middle of the electrode stack or to the portion of
the electrode sheet that is located at the core side of the wound
electrode sheet through air flow paths defined by the uneven
structure of the hygroscopic film more smoothly than in the case in
which the hygroscopic film has an even structure. As a result, a
difference between the air contact area of the electrodes located
in the middle of the electrode stack or the portion of the
electrode sheet located at the core side of the wound electrode
sheet and the air contact area of the electrodes located at the
outer side of the electrode stack or the portion of the electrode
sheet located at the outer side of the wound electrode sheet is
small, whereby it is possible to more easily dry the electrodes or
the electrode sheet. Consequently, it is possible to further reduce
a difference between the moisture content of the electrodes that
are located in the middle of the electrode stack and the moisture
content of the electrodes that are located at the outer side of the
electrode stack or a difference between the moisture content of the
portion of the electrode sheet that is located at the core side of
the wound electrode sheet and the moisture content of the portion
of the electrode sheet that is located at the outer side of the
wound electrode sheet, whereby it is possible to remarkably shorten
the drying time.
[0021] Meanwhile, the hygroscopic film is not particularly
restricted, as long as the hygroscopic film is made of a film type
material that exhibits high hygroscopicity and high resistance to
winding tension. Specifically, the hygroscopic film may be a fiber
film. More specifically, the hygroscopic film may be a film made of
ester fiber, cellulose fiber, or alcohol fiber. Here, the alcohol
fiber may be made of a polyvinyl alcohol (PVA) resin.
[0022] The polyvinyl alcohol resin exhibits high hygroscopicity. In
addition, in the case in which the polyvinyl alcohol resin is wound
in the form of a roll in order to dry an electrode sheet, the
polyvinyl alcohol resin exhibits sufficient stretchability to
withstand the tension that occurs when the polyvinyl alcohol resin
is wound with the electrode sheet. Consequently, the polyvinyl
alcohol resin is more preferably used.
[0023] The thickness of the hygroscopic film may be set in
consideration of the hygroscopicity of the hygroscopic film or the
size of the electrode stack or the roll type electrode sheet.
Specifically, the thickness of the hygroscopic film may be equal to
or smaller than the thickness of each of the electrodes or the
electrode sheet.
[0024] If the thickness of the hygroscopic film is larger than the
thickness of each of the electrodes or the electrode sheet,
although it is advantageous with respect to drying of the
electrodes or the electrode sheet, the volume of the hygroscopic
film increases. As a result, the amount of hygroscopic film that is
placed in a drying furnace having the same volume is reduced,
whereby the total drying time is increased, which is undesirable.
Specifically, the thickness of the hygroscopic film may be 30 to
80% of the thickness of each of the electrodes or the electrode
sheet.
[0025] If the thickness of the hygroscopic film is less than 30% of
the thickness of each of the electrodes or the electrode sheet, the
hygroscopic film may not sufficiently absorb the moisture contained
in the active material layer, which is undesirable.
[0026] Meanwhile, in order to enable the hygroscopic film to more
easily absorb moisture such that the electrodes or the electrode
sheet can be dried more rapidly, an adsorptive material that is
capable of adsorbing moisture (H.sub.2O) may be coated on at least
one surface of the hygroscopic film.
[0027] The adsorptive material may be a hygroscopic material having
a porous structure that is capable of adsorbing moisture. Any
material that is capable of adsorbing an organic solvent as well as
moisture may be more preferably used. For example, the adsorptive
material may be at least one selected from the group consisting of
silica gel, alumina, and zeolite.
[0028] The adsorptive material may be coated on the hygroscopic
film by dipping the film in slurry obtained by mixing ultrafine
particles, such as silica gel, with a binder in an organic solvent
(dip-coating) and drying the film.
[0029] In the case in which the adsorptive material is coated on
the hygroscopic film, the hygroscopic film may have the
above-defined thickness including the thickness of the adsorptive
material coated on the hygroscopic film.
[0030] The adsorptive material may be coated on opposite surfaces
of the hygroscopic film such that the hygroscopic film exhibits
higher hygroscopicity and such that each of the electrodes or the
electrode sheet is dried uniformly. For example, the thickness of
the adsorptive material may be 10 to 50% of the thickness of the
hygroscopic film.
[0031] If the thickness of the adsorptive material is less than 10%
of the thickness of the hygroscopic film, the improvement of
hygroscopicity based on coating of the adsorptive material is
insignificant, which is undesirable. If the thickness of the
adsorptive material is greater than 50% of the thickness of the
hygroscopic film, the coating layer of the adsorptive material
rather reduces the hygroscopicity of the hygroscopic film.
Furthermore, the hygroscopic film is thickened, whereby the total
volume of the hygroscopic film is increased, which is also
undesirable.
[0032] In the case in which each of the electrodes or the electrode
sheet is dried in accordance with the present invention, it is
possible to remarkably reduce the time necessary to completely dry
the electrodes that are located in the middle of the electrode
stack or the portion of the electrode sheet that is located at the
core side of the wound electrode sheet. In the electrode drying
method according to the present invention, the drying step may be
performed at a temperature of 100 to 130.degree. C. for 60 to 300
minutes.
[0033] In the present invention, it is possible to almost uniformly
dry the electrodes that are located in the middle of the electrode
stack and the electrodes that are located at the outer side of the
electrode stack or to almost uniformly dry the portion of the
electrode sheet that is located at the core side of the wound
electrode sheet and the portion of the electrode sheet that is
located at the outer side of the wound electrode sheet. Even when
each of the electrodes or the electrode sheet is dried as described
above, the difference in moisture content is insignificant.
[0034] In accordance with another aspect of the present invention,
there is provided an electrode manufactured through the electrode
drying method described above.
[0035] The electrode undergoes an active material application
process before a drying process, as described above.
[0036] In the case in which the electrode is a positive electrode,
the positive electrode may be manufactured, for example, by
applying a mixture of a positive electrode active material, a
conductive agent, and a binder to a positive electrode current
collector and drying the mixture. A filler may be further added to
the mixture as needed.
[0037] In general, the positive electrode current collector is
manufactured so as to have a thickness of 3 to 500 .mu.m. The
positive electrode current collector is not particularly
restricted, as long as the positive electrode current collector
exhibits high conductivity while the positive electrode current
collector does not induce any chemical change in a battery to which
the positive electrode current collector is applied. For example,
the positive electrode current collector may be made of stainless
steel, aluminum, nickel, titanium, or plastic carbon.
Alternatively, the positive electrode current collector may be made
of aluminum or stainless steel, the surface of which is treated
with carbon, nickel, titanium, or silver. In addition, the positive
electrode current collector may have a micro-scale uneven pattern
formed on the surface thereof so as to increase the force of
adhesion of the positive electrode active material. The positive
electrode current collector may be configured in various forms,
such as a film, a sheet, a foil, a net, a porous body, a foam body,
and a non-woven fabric body.
[0038] The positive electrode active material may be, but is not
limited to, a layered compound, such as a lithium cobalt oxide
(LiCoO.sub.2) or a lithium nickel oxide (LiNiO.sub.2), or a
compound substituted with one or more transition metals; a lithium
manganese oxide represented by the chemical formula
Li.sub.1+xMn.sub.2-xO.sub.4 (where x=0 to 0.33) or a lithium
manganese oxide, such as LiMnO.sub.3, LiMn.sub.2O.sub.3, or
LiMnO.sub.2; a lithium copper oxide (Li.sub.2CuO.sub.2); a vanadium
oxide, such as LiV.sub.3O.sub.8, LiFe.sub.3O.sub.4, V.sub.2O.sub.5,
or Cu.sub.2V.sub.2O.sub.7; an Ni-sited lithium nickel oxide
represented by the chemical formula LiNi.sub.1-xM.sub.xO.sub.2
(where M=Co, Mn, Al, Cu, Fe, Mg, B, or Ga, and x=0.01 to 0.3); a
lithium manganese composite oxide represented by the chemical
formula LiMn.sub.2-xM.sub.xO.sub.2 (where M=Co, Ni, Fe, Cr, Zn, or
Ta, and x=0.01 to 0.1) or the chemical formula
Li.sub.2Mn.sub.3MO.sub.8 (where M=Fe, Co, Ni, Cu, or Zn);
LiMn.sub.2O.sub.4 having Li of a chemical formula partially
replaced by alkaline earth metal ions; a disulfide compound; or
Fe.sub.2(MoO.sub.4).sub.3.
[0039] The conductive agent is generally added so that the
conductive agent has 1 to 30 weight % based on the total weight of
the compound including the positive electrode active material. The
conductive agent is not particularly restricted as long as the
conductive agent exhibits high conductivity without inducing any
chemical change in a battery to which the conductive agent is
applied. For example, graphite, such as natural graphite or
artificial graphite; carbon black, such as carbon black, acetylene
black, Ketjen black, channel black, furnace black, lamp black, or
summer black; conductive fiber, such as carbon fiber or metallic
fiber; metallic powder, such as carbon fluoride powder, aluminum
powder, or nickel powder; conductive whisker, such as zinc oxide or
potassium titanate; a conductive metal oxide, such as titanium
oxide; or conductive materials, such as polyphenylene derivatives,
may be used as the conductive agent.
[0040] The binder is a component assisting in binding between the
active material and the conductive agent and in binding with the
current collector. The binder is generally added in an amount of 1
to 30 weight % based on the total weight of the compound including
the positive electrode active material. As examples of the binder,
there may be used polyvinylidene fluoride, polyvinyl alcohol,
carboxymethylcellulose (CMC), starch, hydroxypropylcellulose,
regenerated cellulose, polyvinyl pyrrolidone, tetrafluoroethylene,
polyethylene, polypropylene, ethylene-propylene-diene terpolymer
(EPDM), sulfonated EPDM, styrene butadiene rubber, fluoro rubber,
and various copolymers.
[0041] The filler is an optional component used to inhibit
expansion of the positive electrode. There is no particular limit
to the filler as long as it does not cause chemical changes in a
battery to which the filler is applied and is made of a fibrous
material. As examples of the filler, there may be used olefin
polymers, such as polyethylene and polypropylene; and fibrous
materials, such as glass fiber and carbon fiber.
[0042] In the case in which the electrode is a negative electrode,
the negative electrode may be manufactured by applying a negative
electrode material to a negative electrode current collector and
drying the same. The above-described components may be selectively
added to the negative electrode active material as needed.
[0043] In general, the negative electrode current collector is
manufactured so as to have a thickness of 3 to 500 .mu.m. The
negative electrode current collector is not particularly
restricted, so long as the negative electrode current collector
exhibits high conductivity and the negative electrode current
collector does not induce any chemical change in a battery to which
the negative electrode current collector is applied. For example,
the negative electrode current collector may be made of copper,
stainless steel, aluminum, nickel, titanium, or plastic carbon.
Alternatively, the negative electrode current collector may be made
of copper or stainless steel, the surface of which is treated with
carbon, nickel, titanium, or silver, or an aluminum-cadmium alloy.
In addition, the negative electrode current collector may have a
micro-scale uneven pattern formed on the surface thereof so as to
increase the force of adhesion of the negative electrode active
material, in the same manner as the positive electrode current
collector. The negative electrode current collector may be
configured in various forms, such as a film, a sheet, a foil, a
net, a porous body, a foam body, and a non-woven fabric body.
[0044] As the negative electrode active material, for example,
there may be used carbon, such as a non-graphitizing carbon or a
graphite-based carbon; a metal composite oxide, such as
Li.sub.xFe.sub.2O.sub.3 (0.ltoreq.x.ltoreq.1), Li.sub.xWO.sub.2
(0.ltoreq.x.ltoreq.1), Sn.sub.xMe.sub.1-xMe'.sub.yO.sub.z (Me: Mn,
Fe, Pb, Ge; Me': Al, B, P, Si, Group 1, 2 and 3 elements of the
periodic table, halogen; 0.ltoreq.x.ltoreq.1; 1.ltoreq.y.ltoreq.3;
1.ltoreq.z.ltoreq.8); lithium metal; lithium alloy; silicon-based
alloy; tin-based alloy; a metal oxide, such as SnO, SnO.sub.2, PbO,
PbO.sub.2, Pb.sub.2O.sub.3, Pb.sub.3O.sub.4, Sn.sub.2O.sub.3,
Sb.sub.2O.sub.4, Sb.sub.2O.sub.5, GeO, GeO.sub.2, Bi.sub.2O.sub.3,
Bi.sub.2O.sub.4, or Bi.sub.2O.sub.5; a conductive polymer, such as
polyacetylene; or a Li--Co--Ni based material.
[0045] The electrode is used in a power storage apparatus, such as
a secondary battery or an electric double layer capacitor. An
example of the secondary battery is a non-aqueous electrolytic
secondary battery, such as a lithium secondary battery.
[0046] The method of manufacturing the lithium secondary battery is
well known in the art to which the present invention pertains.
BRIEF DESCRIPTION OF DRAWINGS
[0047] The above and other objects, features and other advantages
of the present invention will be more clearly understood from the
following detailed description taken in conjunction with the
accompanying drawings, in which:
[0048] FIG. 1 is a schematic view showing an electrode sheet wound
in the form of a roll in an electrode drying method according to an
embodiment of the present invention;
[0049] FIG. 2 is a perspective view showing an uneven structure of
a hygroscopic film according to an embodiment of the present
invention, which is configured to be wound with an electrode
sheet;
[0050] FIG. 3 is a perspective view showing an uneven structure of
a hygroscopic film according to another embodiment of the present
invention, which is configured to be wound with an electrode
sheet;
[0051] FIG. 4 is a perspective view showing an uneven structure of
a hygroscopic film according to another embodiment of the present
invention, which is configured to be wound with an electrode
sheet;
[0052] FIG. 5 is a perspective view showing an uneven structure of
a hygroscopic film according to a further embodiment of the present
invention, which is configured to be wound with an electrode sheet;
and
[0053] FIG. 6 is a schematic view showing a plurality of stacked
electrodes in an electrode drying method according to another
embodiment of the present invention.
BEST MODE
[0054] Now, exemplary embodiments of the present invention will be
described in detail with reference to the accompanying drawings. It
should be noted, however, that the scope of the present invention
is not limited by the illustrated embodiments.
[0055] FIG. 1 is a schematic view showing a structure in which an
electrode sheet has been wound with a hygroscopic film in an
electrode drying method according to an embodiment of the present
invention.
[0056] Referring to FIG. 1, an electrode sheet 100 is wound with a
hygroscopic sheet 200 ( "hygroscopic film" ) in the form of a roll
before the electrode sheet 100 is dried in a drying chamber.
Consequently, the hygroscopic sheet 200 ( "hygroscopic film" ) is
interposed between the overlapping portions of the electrode sheet
100.
[0057] In general, an electrode sheet is dried in the state of
being wound in the form of a roll in order to achieve higher drying
efficiency than in the case in which a plurality of electrodes is
individually dried.
[0058] In the case in which the electrode sheet is dried in the
state of being wound as described above, however, the surface area
of the electrode sheet that comes into contact with air gradually
decreases toward the core of the wound electrode sheet 100 in the
drying chamber, whereby the electrode sheet is not sufficiently
dried. As a result, the moisture content of the portion of the
electrode sheet that is located at the core side of the wound
electrode sheet 100 is different from the moisture content of the
portion of the electrode sheet that is located at the outer side of
the wound electrode sheet 100. In the case in which the electrode
sheet 100 dried as described above is used, batteries may perform
differently. Furthermore, in the case in which an electrode sheet
having a large amount of moisture contained therein is used, the
performance of batteries may be greatly reduced.
[0059] In the present invention, as shown in FIG. 1, the electrode
sheet 100 is wound with the hygroscopic film 200 in the state in
which the hygroscopic film 200 is disposed on either the upper
surface or the lower surface of the electrode sheet 100, and then
the electrode sheet 100 is dried in the drying chamber. The
thickness t of the hygroscopic film 200 may be smaller than the
thickness T of the electrode sheet 100. For example, the thickness
t of the hygroscopic film 200 may be about 70% of the thickness T
of the electrode sheet 100.
[0060] In the case in which the electrode sheet 100 is wound with
the hygroscopic film 200 as described above, the hygroscopic film
200 is located even at the core side of the electrode sheet 100
wound in the form of a roll. Consequently, it is possible to more
easily dry the entirety of the electrode sheet 200 ( "100" )
depending on the hygroscopic component of the hygroscopic film
200.
[0061] In addition, although not shown in detail in FIG. 1, at
least one of the surfaces of the hygroscopic film 200 that are
opposite the electrode sheet 100 has an uneven structure.
[0062] Here, the uneven structure may be a convex structure or a
concave and convex combination structure. In particular, therefore,
air flow paths are formed even at the portion of the electrode
sheet 200 ( "100" ) that is located at the core side of the wound
electrode sheet 100 due to the uneven structure of the hygroscopic
film 200 interposed between the overlapping portions of the
electrode sheet 200 ( "100" ). As a result, air smoothly flows
through the air flow paths, whereby it is possible to more easily
dry the portion of the electrode sheet 100 that is located at the
core side of the wound electrode sheet 100. Consequently, it is
possible to shorten the drying time and to efficiently and
sufficiently dry even the portion of the electrode sheet 100 that
is located at the core side of the wound electrode sheet 100.
Ultimately, it is possible to reduce a difference between the
moisture content of the portion of the electrode sheet that is
located at the core side of the wound electrode sheet 100 and the
moisture content of the portion of the electrode sheet that is
located at the outer side of the wound electrode sheet 100, whereby
it is possible to secure the consistency in the performance of
batteries manufactured using the above electrode sheet and to
prevent a reduction in the performance of the batteries.
[0063] Various examples of the uneven structure of the hygroscopic
film 200 are schematically shown in FIGS. 2 to 5.
[0064] Specifically, FIG. 2 shows an example of a hygroscopic film
210 having curved valleys 212 and curved ridges 211 alternately
formed in a continuous fashion on opposite surfaces thereof.
Referring to FIG. 2, the hygroscopic film 210 has a structure in
which valleys 212 and ridges 211 are alternately formed in a
continuous fashion on opposite surfaces thereof. The valleys 212
and ridges 211 formed on the opposite surfaces of the hygroscopic
film 210 are complementary to each other, whereby the hygroscopic
film 210 is generally formed in the shape of waves.
[0065] FIG. 3 shows an example of a hygroscopic film 220 having
polygonal valleys 222 and polygonal ridges 221, specifically
triangular valleys 222 and triangular ridges 221, alternately
formed in a continuous fashion on opposite surfaces thereof.
Referring to FIG. 3, the hygroscopic film 210 has a structure in
which valleys 222 and ridges 221 are alternately formed in a
continuous fashion on opposite surfaces thereof such that the
valleys 222 and ridges 221 are complementary to each other,
similarly to what is shown in FIG. 2.
[0066] FIG. 4 shows another example of the hygroscopic film.
Specifically, FIG. 4 shows an example of an uneven structure of a
hygroscopic film 230, in which a plurality of embossed curved domes
231 is formed on each surface thereof. Referring to FIG. 3 ( "FIG.
4" ), the hygroscopic film 230 has a convex structure, which is
formed by the embossed curved domes 231 formed on opposite surfaces
of the hygroscopic film 230. The domes 231 formed on the opposite
surfaces of the hygroscopic film 230 correspond to each other,
whereby the hygroscopic film 230 is formed in an embossed
shape.
[0067] FIG. 5 shows an example of a hygroscopic film 240 having an
uneven structure, in which embossed domes 241 are formed on the
hygroscopic film, similarly to what is shown in FIG. 4, but the
shape of each of the embossed domes 241 is polygonal. Referring to
FIG. 5, the embossed polygonal domes 241 are formed on only one
surface of the hygroscopic film 240, unlike what is shown in FIG.
4.
[0068] Meanwhile, FIG. 6 is a schematic view showing a plurality of
stacked electrodes in an electrode drying method according to
another embodiment of the present invention. In this embodiment, a
plurality of electrodes is stacked in order to dry the electrodes,
instead of winding an electrode sheet in the form of a roll.
[0069] Referring to FIG. 6, a plurality of electrodes 100' is
stacked, and hygroscopic films 200' are interposed respectively
between the electrodes 100'. In the case in which the electrodes
100' are dried in the state in which the hygroscopic films 200' are
interposed respectively between the electrodes 100', it is also
possible to sufficiently dry each of the electrodes that are
located in the middle of the electrode stack.
[0070] Each of the hygroscopic films 200' may have the structure
described above. For example, each of the hygroscopic films 200'
may have any of the structures shown in FIGS. 2 to 5.
Example 1
[0071] Artificial graphite, as a negative electrode active
material, Denka Black, as a conductive agent, and styrene butadiene
rubber (SBR), as an aqueous binder, were mixed with water while
having a weight ratio of 96:2:2 to prepare slurry.
[0072] The slurry was coated on opposite surfaces of a copper (Cu)
foil having a thickness of 6 .mu.m to manufacture a temporary
electrode, and the temporary electrode was wound with polyvinyl
alcohol (PVA) having a thickness of 20 .mu.m, as a hygroscopic
film, as shown in FIG. 1. At this time, the hygroscopic film had
the surface structure shown in FIG. 2.
Example 2
[0073] A coating solution obtained by dispersing silica gel in
acetone was coated on opposite surfaces of polyvinyl alcohol (PVA)
having a thickness of 20 .mu.m, as a hygroscopic film (which had a
structure shown in FIG. 2), such that the coating solution had a
thickness of 5 .mu.m and was dried to manufacture a hygroscopic
film coated with silica gel.
[0074] The hygroscopic film was wound with the temporary electrode
manufactured in Example 1, as shown in FIG. 1.
Comparative Example 1
[0075] Only the temporary electrode manufactured in Example 1 was
wound.
Comparative Example 2
[0076] A hygroscopic film (PVA) having a thickness of 20 .mu.m and
an even surface structure (i.e. a smooth structure) was wound with
the temporary electrode manufactured in Example 1.
Experimental Example 1
[0077] The electrodes manufactured in Examples 1 and 2 and
Comparative Examples 1 and 2 were placed in a drying chamber, and
were dried at a temperature of 100 .quadrature. for five hours. The
portion of the electrode located at the innermost side of each of
the wound electrodes was punched so as to have an area of 1.4875
cm.sup.2 (the area of a positive electrode coin cell), and the
moisture content of the punched portion of the electrode was
measured. The results are shown in Table 1 below.
TABLE-US-00001 TABLE 1 Comparative Comparative Example 1 Example 2
Example 1 Example 2 Moisture 214 238 408 342 content (ppm)
[0078] It can be seen from Table 1 that it is possible to easily
dry the inside portion of each of the electrodes according to the
present invention. Particularly, in the case in which a hygroscopic
film having an uneven structure is used, as in the present
invention, it can be definitely seen that it is possible to more
easily dry the portion of the electrode located at the core side of
the wound electrode than in the case in which a hygroscopic film
having an even structure is used (as in Comparative Example 2).
[0079] Although the exemplary embodiments of the present invention
have been disclosed for illustrative purposes, those skilled in the
art will appreciate that various modifications, additions and
substitutions are possible, without departing from the scope and
spirit of the invention as disclosed in the accompanying
claims.
INDUSTRIAL APPLICABILITY
[0080] As is apparent from the above description, an electrode
drying method according to the present invention is performed in
the state in which a hygroscopic film having an uneven structure is
interposed between stacked electrodes or in the state in which an
electrode sheet is wound with a hygroscopic film having an uneven
structure. As a result, air in a drying chamber is brought into
contact with each of the electrodes that are located in the middle
of the electrode stack or the portion of the electrode sheet that
is located at the core side of the wound electrode sheet, and each
of the electrodes that are located in the middle of the electrode
stack or the portion of the electrode sheet that is located at the
core side of the wound electrode sheet can be more easily dried by
the provision of the hygroscopic film. Consequently, it is possible
to shorten the drying time. In addition, since each of the
electrodes that are located in the middle of the electrode stack or
the portion of the electrode sheet that is located at the core side
of the wound electrode sheet is sufficiently dried, a difference
between the moisture content of the electrodes that are located in
the middle of the electrode stack and the moisture content of the
electrodes that are located at the outer side of the electrode
stack, or a difference between the moisture content of the portion
of the electrode sheet that is located at the core side of the
wound electrode sheet and the moisture content of the portion of
the electrode sheet that is located at the outer side of the wound
electrode sheet, is reduced. In the case in which batteries are
manufactured using the electrodes or the electrode sheet dried as
described above, therefore, it is possible to prevent a reduction
in the performance of the batteries due to the moisture remaining
in the electrodes or the electrode sheet.
* * * * *