JP2003187788A - Method for manufacturing electrode plate and coating apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing an electrode plate, together with a coating apparatus, of good yield by allowing the thickness of a coat layer in the width direction of a collector to be constant. <P>SOLUTION: Using a coating apparatus provided with a tapered slit nozzle 1, paste is so applied and dried that a mound section where the coat layer is thicker than those in other sections is formed at both ends in the width direction of the collector. Then, only the mound section is preliminary rolled, and after that, the entire coat width is actually rolled to provide an electrode plate of constant thickness. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for manufacturing an electrode plate, and more particularly to a method and an apparatus for manufacturing an electrode plate for a lithium ion secondary battery having a uniform coating thickness.

[0002]

2. Description of the Related Art In recent years, the performance of mobile electronic devices such as mobile phones and personal digital assistants largely depends not only on the performance of semiconductor elements and electronic circuits, but also on the performance of rechargeable secondary batteries. It is desired to increase the capacity of the rechargeable battery to be mounted, and at the same time, realize weight reduction and compactness. As a secondary battery that meets these demands, a nickel-hydrogen storage battery having an energy density about twice that of a nickel-cadmium storage battery has been developed, and then a lithium-ion secondary battery that exceeds this has been developed and is in the spotlight.

In this lithium ion secondary battery, a positive electrode and a negative electrode are placed in a non-aqueous electrolyte solution, and a positive electrode active material is bound to the surface of the current collector or the surface of the current collector is attached to each electrode plate. It has a structure in which the negative electrode active material is bound to. The battery electrode plate used in this battery is generally rolled after applying an active material (a positive electrode active material or a negative electrode active material), a conductive material, a binder (binder), etc. to a current collector, drying the same. It is manufactured by slitting a thing into a predetermined shape.

As a more specific method for producing an electrode plate, as shown in FIG. 5, a slit-shaped nozzle 100 shown in FIG. 6 is prepared by kneading and dispersing an active material and a binder in an organic solvent or water. To one side or both sides of the band-shaped (hoop-shaped) current collector 2 and dried by passing through a drying oven 3, and then rolled by a rolling roller 4 to a predetermined thickness to a predetermined size. A method of manufacturing an electrode plate by cutting is used.

[0005]

However, when the paste is applied to the current collector, the coating thickness varies in the width direction, and the coating thickness at both ends in the width direction is particularly affected by the sagging during coating. Since it becomes thin and a predetermined amount of active material cannot be secured, it has been a factor of lowering the yield.

Further, when the paste is continuously applied in the running (longitudinal) direction, a peeling step for forming the lead portion is required, and the peeling residue of the active material generated at that time is deposited on the electrode plate. There is a problem that the particles adhere to each other and the discharge capacity decreases as the charging and discharging are repeated. Therefore, a method of applying the paste to the current collector so that uncoated portions appear at regular intervals in the traveling direction of the current collector, that is, an intermittent application method (such as Japanese Patent No. 2842347) has been proposed. Since the pressure must be delicately controlled when starting and stopping the coating, it is necessary to control not only the coating width but also the coating thickness in the traveling direction.

In particular, when the electrode plate is a negative electrode plate, if a portion having a small coating thickness occurs, when facing the positive electrode plate through the separator, the active portion of the portion receiving lithium ions moving from the positive electrode plate during charging. Since the amount of substance becomes relatively small, lithium ions are deposited on the surface of that part,
This may break through the separator and contact the positive electrode plate, causing an internal short circuit.

The present invention is to solve the above problems and provides a method for producing an electrode plate and a coating apparatus that make the thickness of the coating layer in the width direction and the running direction of the current collector uniform and have a good yield. The purpose is to provide.

[0009]

According to the present invention for solving the above-mentioned problems, an electrode plate in which a paste containing at least an active material and a binder is applied on a current collector, dried and then rolled In the manufacturing method, the both ends of the width direction of the coating layer coated with the paste are provided with a raised portion coated so that the coating thickness is thicker than other portions, and after pre-rolling only this raised portion, the entire coating width Main rolling over
A method for producing an electrode plate, which comprises producing an electrode plate, wherein the electrode plate is 3 to 17 mm from the edges of the both ends, preferably 5 mm.
Up to 15 mm inside, a bulge portion that becomes 1.5% to 5.0%, preferably 2.0% to 4.0% thicker than the average of the total thickness of the electrode plate including the collector and the coating layer of the other portion is formed. It is preferable to provide.

The rolling in the manufacturing method of the present invention is
The coating thickness of both widthwise end portions of the coating layer is provided with a raised portion coated so as to be thicker than other portions, and after only this raised portion is pre-rolled, main rolling is performed over the entire coating width to obtain a uniform thickness. This is for manufacturing electrode plates, and this preliminary rolling is different from the conventional rolling of the entire width of the coating layer. By this pre-rolling, the active material of the raised portion applied is moved from the raised portion to the end portion, thereby increasing the coating thickness at the end portion where the coating thickness has become thin due to sagging at the time of coating, and the entire coating layer width. An electrode plate with a uniform amount of active material can be obtained by subjecting the material to a uniform coating thickness and then main rolling.

Further, in the coating apparatus of the present invention, in order to apply the paste at both end portions in the width direction of the current collector so that the coating thickness becomes thicker than other portions, the slit width of the nozzle tip portion of the discharge portion Is provided with a tapered slit nozzle that is gradually narrowed toward the tip, and the slit width at the tip of the nozzle is 6 to 34 mm, preferably 10 from the coating width of the electrode plate. It is preferably narrow by ~ 30 mm.

By using the coating device equipped with the tapered slit nozzle, it is possible to easily form the raised portion by coating so that the coating thickness at both widthwise end portions of the coating width becomes thicker than other portions. .

In the case where intermittent coating is performed in the running direction of the current collector, even if delicate control of pressure is performed at the start and stop of coating, if the same raised portion as described above occurs at the start of coating, Similarly, an electrode plate having a uniform thickness can be manufactured by pre-rolling only this raised portion and then main-rolling the entire coating width.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic view showing a method for manufacturing a lithium-ion secondary battery electrode plate.

When the electrode plate is the positive electrode, the foil is made of aluminum or has a thickness of 10 μm-60 which has been lathed or etched.
A paste prepared by kneading and dispersing a positive electrode active material, a binder, and if necessary, a conductive agent and a thickener in a solvent is applied to one side or both sides of a current collector made of a foil having a thickness of μm.

The positive electrode active material is not particularly limited, but for example, a lithium-containing transition metal compound capable of accepting lithium ions as a guest is used.
For example, a composite metal oxide of at least one metal selected from cobalt, manganese, nickel, chromium, iron and vanadium and lithium, LiCoO ₂ , LiMn.
O ₂ , LiNiO ₂ , LiCo _x Ni _(1-x) O ₂ (0 <x <
1), LiCrO ₂ , αLiFeO ₂ , LiVO _{2 and the} like are preferable.

The binder is not particularly limited as long as it can be kneaded and dispersed in a solvent. For example, a fluorine-based binder, acrylic rubber, modified acrylic rubber, styrene-butadiene rubber (SBR), Acrylic polymer,
A vinyl polymer or the like can be used alone, or as a mixture or copolymer of two or more kinds. As the fluorine-based binder, for example, polyvinylidene fluoride, a copolymer of vinylidene fluoride and propylene hexafluoride, or a dispersion of polytetrafluoroethylene resin is preferable.

If desired, a conductive agent and a thickener can be added. As the conductive agent, acetylene black, graphite, carbon fiber or the like is preferably used alone or as a mixture of two or more kinds thereof. As the thickener, ethylene- Vinyl alcohol copolymer, carboxymethyl cellulose, methyl cellulose and the like are preferable.

As the solvent, a solvent capable of dissolving the binder is suitable, and in the case of an organic binder, N-methyl-2-pyrrolidone, N, N-dimethylformamide, tetrahydrofuran, dimethylacetamide, dimethylsulfoxide. , Hexamethylsulforamide, tetramethylurea,
An organic solvent such as acetone or methyl ethyl ketone is preferably used alone or a mixed solvent obtained by mixing these is preferable. In the case of an aqueous binder, water or warm water is preferable.

When the electrode plate is a negative electrode, a negative electrode active material and a binder are provided on one side or both sides of a collector made of a copper foil or a lath-processed or etched foil having a thickness of 10 μm to 50 μm.
If necessary, a paste prepared by kneading and dispersing a thickener in a solvent is applied.

The negative electrode active material is not particularly limited, but for example, a carbon material obtained by firing an organic polymer compound (phenol resin, polyacrylonitrile, cellulose, etc.), coke or pitch is fired. The carbon material thus obtained, artificial graphite, natural graphite, or the like can be used in the shape of a sphere, a scale, or a lump.

As the binder and, if necessary, the thickener added, the same binder as used for the positive electrode plate can be used.

By the way, the method of kneading and dispersing the active material, the binder, the thickener added as necessary, and the conductive agent in the solvent in the present invention to prepare the paste mixture is not particularly limited. For example, a planetary mixer, a homomixer, a pin mixer, a kneader, a homogenizer, etc. can be used. These may be used alone or in combination.

It is also possible to add various dispersants, surfactants, stabilizers, etc., when necessary, at the time of kneading and dispersing the above-mentioned paste mixture.

The paste thus kneaded and dispersed is
Coating is performed on the hoop-shaped current collector 2 traveling at a constant speed using a coating device as shown in FIGS. 1 and 2.

As shown in FIG. 2B, the slit width of the tip portion of the discharge portion 6 of the slit-shaped nozzle 1 is gradually narrowed symmetrically from the inside of the nozzle toward the nozzle tip 7, and is a tapered slit nozzle. By applying using a coating apparatus having the above, a raised portion as shown in FIG. 3 (a) is provided in which both end portions of the coating width are thicker than other portions.

This slit-shaped nozzle 1 is shown in FIGS.
As shown in (c), the nozzle upper plate 1a and the nozzle lower plate 1b
And the manifold 1c and the discharge portion 6 are formed between the nozzles 1 and 2, and side tapes 1d and 1d are arranged between the nozzle upper plate 1a and the nozzle lower plate 1b on both sides of the discharge portion 6,
The shape is formed as shown in FIGS. 2B and 2C. By selecting the shape of the side tape 1d, it is possible to adjust the swelling values of the swelling portions at the both ends.

Drying is preferably close to natural drying, but in consideration of productivity, the drying furnace 3 is used to successively increase the temperature in the range of 50 ° C. to 150 ° C. for 2 to 20 minutes. Is preferred.

The rolling is carried out by pre-rolling only the ridges at both ends in the width direction which are applied so as to be thicker than the other parts of the coating width by the pre-rolling roller 5, and then by the main rolling roller 5 over the entire coating width. In order to produce an electrode plate having a uniform thickness, the active material of the raised portion applied by this pre-rolling is moved to the end portion where the application thickness is thinned due to sagging at the time of application. An electrode plate with a uniform amount of active material can be obtained by subjecting the entire width to a uniform coating thickness and then performing main rolling.

The pressure during the preliminary rolling is 0.05 MPa to
The range of 0.5 MPa is preferable. If it is less than 0.05 MPa, it is difficult to roll the active material in the swelling portion, and it is difficult to move it to the end portion where the coating thickness has become thin due to sagging during coating, and if it exceeds 0.5 MPa. Although it is possible to roll the active material in the raised portion, it is not preferable because it is difficult to move the active material to the end portion where the coating thickness becomes thin due to sagging during coating.

The pressure during the main rolling is 5 MPa to
A range of 25 MPa is preferred. If it is less than 5 MPa, it is difficult to secure the target thickness of the electrode plate,
Even if it exceeds 5 MPa, the thickness does not change and the rolling equipment becomes large, which is not preferable.

[0033]

EXAMPLES The present invention will be described in detail with reference to Examples and Comparative Examples, but these do not limit the present invention in any way.

Example 1 First, 100 parts by weight of spherical graphite powder as a negative electrode active material, 126 parts by weight of an aqueous solution prepared by dissolving 1 part by weight of carboxymethyl cellulose in 100 parts by weight of water as a thickener, and polyethylene as a binder. 11 parts by weight of an aqueous dispersion of resin was mixed, kneaded and dispersed to prepare a paste.

The paste thus kneaded and dispersed is
As shown in FIGS. 2A to 2C, the manifold 1c and the discharge portion 6 are formed between the nozzle upper plate 1a and the nozzle lower plate 1b, and the inner width of the nozzle is 400 mm. 10 mm from the inner position toward the nozzle tip 7 in a symmetrical manner and gradually narrowed, and using a coating device equipped with a slit nozzle 1 having a nozzle tip width of 380 mm, a thickness of 14 μm that runs at a constant speed. It was applied on the hoop-shaped current collector 2 made of copper foil. Then, FIG. 4A shows the distribution of the electrode plate thickness in the width direction of the electrode plate 8 obtained by sequentially increasing the temperature from 60 ° C. to 110 ° C. in the drying furnace 3 and drying for 5 minutes. Here, the vertical axis represents a width direction distance of 40.
The average value of the electrode plate thickness is a relative distribution of the electrode plate thickness when the average of the electrode plate thickness (sum of the thickness of the current collector and the thickness of the active material coating layer) in the middle part of ~ 360 mm is 100%. Is 29
The thickness of the electrode plate is 5 μm, and the thickness of the electrode plate at a position 15 mm from both ends of the coating width (set to 400 mm) is 12 μm, that is, 4% thicker than the middle portion.
a and 8b were obtained.

Next, the raised portions 8a, 8 at both ends
By rolling only b on the pre-rolling roller 5 as shown in FIG. 3 (a) at a pressure of 0.5 MPa, the active material of the raised portions 8a and 8b is thinned by coating during coating to reduce the coating thickness. By moving the electrode plate to the end of the width of the coating, as shown in FIG. 4 (b), the thickness of the electrode plate at a position 5 mm from both ends in the width direction is 6 μm less than the thickness of the electrode plate at the middle portion.
m, ie 2.0% thick only.

Then, the entire electrode plate 8 is rolled at a pressure of 8 MPa using the main rolling roller 4 so that the electrode plate thickness at both ends of the coating width is 3 μm or less with respect to the intermediate electrode plate thickness of 196 μm. That is, it could be 1.6% or less, and an electrode plate having good thickness uniformity over the entire coating width could be obtained.

(Example 2) First, 100 parts by weight of lithium cobalt oxide as a positive electrode active material, 3 parts by weight of acetylene black as a conductive agent, and 4 parts by weight of polytetrafluoroethylene (PTFE) resin as a binder in solid content. Parts and 0.8 parts by weight of carboxymethyl cellulose were added, and kneaded and dispersed with water as a solvent to prepare a paste.

The paste thus kneaded and dispersed is
As shown in FIGS. 2A to 2C, the manifold 1c and the discharge portion 6 are formed between the nozzle upper plate 1a and the nozzle lower plate 1b, and the inner width of the nozzle is 400 mm. 5 mm from the position inside to the nozzle tip 7, symmetrically gradually narrowing, and using a coating device equipped with a tapered slit nozzle 1 having a nozzle tip width of 390 mm, a thickness that runs at a constant speed. 20
450 on the hoop-shaped collector 2 made of aluminum foil of μm
Intermittent coating was performed so that an uncoated portion of 10 mm was formed every mm.

Then, in the drying oven 3, the temperature is from 80 ° C to 130 ° C.
The distribution of the electrode plate thickness in the width direction of the electrode plate 8 obtained by successively increasing the temperature and drying for 10 minutes showed the same tendency as in FIG. 4 (a). In addition, the distribution of the electrode plate thickness in the traveling direction is shown in FIG.
As shown in (c).

In Example 2, the widthwise distance is 40 to 3
The average value of the electrode plate thickness (sum of the thickness of the current collector and the thickness of the active material coating layer) in the middle portion of 60 mm was 310 μm, and the electrode plate thickness at a position of 5 mm from both ends of the coating width was smaller than that of the middle portion. Also, a raised portion having a thickness of 6 μm, that is, 2% thick was obtained.

The vertical axis in FIG. 4 (c) is the thickness of the electrode plate (the sum of the thickness of the current collector and the thickness of the active material coating layer) at the intermediate portion where the distance in the running direction from the intermittent coating start position is 40 to 410 mm. The average value of the electrode plate thickness is 305 μm, and the electrode plate thickness of the raised portion 8c at a position 5 mm from the application start end in the traveling direction is an intermediate value. It was 9 μm thicker than the portion, that is, 3% thicker, but no swelling portion was formed at the end of coating.

Next, only the raised portions 8a and 8b are shown in FIG.
0.1M using the pre-rolling roller 5 as shown in (a)
By rolling at a pressure of Pa, the active material of the raised portions 8a and 8b is moved to the end portion where the coating thickness becomes thin due to sagging at the time of coating, as shown in FIG.
The thickness of the electrode plate at a position 3 mm from both ends of the coating width as shown in Fig. 4 is 4 μm than the thickness of the electrode plate in the middle portion, that is, 1.3%.
It was only thick.

Further, only the raised portion 8c is shown in FIG.
By rolling at a pressure of 0.1 MPa using the pre-rolling roller 5 as shown in Fig. 4, the active material of the raised portion 8c is moved to the coating start end, and the position 4 mm from the coating start end is reached. The electrode plate thickness was 6 μm, that is, 2.0% thicker than the electrode plate thickness in the middle portion.

Further, by rolling the entire electrode plate 8 using the main rolling roller 4 at a pressure of 20 MPa, the electrode plate thickness at both ends of the coating width is 2 μm or less with respect to the intermediate electrode plate thickness of 190 μm. That is, it can be 1.1% or less, and an electrode plate having good thickness uniformity over the entire coating width can be obtained, and the electrode plate thickness at the application start end portion in the running direction is compared with the electrode plate thickness 191 μm in the middle portion. It was possible to obtain an electrode plate having a thickness of 3 μm or less, that is, 1.6% or less, and a good coating thickness in the running direction.

(Comparative Example) In the same manner as in Example 1, the negative electrode paste kneaded and dispersed was, as shown in FIGS. 6 (a) and 6 (b), the discharge portion from the inside of the nozzle to the nozzle tip portion 7 in parallel. In the same manner as in Example 1, using a coating device equipped with a slit nozzle 100 having a width of 400 mm,
FIG. 7 shows the distribution of the electrode plate thickness in the width direction of the electrode plate 8 obtained by drying.

Here, the vertical axis is the relative distribution of the electrode plate thickness when the average of the electrode plate thickness in the middle portion having the widthwise distance of 40 to 360 mm is taken as 100%, as in the first embodiment. The average value of the plate thickness was 295 μm, but it decreased outward from the positions 30 mm from both ends of the coating width, and the electrode plate thickness was 21 μm, 7%, which was small at both ends.

Then, the entire electrode plate 8 was subjected to main rolling in the same manner as in Example 1, so that the thickness of the middle portion of the coating width was 196.
Although it was μm, it decreased outward from the positions of 30 mm from both ends of the coating width, and the coating thickness was 13 μm at both ends, which was as small as 6.7% as before the main rolling. Became out of the design range, and the yield decreased.

[0049]

As described above, according to the present invention, it is possible to provide a method for producing an electrode plate and a coating apparatus that make the thickness of the coating layer in the width direction of the current collector uniform and have a good yield. did it.

[Brief description of drawings]

FIG. 1 is a schematic view showing a method for manufacturing an electrode plate of the present invention.

FIG. 2A is a vertical sectional view of a tapered slit nozzle of the present invention. (B) Aa sectional drawing of (a). (C) An exploded perspective view of a main part.

FIG. 3A and FIG. 3B are diagrams showing rolling of a raised portion by a pre-rolling roller.

FIG. 4 (a) is a distribution diagram of the electrode plate thickness in the width direction of the current collector when the tapered slit nozzle according to the present invention is used. (B) Distribution map of the electrode plate thickness in the width direction of the current collector after preliminary rolling according to the present invention.

FIG. 5 is a schematic view showing a conventional electrode plate manufacturing method.

FIG. 6A is a vertical cross-sectional view of a conventional slit nozzle. (B) bb sectional drawing of (a).

FIG. 7 is a distribution diagram of the electrode plate thickness in the width direction of the current collector when the conventional slit-shaped nozzle is used.

[Explanation of symbols]

1 Slit nozzle 1a Nozzle upper plate 1b nozzle bottom plate 1c manifold 2 Current collector 3 drying oven 4 rolling rollers 5 Pre-rolling roller 6 Discharge end 7 Nozzle tip 8 plates 8a, 8b raised portion

Claims (4)

[Claims] 1. A method for manufacturing an electrode plate, comprising: applying a paste containing at least an active material and a binder onto a current collector; drying the paste; and rolling the electrode plate in a width direction of a coating layer applied with the paste. It is characterized in that both end portions are provided with a raised portion coated so that the coating thickness is thicker than other portions, only this raised portion is pre-rolled, and then main rolling is performed over the entire coating width to produce a polar plate. Method of manufacturing electrode plate. 2. A raised portion that is 1.5% to 5.0% thicker than the average of the total thickness of the electrode plates, which is the total of the current collector and the coating layer in the other portion, 3 to 17 mm inside from the edges of the both ends. The method for manufacturing an electrode plate according to claim 1, further comprising: 3. A coating device used in the method for manufacturing an electrode plate according to claim 1, wherein a taper slit nozzle is provided in which the slit width of the nozzle tip portion of the discharge portion is gradually narrowed toward the tip. A coating device characterized by being provided. 4. The coating apparatus according to claim 3, wherein the slit width at the tip of the nozzle is 6 to 34 mm narrower than the coating width of the electrode plate.