JP2001357880A - Manufacturing method for nonaqueous electrolyte secondary battery having polymer electrolyte - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the high-rate discharge characteristic of a nonaqueous electrolyte secondary battery using polymer electrolyte. SOLUTION: An electrode sheet 10 is passed through a polymer solution and pinched by squeeze rolls 24 to remove excessive polymer solution from the surface, and then a non-heated air is sprayed in film form to the surface of the electrode sheet 10 from a nozzle 28 having a slit extending in the direction across the width of the sheet 10 so that the excessive polyer solution is removed completely.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for manufacturing a non-aqueous electrolyte secondary battery having a polymer electrolyte.

[0002]

2. Description of the Related Art In recent years, in non-aqueous electrolyte secondary batteries,
For the purpose of reducing the amount of free electrolyte and improving the safety of a battery, the use of a polymer electrolyte instead of a conventional liquid electrolyte is attracting attention. This polymer electrolyte has a structure in which an electrolyte salt having ionic conductivity or an electrolyte is compatible with and held by a polymer having a solid or gel network structure.

An example of a conventional method for manufacturing a non-aqueous electrolyte secondary battery having a polymer electrolyte is as follows. First, a mixture is applied to both sides of a current collector made of a strip-shaped metal foil, and a dried electrode sheet is continuously manufactured, and this is passed through a polymer solution obtained by dissolving a polymer in a solvent to form a mixture in the mixture layer. The polymer solution is impregnated (polymer impregnation step). Note that the mixture contains an active material, a conductive assistant, and a binder. Thereafter, the electrode sheet is immersed in water, and the solvent in the polymer is eluted into water, thereby exchanging the solvent with water (solvent extraction step) and drying the same. Then, fine holes are formed after moisture in the polymer is released, and the polymer has a porous network structure. Then, when this electrode sheet is immersed in the electrolytic solution, the electrolytic solution penetrates into the network structure of the polymer, and the electrolytic solution is held in the mixture by the polymer (electrolyte solution impregnating step). Then, the electrode sheet is cut into a required length and width, and wound together with the electrode sheet and the separator of the counter electrode to form a battery.

[0004]

However, the above-described method for manufacturing a non-aqueous electrolyte secondary battery has the following problems. Since the polymer solution used in the polymer impregnation step has high viscosity, it is inevitable that an excessive amount of the polymer solution adheres to the surface of the electrode sheet that has passed through the polymer solution. If this is left as it is and the next step is proceeded, a relatively thick polymer layer will be formed on the electrode surface. Although the polymer layer is impregnated with the electrolytic solution, the polymer itself is an insulator, so when wound as a battery, the volume becomes a wasteful volume that does not contribute to the battery operation, and the energy density is reduced.

It is conceivable to scrape off the excess polymer solution, for example, by applying a metal blade to the electrode sheet, but this is not preferable because the mixture may be scraped off.
It is also conceivable to squeeze the polymer solution on the surface by sandwiching the electrode sheet passed through the polymer solution between a pair of rollers, but this alone results in an uneven amount of the polymer solution remaining on the surface. In particular, there is a problem that the capacity at the time of high-rate discharge is reduced and the variation between cells is increased.

The present invention has been made in view of the above circumstances, and it is possible to uniformly remove excess polymer solution from the surface of the electrode sheet after the polymer impregnation step, thereby increasing the capacity and reducing the variation. An object of the present invention is to provide a method for manufacturing a water electrolyte secondary battery.

[0007]

According to a first aspect of the present invention, there is provided a method of manufacturing a non-aqueous electrolyte secondary battery in which at least one of a positive electrode and a negative electrode holds a polymer electrolyte. An electrode sheet formed by applying a mixture to both sides of a belt-shaped current collector is passed through a solution in which the polymer is dissolved in a solvent, and the polymer solution is impregnated in the mixture layer of the electrode sheet. Then, after removing the solvent, in the method for producing a non-aqueous electrolyte secondary battery in which the polymer in the electrode sheet retains the electrolytic solution, the electrode sheet passed through the polymer solution is pressed with a roller to form a surface. After removing excess polymer solution, air is blown from a nozzle having a slit extending in the width direction of the electrode sheet on the surface of the electrode sheet.

[0008] A second aspect of the present invention is characterized in that, in the first aspect of the present invention, the roller for pressing the electrode sheet is disposed above the polymer impregnation tank storing the polymer solution. A third aspect of the present invention is characterized in that, in the first or second aspect of the invention, the air blown from the nozzle is unheated air.

[0009]

According to the first aspect of the present invention, most of the excess polymer solution on the surface is first removed by passing the polymer sheet through the polymer solution and clamping the electrode sheet by the roller. Then, after that, since air is blown from a nozzle having a slit extending in the width direction of the electrode sheet onto the surface of the electrode sheet, the polymer solution remaining slightly adhered to the surface of the electrode sheet is also peeled off from the electrode sheet surface. So that the polymer solution is sufficiently removed from the surface. As a result, the useless insulator becomes extremely thin and the discharge capacity per volume can be increased, and the uniform electrode thickness can improve the high rate discharge performance.

According to the second aspect of the present invention, since the roller is above the polymer impregnation tank, the polymer solution squeezed by the roller immediately falls into the polymer impregnation tank, and the polymer solution is wasted. And the structure is simple. By the way, the reason why the electrolyte solution is retained in the polymer network is that the solvent in the polymer solution is replaced with water, and then the water is removed by a drying process, so that a fine network structure is formed. Yes, when the solvent is evaporated directly from the polymer solution, the polymer does not form a network. In view of this point, according to the invention of claim 3,
Since the air blown from the nozzle is unheated air, volatilization of the solvent can be prevented as much as possible, and the porosity of the polymer can be ensured.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is applied to the manufacture of a lithium ion secondary battery will be described below with reference to the drawings. Although not shown in detail, the lithium ion secondary battery has a well-known structure in which both a band-shaped positive electrode and a negative electrode are wound around a separator made of, for example, a polyolefin-based porous film. For example, graphite or the like is coated on both sides of a copper foil, and the positive electrode is formed by coating LiCoO2 or the like as a mixture on both sides of an aluminum foil, for example. Is impregnated.

FIG. 1 shows an overall structure of an apparatus for impregnating a polymer into a positive electrode. Here, the electrode sheet 10 for the positive electrode is supplied from the right side in the figure, and runs toward the left side. The electrode sheet 10 is formed by applying the mixture to a strip-shaped aluminum foil as described above, and the mixture is applied to both sides, and the uncoated portion where the mixture is not applied at predetermined intervals. (Not shown) are formed. The electrode sheet 10 is continuously supplied to the present apparatus and is continuously processed. However, in the final stage, the electrode sheet 10 is cut at the non-applied portion and a lead is welded to the non-applied portion and wound with the negative electrode and the separator. This is accommodated in a case and an electrolyte is injected (electrolyte impregnation step).

Now, the present apparatus has a polymer impregnation stage 2
0, solvent extraction stage 40, polymer wiping stage 60
And a drying stage 80 in order. The polymer impregnation stage 20 is provided with an impregnation tank 21 storing a polymer solution, and a polymer impregnation step is performed. As shown in detail in FIG. 2, an impregnation roll 22 is rotatably arranged in the impregnation tank 21, and the electrode sheet 10 guided by the guide roll 23 is continuously supplied into the impregnation tank 21, Impregnation tank 21 while being turned upward by
The polymer solution stored therein is impregnated in the mixture layer of the electrode sheet 10. The electrode sheet 10 turned upward from the impregnation roll 22 passes between a pair of squeezing rolls 24,
It is guided to the solvent extraction stage 40 side through the first roll 25, the intermediate roll 26 and the second roll 27 in order.

In this embodiment, a polymer solution is prepared by dissolving a polymer (copolymer of vinylidene fluoride and hexafluoropropylene) in NMP (N methyl 2-pyrrolidone) as a solvent (concentration: 2 to 10% by weight). ).

Returning to FIG. 1, in the solvent extraction stage 40,
The two extraction tanks 41 and 42 are arranged in order, and the electrode sheet 10 is stretched between a plurality of guide rolls 43 arranged alternately up and down in the extraction tanks 41 and 42. Travels meandering in the water stored in the extraction tanks 41 and 42. As a result, the solvent component of the polymer solution impregnated in the mixture layer of the electrode sheet 10 dissolves into water, and the water permeates into the network structure of the polymer instead. Then, the electrode sheet 10 that has passed through the latter extraction tank 42 is drawn upward, and sent to the next-stage polymer wiping stage 60 via the turning rollers 44 and 45 and the outlet device 46.

In the polymer wiping stage 60, a nonwoven fabric belt 62 wound around a reel 61 is provided so as to be able to run, and the running nonwoven fabric belt 62 is pressed against the electrode sheet 10 by the wiping roll 63 to form a non-woven fabric belt 62. The polymer solution adhering to the non-applied portion where the agent is not applied is wiped off. Although not shown in detail, an optical sensor is provided on the entrance side of the wiping roll 63, which detects a non-coated portion of the electrode sheet 10, and the wiping roll 63 is configured to wipe only the non-coated portion. It is pressed against the electrode sheet 10. The wiping device 64 described above is used.
Are provided on the upper and lower sides, and the polymer solution is wiped on both the front and back surfaces of the non-coated portion of the electrode sheet 10.

Then, the electrode sheet 10 pulled out from the wiping device 64 at the subsequent stage is introduced into the drying stage 80 and travels inside the drying furnace 81. This removes water that has penetrated into the polymer network, and the polymer becomes a network. The polymer does not have to be porous, but can hold a large amount of electrolyte in the polymer layer.
It is preferable that the porous material is porous because the conductivity is increased and a battery having excellent high-rate discharge characteristics can be obtained. Although not shown, after this, the electrode sheet 10 is wound on a reel, sent to a battery winding device, spirally wound together with an electrode sheet for negative electrode and a separator, and injected with an electrolytic solution. Then, the electrolytic solution permeates into the network structure of the polymer and is held by the polymer.

The feature of the present invention resides in the polymer impregnation stage 20, which will be described in more detail. As shown in FIG. 2, a pair of squeezing rolls 2
Reference numerals 4 and 24 are provided so that the polymer solution excessively attached to the surface of the electrode sheet 10 is squeezed out. Since the squeezing roll 24 is disposed directly above the impregnation tank 21, the excess polymer solution that has been squeezed out is removed from the impregnation tank 21.
It does not drip inside, pollute the surroundings, or waste the polymer solution.

The electrode sheet 1 is provided above the first roll 25.
A nozzle 28 having a slit (not shown) extending in the width direction of 0 is provided, to which compressed air from a compressor not shown is supplied. The compressed air is not heated, but is cooled to room temperature if necessary. Thereby, the air blown out from the slit of the nozzle 28 is blown in a film shape on the surface of the electrode sheet 10, and the excess polymer solution remaining on the surface of the electrode sheet 10 is blown off.
A container-like cover 29 having an open top is provided around the first roll 25, and the polymer solution blown off from the surface of the electrode sheet 10 is collected in the cover 29. Further, the nozzle 28 is rotatably held by a shaft 30 arranged in the axial direction with the first roll 25, and a handle 31 is provided. By operating the handle 31 only, the compression blown out from the nozzle 28 is compressed. The direction of air blowing can be adjusted. The nozzle 28 and the cover 29 are also provided on the upper part (the same parts are denoted by the same reference numerals in FIG. 3 and are shown in detail in FIG. 3). Can be blown off.

According to the above configuration, when an excessive amount of the polymer solution adheres to the surface of the electrode sheet 10 at the polymer impregnation stage 20, the polymer solution is first squeezed out by the squeezing rolls 24, 24 and falls into the impregnation tank 21. At this time, even if the polymer solution remains on the surface thinly without being completely removed by the squeezing roll 24, a nozzle 28 is provided behind the squeezing roll 24, from which compressed air is blown in a film form. Therefore, the remaining polymer solution is also scattered so as to be peeled off from the electrode sheet, and the polymer solution is sufficiently removed from the surface.

This means that wasteful insulators can be prevented from being thickly attached to the surface of the mixture layer of the electrode sheet 10. Therefore, when the battery is completed, the discharge capacity per volume is increased. You can do it. Also,
When the polymer layer remains on the electrode surface, the variation increases due to the non-uniformity of the thickness of the layer, and it is not possible to secure a capacity particularly at the time of high-rate discharge. Since it can be almost completely removed from the surface of the electrode sheet 10, sufficient capacity at the time of efficient discharge can be secured. By the way, the following table shows the capacity ratio at the time of high-rate discharge between the comparative example in which the nozzle 28 of this embodiment is omitted, and some examples in which the pressure of the compressed air supplied to the nozzle 28 is variously changed. . Here, the capacity ratio indicates the capacity at the time of 2 CmA discharge / the capacity at the time of 0.2 CmA discharge in percentage, and the larger the value, the better the high rate discharge characteristic. The higher the supplied air pressure, the more completely the polymer solution on the surface can be removed. However, if the supplied air pressure is excessive, the running electrode sheet 10 may vibrate to generate "wrinkles". The upper limit value is considered to be different depending on the thickness and tension of the electrode sheet 10, but was 30 Kpa in the present embodiment.

The presence or absence of the nozzle 28 Air pressure Capacity ratio Comparative example No-69 Example 1 Yes 0.5 74 Example 2 Yes 1 75 Example 3 Yes 3 77 Example 4 Yes 5 80 Example 5 Yes 7 83 Example 6 Yes 10 83 Example 7 Yes 15 83 Example 8 Yes 20 83

Also, according to the present embodiment, in particular, since the squeezing roll 24 is disposed above the impregnation tank 21, the polymer solution squeezed out by the squeezing roll 24 immediately falls into the impregnation tank 21 and the polymer solution is wasted. Without becoming
Moreover, the structure is simple. When the battery is configured, the electrolyte is held in the network of the polymer because the solvent in the polymer solution is in the solvent extraction stage 40.
Is replaced with water, and then the water is removed in the drying stage 80, so that a fine network structure is formed in the polymer. Thus, when the solvent is evaporated directly from the polymer solution, the polymer does not form a network. In view of this point, according to the present embodiment, since the air blown from the nozzle 28 is unheated air, volatilization of the solvent can be prevented as much as possible, and the porosity of the polymer can be ensured.

The present invention is not limited to the above-described embodiment. For example, the following embodiments also belong to the technical scope of the present invention. (1) As the polymer component of the polymer electrolyte used in the present invention, a copolymer of vinylidene fluoride (VdF) and hexafluoropropylene (HFP) is preferable, but not limited thereto, for example, polyacrylonitrile (PAN) or Other materials such as polymethyl methacrylate (PMMA) or a mixture or copolymer thereof may be used.
The weight average molecular weight of these polymers is 100,000 to 1
One million is preferred. When the molecular weight is 1,000,000 or more, the viscosity of the electrolytic solution becomes high when dissolved in a solvent, it is difficult to impregnate the electrode, and when the molecular weight is 100,000 or less, the polymer is dissolved in the solvent and the network structure itself of the polymer is broken. Therefore, neither is preferable.

(2) As the organic solvent for dissolving or dispersing the polymer, in addition to N-methyl-2-pyrrolidone, for example, dimethylformamide, methyl ethyl ketone, methyl isobutyl ketone, toluene, xylene, tetrahydrofuran, acetone, acetonitrile, dimethyl Carbonate, ethyl acetate, butyl acetate and the like can be used.

(3) In the above embodiment, the polymer is impregnated in the positive electrode. However, the polymer may be impregnated in the negative electrode. As the positive electrode mixture, it is preferable to use an oxide capable of inserting and extracting lithium ions. Examples of such an oxide include a lithium cobalt oxide such as LiCoO 2, a lithium manganese oxide such as LiMn 2 O 4, and L
lithium nickel oxide such as iNiO2, LiV2O4
Such as lithium vanadium oxides, these composite oxides,
There are mixtures and the like. As the negative electrode mixture, a carbon-based material, a lithium metal, a lithium alloy, an oxide material, or the like is used. As the carbon-based material, for example, artificial or natural graphite, pyrolytic carbons, cokes, glassy carbons, fired bodies of organic polymer compounds, mesocarbon microbeads, activated carbon, graphite, carbon fibers, and the like are used. As the oxide, a compound mainly composed of tin oxide is used. These are used in a powder state.
In addition, as a separator, a nonwoven fabric, a porous film, etc. can be used, for example. Furthermore, the nonaqueous electrolyte battery of the present invention can be used in any of a cylindrical type, a square type, a sheet type, a stacked type, a coin type, a pin type, and the like, and the shape is not particularly limited.

(4) In the above embodiment, the compressed air is blown onto the electrode sheet 10 in the form of a film.
The compressed air uniformly hits the surface of the electrode sheet 10 so that the removal of the polymer solution is also performed uniformly. But,
Alternatively, compressed air may be blown from a circular nozzle onto the electrode sheet.

[Brief description of the drawings]

FIG. 1 is a schematic side view of a manufacturing apparatus showing one embodiment of the present invention.

FIG. 2 is a schematic longitudinal sectional view showing a polymer impregnation stage.

FIG. 3 is a sectional view showing a nozzle portion.

[Explanation of symbols]

 Reference Signs List 10 electrode sheet 20 polymer impregnation stage (impregnation step) 21 impregnation tank 24 squeezing roll 28 nozzle 29 cover 40 solvent extraction stage 60 polymer wiping stage 80 drying stage

 ──────────────────────────────────────────────────の Continuing from the front page (72) Inventor Yoshihiro Kuwahara 1st Kinoshoin Nishinosho Ino Babacho, Minami-ku, Kyoto City Inside Nippon Battery Co., Ltd. (72) Inventor Takeshi Hazumi Nishinosho Nishinosho, Minami-ku, Kyoto City No. 1, Nobabacho, Japan Battery Co., Ltd. (72) Naoto Matsueda, Inventor Naoto Matsueda, Kichijoin, Minato-ku, Kyoto 5 No.1, Nitta Ichidandan-cho, Japan Mercury Tech Co., Ltd. (72) Koichi Imai, Kichijoin, Minami-ku, Kyoto 5nd in Ichidandancho, Nitta, GS Melcotec Co., Ltd. (72) Inventor Kazuki Tagawa 5th in Ichidandan, Nitta, Kichijoin, Minami-ku, Kyoto F term in GS Mercotec Co., Ltd. 5H029 AJ14 AK03 AL02 AL06 AL07 AL08 AL12 AM16 BJ02 BJ03 BJ04 CJ00 CJ03 CJ12 CJ22 CJ23 CJ28 CJ30 DJ04 DJ09 EJ12 HJ12

Claims (3)

[Claims] 1. A method for producing a non-aqueous electrolyte secondary battery in which a polymer electrolyte is held on at least one of a positive electrode and a negative electrode, comprising applying a mixture to both surfaces of a belt-shaped current collector. The electrode sheet is passed through a polymer solution in which the polymer is dissolved in a solvent to impregnate the polymer solution in the mixture layer of the electrode sheet,
After removing the solvent, in the method for producing a non-aqueous electrolyte secondary battery in which the polymer in the electrode sheet retains an electrolytic solution, the electrode sheet passed through the polymer solution is squeezed by a roller to remove excess surface. A method for producing a non-aqueous electrolyte secondary battery, comprising: removing a polymer solution, followed by blowing air from a nozzle having a slit extending in the width direction of the electrode sheet onto the surface of the electrode sheet. 2. The method for producing a non-aqueous electrolyte secondary battery according to claim 1, wherein the roller is disposed above a polymer impregnation tank storing the polymer solution. 3. The method for manufacturing a non-aqueous electrolyte secondary battery according to claim 1, wherein the air blown from the nozzle is non-heated air.