JPH1012230A - Manufacture of electrode for battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To shorten a time for drying coating slurry by specifying a component of slurry coating a substrate. SOLUTION: First, a powdery component related to battery reaction and a prescribed solution are mixed so as to prepare slurry. The powdery component is mainly composed of a hydrogen storage alloy. The solution is fused with powder of polyfluorovinylidene in n-methyl-2-pyrolidone. Next, after coating of the slurry in a conductive substrate immediately the substrate is put into the water. By this treating, n-methyl-2-pyrolidone in the slurry is moved to the water, the polyfluoro vinylidene is uniformly precipitated in the coating slurry as a solid. Thereafter, the substrate is taken out from in the water, water adhering to a surface is dried and removed. Here, without n-methyl-2- pyrolidone which is a solvent, necessity for heat drying for a long time is eliminated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a battery electrode, and more particularly, to a method for manufacturing a battery electrode more simply and in a shorter time than before.

[0002]

2. Description of the Related Art Most of the positive and negative electrodes of sealed alkaline secondary batteries usually have a structure in which a conductive substrate carries a powder component that participates in a battery reaction peculiar to the battery, for example, as an active material. . For example, in recent years, nickel-hydrogen secondary batteries, which have been rapidly commercialized as high capacity batteries,
The following hydrogen storage alloy electrodes are known as negative electrodes incorporated therein.

That is, a predetermined amount of a powder of a hydrogen storage alloy capable of electrochemically storing and releasing hydrogen as an active material is applied to a conductive substrate such as a conductive mesh sheet or a punched metal sheet having a desired aperture ratio. Is applied or filled and carried. Such a hydrogen storage alloy electrode,
Conventionally, it is generally manufactured as follows.

First, a slurry of a hydrogen storage alloy powder is prepared. That is, a predetermined amount of one or more thickeners such as methylcellulose, carboxymethylcellulose, polyethylene oxide, and polyvinyl alcohol is dissolved in ion-exchanged water or distilled water to prepare a thickener aqueous solution. Then, a predetermined amount of the hydrogen storage alloy powder having a predetermined particle size is dispersed to prepare a slurry having a desired viscosity. During the preparation of the slurry, when the hydrogen-absorbing alloy powder is supported on the conductive substrate in a layered manner, the interconnectivity of each alloy powder in the formed hydrogen-absorbing alloy layer is increased, and the slurry is dropped from the conductive substrate. In order to prevent this, a predetermined amount of, for example, polytetrafluoroethylene powder, polyethylene powder, polypropylene powder, polyvinylidene fluoride powder or the like is further blended as a binder, or the conductivity of the hydrogen storage alloy layer is increased. For example, a predetermined amount of a nickel powder, a cobalt powder, a copper powder, a carbon powder or the like is blended in order to improve the current collecting ability as a negative electrode.

After the above-mentioned conductive substrate is immersed in the slurry thus prepared, it is pulled up at a predetermined speed. As a result, when the conductive substrate is a mesh sheet, the viscous slurry fills the openings of the punched metal sheet and adheres to the surface at the same time, forming a slurry layer of a desired thickness. The obtained slurry-coated substrate was then treated with 8
After performing drying treatment at a temperature of 0 to 100 ° C. to remove water from the coating slurry and drying, by performing a rolling treatment at a predetermined pressure on the whole, the entire thickness is adjusted to a predetermined thickness, The dried slurry is carried in a state in which the slurry is in close contact with the conductive substrate.

When polyvinylidene fluoride powder is used as a binder, a heat treatment is performed for a desired time in a nitrogen atmosphere of, for example, about 150 to 210 ° C., following the above-mentioned rolling treatment. Measures have been taken to soften and bind the agent. As described above, when producing the hydrogen storage alloy electrode, powder components such as the hydrogen storage alloy powder, the conductive material powder, and the binder powder are formed into a viscous slurry with a thickener aqueous solution, and the slurry is applied to a conductive substrate. After that, a drying process and a rolling process are sequentially performed.

In the case of a positive electrode of a nickel-hydrogen secondary battery, a viscous paste is prepared by mixing powder components such as nickel hydroxide powder and conductive material powder which function as a positive electrode active material with water. It is manufactured by filling or coating a conductive substrate, followed by drying and rolling.
In either case, a slurry (or paste) in which the powder component is uniformly dispersed is prepared by mixing the solid powder component and the liquid thickener aqueous solution or water, and the slurry (or paste) is applied to the conductive substrate. It will be painted.

[0008]

In the above-described conventional method for manufacturing an electrode, when powders of a fluorine-based resin such as polytetrafluoroethylene or polyvinylidene fluoride are blended as a binder, these powders are formed into a slurry. It is preferable that they are uniformly dispersed in the inside. If it is unevenly distributed in the slurry, it will be unevenly distributed in the formed hydrogen storage alloy layer. And since all of these powders have strong water repellency, the places where these powders are unevenly distributed also show strong water repellency.

However, such a state impedes the battery reaction on the electrode surface, that is, the battery reaction that proceeds on the premise that the gas-liquid coexistence region is properly formed. Absent. Therefore, when a fluorine-based resin such as polytetrafluoroethylene or polyvinylidene fluoride is used as a binder,
Rather than using these in the form of solid powder, if they can be used in the form of a solution by dissolving them in a solvent, the binder can be uniformly present in the prepared slurry. The inconvenience can be almost completely eliminated.

As such a solvent, up to now, n- which can dissolve polyvinylidene fluoride is used.
Methyl-2-pyrrolidone is known and has been proposed to be applied to the production of lithium batteries (Japanese Patent Application Laid-Open No. Hei 6-3).
See JP-A-33566 and JP-A-7-335263). As described in the above prior art, this n-methyl-2-pyrrolidone is capable of dissolving polyvinylidene fluoride, and the resulting solution exhibits an appropriate viscosity. Can be prepared. That is, the solution is
It can be said that it also has the function as the above-mentioned aqueous solution of the thickener for the above-mentioned powder component.

However, since the boiling point of this n-methyl-2-pyrrolidone is 202 ° C., a conventional drying process for removing the n-methyl-2-pyrrolidone after the slurry is applied to the conductive substrate is used. If a temperature of about 140 to 180 ° C. employed during the drying process is applied, it takes a very long time to finish the drying. As described above, the use of n-methyl-2-pyrrolidone is effective in that polyvinylidene fluoride as a binder is uniformly present on the electrode surface, but on the other hand, lowers productivity during electrode production. This leads to the problem of causing

The present invention solves the above-mentioned problem when the powder component involved in the battery reaction is bound with polyvinylidene fluoride and the polyvinylidene fluoride is dissolved in n-methyl-2-pyrrolidone and used. It is another object of the present invention to provide a method for manufacturing a battery electrode which can shorten the drying time of the coating slurry.

[0013]

The present inventors have studied the properties of n-methyl-2-pyrrolidone in order to achieve the above object, and have obtained the following findings. First,
This n-methyl-2-pyrrolidone, as described above,
Dissolves polyvinylidene fluoride well. Then, the obtained solution becomes viscous.

Further, the n-methyl-2-pyrrolidone is freely mixed with water, and the polarity at that time is more stabilized than the polarity when polyvinylidene fluoride is dissolved. Therefore, n- in which polyvinylidene fluoride is dissolved
When methyl-2-pyrrolidone comes into contact with water, n-methyl-
2-Pyrrolidone moves toward water, and eventually, the dissolved polyvinylidene fluoride precipitates as a solid.

Based on the above findings, the present inventor has determined that a slurry prepared by using a solution of polyvinylidene fluoride dissolved in n-methyl-2-pyrrolidone is coated on a conductive substrate with water. The present invention was developed based on the idea that n-methyl-2-pyrrolidone would move toward water and polyvinylidene fluoride as a binder could remain on the coating slurry side if it was contacted. I came to.

That is, according to the method for producing a battery electrode of the present invention, a slurry is prepared by mixing a solution obtained by dissolving polyvinylidene fluoride in n-methyl-2-pyrrolidone and a powder component involved in a battery reaction. The slurry is applied to a conductive substrate to form a slurry-coated substrate, and then the slurry-coated substrate is brought into contact with water.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, first, a slurry is prepared by mixing a powder component involved in a battery reaction with a solution described later. Here, the powder component involved in the battery reaction is, as described above, a powder such as a hydrogen storage alloy powder, a nickel hydroxide powder, and a conductive material powder necessary for realizing a target battery reaction in an electrode to be manufactured. That is, these powder components are used for slurry preparation in a state where they are mixed at a predetermined ratio.

The above solution is obtained by dissolving polyvinylidene fluoride powder in n-methyl-2-pyrrolidone. At this time, the amount of polyvinylidene fluoride dissolved in n-methyl-2-pyrrolidone is set as follows. That is, the amount is such that the above-mentioned powder components can be properly bound while considering the solubility in n-methyl-2-pyrrolidone. If the amount to be dissolved is too large, the binding ability to the powder component becomes good, but on the other hand, the water repellency also becomes strong and hinders a good battery reaction, while if the amount to be dissolved is too small, This is because the binding ability to the powder component is reduced.

For this reason, the amount of polyvinylidene fluoride dissolved is preferably 0.1 to 5 parts by weight based on 100 parts by weight of the powder component. At this time, n-methyl-2-
The concentration of polyvinylidene fluoride dissolved in pyrrolidone is not particularly limited, but if the dissolved concentration is too high, the viscosity of the solution also increases, making it difficult to perform a slurry preparation operation of the powder component. If the viscosity is too low, the viscosity of the slurry will be too low, causing a problem of sagging after coating. Therefore, the solubility of polyvinylidene fluoride in n-methyl-2-pyrrolidone is 1%.
It is preferably about 15% by weight.

The solution thus prepared is mixed with the powder component to prepare a slurry having a desired viscosity.
Then, the slurry is applied to a conductive substrate in the same manner as in the related art, and immediately, the slurry-coated substrate is brought into contact with water. Specifically, the slurry-coated substrate may be put into water. As the water, for example, ion-exchanged water or distilled water is used, and the water temperature is preferably 50 ° C. or less.

By this treatment, n-methyl-2-pyrrolidone contained in the coating slurry moves toward water, and polyvinylidene fluoride is uniformly precipitated as a solid in the coating slurry. Thereafter, the slurry-coated substrate is taken out of the water, and the water adhering to the surface is dried and removed, for example, and then subjected to a rolling treatment in the same manner as in the related art to obtain a target electrode.

[0022]

EXAMPLES composition MmNi _3.3 Co _1.0 Mn _0.4 Al
A hydrogen storage alloy of _0.3 (Mm is a misch metal) is pulverized into a hydrogen storage alloy powder of 150 mesh or less (Tyler sieve), and a nickel powder having an average particle size of about 0.7 μm is added to 91 parts by weight of the alloy powder. Parts by weight were mixed to obtain a powder component.

On the other hand, 18 g of n-methyl-2-pyrrolidone
Was dissolved in 2 g of polyvinylidene fluoride powder having an average particle size of about 5 μm to prepare a solution having a polyvinylidene fluoride concentration of 10% by weight. The solution 2 was added to 100 parts by weight of the powder component.
0 parts by weight were added, and the whole was stirred and mixed to prepare a slurry.

Then, a punched nickel sheet (opening diameter 1.5 mm, opening ratio 38%, thickness 0.65 m) was added to the slurry.
m) was immediately immersed in distilled water (room temperature). Ten seconds later, when taken out of distilled water, the alloy powder and the nickel powder formed a film together with polyvinylidene fluoride. Thereafter, a drying treatment was performed at a temperature of 80 ° C. for 10 minutes. Then, rolling treatment was performed to form a 0.35 mm-thick hydrogen-absorbing alloy electrode of the example.

For comparison, a punching nickel sheet coated with a slurry was subjected to a drying treatment without being poured into distilled water. To remove n-methyl-2-pyrrolidone by drying, a temperature of 100 ° C. was used. Required a heat treatment of 60 minutes. Thereafter, a hydrogen storage alloy electrode was manufactured in the same manner as in the example, and this was used as a comparative example electrode.

These electrodes are set in an aqueous KOH solution having a concentration of 30%, and discharged at 70 mA / g at 70 mA / g for 5 hours, and discharged at 70 mA to a final voltage of 0.75 V (vsHg / HgO). Then, the discharge capacity of each electrode was examined. In each case, the discharge capacity per gram of the hydrogen storage alloy was 27.
It was 0 mAh.

[0027]

As is apparent from the above description, when a hydrogen storage alloy electrode is produced by the method of the present invention, the discharge capacity characteristics are not inferior to the conventional case without using a thickener aqueous solution during slurry preparation. It can be an electrode. This is because a solution obtained by dissolving polyvinylidene fluoride in n-methyl-2-pyrrolidone used in preparing the slurry is used as a thickener,
It also shows that it also functions as a binder.

In the present invention, the solvent applied to the conductive substrate is brought into contact with water to remove n-methyl-2-pyrrolidone, which is the solvent of the solution, in a short time. Long-time heat drying for removing the solvent is not required, and the process time can be reduced.

Claims (2)

[Claims] 1. A slurry prepared by mixing a solution obtained by dissolving polyvinylidene fluoride in n-methyl-2-pyrrolidone and a powder component involved in a battery reaction, and applying the slurry to a conductive substrate. Producing a slurry-coated substrate, and then contacting the slurry-coated substrate with water. 2. The method for producing an electrode for a battery according to claim 1, wherein the powder component involved in the battery reaction is mainly composed of a hydrogen storage alloy powder.