JP2000123837A - Paste for alkaline secondary battery, manufacture of paste type electrode and manufacture of alkaline secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide paste capable of restraining a viscosity change during storage without impairing a charge/discharge characteristic by including an active material, an organic binder and a specific quantity of ammonia. SOLUTION: Ammonia not more than 800 ppm to weight of an organic binder is included. A paste type electrode is desirably manufactured by having a process of adjusting paste containing an active material, an organic binder and ammonia not more than 800 ppm to weight of the organic binder and a process of filling the paste in a conductive core body. A positive electrode 2, a separator 3 and a negative electrode 4 are laminated and wound to be housed in a vessel 1. The negative electrode 4 is arranged on the outermost periphery in contact with the vessel 1. An insulating gasket 8 airtightly fixes a sealing plate 7 by calking for reducing the opening part of the vessel 1. In a positive electrode lead 9, one end is connected to the positive electrode, and the other end is connected to the under surface of the sealing plate 7. A rubber-made safety valve 11 is arranged so as to block up a hole 6, and an enclosing tube 13 covers the side surface of the vessel 1, a presser plate 12 and the bottom part peripheral edge.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing a paste for an alkaline secondary battery, a paste-type electrode, and a method for producing an alkaline secondary battery.

[0002]

2. Description of the Related Art As alkaline secondary batteries, nickel cadmium secondary batteries and nickel hydrogen secondary batteries are known. Due to the increasing demand for high-capacity batteries due to the recent spread of PCs (personal computers) and mobile phones, and environmental issues, nickel-metal hydride secondary batteries have become mainstream as alkaline secondary batteries.

By the way, the positive electrode of an alkaline secondary battery includes:
Pasted nickel positive electrodes have been widely used in place of conventional sintered nickel positive electrodes. Paste nickel positive electrode
For example, a paste is prepared by kneading nickel hydroxide powder as an active material, a cobalt compound as a conductive auxiliary, a binder and water, filling the conductive core with the paste, drying and rolling, It is produced by cutting to desired dimensions.

As the binder of the paste, one containing an organic binder is used. The organic binder serves as a kneading agent and a binder in the paste, enhances the fluidity of the paste, and plays a role in suppressing sedimentation and separation when the paste is stored. Such organic binders include, for example, carboxymethyl cellulose (CMC), methyl cellulose (MC), sodium polyacrylate (SPA),
Hydroxypropyl methylcellulose (HPMC). The viscosity of the paste can be adjusted by combining several types of organic binders.

[0005]

However, in the paste containing the organic binder, bacteria may propagate during storage and the viscosity may fluctuate. If the viscosity of the paste deviates from an appropriate value, it becomes difficult to uniformly fill the conductive core with the paste, so that the amount of paste filling in the positive electrode is biased. When an alkaline secondary battery is assembled from such a positive electrode, charge / discharge reactions occur nonuniformly in the positive electrode, so that sufficient charge / discharge characteristics cannot be obtained. Therefore, when an alkaline secondary battery is manufactured using the paste containing the organic binder, there is a problem that the yield is low.

The present invention relates to an alkaline secondary battery paste containing an organic binder, which can suppress a change in viscosity during storage without impairing the charge / discharge characteristics of the alkaline secondary battery. It is intended to provide.

According to the present invention, in a method of manufacturing a paste type electrode using a paste containing an organic binder, a change in viscosity during storage of the paste can be suppressed without impairing the charge / discharge characteristics of the alkaline secondary battery, and the yield can be reduced. It is an object of the present invention to provide an improved paste-type electrode manufacturing method.

The present invention relates to a method of manufacturing an alkaline secondary battery having a paste-type electrode in which a paste containing an organic binder is filled in a conductive core, wherein a change in viscosity during storage of the paste is suppressed without impairing charge / discharge characteristics. It is an object of the present invention to provide a method of manufacturing an alkaline secondary battery that can improve the yield.

[0009]

The paste for an alkaline secondary battery according to the present invention contains an active material, an organic binder and 800 ppm or less of ammonia based on the weight of the organic binder. is there.

The method for producing a paste electrode according to the present invention comprises the steps of preparing a paste containing an active material, an organic binder, and 800 ppm or less of ammonia based on the weight of the organic binder; And filling the body.

In the method for manufacturing an alkaline secondary battery according to the present invention, at least one of the positive electrode and the negative electrode may contain 800 ppm or less of ammonia, based on the weight of the active material, the organic binder, and the organic binder. And a step of filling the conductive core with the paste.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An alkaline secondary battery (for example, a cylindrical alkaline secondary battery) manufactured by the method according to the present invention will be described below with reference to FIG.

An electrode group 5 produced by laminating a positive electrode 2, a separator 3, and a negative electrode 4 and winding them in a spiral shape is accommodated in a bottomed cylindrical container 1. The negative electrode 4 is arranged at the outermost periphery of the electrode group 5 and is in electrical contact with the container 1. The alkaline electrolyte is contained in the container 1. A circular first sealing plate 7 having a hole 6 in the center is arranged at the upper opening of the container 1. The ring-shaped insulating gasket 8 is
Is arranged between the periphery of the container and the inner surface of the upper opening of the container 1,
The sealing plate 7 is airtightly fixed to the container 1 via the gasket 8 by caulking to reduce the diameter of the upper opening inward. One end of the positive electrode lead 9 is connected to the positive electrode 2, and the other end is connected to the lower surface of the sealing plate 7. The positive electrode terminal 10 having a hat shape is attached on the sealing plate 7 so as to cover the hole 6. Rubber safety valve 1
1 is arranged so as to close the hole 6 in a space surrounded by the sealing plate 7 and the positive electrode terminal 10. A circular holding plate 12 made of an insulating material having a hole in the center is provided on the positive electrode terminal 10 so that the projection of the positive electrode terminal 10 is provided on the holding plate 1.
2 so as to protrude from the holes. The outer tube 13 covers the periphery of the holding plate 12, the side surface of the container 1, and the periphery of the bottom of the container 1.

Next, the positive electrode 2, the negative electrode 4, the separator 3
And the electrolyte will be described.

2) Positive Electrode 2 The positive electrode 2 includes, for example, nickel hydroxide powder as an active material, a conductive auxiliary, an organic binder, and a paste containing 800 ppm or less of ammonia and water based on the weight of the organic binder. It is prepared by filling the paste into a conductive substrate, drying it, and pressing it. In addition, cutting is performed after pressure molding as needed. Cutting may be performed after drying and after pressing.

As the nickel hydroxide powder, for example, a single nickel hydroxide powder or a nickel hydroxide powder in which a metal such as zinc, cobalt, bismuth, or copper is coprecipitated with metallic nickel can be used. In particular, the latter positive electrode containing nickel hydroxide powder can further improve the charging efficiency in a high-temperature state.

Examples of the conductive auxiliary include metal cobalt, cobalt oxide, cobalt hydroxide and the like.

Examples of the organic binder include:
A copolymer of a monomer having a carboxyl group such as acrylic acid and vinyl alcohol, carboxymethylcellulose (CMC), methylcellulose (MC), hydroxypropylmethylcellulose (HPMC), polyacrylates, such as sodium polyacrylate (SPA);
Potassium polyacrylate｝, polyvinyl alcohol (P
VA), polyethylene oxide, polyethylene, polypropylene and the like. As the organic binder, one or more kinds selected from the above-mentioned kinds can be used. Among them, a copolymer of a monomer having a carboxyl group such as acrylic acid and vinyl alcohol, CMC, HPMC, and SPA are preferred.

The paste may include another kind of binder different from the organic binder. Examples of such a binder include a rubber-based binder such as a fluorine-based resin {for example, polytetrafluoroethylene (PTFE)} and styrene-butadiene rubber (SBR). PTFE can be used in the form of a dispersion.

The reason why the amount of ammonia contained in the paste is set to 800 ppm or less based on the weight of the organic binder is that if it is more than 800 ppm, the self-discharge rate of the alkaline secondary battery may increase. This is presumed to be due to the mechanism described below. That is, when the amount of ammonia in the paste increases, nitrite ions and nitrate ions are easily generated. The nitrite ion is oxidized by oxygen generated by the decomposition of NiOOH contained in the charged positive electrode to become nitrate ion. On the other hand, nitrate ions are reduced at the negative electrode into nitrite ions. This nitrite ion reacts with newly generated oxygen due to the decrease in oxygen partial pressure, and becomes nitrate ion again. Since the self-discharge reaction is promoted by the shuttle effect in which the reduction of nitrate ions and the oxidation of nitrite ions are repeated between the positive and negative electrodes, the self-discharge rate tends to increase. Incidentally, it is desirable that the lower limit of the amount of ammonia in the paste is 10 ppm based on the weight of the organic binder. If the amount of ammonia is less than 10 ppm, it may be difficult to sufficiently suppress the growth of bacteria during paste storage. Therefore, the amount of ammonia in the paste is preferably in the range of 10 to 800 ppm based on the weight of the organic binder.

The conductive core may be, for example, a two-dimensional material such as a mesh, sponge, fibrous, or felt metal porous body made of nickel, stainless steel, or nickel-plated metal, and punched metal. A material having irregularities on the periphery of the hole of the substrate can be used.

2) Negative Electrode 4 The negative electrode 4 is made of, for example, a hydrogen storage alloy powder as a host matrix of hydrogen as an active material, a conductive material, an organic binder, and 800 p with respect to the weight of the organic binder.
After preparing a paste containing ammonia and water at pm or less, filling the paste into a conductive substrate, and drying,
It is produced by pressure molding. In addition, cutting is performed after pressure molding as needed. Cutting may be performed after drying and after pressing.

As the hydrogen storage alloy, for example, La
Ni _5, MmNi ₅ (Mm is misch metal), LmN
i ₅ (Lm is a La-enriched misch metal), and a multi-element alloy in which a part of Ni of these alloys is substituted by at least Al and Mn. The above-described multi-element hydrogen storage alloy has Al and Mn as substitution elements for Ni.
In addition, at least one element selected from Co, Ti, Cu, Zn, Zr, Cr and B may be included.
Above all, the general formula _{LnNi w Co x Al y Mn z} ( However, Ln is a rare earth element, the atomic ratio w, x, y, z respectively 3.30 ≦ w ≦ 4.50,0.50 ≦ x ≦ 1.10 ,
0.20 ≦ y ≦ 0.50, 0.05 ≦ z ≦ 0.20,
And the total value is 4.90 ≦ w + x + y + z ≦ 5.50
Is preferably used. More preferable values of the atomic ratio w, x, y, z are 3.80 ≦ w ≦ 4.20, 0.70 ≦ x ≦ 0.90, respectively.
0.30 ≦ y ≦ 0.40, 0.08 ≦ z ≦ 0.13,
And the total value is 5.00 ≦ w + x + y + z ≦ 5.20
It is.

As the conductive material, for example, carbon black, graphite or the like can be used.

As the organic binder, at least one selected from the same types as those described for the positive electrode can be used. Among them, a copolymer of a monomer having a carboxyl group such as acrylic acid and vinyl alcohol, CMC, HPMC, and SPA are preferred.

The paste may contain another type of binder different from the organic binder. Examples of such a binder include those similar to those described above for the positive electrode.

The reason why the amount of ammonia contained in the paste is set to 800 ppm or less based on the weight of the organic binder is that if it exceeds 800 ppm, the self-discharge rate of the alkaline secondary battery may increase. The lower limit of the amount of ammonia in the paste is desirably 10 ppm based on the weight of the organic binder. If the amount of ammonia is less than 10 ppm, it may be difficult to sufficiently suppress the growth of bacteria during paste storage. Therefore, the amount of ammonia in the paste is preferably in the range of 10 to 800 ppm based on the weight of the organic binder.

Examples of the conductive core include a two-dimensional substrate such as punched metal, expanded metal, and wire mesh, and a three-dimensional substrate such as a felt-like metal porous body and a sponge-like metal substrate.

As the negative electrode 4, a dry-type hydrogen storage alloy negative electrode or a sintered-type hydrogen storage alloy negative electrode described below can be used instead of the paste-type hydrogen storage alloy negative electrode described above.

The dry hydrogen storage alloy negative electrode is manufactured by kneading a hydrogen storage alloy powder, a conductive material and a fluorine-based resin as a binder to form a sheet, and pressing the obtained sheet to a conductive core. As the hydrogen storage alloy, the conductive material, the fluororesin, and the conductive core, the same materials as described above can be used.

3) Separator 3 Examples of the separator 3 include a nonwoven fabric made of polyamide fiber, a nonwoven fabric made of polyolefin fiber such as polyethylene and polypropylene, or a nonwoven fabric provided with a hydrophilic functional group.

4) Alkaline Electrolyte As the alkaline electrolyte, for example, a mixed solution of sodium hydroxide (NaOH) and lithium hydroxide (LiOH),
A mixture of potassium hydroxide (KOH) and LiOH, KOH
And a mixed solution of LiOH and NaOH.

The above-described paste for an alkaline secondary battery according to the present invention contains an active material, an organic binder, and 800 ppm or less of ammonia based on the weight of the organic binder. In such a paste, the propagation of bacteria can be suppressed by the effect of the preservative of ammonia, so that the viscosity can be maintained substantially constant during storage. For this reason, by filling the conductive core with the paste, it is possible to produce a paste electrode having a uniform paste filling amount with a high yield. Further, when a paste-type electrode containing an organic binder is used as at least one of the positive electrode and the negative electrode of the alkaline secondary battery, by manufacturing this electrode using the paste containing the specific concentration of ammonia described above, The yield can be improved while maintaining excellent self-discharge characteristics.

[0034]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below in detail with reference to the drawings.

(Examples 1 to 3 and Comparative Example 1) <Preparation of Paste for Positive Electrode> A mixture composed of 90 parts of nickel hydroxide powder and 10 parts of cobalt monoxide was stirred with a mixer, and then 0.2 parts of CMC and 0.2 parts of SPA were mixed. Parts of an organic binder and 40 parts of water were added and kneaded,
The amount of ammonia shown in Table 1 below was added to the weight of the organic binder, and the mixture was further wet-stirred to prepare a paste having a viscosity of 20,000 cp.

Table 1 Amount of ammonia based on the weight of organic binder Example 1 10 ppm Example 2 100 ppm Example 3 800 ppm Comparative example 1 1000 ppm (Comparative example 2) <Preparation of positive electrode paste> 90 parts of nickel hydroxide powder and cobalt monoxide After stirring the mixture consisting of 10 parts with a mixer, an organic binder consisting of 0.2 parts of CMC and 0.2 parts of SPA and 40 parts of water were added and kneaded.
The amount of ammonia shown in Table 1 below was added to the weight of the organic binder, and the mixture was further wet-stirred to prepare a paste having a viscosity of 20,000 cp.

The obtained pastes of Examples 1 to 3 and Comparative Examples 1 and 2 were stored at room temperature and stored for 1 day, 3 days, 5 days.
On days 10 and 10, the paste viscosity was measured with a B-type viscometer, and the results are shown in FIG.

As is clear from FIG. 2, the pastes of Examples 1 to 3 and Comparative Example 1 containing ammonia can maintain a constant viscosity during storage. In contrast, it can be seen that the viscosity of Comparative Example 2 containing no ammonia increases during storage.

Then, pastes of Examples 1 to 3 and Comparative Examples 1 and 2 were newly prepared, and an alkaline secondary battery was assembled using each paste.

First, each paste was filled in a three-dimensional fiber substrate, dried, and then rolled to produce five types of positive electrodes.

<Preparation of Negative Electrode> The composition was LmNi _4.0 Co
Hydrogen storage alloy powder 10 represented by _0.4 Mn _0.3 Al _0.3
0% by weight of sodium polyacrylate 0.5% by weight, carboxymethyl cellulose (CMC) 0.12% by weight,
A paste was prepared by adding 1.0% by weight of carbon black as a conductive material and mixing with 50% by weight of water. The obtained paste was applied to a punched metal as a conductive substrate, dried, and further pressed to produce a negative electrode.

Next, a separator made of a non-woven fabric made of polyolefin subjected to a hydrophilic treatment was interposed between each of the negative electrode and the positive electrode, and spirally wound to form an electrode group. After storing such an electrode group in a bottomed cylindrical container,
Containing an alkaline electrolyte mainly composed of potassium hydroxide,
An AA-size cylindrical nickel-metal hydride secondary battery having the above-described structure shown in FIG. 1 and having a theoretical capacity of 1200 mAh was assembled by performing sealing and the like.

The obtained Examples 1-3 and Comparative Examples 1-2
Was subjected to three cycles of charge and discharge, and the reference capacity was measured. Next, the battery was charged at 0.2 C at 150%, stored at 45 ° C. for 14 days, and the discharge capacity was measured. The difference between the reference capacity and the discharge capacity after storage was calculated, and the self-discharge rate was determined from the ratio of this capacity difference to the reference capacity. The result is shown in FIG.

As is apparent from FIG. 3, Examples 1 to 3 each having a positive electrode produced using a paste in which the amount of ammonia relative to the weight of the organic binder is 800 ppm or less.
It can be seen that the secondary battery of Comparative Example 1 has a lower self-discharge rate than the secondary battery of Comparative Example 1 including the positive electrode manufactured using the paste having an ammonia amount exceeding 800 ppm.

Therefore, it can be seen from FIGS. 2 and 3 that the yield can be improved without impairing the self-discharge characteristics by manufacturing an alkaline secondary battery using a paste in which the amount of ammonia relative to the weight of the organic binder is 800 ppm or less. I understand.

In the above-described embodiment, the separator is interposed between the positive electrode and the negative electrode and spirally wound and accommodated in the cylindrical container 1 having a bottom. It is not limited to a simple structure. For example, the present invention can be similarly applied to a prismatic alkaline secondary battery in which a separator is interposed between a positive electrode and a negative electrode, and a laminate of a plurality of such layers is housed in a bottomed rectangular cylindrical container.

[0047]

As described above, according to the present invention, there is provided a paste for an alkaline secondary battery capable of suppressing a change in viscosity during storage without impairing the charge / discharge characteristics of the alkaline secondary battery. Can be. Further, according to the present invention, it is possible to provide a method of manufacturing a paste-type electrode in which the change in viscosity during paste storage can be suppressed without impairing the charge / discharge characteristics of the alkaline secondary battery, and the yield is improved. . Further, according to the present invention, it is possible to provide a method for manufacturing an alkaline secondary battery in which a change in viscosity during paste storage can be suppressed without impairing charge / discharge characteristics, and the yield is improved.

[Brief description of the drawings]

FIG. 1 is a perspective view showing an alkaline secondary battery manufactured by a method according to the present invention.

FIG. 2 is a characteristic diagram showing a relationship between paste storage days and paste viscosity in the alkaline secondary batteries of Examples 1 to 3 and Comparative Examples 1 and 2.

FIG. 3 is a characteristic diagram showing the relationship between the amount of ammonia in a paste and the self-discharge rate in the alkaline secondary batteries of Examples 1 to 3 and Comparative Examples 1 and 2.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Container, 2 ... Positive electrode, 3 ... Separator, 4 ... Negative electrode, 5 ... Electrode group, 7 ... Sealing plate, 8 ... Insulating gasket.

Claims (3)

[Claims] 1. A paste for an alkaline secondary battery, comprising an active material, an organic binder, and 800 ppm or less of ammonia based on the weight of the organic binder. 2. A process for preparing a paste containing 800 ppm or less of ammonia based on the weight of the active material, the organic binder, and the organic binder, and filling the conductive core with the paste. A method for producing a paste-type electrode. 3. A step of preparing a paste containing at least one of a positive electrode and a negative electrode, the paste containing an active material, an organic binder, and 800 ppm or less of ammonia based on the weight of the organic binder. And a step of filling the conductive core.