JP2000277102A - Manufacture of alkaline secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a secondary battery having high discharge capacity even if cobalt monoxide powder which has been kept on standby for a long time is utilized by providing a positive electrode containing cobalt monoxide powder formed by firing cobalt hydroxide powder with an antioxidant deposited on at least part of the surface of its each particle, and nickel hydroxide. SOLUTION: Cobalt hydroxide powder with an antioxidant deposited on at least part of the surface of its each particle is made by mixing an organic compound-based antioxidant such as phenyl-β-naphthylamine with cobalt hydroxide powder. Paste is prepared by adding nickel hydroxide powder, a binder such as polytetrafluoroethylene and water to the cobalt hydroxide powder and by kneading them, and a positive electrode 2 is made by applying the paste to a collector such as a punched metal, by drying it and by shaping the collector. This alkaline secondary battery is made by receiving an electrode group 5 composed by laminating and spirally rolling the positive electrode 2, a separator 3 and a negative electrode 4 in a bottomed cylindrical container 1 and by injecting an alkaline electrolyte such as a sodium hydroxide aqueous solution.

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 an alkaline secondary battery.

[0002]

2. Description of the Related Art Nickel cadmium secondary batteries and nickel hydrogen secondary batteries are known as alkaline secondary batteries. 2. Description of the Related Art In recent years, nickel-hydrogen secondary batteries have become mainstream due to the importance of high-capacity secondary batteries due to the spread of personal computers and mobile phones and environmental issues. Recently, electric vehicles (EVs) and assist type electric vehicles (HEs) which replace conventional gasoline engines have been developed.
V) has been actively developed, and a nickel-metal hydride secondary battery is used as a power source for these devices.

The positive electrode of a nickel hydride secondary battery is, for example,
By preparing a paste by kneading the nickel hydroxide powder, binder and conductive auxiliary agent in the presence of water, filling the paste into a current collector, drying, rolling, and cutting to a desired size. It is made. As the conductive auxiliary, for example,
Cobalt compounds such as cobalt monoxide and cobalt hydroxide;
Metal cobalt and the like can be mentioned. Cobalt monoxide among the conductive aids is dissolved in an alkaline electrolyte after assembling the secondary battery, precipitated on the surface of the nickel hydroxide powder as cobalt hydroxide, and is charged with cobalt oxyhydroxide (C
(OOOH). This conductive cobalt compound ensures conduction between the nickel hydroxides and between the nickel hydroxide and the current collector.

[0004] Cobalt monoxide powder is produced by firing cobalt hydroxide powder.

[0005]

However, when the cobalt monoxide powder produced by such a method is exposed to the atmosphere, the oxidation reaction proceeds, and a higher-order oxide (for example, It changes to cobalt (Co ₂ O ₃ ) or cobalt trioxide (Co ₃ O ₄ ). A positive electrode is manufactured using the cobalt monoxide powder containing a large amount of the higher oxide, and the obtained positive electrode is incorporated in an alkaline secondary battery and subjected to initial charging and the like. Since it is difficult to dissolve in the electrolyte, the amount of the conductive cobalt compound generated is insufficient. As a result, the obtained secondary battery has a problem that the utilization rate of the positive electrode is low and a high discharge capacity cannot be obtained.

[0006] For this reason, Japanese Patent Application Laid-Open No. H08-1043
No. 61 discloses that cobalt monoxide powder before use is stored in a film having a multilayer structure.
Further, Japanese Patent Application Laid-Open No. 7-134991 discloses that the surface of a cobalt monoxide powder is coated with a cobalt carbonate layer. However, such a storage method increases the manufacturing cost.

An object of the present invention is to provide a method of manufacturing an alkaline secondary battery capable of obtaining a high discharge capacity even using cobalt monoxide powder which has been kept on standby for a long period of time. is there.

[0008]

According to the present invention, there is provided a process for producing a cobalt monoxide powder by calcining a cobalt hydroxide powder having an antioxidant adhered to at least a part of its surface; Producing a positive electrode containing the cobalt monoxide powder. A method for producing an alkaline secondary battery, comprising:

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an alkaline secondary battery manufactured by the method according to the present invention will be described in detail with reference to FIG.

That is, an electrode group 5 produced by laminating the positive electrode 2, the separator 3, and the negative electrode 4 and winding them in a spiral shape is accommodated in the 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 disposed between the peripheral edge of the sealing plate 7 and the inner surface of the upper opening of the container 1, and the sealing plate is attached to the container 1 by caulking to reduce the diameter of the upper opening inward. 7 is hermetically fixed via the gasket 8. 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 provided with the sealing plate 7.
It is attached so as to cover the hole 6 above. A rubber safety valve 11 is disposed so as to close the hole 6 in a space surrounded by the sealing plate 7 and the positive electrode terminal 10.
Circular holding plate 12 made of an insulating material having a hole in the center
Are arranged on the positive electrode terminal 10 such that the protrusions of the positive electrode terminal 10 protrude from the holes of the holding plate 12. The outer tube 13 is provided on the periphery of the holding plate 12,
The side surface of the container 1 and the periphery of the bottom of the container 1 are covered.

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

1) Positive electrode 2 This positive electrode 2 is manufactured by the method described below. (First Step) A cobalt monoxide powder is prepared by firing a cobalt hydroxide powder having an antioxidant attached to at least a part of its surface.

It is desirable to use an organic compound-based antioxidant as the antioxidant. The organic compound-based antioxidant is preferable because it is decomposed at the time of firing and hardly remains in the produced cobalt monoxide powder. If the antioxidant remains, there is a possibility that the paste described later will have a variation such as an increase in viscosity, causing a variation in the filling property. Examples of the organic compound-based antioxidant include a free radical chain terminator that directly participates in the oxidation reaction to prevent oxidation, a peroxide decomposer, and a metal deactivator that acts as a catalyst in the oxidation reaction. Can be. Specifically, phenyl-β-naphthylamine, vitamin E,
Vitamin C, dibutyloxytoluene, guaiac butter and the like can be mentioned. As the antioxidant, one type or two or more types selected from the types described above can be used.

The cobalt hydroxide powder having an antioxidant adhered to at least a part of its surface is prepared, for example, by mixing the powdered antioxidant and the cobalt hydroxide powder, and coating the surface of the cobalt hydroxide powder with the antioxidant. It can be obtained by adding, applying a liquid antioxidant to the surface of the cobalt hydroxide powder, or attaching the antioxidant to the surface of the cobalt hydroxide powder by sputtering.

(Second step) The above-mentioned cobalt monoxide powder is added to the nickel hydroxide powder, and kneaded with a binder and water to prepare a paste. The paste is filled in a current collector, dried, and then dried. The positive electrode is manufactured by molding.

As the nickel hydroxide powder, for example, a powder consisting of nickel hydroxide alone or a nickel hydroxide powder in which zinc and / or cobalt are eutectic can be used. The latter positive electrode containing nickel hydroxide powder can further improve the charging efficiency in a high temperature state.

Examples of the binder include polytetrafluoroethylene, carboxymethylcellulose, methylcellulose, polyacrylates such as sodium polyacrylate and potassium polyacrylate, polyvinyl alcohol, and styrene butadiene rubber (SBR). be able to.

Examples of the current collector include a conductive substrate having a two-dimensional structure such as punched metal, expanded metal, and wire mesh, a foamed metal, and a fibrous three-dimensional substrate.

2) Negative Electrode 4 The negative electrode 4 is prepared by kneading a negative electrode active material, a conductive material and a binder together with water to prepare a paste, filling the paste into a conductive substrate, drying, and then molding. It is manufactured by

Examples of the negative electrode active material include a hydrogen storage alloy.

The hydrogen storage alloy is not particularly limited, and may be any as long as it can store hydrogen electrochemically generated in an electrolytic solution and can easily release the stored hydrogen during discharge. For example, LaNi ₅ , MmNi
₅ (Mm is misch metal), LmNi ₅ (Lm is La
At least one element selected from the group consisting of rare earth elements including Al), Mn, Co, Ti, Cu,
Examples thereof include a multi-element-based material substituted with an element such as Zn, Zr, Cr, and B, a TiNi-based material, and a TiFe-based material. In particular, the general formula LmNi _w Co _x Mn _y A
l _z (the total value of the atomic ratios w, x, y, z is 5.00 ≦ w +
(x + y + z ≦ 5.50) The hydrogen storage alloy having the composition represented by the formula (1) is preferable because it suppresses the pulverization accompanying the progress of the charge / discharge cycle and can improve the charge / discharge cycle life.

Examples of the conductive material include carbon black and graphite.

Examples of the binder include those similar to those described above for the positive electrode.

Examples of the conductive substrate include a two-dimensional substrate such as a punched metal, an expanded metal, and a nickel net, a 2.5-dimensional substrate formed by forming irregularities on the two-dimensional substrate, and a felt-like substrate. Metal porous body,
Examples include a three-dimensional substrate such as a sponge-like porous metal body.

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

4) Alkaline Electrolyte As the alkaline electrolyte, for example, an aqueous solution of sodium hydroxide (NaOH), lithium hydroxide (LiOH)
Aqueous solution, potassium hydroxide (KOH) aqueous solution, NaO
H and LiOH mixed solution, KOH and LiOH mixed solution, K
A mixed solution of OH, LiOH, and NaOH can be used.

In FIG. 1 described above, a separator is interposed between the positive electrode and the negative electrode, and the electrode group produced by spirally winding the separator is housed in the container.
For example, a laminate made by alternately stacking a positive electrode and a negative electrode with a separator interposed therebetween may be housed in a bottomed rectangular cylindrical container.

As described above, according to the method for manufacturing an alkaline secondary battery according to the present invention, a cobalt hydroxide powder having an antioxidant adhered to at least a part of its surface is fired to produce a cobalt monoxide powder. This can suppress the progress of the oxidation reaction when the cobalt monoxide powder is exposed to the atmosphere. By preparing such a positive electrode containing cobalt monoxide powder and nickel hydroxide and incorporating it into an alkaline secondary battery, the positive electrode can be prepared using the cobalt monoxide powder that has been on standby for a long time. An alkaline secondary battery having high utilization and discharge capacity can be realized.

That is, since the cobalt hydroxide powder lacks stability, it is easily oxidized during standby. Further, as compared with cobalt monoxide, higher-order oxides (dicobalt trioxide (Co ₂ O ₃ ) or cobalt trioxide (Co ₃ O ₄ ))
Etc.) are more stable. For this reason, the cobalt hydroxide powder is liable to change to a higher oxide instead of cobalt monoxide during standby. Cobalt monoxide powder produced by sintering cobalt hydroxide powder containing a large amount of high-order oxide contains a large amount of high-order oxide, and the oxidation reaction easily proceeds.

By adhering an antioxidant to at least a part of the surface of the cobalt hydroxide powder as in the present invention, oxidation of the cobalt hydroxide powder during standby can be suppressed. By calcining this cobalt hydroxide powder, a cobalt monoxide powder having a low content of higher oxides can be produced, so that a positive electrode is produced using this powder, and an alkaline secondary battery is assembled. Also, since a sufficient amount of cobalt monoxide powder can be dissolved in the alkaline electrolyte, the conductive cobalt compound can be sufficiently and uniformly generated in the positive electrode by initial charging or the like, and the discharge capacity is high. An alkaline secondary battery can be realized.

[0031]

Embodiments of the present invention will be described below in detail with reference to the drawings.

Example <Preparation of Positive Electrode> A cobalt monoxide powder was prepared by calcining a cobalt hydroxide powder having vitamin C as an antioxidant adhered to the surface.

The obtained cobalt monoxide powder was divided into six, and the first was placed in an atmosphere at 45 ° C. and a relative humidity of 50%.
Stored for days. The second was kept in the same atmosphere for 3 days. The third was kept in the same atmosphere for 5 days. Fourth is the same atmosphere 7
Stored for days. The fifth was kept in the same atmosphere for 10 days.
The rest were not stored.

10% by weight of each cobalt monoxide powder is added to 90% by weight of nickel hydroxide powder, and a binder consisting of 5% by weight of polytetrafluoroethylene and 3% by weight of carboxymethyl cellulose and 45% by weight of water are further added. A paste was prepared by adding and kneading. This paste is filled into a three-dimensional fiber substrate as a current collector, dried, roll-formed, and welded with a positive electrode lead to form a 6-dimensional fiber substrate.
Various kinds of positive electrodes were produced.

<Preparation of Negative Electrode> A binder composed of 1.5% by weight of polytetrafluoroethylene, 0.5% by weight of sodium polyacrylate and 0.12% by weight of carboxymethylcellulose was added to 100% by weight of a hydrogen storage alloy powder. A paste was prepared by adding and mixing 1% by weight of carbon black and 50% by weight of water as conductive agents. This paste was applied to punched metal, dried, and then pressed to form a negative electrode.

Next, a nonwoven fabric made of polyolefin having been subjected to hydrophilic treatment was interposed between each of the positive electrode and the negative electrode as a separator, and spirally wound to form an electrode group.
After this electrode group is housed in a cylindrical container having a bottom, 2.5 ml of an alkaline electrolyte mainly composed of KOH is injected, and the AA size (theoretical capacity: 1200
Six types of mAh) cylindrical nickel-metal hydride secondary batteries were assembled.

Comparative Example A cobalt monoxide powder was prepared by calcining a cobalt hydroxide powder containing no antioxidant. Divide the obtained cobalt monoxide powder into six,
The five groups were stored under the same conditions as described above. The rest was not stored.

Except for using such cobalt monoxide powder, six types of cylindrical nickel-metal hydride secondary batteries were assembled in the same manner as in the above-described embodiment.

With respect to the obtained secondary batteries of Examples and Comparative Examples, after discharging for 15 hours at 0.1 CA and discharging to 1.0 V at 0.2 CA, the discharge capacity was measured. Shown in

As is apparent from FIG. 2, the secondary battery of the embodiment including the cobalt monoxide powder produced by calcining the cobalt hydroxide powder having an antioxidant adhered to the surface thereof is high in temperature and high humidity. It can be seen that high discharge capacity can be maintained even when cobalt monoxide stored in air for 10 days is used.

On the other hand, the secondary battery of the comparative example containing the cobalt monoxide powder prepared by calcining the cobalt hydroxide powder to which no antioxidant was added was stored in a humid air at a high temperature. When using cobalt monoxide, it turns out that discharge capacity falls as storage days increase.

[0042]

As described in detail above, according to the present invention, it is possible to manufacture an alkaline secondary battery capable of obtaining a high discharge capacity even using cobalt monoxide powder which has been kept on standby for a long period of time. A method can be provided.

[Brief description of the drawings]

FIG. 1 is a partially cutaway perspective view showing an example of an alkaline secondary battery according to the present invention.

FIG. 2 is a characteristic diagram showing a relationship between storage conditions and discharge capacity of cobalt monoxide powder in the nickel-metal hydride secondary batteries of Examples and Comparative Examples.

[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 (1)

[Claims] 1. A step of producing a cobalt monoxide powder by firing a cobalt hydroxide powder having an antioxidant attached to at least a part of its surface; and producing a positive electrode containing nickel hydroxide and said cobalt monoxide powder. A method for producing an alkaline secondary battery.