JPH10255779A - Method for manufacturing nickel-metal hydride storage battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form a surface layer having high catalytic ability for hydrogen electrode reaction on a hydrogen storage alloy powder by a simpler operation and more stably, and to use such a material as a negative electrode constituting material. It is an object of the present invention to provide a method of manufacturing a nickel-metal hydride storage battery having improved high-current discharge characteristics and low-temperature characteristics at the beginning of a cycle. SOLUTION: A positive electrode containing nickel hydroxide, a negative electrode,
A method for producing a nickel-metal hydride storage battery comprising an alkaline electrolyte, comprising: a step of immersing a hydrogen storage alloy powder in an acidic aqueous solution containing nickel ions; and a step of producing a negative electrode containing the hydrogen storage alloy powder. A method for manufacturing a nickel-metal hydride storage battery.

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 nickel-metal hydride battery having an improved negative electrode.

[0002]

2. Description of the Related Art A nickel-metal hydride storage battery having a structure using a hydrogen storage alloy as a negative electrode has a larger capacity per volume than a conventional nickel cadmium storage battery, and is therefore widely used as a power source for portable equipment. On the other hand, portable devices are required to have higher performance, and accordingly, power consumption is increasing remarkably. For this reason, nickel-metal hydride storage batteries tend to be required to be discharged by a larger current. The large current discharge characteristics of the nickel-metal hydride storage battery are improved by increasing the surface area of the hydrogen storage alloy as the pulverization of the hydrogen storage alloy progresses with the progress of charge / discharge, but the charge / discharge characteristic of the alloy having a small surface area is increased. Especially low at the beginning of the cycle.

As a means for improving the large current discharge characteristics, a hydrogen storage alloy powder is immersed in a high-concentration aqueous alkali solution or a dilute acid aqueous solution, the powder surface is etched, and the hydrogen electrode among the components contained in the alloy is removed. There is known a method of forming a surface layer containing a large amount of a component having a high catalytic activity (for example, nickel) in an alloy powder, increasing the surface area of the alloy powder, and manufacturing a negative electrode using such an alloy powder. .

However, in the treatment with an aqueous alkali solution, it is essential to use an aqueous solution having an extremely high alkali concentration. In addition, since the progress is slow near room temperature, it is necessary to maintain the liquid temperature at a high temperature during the treatment. There is a problem. On the other hand, the treatment with an acid is more corrosive than the treatment with an alkaline aqueous solution, so that treatment at room temperature is possible and treatment with a dilute solution that does not affect the human body is possible, If the processing conditions fluctuate, a surface having high catalytic ability may not be obtained even when corrosion is in progress, and there is a problem that it is difficult to obtain stable characteristics. Moreover, according to the acid treatment, it is difficult to selectively leave only the target component on the alloy surface,
The catalytic ability of the surface layer was likely to be insufficient, and satisfactory large-current discharge characteristics could not be obtained.

There is also known an electroless plating method in which a hydrogen storage alloy powder is immersed in a solution containing nickel or copper, and a reducing agent is added thereto to coat the alloy particles with a metal precipitated. However, there is a problem that the processing procedure is complicated.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to form a surface layer having a high catalytic activity for a hydrogen electrode reaction on a hydrogen storage alloy powder by a simpler operation and more stably. An object of the present invention is to provide a method for manufacturing a nickel-metal hydride storage battery in which a large current discharge characteristic and a low-temperature characteristic are improved particularly in the early stage of a cycle by using the material.

[0007]

A method of manufacturing a nickel-metal hydride storage battery according to the present invention is a method of manufacturing a nickel-metal hydride storage battery including a positive electrode containing nickel hydroxide, a negative electrode, and an alkaline electrolyte. It is characterized by comprising a step of immersing the hydrogen storage alloy powder in an acidic aqueous solution containing ions and a step of producing a negative electrode containing the hydrogen storage alloy powder.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An example of a nickel-metal hydride storage battery (cylindrical nickel-metal hydride storage battery) manufactured by the method according to the present invention will be described below with reference to FIG. An electrode group 5 formed by laminating a positive electrode 2, a separator 3, and a negative electrode 4 in a cylindrical container 1 with a bottom and winding it spirally.
Is stored. 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 formed on the container 1 by caulking to reduce the diameter of the upper opening inward. 7 is hermetically fixed via the gasket 8. Positive electrode lead 9
Has one end connected to the positive electrode 2 and the other end connected to the lower surface of the sealing plate 7. The positive electrode terminal 10 having a hat shape is
It is mounted on the sealing plate 7 so as to cover the hole 6. 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. A circular holding plate 12 made of an insulating material having a hole in the center is provided on the positive terminal 10 on the positive terminal 10.
Are arranged so as to protrude from the holes of the holding plate 12. The outer tube 13 is provided with the holding plate 1.
2, the side of the container 1 and the bottom of the container 1.

Next, the positive electrode 2, the negative electrode 4, the separator 3
And the electrolyte will be described. 1) Positive electrode 2 The positive electrode 2 is prepared, for example, by adding a conductive material to nickel hydroxide powder as an active material, kneading the mixture with a polymer binder and water to prepare a paste, and filling the paste into a conductive substrate. After drying and drying, it is produced by molding.

Examples of the conductive material include cobalt oxide, cobalt hydroxide, metallic cobalt, metallic nickel, carbon and the like. Examples of the polymer binder include carboxymethyl cellulose, methyl cellulose, sodium polyacrylate, and polytetrafluoroethylene.

As the conductive substrate, for example, a mesh-like, sponge-like, fiber-like, or felt-like porous metal body formed of nickel, stainless steel, or nickel-plated metal can be given.

2) Negative electrode 4 The negative electrode 4 includes, for example, a step of immersing the hydrogen storage alloy powder in an acidic aqueous solution containing nickel ions, a step of washing the alloy powder with water and drying it in an inert atmosphere. A step of preparing a paste by kneading the alloy powder, the conductive material and the binder in the presence of a solvent (for example, water); a step of filling the paste into a conductive substrate; a step of drying; And a method comprising the steps of:

The hydrogen storage alloy is not particularly limited, and may be any alloy capable of storing hydrogen electrochemically generated in an electrolytic solution and easily releasing the stored hydrogen during discharge. . As this hydrogen storage alloy,
For example, (a) a rare earth - Ni-based hydrogen storage alloy (for _{example, LaNi 5, MmNi 5 (Mm} ; misch metal), LmNi ₅ (Lm; lanthanum enriched misch metal), or some of these Ni Al, Mn, C
o, Ti, Cu, Zn, Zr, Cr, B, etc.), (b) Ti-Ni hydrogen storage alloy, (c) Ti-Fe hydrogen storage alloy, e) Ti
-V-Ni-based hydrogen storage alloys, (f) Zr-V-Ni-based hydrogen storage alloys, (g) Mg-based hydrogen storage alloys, and (h) Laves phase hydrogen storage alloys. Above all, a rare earth-nickel-based hydrogen storage alloy is preferable. In particular, the general formula L
mNi _x Mn _y A _z (However, A is shown Al, at least one metal selected from Co, the atomic ratio x, y, z is the total value of 4.8 ≦ x + y + z ≦ 5.4) is represented by Are preferred.

The average particle size of the hydrogen storage alloy powder is 20
It is good to set it in the range of μm to 50 μm. The acidic aqueous solution containing nickel ions means an aqueous solution containing nickel ions having a pH of 1 or more and less than 7. Above all, from the viewpoint of removing the surface oxide of the alloy to some extent quickly and suppressing the elution rate of the alloy to an appropriate range, the pH is suitably 2 to 4.

The concentration of the nickel ions is 0.05 m
It is preferably in the range of ol / l to 0.5 mol / l. This is due to the following reasons. When the concentration is less than 0.05 mol / l, the time required for the reaction is prolonged, and the workability may be reduced. On the other hand, when the concentration exceeds 0.5 mol / l, precipitation may occur when other salts or acids for adjusting pH are added.
A more preferable concentration is 0.08 mol / l to 0.4 mo.
1 / l range.

The acidic aqueous solution containing nickel ions is as follows:
Cobalt ions may be added. By treating the hydrogen storage alloy powder with such an aqueous solution, the high current discharge characteristics and the low temperature characteristics of the nickel-metal hydride storage battery can be further improved.

The concentration of the cobalt ion is preferably in the range of 0.05 mol / l to 0.5 mol / l for the same reason as described for the nickel ion concentration. A more preferred concentration is 0.08 mo
It is in the range of 1 / l to 0.4 mol / l.

Examples of the binder include those similar to those used in the positive electrode 2. As the conductive material, for example, carbon black or the like can be used.

Examples of the conductive substrate include a two-dimensional substrate such as a punched metal, an expanded metal, a perforated rigid plate, and a nickel net, and a three-dimensional substrate such as a felt-like metal porous body and a sponge-like metal substrate. be able to.

3) Separator 3 The separator 3 is made of, for example, a polymer non-woven fabric such as a polypropylene non-woven fabric, a nylon non-woven fabric, or a non-woven fabric obtained by mixing polypropylene fibers and nylon fibers. In particular, a polypropylene nonwoven fabric whose surface has been hydrophilized is suitable as a separator.

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.

In FIG. 1 described above, the separator 3 is interposed between the positive electrode 2 and the negative electrode 4 and spirally wound and accommodated in the bottomed cylindrical container 1, but can be obtained by the method of the present invention. The nickel-metal hydride storage battery is not limited to such a structure. For example, the present invention can be similarly applied to a square nickel-metal hydride storage battery having a configuration in which a stacked body in which a plurality of positive and negative electrodes are stacked with a separator interposed therebetween is housed in a bottomed rectangular cylindrical container.

As described in detail above, according to the method for manufacturing a nickel-metal hydride storage battery according to the present invention, a negative electrode is manufactured by a method including a step of immersing a hydrogen storage alloy powder in an acidic aqueous solution containing at least nickel ions. By performing such an immersion treatment, the oxide film formed on the surface of the alloy powder can be eluted and removed in the aqueous solution, and nickel or a nickel compound can be precipitated on the surface of the alloy powder. . When a negative electrode is manufactured from such an alloy powder and a nickel-metal hydride battery is manufactured, most of the nickel compounds deposited on the surface of the alloy powder are reduced to metal at the first charge, so that the abundance ratio of metallic nickel on the surface of the alloy powder is reduced. Can be formed. By increasing the existing ratio of metallic nickel in the surface layer,
The catalytic ability of the surface layer in the hydrogen electrode reaction can be improved. As a result, the storage battery can realize excellent large-current discharge characteristics and low-temperature discharge characteristics even at the beginning of a charge / discharge cycle. Further, by adding cobalt ions to the acidic aqueous solution, it is possible to form a layer having a high content ratio of metallic nickel and metallic cobalt on the surface of the alloy powder. It is presumed that such a surface layer not only can improve the catalytic ability in the hydrogen electrode reaction, but also can improve the hydrogen storage / release reaction rate and oxidation resistance of the alloy. Discharge characteristics can be further improved.

It is presumed that the metal nickel layer can be selectively formed on the surface of the alloy powder by the immersion treatment due to the mechanism described below. That is, a hydrogen storage alloy (for example, a rare earth-nickel system) has a high reactivity with hydrogen and an electrochemically low element (for example,
La etc.). When such an alloy powder is immersed in an acidic aqueous solution containing electrochemically noble ions such as nickel ions, the above-mentioned noble elements are eluted into the solution, and the noble ions are reduced and the Precipitates on the alloy powder surface. Since a relatively large amount of hydrogen ions is present in an acidic aqueous solution, whether or not an element having a redox potential close to that of hydrogen, such as nickel, is reduced to a metal usually depends on the acid concentration of the solution. Since the hydrogen storage alloy contains an electrochemically low element as described above, even under conditions where reduction to metal does not easily occur,
The hydrogen ion concentration is gradually lowered by eluting the base element of the alloy into the acidic aqueous solution, and nickel ions in the aqueous solution are hydrolyzed near the surface of the alloy powder to form a compound such as a hydroxide, Precipitates on the surface of the alloy particles. When a negative electrode is manufactured using such an alloy powder as a raw material and a nickel-metal hydride storage battery is manufactured, the negative electrode potential becomes a low value during charging, and the element reduced to metal at this potential forms a metal layer on the surface of the hydrogen storage alloy. Can be formed.
Nickel is an element that is reduced to a metal at such a negative electrode potential. Therefore, by performing the immersion treatment as in the present invention, it is possible to form a surface layer in which the content ratio of metallic nickel is improved in the hydrogen storage alloy powder.

[0025]

Embodiments of the present invention will be described below in detail with reference to the drawings. (Example 1) <Preparation of paste type negative electrode> A hydrogen storage alloy having a composition of MmNi _4.0 Co _0.4 Mn _0.3 Al _0.3 (Mm; misch metal) prepared by an induction melting method was prepared. The hydrogen storage alloy was pulverized in an inert atmosphere to obtain a powder having a size of 200 mesh or less (about 75 μm or less). A part of this powder was fractionated, and to 100 g of the alloy powder, 500 ml of a 0.2 mol / l aqueous solution of nickel sulfate adjusted to pH 3 by adding acetic acid was added, followed by stirring at room temperature for 3 hours. After that, discard the supernatant, wash the remaining alloy powder with water,
Dry in an inert atmosphere.

100 parts by weight of the hydrogen storage alloy powder after drying,
A paste was prepared by mixing 0.2 parts by weight of sodium polyacrylate, 0.2 parts by weight of carboxymethyl cellulose (CMC) and 1.5 parts by weight of polytetrafluoroethylene together with 50 parts by weight of water. This paste is applied to perforated nickel-plated iron sheet and dried,
A paste-type negative electrode was prepared by press-regulating the pressure. <Preparation of Paste-Type Positive Electrode> Nickel hydroxide particles, cobalt monoxide, carboxymethyl cellulose and water were mixed with 10
The mixture was kneaded at a weight ratio of 0: 5: 0.3: 30 to prepare a paste. The paste was filled in a sponge-like nickel porous body, dried, rolled, and then a lead was welded to produce a paste-type nickel positive electrode. <Assembly of Battery> An electrode group was prepared by spirally winding a nonwoven fabric mainly composed of polypropylene fiber as a separator between the positive electrode and the negative electrode. The obtained electrode group is housed in a bottomed cylindrical container, and 7
An alkaline electrolyte comprising mol / l KOH and 1 mol / l LiOH was housed and sealed, and a nickel-metal hydride storage battery having the above-described structure shown in FIG. 1 and having a theoretical capacity of 1300 mAh was assembled. (Example 2) Except for using the negative electrode described below,
A nickel-metal hydride storage battery having the same configuration as in Example 1 was assembled.

100 g of hydrogen storage alloy powder obtained by performing the induction melting method and the pulverization in the same manner as in Example 1.
To the mixture was added 500 ml of an aqueous solution in which nickel sulfate and cobalt sulfate each having a pH of 3 adjusted by adding acetic acid were each dissolved at 0.1 mol / l, followed by stirring for 3 hours. After that, discard the supernatant, wash the remaining alloy powder with water,
Drying was performed in the same inert atmosphere as in Example 1. A paste-type negative electrode was produced in the same manner as in Example 1 from the dried hydrogen storage alloy powder. (Comparative Example 1) Except for using the negative electrode described below,
A nickel-metal hydride storage battery having the same configuration as in Example 1 was assembled.

In the same manner as in Example 1, 100 parts by weight of a hydrogen storage alloy powder obtained by performing the induction melting method and pulverization, 0.2 parts by weight of sodium polyacrylate, 0.2 parts by weight of carboxymethyl cellulose (CMC) And 1.5 parts by weight of polytetrafluoroethylene together with 50 parts by weight of water to prepare a paste. This paste was applied to a perforated nickel-plated iron thin plate, dried, and then press-regulated to produce a paste-type negative electrode. (Comparative Example 2) Except for using the negative electrode described below,
A nickel-metal hydride storage battery having the same configuration as in Example 1 was assembled.

100 g of hydrogen storage alloy powder obtained by performing the induction melting method and the pulverization in the same manner as in Example 1.
Then, 500 ml of a 0.2 mol / l aqueous solution of cobalt sulfate adjusted to pH 3 by adding acetic acid was added thereto, followed by stirring for 3 hours. Thereafter, the supernatant was discarded, the remaining alloy powder was washed with water, and dried in the same inert atmosphere as in Example 1.
A paste-type negative electrode was produced in the same manner as in Example 1 from the dried hydrogen storage alloy powder. (Comparative Example 3) Except for using the negative electrode described below,
A nickel-metal hydride storage battery having the same configuration as in Example 1 was assembled.

100 g of hydrogen storage alloy powder obtained by performing the induction melting method and the pulverization in the same manner as in Example 1.
Was added to 500 ml of an aqueous solution of acetic acid having a pH of 3,
Stir for 3 hours. Thereafter, the supernatant was discarded, the remaining alloy powder was washed with water, and dried in the same inert atmosphere as in Example 1. A paste-type negative electrode was produced in the same manner as in Example 1 from the dried hydrogen storage alloy powder.

With respect to the obtained storage batteries of Examples 1 and 2 and Comparative Examples 1 to 3, 15 mA at 130 mA at room temperature (20 ° C.).
After charging for 130 hours, the battery was charged / discharged at 130 mA to 1.0 V and activated. Next, these batteries were charged at −130 mA for 15 hours at room temperature, and then charged to −2.
The battery was cooled to 0 ° C and discharged at 650 mA, and the battery voltage was 1.0
The discharge capacity up to V was measured. The results are shown in Table 1 below.

[0032] As is evident from Table 1, the secondary batteries of Examples 1 and 2 obtained by subjecting the hydrogen storage alloy powder to immersion treatment with an acidic aqueous solution containing nickel ions and producing a negative electrode from such an alloy powder include: It can be seen that the discharge capacity at low temperatures can be improved. In particular, it can be seen that the secondary battery of Example 2 in which cobalt ions were added to the acidic aqueous solution had higher low-temperature discharge characteristics than Example 1 in which cobalt ions were not added.

On the other hand, Comparative Example 1 without immersion treatment
The secondary battery of Comparative Example 2, in which the treatment is performed with an acidic aqueous solution containing only cobalt ions, and the secondary battery of Comparative Example 3, in which the treatment is performed with an acidic aqueous solution containing no metal ions, are Examples 1 and 2. It can be seen that the discharge capacity at low temperature is lower than that of No. 2.

[0034]

As described in detail above, according to the present invention, it is possible to provide a method for manufacturing a nickel-metal hydride storage battery having improved high-rate discharge characteristics and low-temperature characteristics immediately after the start of use.

[Brief description of the drawings]

FIG. 1 is a partially cutaway perspective view showing an example of a nickel-metal hydride storage battery manufactured by a method according to the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... container, 2 ... positive electrode, 3 ... separator, 4 ... negative electrode, 7 ...
Sealing plate, 8 ... insulating gasket.

Claims (1)

[Claims] 1. A positive electrode containing nickel hydroxide, a negative electrode,
A method for producing a nickel-metal hydride storage battery comprising an alkaline electrolyte, comprising: a step of immersing a hydrogen storage alloy powder in an acidic aqueous solution containing nickel ions; and a step of producing a negative electrode containing the hydrogen storage alloy powder. A method for producing a nickel-metal hydride storage battery.