JP2001223000A - Alkaline secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an alkaline secondary battery in which a charging and discharging life is made stably longer, and a negative electrode obtains improved strength along with a large capacity. SOLUTION: The negative electrode containing powder of hydrogen absorbing metal alloys in which the following features are realized; the main crystal phase has no CaCu5 structure, but is expressed in the general equation of Ln1-xMgx(Ni1-y-zAlyTz)w [in which Ln is a lanthanoid element, and at least one of the elements selected from Ca, Sr, Sc, Y, Ti, Zr and Hf, and T is at least one of the elements selected from Li, V, Nb, Ta, Cr, Mo, Mn, Fe, Co, Ga, Zn, Sn, In, Cu, Si, P and B, and x, y, z and w are respectively 0<x<1,0<=y+z<=0.5, 2.5<=w<=4.5], and in which eluted Al is regulated around 2-200 ppm under specific conditions.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an alkaline secondary battery having an improved negative electrode containing a hydrogen storage alloy for electrochemically storing and releasing hydrogen.

[0002]

2. Description of the Related Art Nickel-cadmium secondary batteries and nickel-metal hydride secondary batteries are known as high-capacity secondary batteries. Among them, nickel-metal hydride secondary batteries provided with a negative electrode containing a hydrogen storage alloy that stores and releases hydrogen are widely used in portable electronic devices and the like as small sealed secondary batteries having excellent environmental compatibility.

In the nickel-metal hydride secondary battery, the hydrogen storage alloy that plays an important role as a negative electrode active material is mainly MmNi ₅ (Mm; misch metal) or TiMn.
_Two series alloys are used.

However, in a nickel-metal hydride secondary battery provided with a negative electrode containing an MmNi ₅ (Mm: misch metal) or TiMn ₂ -based hydrogen storage alloy, the hydrogen storage capacity of the hydrogen storage alloy is limited. It was difficult to increase the capacity of the battery.

[0005] From the above, V-Ti, TiF
e-based and Ti ₂ Ni-based hydrogen storage alloys have been developed.
However, although these hydrogen storage alloys are excellent in direct reactivity with hydrogen gas at high temperatures, they have poor reactivity with hydrogen at room temperature and have a problem that initial activation is difficult.

On the other hand, hydrogen storage alloys containing magnesium, nickel and rare earth elements as main constituent elements are:
Both the capacity density per volume and the capacity density per weight are higher than those of widely used MmNi ₅ alloys, the activation is faster than TiMn ₂ alloys, and the high rate charge / discharge characteristics are excellent. There is a feature that there is. For this reason, by using the negative electrode containing the hydrogen storage alloy, the charge / discharge rate is higher than when using the negative electrode containing the TiMn ₂ -based alloy with a higher capacity than when using the negative electrode containing the MmNi ₅ -based alloy. It is possible to realize a secondary battery having excellent characteristics.

[0007]

However, an alkaline secondary battery provided with a negative electrode containing a hydrogen storage alloy containing magnesium, nickel and a rare earth element as main constituent elements is an electrolytic solution of the constituent elements of the hydrogen storage alloy powder. There is a problem that corrosion due to elution into the metal is apt to occur, which causes an increase in internal resistance and causes an internal short circuit to shorten the cycle life.

Therefore, it has been found that a reduction in cycle life is suppressed by replacing some of the constituent elements of the hydrogen storage alloy with Al. However, Al
May elute into the electrolytic solution.

That is, when a hydrogen storage alloy containing magnesium, nickel and a rare earth element as main constituent elements contains Al as a constituent element, particularly, Al having high solubility in an electrolytic solution is eluted and corroded. In addition, the paste electrode using the hydrogen storage alloy containing Al as the negative electrode active material is not always strong enough, and the current from the current collector may be increased due to expansion due to the permeation of the electrolytic solution or deposition expansion due to hydrogen storage of the hydrogen storage alloy. Exfoliation and falling off of the active material are caused, resulting in insufficient current collection. As a result, the cycle life may be reduced. Although a binder is added to improve the strength of the electrode, the problem of strength of the electrode is improved by increasing the amount, but from the viewpoint of increasing the electric capacity, that is, the filling amount of the active material, the binder is added. There are certain restrictions on increasing the volume.

An object of the present invention is to provide an alkaline secondary battery having a negative electrode with improved strength while realizing a high capacity and capable of stably extending the charge / discharge cycle life.

[0011]

Means for Solving the Problems The present inventors have found that, in a hydrogen storage alloy containing Al as a constituent element, Al is eluted into an electrolyte to lower the cycle characteristics, It was found that the electrode strength and cycle life could be improved by regulating the amount of Al elution, and the alkaline secondary battery of the present invention was completed by using this hydrogen storage alloy as a negative electrode active material. Such a hydrogen storage alloy can be obtained by controlling its composition and manufacturing process. In addition, the improvement of the electrode strength by defining the elution amount of Al into the electrolytic solution is as follows.
Although it is not clear, it is presumed that Al eluted in the electrolytic solution forms a salt with the binder and forms a strong network.

That is, in the alkaline secondary battery according to the present invention, the main crystal phase does not have a CaCu ₅ type structure, is represented by the following general formula (I), and is added to an 8N aqueous solution of potassium hydroxide at 45 ° C. A negative electrode containing a hydrogen storage alloy powder having an Al elution amount of 2 to 200 ppm with respect to the total amount after immersion for 48 hours is provided.

[0013] _{Ln 1-x Mg x (Ni} 1-yz Al y T z) w ... (I) where, Ln is lanthanoid elements in the formula, Ca, Sr,
At least one element selected from Sc, Y, Ti, Zr and Hf, and T is Li, V, Nb, Ta, Cr, M
o, Mn, Fe, Co, Ga, Zn, Sn, In, C
at least one element selected from u, Si, P and B, x, y, z and w are each 0 <x <1, 0 ≦ y + z
≤0.5, 2.5≤w≤4.5.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an alkaline secondary battery (for example, a cylindrical alkaline secondary battery) according to the present invention will be described with reference to FIG.

An electrode group 5 formed by laminating a positive electrode 2, a separator 3, and a negative electrode 4 and spirally winding them 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 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 provided between the periphery of the sealing plate 7 and the container 1.
The sealing plate 7 is air-tightly 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.

A safety valve 11 made of rubber 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 arranged on the positive electrode terminal 10 such that a projection of the positive electrode terminal 10 projects from the hole of the holding plate 12. 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.

1) Positive electrode 2 This positive electrode 2 contains a nickel compound as an active material.

Examples of the nickel compound include nickel hydroxide, nickel oxide and nickel oxide in which nickel hydroxide, zinc and cobalt are coprecipitated.
Particularly, nickel hydroxide in which zinc and cobalt are coprecipitated is preferable.

The positive electrode (paste-type positive electrode) is prepared, for example, by kneading a nickel compound as an active material, a conductive material and a binder together with water to prepare a paste, filling the paste into a conductive core, and drying the paste. It is produced by performing pressure molding as required.

As the conductive material, for example, at least one selected from a cobalt compound and metallic cobalt is used. As the cobalt compound,
For example, cobalt hydroxide [Co (OH) ₂ ], cobalt monoxide (CoO), and the like can be given. In particular, it is preferable to use cobalt hydroxide, cobalt monoxide, or a mixture thereof as the conductive material.

Examples of the binder include hydrophobic polymers such as polytetrafluoroethylene, polyethylene, and polypropylene; cellulosic materials such as carboxymethylcellulose, methylcellulose and hydroxypropylmethylcellulose; acrylates such as sodium polyacrylate; Examples include hydrophilic polymers such as polyvinyl alcohol and polyethylene oxide; and rubber-based polymers such as latex.

Examples of the conductive core include a mesh-like, sponge-like, fiber-like, or felt-like porous metal body made of nickel, stainless steel, or nickel-plated metal.

[0025] 2) the negative electrode 4 This negative electrode 4, the main crystal phase does not have a CaCu ₅ type structure, formula _{Ln 1-x Mg x (Ni} 1-yz Al y T z) w ... (I) where Ln in the formula is a lanthanoid element, Ca, Sr,
At least one element selected from Sc, Y, Ti, Zr and Hf, and T is Li, V, Nb, Ta, Cr, M
o, Mn, Fe, Co, Ga, Zn, Sn, In, C
at least one element selected from u, Si, P and B, x, y, z and w are each 0 <x <1, 0 ≦ y + z
≦ 0.5, 2.5 ≦ w ≦ 4.5.
And the amount of Al eluted after immersion in an 8N aqueous potassium hydroxide solution at 45 ° C. for 48 hours is 2 to 200 pp
m containing a hydrogen storage alloy powder.

Among Ln in the general formula (I), a lanthanoid element is particularly preferred.

In the general formula (I), x, y, z and w are respectively 0.15 ≦ x ≦ 0.4, 0.1 ≦ y + z ≦ 0.
4. It is more desirable that 0.01 ≦ y ≦ 0.08, 2.6 ≦ z ≦ 3.7 (more preferably, 2.7 ≦ z ≦ 3.6).

The reason why the amount of Al eluted in the hydrogen storage alloy under the predetermined conditions is defined as 2 to 200 ppm is as follows.
This is for the following reasons. The Al elution amount is 2
A hydrogen storage alloy having a concentration of less than 1 ppm has less corrosion and has a long charge / discharge cycle of the hydrogen storage alloy itself.However, since the negative electrode containing the hydrogen storage alloy has low strength, the alkaline secondary battery provided with the negative electrode cannot be charged and discharged. The cycle life may be shortened. On the other hand, a hydrogen storage alloy having an Al elution amount of more than 200 ppm is highly corroded by the elution of Al, and an alkaline secondary battery provided with a negative electrode containing this hydrogen storage alloy may have a shorter charge / discharge cycle life.

The negative electrode (paste type negative electrode) is prepared, for example, by kneading a hydrogen storage alloy powder, a conductive material and a binder together with water to prepare a paste, filling the paste into a conductive core, drying, and drying the paste. It is produced by applying pressure molding according to

Examples of the binder include those similar to those used in the positive electrode 2. This binder is
0.5 to 6 with respect to 100 parts by weight of the hydrogen storage alloy powder
It is preferable to mix by weight.

As the conductive material, for example, carbon black such as acetylene black, Ketjen black (trade name, manufactured by Lion Aguso), furnace black, or graphite can be used. This conductive material is preferably blended in an amount of 5 parts by weight or less based on 100 parts by weight of the hydrogen storage alloy powder.

Examples of the conductive core include those having a two-dimensional structure such as a punched metal, an expanded metal, a perforated steel sheet, a wire mesh, and a three-dimensional structure such as a foamed metal or an Amejo sintered metal fiber. Can be.

3) Separator 3 This separator 3 is made of, for example, an olefin-based nonwoven fabric such as a nonwoven fabric made of polyethylene fiber, a nonwoven fabric made of ethylene-vinyl alcohol copolymer fiber, or a nonwoven fabric made of polypropylene fiber, or an olefin such as a nonwoven fabric made of polypropylene fiber. Examples thereof include nonwoven fabrics made of a nonwoven fabric made of a base fiber and hydrophilic functional groups, and nonwoven fabrics made of polyamide fibers such as nylon 6,6. In order to impart a hydrophilic functional group to the olefin fiber nonwoven fabric, for example, corona discharge treatment, sulfonation treatment, graft copolymerization, or application of a surfactant or a hydrophilic resin can be employed.

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 alkaline secondary battery according to the present invention described above, the general formula _{(I) Ln 1-x Mg} x (Ni 1-yz Al y T
_z ) A negative electrode containing a hydrogen storage alloy powder represented by _w and having an Al elution amount of 2 to 200 ppm relative to the total amount after immersion in an 8N aqueous potassium hydroxide solution at 45 ° C. for 48 hours is provided. . This negative electrode, while realizing high capacity,
Since the strength is improved, it is possible to obtain an alkaline secondary battery in which the charge / discharge cycle life is stably improved.

That is, the hydrogen storage alloy represented by the general formula (I) can increase the reversible hydrogen storage amount. In particular, the general formula (I) in the (Ni _1-yz Al _y T
_The hydrogen storage alloy in which w indicating the ratio of _z ) satisfies 2.7 ≦ w ≦ 3.6 can further increase the reversible hydrogen storage amount. As a result, the absolute capacity of the negative electrode can be reduced by increasing the negative electrode capacity, and the volume of the positive electrode can be increased accordingly, so that the capacity of the entire battery can be increased.

When a hydrogen storage alloy containing magnesium, nickel, aluminum and rare earth elements as main constituent elements is immersed under the above-described conditions, the hydrogen storage alloy powder is corroded by an aqueous potassium hydroxide solution, and the Al in the hydrogen storage alloy is eroded.
Elutes in the aqueous potassium hydroxide solution. The hydrogen storage alloy having a large amount of Al elution causes a reduction in the charge / discharge cycle life due to corrosion. On the other hand, a hydrogen storage alloy with a small amount of Al eluted has insufficient salt formation with a binder, so that an improvement in strength cannot be expected. As a result, it is difficult to suppress a decrease in the charge / discharge cycle life.

Therefore, the elution amount of Al is 2 to 200 pp.
The hydrogen storage alloy powder of general formula (I) containing m, magnesium, nickel, aluminum and rare earth as main constituent elements reduces the charge-discharge cycle life caused by corrosion of the hydrogen storage alloy while improving the strength of the negative electrode. Can be suppressed.
As a result, by forming a negative electrode using this hydrogen storage alloy, it is possible to obtain an alkaline secondary battery having improved strength and a stable improvement in charge / discharge cycle life.

[0039]

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 7 and Comparative Examples 1 to 4) <Preparation of Paste Type Negative Electrode> Alloy composition is La _0.72 Mg _{0.28
(Ni 0.8 Co 0.15 Cr 0.01 Mn} 0.01 Al 0.03) 3 so as to _{.3 La, Mg, Ni, Co} , Cr, Mn, each element of Al were mixed, melted in an argon atmosphere using a high frequency melting furnace・ Cooled. This ingot is heat-treated and homogenized, pulverized in an inert atmosphere, and sieved so as to have a particle size of 75 μm or less. Eleven kinds of hydrogen storage alloy powders were obtained.

The Al elution amount of the hydrogen storage alloy powder was measured by the following method. First, the particle size is 75
After immersing 1 g of the hydrogen storage alloy powder having a size of not more than μm in 2 mL of 8N aqueous potassium hydroxide at 45 ° C. for 48 hours, it was washed with distilled water. The amount of Al in the filtrate was determined by analyzing by an ICP analysis method.

Then, carboxymethylcellulose (CM) was used as a binder in 100 parts by weight of each of the hydrogen storage alloy powders.
C) After adding together with 0.2 part by weight and 50 parts by weight of water, 11 kinds of pastes were prepared by kneading.
Subsequently, after filling each paste into foamed nickel having a porosity of 95%, the paste was dried at 125 ° C., pressed into a thickness of 0.3 mm, and further cut into a width of 60 mm and a length of 168 mm to obtain 11 kinds of pastes. A paste type negative electrode was manufactured.

<Preparation of Paste-Type Positive Electrode> To a mixed powder consisting of 90 parts by weight of nickel hydroxide powder and 10 parts by weight of cobalt monoxide powder, 1 part by weight of polytetrafluoroethylene and 0.2 part by weight of carboxymethyl cellulose were added. A paste was prepared by adding 60 parts by weight of pure water to these and kneading them. Subsequently, this paste was filled in foamed nickel, dried, and then press-molded to obtain a width of 60 mm, a length of 135 mm, and a thickness of 0.75 m.
m of paste-type positive electrodes were prepared.

Next, a nonwoven fabric made of polypropylene fiber was interposed between each of the negative electrode and the positive electrode, and spirally wound to form an electrode group. After each such electrode group is accommodated in a bottomed cylindrical container, an electrolytic solution comprising a potassium hydroxide aqueous solution having a specific gravity of 1.31 is injected into the container, and the container is sealed and the like, as shown in FIG. 1 described above. 11 types of 4 /
3A size cylindrical nickel-metal hydride secondary battery (capacity 420
0 mAh).

The obtained Examples 1 to 7 and Comparative Examples 1 to 4
The secondary battery was charged at 25 ° C. for 10 hours at a rate of 13 hours, and subjected to a cycle test in which charge and discharge were repeated at 25 ° C. at a rate of 5 hours to a final voltage of 1.0 V. Examined. The initial capacity is 1
It was determined from the discharge capacity at the cycle. The cycle life was determined as an average value of the number of cycles until the capacity of the secondary battery reached 80% of the initial capacity.

The results are shown in Table 1 below.

[0047]

[Table 1]

As is apparent from Table 1 above, La _0.72 Mg
_0.28 (Ni _0.8 Co _0.15 Cr _0.01 Mn _0.01 Al _0.03 ) _3.3
The secondary batteries of Examples 1 to 7 including the negative electrode containing a hydrogen storage alloy powder having a composition of and having a hydrogen storage alloy powder having an Al elution amount of 2 to 200 ppm after being immersed under the above-described conditions may have a long cycle life. Understand.

On the other hand, the secondary batteries of Comparative Examples 1 and 2 provided with the negative electrode containing the hydrogen storage alloy powder having the same composition and having the Al elution amount of less than 2 ppm after being immersed under the above-mentioned conditions had a short cycle life. I understand. This is because the strength of the negative electrode is low.

Further, it can be seen that the cycle life of the secondary batteries of Comparative Examples 3 and 4 provided with the negative electrode containing the hydrogen storage alloy powder having the same composition and the elution amount of Al exceeding 200 ppm after immersion under the above-described conditions was short. .

It should be noted that even when a hydrogen storage alloy represented by the general formula (I) other than the hydrogen storage alloy having the composition used in Examples 1 to 7 was used, the same excellent characteristics as those in Examples 1 to 7 were obtained. The following alkaline secondary battery can be obtained.

In the above-described embodiment, an example in which the present invention is applied to a nickel-metal hydride secondary battery from the viewpoint of manufacturing, such as a cylindrical shape, has been described. The present invention can be similarly applied to a nickel hydride secondary battery.

[0053]

As described above, according to the present invention, a negative electrode having an improved strength while realizing a higher capacity is provided.
An alkaline secondary battery capable of stably extending the charge / discharge cycle life can be provided.

[Brief description of the drawings]

FIG. 1 is a perspective view of a nickel-metal hydride secondary battery which is an example of an alkaline secondary battery according to the present invention.

[Explanation of symbols]

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

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Chizuru Hatanaka 3-4-10 Minamishinagawa, Shinagawa-ku, Tokyo Toshiba Battery Corporation F-term (reference) 4K018 AA08 BC11 BC12 BD10 HA03 KA38 5H028 CC12 EE01 HH00 HH01 HH08

Claims (1)

[Claims] 1. The main crystal phase does not have a CaCu ₅ type structure, is represented by the following general formula (I), and the amount of Al eluted after immersion in an 8N aqueous potassium hydroxide solution at 45 ° C. for 48 hours. An alkaline secondary battery comprising a negative electrode containing a hydrogen storage alloy powder having a content of 2 to 200 ppm based on the total amount. _{Ln 1-x Mg x (Ni} 1-yz Al y T z) w ... (I) provided that, Ln in the formula is a lanthanoid element, Ca, Sr,
At least one element selected from Sc, Y, Ti, Zr and Hf, and T is Li, V, Nb, Ta, Cr, M
o, Mn, Fe, Co, Ga, Zn, Sn, In, C
at least one element selected from u, Si, P and B, x, y, z and w are each 0 <x <1, 0 ≦ y + z
≤0.5, 2.5≤w≤4.5.