JP2001210322A - Alkaline secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an alkaline secondary battery with a negative electrode which contains a corrosion-resistant hydrogen occlusion alloy of high hydrogen occlusion/discharge ability. SOLUTION: The battery is equipped with the negative electrode 4 which contains the hydrogen occlusion alloy including rare-earth elements, Ce and La, and Ni and Co. The mol ratio of Ce and La, x and y respectively considering that of the rare-earth elements is 1, satisfies the formula, 4.5<=y/x<=9.0. Furthermore, the amount of La involved is more than 24 wt.%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an alkaline secondary battery having an improved negative electrode containing a hydrogen storage alloy.

[0002]

2. Description of the Related Art A nickel-hydrogen secondary battery, which is an example of an alkaline secondary battery, has a structure in which an electrode group in which a separator is interposed between a positive electrode and a negative electrode and an alkaline electrolyte are contained in a container. This nickel-hydrogen secondary battery can be miniaturized because of its high energy density. Therefore, it is often used for small communication devices. Small communication equipment
Today, the processing speed has been greatly improved, and the power consumption has been increased accordingly. Therefore, secondary batteries are required to have improved discharge capacity.

In a nickel-metal hydride secondary battery, the capacity regulating electrode is a positive electrode. Simply increasing the positive electrode capacity (discharge capacity)
Since the capacity of the electrode group is increased and the electrode group cannot be housed in the container, a problem occurs such as increasing the capacity per unit volume of the negative electrode to reduce the volume occupied by the negative electrode per fixed capacity, and reducing the positive electrode by the reduced amount. It is necessary to increase the capacity. That is, in order to achieve high capacity, the capacity (hydrogen / storage / release amount) of the hydrogen storage alloy contained in the negative electrode must be increased.

Incidentally, AB ₂ type and AB ₅ type are known as hydrogen storage alloys contained in the negative electrode of the nickel-metal hydride secondary battery. At the moment, AB
Type ₅ is the mainstream. The AB ₅ type rare earth elements such as misch metal, nickel hydrogen storage alloy having a composition comprising cobalt and manganese are known.

[0005] As a method of increasing the capacity of the hydrogen storage alloy, La included in the misch metal which is the element on the A side is used.
It is known to increase the amount of Mn belonging to the B and B-side elements, or to decrease the B / A ratio. However, such a hydrogen storage alloy has poor durability.

Further, as a method for improving the durability of the hydrogen storage alloy, it is known that a large amount of Co is contained or the B / A ratio is increased contrary to the case of increasing the capacity.

[0007]

That is, there is a trade-off relationship between the capacity and durability of the hydrogen storage alloy. It is difficult to improve the capacity while maintaining the durability of the hydrogen storage alloy. there were.

An object of the present invention is to provide an alkaline secondary battery provided with a negative electrode containing a hydrogen storage alloy which has a high hydrogen storage / release amount and is hardly corroded.

[0009]

According to the present invention, there is provided an alkaline secondary battery comprising a rare earth component containing Ce and La;
When the molar ratio x of Ce and the molar ratio y of La satisfy the following formula (1) when the molar ratio of the rare earth component is set to 1, and the La content is 24% by mass or more, A negative electrode containing a certain hydrogen storage alloy is provided.

4.5 ≦ y / x ≦ 9.0 (1)

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION An alkaline secondary battery according to the present invention comprises a rare earth component containing Ce and La, Ni and Co, and the molar ratio of Ce when the molar ratio of the rare earth component is set to 1. The molar ratio y of x and La satisfies the following formula (1);
A negative electrode containing a hydrogen storage alloy having a La content of 24% by mass or more, a positive electrode, a separator disposed between the positive electrode and the negative electrode, and an alkaline electrolyte.

4.5 ≦ y / x ≦ 9.0 (1) Next, the negative electrode, the positive electrode, the separator, and the electrolytic solution will be described.

1) Negative Electrode The negative electrode contains a hydrogen storage alloy having a composition represented by AB _n (n> 0). A is a rare earth component containing Ce and La. On the other hand, the elements on the B side include Ni and Co. Further, when the molar ratio of the rare earth component A is set to 1, C
The molar ratio x of e and the molar ratio y of La satisfy the expression (1). Further, the La content of the hydrogen storage alloy is 2
4% by mass or more.

The rare earth component A is, for example, La, P
It is preferable to be composed of a misch metal containing r, Ce and Nd. As misch metal, for example, L
a. Rich misch metal and Ce-rich misch metal.

The reason why the molar ratio x of Ce and the molar ratio y of La are defined by the above formula (1) will be described. When y / x is less than 4.5, the amount of hydrogen occlusion and release of the alloy decreases, and the capacity of the negative electrode decreases. Therefore, the negative electrode is easily regulated, and a long life cannot be obtained. In addition, it is difficult to increase the capacity. On the other hand, when y / x is larger than 9.0, the hydrogen storage alloy is easily corroded by oxygen or an alkaline electrolyte generated at the time of charging. When corrosion occurs, it becomes a resistance component and the amount of electrolyte decreases, so that the impedance increases and a long life cannot be obtained. A more preferred range is from 5.0 to 6.0.

The La content in the hydrogen storage alloy is preferably set to 24% by mass or more. If the content is less than 24% by mass, a high amount of hydrogen storage / release cannot be obtained despite satisfying the relationship of the above-mentioned formula (1). Also, L
The upper limit of the content of a is preferably 30% by mass.
If the La content exceeds 30% by mass, corrosion of the hydrogen storage alloy is likely to occur, and a long life may not be obtained. In addition, the production cost of the hydrogen storage alloy may increase.

The elements on the B side are Ni, Co, Mn and Al
It is desirable to include

The molar ratio of Ni (the molar ratio of rare earth component A is 1
) Is preferably in the range of 3.85 to 4.30. This is due to the following reasons. Ni
If the molar ratio is less than 3.85, it may be difficult to obtain high low-temperature discharge characteristics. On the other hand, when the molar ratio of Ni is larger than 4.30, a long life may not be obtained. A more preferred range of the molar ratio of Ni is 3.
9 to 4.2.

[0019] The Co content in the hydrogen storage alloy is 7.
The content is preferably in the range of 5 to 9.0% by mass. This is due to the following reasons. Co content 7.5
If the content is less than mass%, the pulverization of the hydrogen-absorbing alloy may proceed and a long life may not be obtained. On the other hand, if the Co content is more than 9.0% by mass, the effect of improving the life may not be expected, and the production cost of the alloy may be increased.

The reason why manganese is contained in the hydrogen storage alloy will be described. In a hydrogen storage alloy having a composition satisfying the above formula (1), cobalt is easily eluted when the secondary battery is stored in a high-temperature environment. Because cobalt has high conductivity,
Precipitation in the separator causes an internal short circuit, causing a voltage drop. Since manganese is an element that is more soluble in aqueous alkaline solutions than cobalt, by including manganese in the hydrogen storage alloy, manganese can be eluted instead of cobalt when stored in a high-temperature environment. Can be suppressed. Further, since manganese has lower conductivity than cobalt, even if it is deposited in the separator, almost no internal short circuit occurs.

The molar ratio of Mn (the molar ratio of rare earth component A is 1
) Is preferably in the range of 0.20 to 0.35. This is due to the following reasons. Mn
If the molar ratio is less than 0.20, it may be difficult to suppress the elution of cobalt into the alkaline electrolyte. On the other hand, when the molar ratio of Mn is larger than 0.35, the amount of manganese deposited increases, and thus the conductivity of the positive electrode or the negative electrode and the activity on the surface may be reduced.
For this reason, it may be difficult to sufficiently improve low-temperature discharge characteristics and cycle characteristics.

By including aluminum in the hydrogen storage alloy, the equilibrium pressure of the alloy can be adjusted to an appropriate value. The molar ratio of Al (the molar ratio of the rare earth component A is 1) is preferably in the range of 0.2 to 0.4.
This is due to the following reasons. If the molar ratio of Al is less than 0.2, the equilibrium pressure of the hydrogen storage alloy may deviate from an appropriate value. On the other hand, if the molar ratio of Al exceeds 0.4, it may be difficult to obtain excellent discharge characteristics at low temperatures.

The molar ratio n in the AB _n is 5.00
It is preferable to set it in the range of -5.25. This is due to the following reasons. When the molar ratio n is less than 5.00, the proportion of the element on the A side in the alloy is increased, so that corrosion may easily occur. on the other hand,
If the molar ratio n exceeds 5.25, the ratio of the element on the A side in the alloy becomes low, so that a high negative electrode capacity may not be obtained.

The negative electrode may be, for example, the following (1):
It can be manufactured by the method described in (2).

(1) A conductive material is added to the powder of the hydrogen storage alloy and kneaded with a binder and water to prepare a paste. The paste is filled in a conductive substrate and dried,
It is manufactured by molding.

Examples of the binder include carboxymethyl cellulose (CMC), methyl cellulose, sodium polyacrylate, polytetrafluoroethylene, polyvinyl alcohol (PVA), and styrene butadiene rubber (SBR).

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

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

(2) It is manufactured by adding a conductive material and a binder to the powder of the above-mentioned hydrogen storage alloy, kneading to form a sheet, and laminating the obtained sheet on a conductive substrate.

Examples of the binder include polytetrafluoroethylene.

As the conductive material and the conductive substrate,
The same one as described in the above (1) can be used.

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

2) Positive Electrode This positive electrode has a structure in which a positive electrode material containing nickel hydroxide particles as an active material, a conductive material and a binder is supported on a conductive substrate.

As the nickel hydroxide particles, for example, single nickel hydroxide particles or nickel hydroxide particles 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 particles can further improve the charging efficiency in a high-temperature state.

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

Examples of the binder include carboxymethyl cellulose, methyl cellulose, sodium polyacrylate, and polytetrafluoroethylene.

As the conductive substrate, for example, a two-dimensional substrate such as a mesh-like, sponge-like, fiber-like, or felt-like porous metal body or a punched metal made of nickel, stainless steel, or nickel-plated metal is used. Having irregularities on the periphery of the hole.

The positive electrode is prepared by adding a conductive material to, for example, nickel hydroxide particles as an active material, kneading the mixture with a polymer binder and water to prepare a paste, filling the paste into a conductive substrate, and drying the paste. After that, it is produced by molding.

3) Separator Examples of the separator 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 alkaline secondary battery according to the present invention described above comprises a rare earth component containing Ce and La, Ni, and Co.
And when the molar ratio of the rare earth component is 1,
And a molar ratio x of La and a molar ratio y of La satisfy the following formula (1), and a negative electrode containing a hydrogen storage alloy having a La content of 24% by mass or more is provided.

La is added to the rare earth nickel-based hydrogen storage alloy
When the content is 4% by mass or more, the amount of hydrogen occlusion and release of the alloy increases, but corrosion due to oxygen or an alkaline electrolyte generated at the time of charging easily proceeds. As a result, the performance of the hydrogen storage alloy is deteriorated, and the amount of the electrolyte is reduced, so that the impedance is increased and a long life cannot be obtained. When the La content in the alloy is 24% by mass or more,
When the molar ratio y of a and the molar ratio x of Ce satisfy the above expression (1), the amount of hydrogen occlusion / release of the alloy can be increased, and corrosion of the alloy can be suppressed. As a result, the capacity per unit volume of the negative electrode can be increased and the deterioration of the negative electrode can be suppressed, so that the charge / discharge cycle life of the secondary battery can be improved.
Further, since the capacity per unit volume of the negative electrode is improved, the capacity of the secondary battery can be increased.

When the rare earth component is A and the other elements including Ni and Co are B, the molar ratio of B to the molar ratio of A (B / A) is 5.00 to 5.2.
By setting it to 5, the amount of hydrogen occlusion and release of the alloy can be further improved and the corrosion of the alloy can be further suppressed, so that the life of the negative electrode and the capacity per unit volume can be further improved. .

[0044]

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

(Examples 1 and 2 and Comparative Examples 1 to 3) <Preparation of Negative Electrode> Lanthanum-enriched misch metal Lm
And Ni, Co, Mn, and Al were mixed to produce a rare earth nickel-based hydrogen storage alloy ingot having the composition shown in Table 1 below in an arc melting furnace. In Table 1, the La content of each hydrogen storage alloy, the molar ratio of La to the molar ratio x of Ce when the molar ratio of Lm is 1, y (y / x), and A (L
The molar ratio of B (comprising Ni, Co, Mn and Al) to the molar ratio of m) (B / A) and the Co content are also shown.

Each hydrogen storage alloy ingot is mechanically pulverized,
A hydrogen storage alloy powder having an average particle size of 50 μm was prepared. 3 g of sodium polyacrylate, 1.25 g of carboxymethyl cellulose (CMC), 41.7 g of a polytetrafluoroethylene suspension, and 10 g of carbon black as a conductive material were added to 1000 g of each of the obtained hydrogen storage alloy powders as a binder. Then, a paste was prepared by mixing with 500 g of water. These pastes were applied to a punched metal as a conductive substrate, dried, and further pressed with a roller, and then cut into desired dimensions to produce five types of negative electrodes.

<Preparation of Positive Electrode> To a mixed powder composed of 90% by weight of nickel hydroxide powder and 10% by weight of cobalt monoxide powder, 3% by weight of carboxymethyl cellulose (CMC) and 5% by weight of polytetrafluoroethylene were added. A paste was prepared by mixing with 45% by weight of pure water. Subsequently, this paste was filled in a foamed substrate, dried, and then rolled to produce a positive electrode.

Next, a separator made of a non-woven fabric made of polyolefin and subjected to a hydrophilic treatment was interposed between 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,
An alkaline electrolyte composed of an 8N aqueous solution of potassium hydroxide was accommodated, sealed, and the like, to complete a AAA-size cylindrical nickel-metal hydride secondary battery having the structure shown in FIG.

That is, in the bottomed cylindrical container 1, an electrode group 5 produced by stacking the positive electrode 2, the separator 3, and the negative electrode 4 and winding them in a spiral shape is accommodated. 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 projections 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.

The obtained Examples 1-2 and Comparative Examples 1-3
Of the secondary battery was subjected to predetermined initial charge and discharge. Subsequently, after performing 2C charging of -dv control, 1.0 at 2C.
The charge / discharge cycle of discharging to V was repeated 500 times at room temperature, and the rate of increase in impedance after 500 cycles was measured. The result is shown in FIG. The rate of increase in impedance after 500 cycles is the percentage of increase after 500 cycles, where the impedance in the first cycle is 100.

[0051]

[Table 1]

As is clear from Table 1 and FIG. 2, Example 1 provided with a negative electrode containing a hydrogen storage alloy having a La content of 24% by mass or more and having a composition satisfying the above formula (1).
The secondary batteries of Nos. 1 to 2 have a La content of 24% by mass or more and have a La content of not less than 500% as compared with the secondary batteries of Comparative Examples 1 to 3 including negative electrodes containing a hydrogen storage alloy that does not satisfy the above formula (1). It can be seen that the rate of increase in impedance after the cycle is low. It is presumed that the high rate of increase in the impedance of the secondary batteries of Comparative Examples 1 to 3 was due to a decrease in the electrolyte due to gas generation due to electrolysis of the electrolyte accompanying the deterioration of the alloy.

In the above-described embodiment, the separator is interposed between the positive electrode and the negative electrode and spirally wound and housed in a cylindrical container having a bottom. It is not limited to the 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.

[0054]

As described above, according to the present invention, a negative electrode containing a hydrogen storage alloy having an improved hydrogen storage / release amount and reduced corrosion is provided, and a long life and high capacity are achieved. Can be provided.

[Brief description of the drawings]

FIG. 1 is a partially cutaway perspective view showing a nickel-metal hydride secondary battery of Example 1. FIG.

FIG. 2 is a characteristic diagram showing impedance rise rates in the secondary batteries of Examples 1 and 2 and Comparative Examples 1 to 3.

[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.

 ────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Katsuyuki Hata 3-4-10 Minamishinagawa, Shinagawa-ku, Tokyo Toshiba Battery Corporation F-term (reference) 5H003 AA02 AA04 BB02 BC01 BD03 BD04 5H016 AA01 EE01 HH01

Claims (1)

[Claims] 1. A rare earth component containing Ce and La and Ni
When the molar ratio x of Ce and the molar ratio y of La satisfy the following formula (1) when the molar ratio of the rare earth component is set to 1, and the La content is 24% by mass or more, An alkaline secondary battery comprising a negative electrode containing a hydrogen storage alloy. 4.5 ≦ y / x ≦ 9.0 (1)