JPH10188994A - Alkaline storage battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate the volume of a negative electrode core material, which occupies in the whole of a negative electrode, so as to provide an alkaline storage battery having high energy density by using a hole drilled steel plate, which is plated with Ni at a specified total thickness and which is heated for a specified time so as to obtain tensile strength and ductility of specified values or more, as a core material of a negative electrode for alkaline storage battery. SOLUTION: In an alkaline storage battery formed of a positive and a negative electrodes, a separator and the alkali electrolyte, a hole drilled steel plate, which is plated with Ni at 0.5-3μm of thickness for corrosion resistance, is used for negative electrode core material. This Ni plated hole drilled steel plate for an negative electrode core material has total thickness at 20-50μm, and it is heated at 500-700 deg.C for a specified time as to be obtain Vickers hardness at 70-130HV, and a required tensile strength and ductility are obtained. Volume of a part, which does not contribute to the electrode capacity, can be eliminated so as to improve the energy density of the battery. In a nickel- hydrogen storage battery, ratio of the mean particle diameter of hydrogen storage alloy of the negative electrode active material to the thickens of a core material thereof is desirably set at 1; (1-2.5).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an alkaline storage battery such as a nickel-hydrogen storage battery or a nickel-cadmium storage battery using a perforated steel sheet plated with Ni on a negative electrode core material.

[0002]

2. Description of the Related Art In recent years, alkaline storage batteries used as various power sources can be expected to have high reliability and can be reduced in size and weight. For this reason, small batteries are used for various portable devices, and large batteries are used for industrial purposes. It is widely used as a power source.
In such an alkaline storage battery, a paste-type nickel electrode is used as a positive electrode in addition to a conventionally used sintered nickel electrode. On the other hand, in addition to the nickel-cadmium storage battery using cadmium for the negative electrode,
As a battery system with a higher energy density,
A nickel-hydrogen storage battery using a hydrogen storage alloy capable of reversibly storing and releasing hydrogen has been developed and its capacity has been increased.

As a negative electrode of this nickel-hydrogen storage battery, a method of sintering a hydrogen storage alloy powder together with a conductive agent powder to form a hydrogen storage alloy electrode (for example, Japanese Patent Publication No. 58-4682)
No. 7), a method of filling a three-dimensional metal porous body such as a foamed nickel carrier with a hydrogen storage alloy powder to form an electrode (for example, JP-A-53-33332), a paste containing a polymer binder Is applied to a perforated steel sheet plated with Ni to form an electrode (for example, Japanese Patent Application Laid-Open No. 61-163569).
And the like have been proposed.

[0004]

However, with recent rapid miniaturization and high performance of various portable devices, there is a demand for higher energy density and higher performance of batteries. In the case of the sintering method, the surface of the hydrogen storage alloy powder is oxidized and passivated during sintering, causing a problem that the conductivity of the electrode is reduced and the discharge voltage is reduced. In the case of the method of filling the three-dimensional metal porous body, in addition to the fact that the three-dimensional porous body of nickel as the substrate is expensive, in addition to the current collecting structure, there are many portions that do not contribute to the electrode capacity,
There is a problem that the electrode capacity cannot be sufficiently increased and the energy density is low. In addition, a method in which a paste prepared by adding a polymer binder to the hydrogen storage alloy powder and applying the paste to a Ni-plated perforated steel sheet is less expensive than a three-dimensional porous body. The method using a perforated steel sheet plated with Ni of 80 μm is becoming the mainstream of nickel-hydrogen storage batteries, but the volume of the core material portion that does not contribute to the electrode capacity occupies about 15% of the entire negative electrode.

The present invention solves the problem of using a perforated steel sheet plated with Ni for such a negative electrode core material, and reduces the volume of the Ni-plated perforated steel sheet as the negative electrode core material in the entire negative electrode. Another object of the present invention is to provide an alkaline storage battery having a higher energy density than before.

[0006]

In order to achieve the above-mentioned object, the present invention uses a perforated steel sheet having a total thickness of 20 to 50 μm and plated with Ni as a negative electrode core material. Heat treatment at a temperature of up to 700 ° C. for a certain time to reduce the volume of a part that does not contribute to the electrode capacity by providing a certain tensile strength and malleability (Vickers hardness), thereby increasing the energy density of the alkaline storage battery. It can be performed.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Ni-plated perforated steel sheets having a total thickness of 60 to 80 μm have been used for the following reasons. One is that when the core material is made thinner, the tensile strength naturally decreases, and tensile stress acts when applying a paste or forming a group of spirally-shaped electrode plates to increase the packing density of the active material thereafter. There was a risk that the electrode plate would be cut during the process. That is, in order to maintain a certain or more tensile strength as the core material, the total thickness had to be 60 to 80 μm.

[0008] However, even if the tensile strength is low, if the electrode plate (core material) has malleability, it is possible to suppress the breakage. For example, by subjecting the core material to a heat treatment to recrystallize Fe of the core material and to enhance the malleability correlated with the Vickers hardness, the core material can be made thinner than before. However, if this is not performed under optimal conditions, the core material may be curved and the core material resistance may increase, causing uneven paste application and lowering battery performance.

The present invention according to claim 1 has a total thickness of 20 to 5 mm.
The present invention solves the above-mentioned problems by providing a core material with a certain or more tensile strength and malleability (Vickers hardness) by heat-treating a perforated steel sheet plated with Ni of 0 μm at a temperature of 500 to 700 ° C. for a certain time. . As a result, the volume occupied by the Ni-plated perforated steel plate, which is the negative electrode core material, in the negative electrode is reduced, and an alkaline storage battery having a higher energy density than before can be provided.

Further, according to the present invention, the ratio of the particle size of the hydrogen-absorbing alloy powder as the negative electrode active material to the thickness of the Ni-plated perforated steel sheet is set to 1: 1 to 2.5, so that Ni plating Reduction of occupied volume by thinning steel sheets,
This makes it possible to increase the reactivity of the hydrogen storage alloy powder. In other words, by optimizing the thickness of the Ni-plated perforated steel sheet and the average particle diameter of the hydrogen storage alloy powder,
It is possible to further increase the energy density of the nickel-hydrogen storage battery.

[0011]

EXAMPLES The details of the present invention will be described in the following examples.
The present invention will be described based on the following examples.
It is not specified and within the scope that does not change the gist
It is possible to change and implement as appropriate. (Example 1) 0.5 to 3 μm on the surface, here 1 μm
Ni-plated Ni-plated with a total thickness of 35 μm
The perforated steel plate is heated to 200 ° C to 750 ° C, preferably 550 ° C.
Heat treatment was performed at a temperature for 0 to 10 hours. Work in this way
Commercially available hydrogen storage alloy (Mm
Ni_FiveMmNi, one of the types_3.7Mn_0.4Al
_0.3Co_0.6), And the average particle diameter is 20 μm
After that, 100 parts by weight of the hydrogen storage alloy powder was added to a thickener.
0.15 parts by weight of CMC and carbon as a conductive agent
0.3 parts by weight of black, styrene-buta as a binder
0.8 part by weight of diene copolymer, water added as dispersant
Apply the adjusted paste and press to the specified thickness
And cut into 4 / 5A size plates to produce negative plates
Was.

The negative electrode plate and the positive electrode mainly composed of nickel hydroxide were spirally grouped through a polypropylene nonwoven fabric separator and housed in a battery outer can. FIG.
Fig. 2 shows the relationship between the heat treatment temperature of the Ni-plated perforated steel sheet used for the negative electrode core material and the falling rate of the applied paste. 500
In the case of heat treatment at a temperature lower than ℃, the dropout rate is extremely high, which is the same level as the case without heat treatment.

FIG. 2 shows the relationship between the heat treatment temperature of a perforated Ni-plated steel sheet, the elongation percentage in a tensile test, and Vickers hardness (HV). The elongation is less than 5% in the heat treatment at a temperature lower than 500 ° C., which is almost the same as that in the case where the heat treatment is not performed at 450 ° C. Vickers hardness also shows almost the same behavior as elongation. In other words, when applying a hydrogen storage alloy to a Ni-plated perforated steel sheet and then pressing it to a predetermined thickness, pressure and tensile stress are naturally applied to the electrode plates. At this time, in the heat treatment at a temperature of less than 500 ° C., the hydrogen storage alloy among the electrode plates tends to expand, but the Ni-plated perforated steel plate cannot be expanded, so that a gap between the hydrogen storage alloy and the Ni-plated perforated steel plate occurs. Occurs. It is considered that the hydrogen storage alloy is likely to fall off from the perforated Ni-plated steel sheet when the group is formed due to the deviation. Therefore, in order to obtain a normal electrode plate, it is necessary to heat-treat the perforated Ni-plated steel sheet at 500 ° C. or higher. However, as shown in FIG.
When the treatment is performed at a high temperature such as 00 ° C. or more, the diffusion of Fe into the Ni plating layer progresses, and the conductivity as the core material decreases and the electric resistance increases. Therefore, the heat treatment temperature is preferably 500 ° C. to 700 ° C., and the Vickers hardness (HV) of the perforated Ni-plated steel sheet is preferably 70 to 130.

Next, the temperature was fixed at 550 ° C., and the heat treatment time was examined. FIG. 4 shows the relationship between the heat treatment time at 550 ° C. and the detachment rate of the paste, and FIG. 5 shows the relationship between the elongation rate in a tensile test and Vickers hardness. In each case, a constant behavior is shown by heat treatment for 2 hours or more. The result is 5
In the range of 00 to 700 ° C., the behavior is the same in any case, and the heat treatment time is preferably 2 hours or more.

The Ni plating on the perforated steel sheet is necessary for preventing rust from occurring upon standing and stabilizing the alkaline electrolyte in the battery. (Table 1) shows a period until rusting occurs when left under high temperature and high humidity.
When Ni plating was not performed, rust almost occurred after 2 days, but no rust was observed for 3 months or more with Ni plating of 0.5 μm or more. However, as the Ni plating becomes thicker, the volume in which the active material can be applied is reduced by that volume. Therefore, the Ni plating thickness is preferably as thin as possible, and preferably about 0.5 to 3 μm.

[0016]

[Table 1]

Next, an electrolytic solution in which 30 g / l of lithium hydroxide was dissolved in KOH having a specific gravity of 1.30 was injected to assemble a 4/5 A nickel-hydrogen storage battery having a rated capacity of 2000 mAh. After the battery was left at an ambient temperature of 25 ° C. for 12 hours, it was initially charged and discharged (charge: 0.1 C for 15 hours, discharge:
(0.2 C for 5 hours) to obtain a battery A based on this example. For comparison, 60 μm conventionally used
A battery manufactured in the same manner using the perforated Ni-plated steel sheet of Example 1 is referred to as a battery B of a comparative example.

The discharge capacities when the batteries A and B were charged at 0.1 C for 15 hours and then discharged at 0.2 C to 1.0 V are shown in Table 2. In the battery A according to the present embodiment, a high capacity was made possible by reducing the thickness of the perforated Ni-plated steel sheet used for the negative electrode plate.

[0019]

[Table 2]

Example 2 Next, a 35 μm-thick perforated steel sheet having a surface plated with 1 μm was heat-treated at 550 ° C. for 4 hours, and then hydrogen-absorbing alloys having various particle diameters were produced in the same manner as in Example 1. Was applied to form an electrode plate.
Using the negative electrode plate thus produced, a battery was assembled in the same manner as in Example 1, and the battery was initially charged and discharged to obtain a 4/5 A nickel-hydrogen storage battery.

FIG. 6 shows the relationship between the core material thickness / particle diameter ratio of the hydrogen storage alloy powder and the internal pressure of the battery. Note that the battery internal pressure is a value obtained when the battery was charged at 1 C for 1.5 hours. Since the ratio of the core material thickness to the particle diameter of the hydrogen storage alloy powder is 2.5 or more, the battery internal pressure increases. The cause is considered as follows. Normally, hydrogen can move and react in the hydrogen storage alloy on both sides of the electrode plate through the hydrogen storage alloy particles through the perforated portion of the core material. Therefore, as shown in the schematic diagram of FIG. 7B, when the thickness of the core material is 60 μm and the ratio of the thickness of the core material to the particle diameter of the hydrogen storage alloy powder is increased, the amount of the hydrogen storage alloy powder particles located in the perforated portion is increased. And the reactivity decreases accordingly. On the other hand, as shown in FIG. 7A, when the thickness of the core material is 35 μm, the amount of alloy particles located in the perforated portion is small, and the reactivity becomes good.

This tendency is the same not only in the case of a core material having a thickness of 35 μm but also in other thicknesses. It depends. However, when the thickness of the Ni-plated perforated steel sheet was 35 μm and the average particle diameter of the hydrogen storage alloy powder was 20 μm as in this example, the capacity was
Most preferable from other battery characteristics.

By optimizing the thickness of the core material and the average particle size of the hydrogen storage alloy powder in this way, the reactivity of the hydrogen storage alloy can be improved and the capacity can be increased. Although the embodiment has been described using a nickel-hydrogen storage battery,
Similar effects can be obtained by using a nickel-cadmium storage battery.

[0024]

As described above, the present invention does not contribute to the electrode capacity by using a Ni-plated perforated steel sheet having a total thickness of 20 to 50 μm heat-treated at 500 to 700 ° C. as the negative electrode core material of the alkaline storage battery. The occupied volume of the portion is reduced, and the energy density of the alkaline storage battery can be increased.

[Brief description of the drawings]

FIG. 1 is a diagram showing a relationship between a heat treatment temperature of a negative electrode core material and an electrode plate falling rate in an example of the present invention.

FIG. 2 is a graph showing the relationship between the heat treatment temperature, elongation, and Vickers hardness of the negative electrode core material.

FIG. 3 is a diagram showing a relationship between a heat treatment temperature and an electric resistance of the negative electrode core material.

FIG. 4 is a diagram showing a relationship between a heat treatment time of the negative electrode core material and a paste falling rate.

FIG. 5 is a graph showing the relationship between heat treatment time, elongation, and Vickers hardness of the negative electrode core material.

FIG. 6 is a diagram showing the relationship between the thickness of the negative electrode core material / alloy particle diameter and the internal pressure of the battery.

FIG. 7 is a schematic diagram showing the thickness / alloy particle diameter ratio of the negative electrode core material.

Continued on the front page (72) Inventor Takashi Takano 1006 Kadoma Kadoma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (4)

[Claims] An alkaline storage battery comprising a positive electrode, a negative electrode, a separator and an alkaline electrolyte, wherein the core material of the negative electrode is a Ni-plated perforated steel sheet having a total thickness of 20 to 50 μm.
An alkaline storage battery that has been heat-treated at a temperature of 700 ° C. 2. The alkaline storage battery according to claim 1, wherein the negative electrode core material has a Vickers hardness (HV) of 70 to 130 HV. 3. The alkaline storage battery according to claim 1, wherein the negative electrode core material has a steel plate surface plated with Ni having a thickness of 0.5 to 3 μm. 4. A nickel-hydrogen storage battery comprising a positive / negative electrode, a separator and an alkaline electrolyte, wherein the core material of the negative electrode is a perforated steel sheet plated with Ni having a total thickness of 20 to 50 μm, Nickel whose ratio between the average particle diameter of the storage alloy and the thickness of the core material is 1: 1 to 2.5.
Hydrogen storage battery.