JPH11288726A - Electrode for alkaline storage battery, its manufacture, and alkaline storage battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an inexpensive iron sintered substrate and an inexpensive alkaline storage battery using it, by improving the iron sintered substrate having three-dimensionally continuous space used for the alkaline storage battery. SOLUTION: This alkaline storage battery is constituted by nickel-plating an iron powder sintered substrate having three-dimensionally continuous space, and filling active material powder into the space part of the substrate 1. Here, nickel-iron alloy layers 3a, 3b are formed on the surface of an iron base portion of the substrate 1, and nickel density is higher than iron density in the alloy layers 3a formed under the nickel-plate layers 2, while the nickel density is lower than the iron density in the alloy layer 3b formed on the iron base portion without the nickel layers 2 thereon.

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, and more particularly, to an improved iron sintered substrate having a three-dimensionally continuous space, and to provide an inexpensive substrate and an inexpensive alkaline storage battery using the same. To provide.

[0002]

2. Description of the Related Art In recent years, as portable devices and cordless devices have been rapidly advanced, demands for small, lightweight, and high energy density secondary batteries as power sources for these devices have been increasing. In the market, there is a demand for particularly high-capacity and inexpensive secondary batteries. For this reason, there is a strong demand for cost reduction of alkaline storage batteries typified by nickel-cadmium storage batteries and nickel-hydrogen storage batteries.

[0003] As an electrode for an alkaline storage battery, a sponge-like substrate mainly composed of pure nickel having a three-dimensionally continuous space and filled with an active material is used. However, this substrate is an expensive material so as to account for about 1/4 of the material and parts cost of the battery using the substrate.

[0004] Therefore, in order to reduce the material cost of the alkaline storage battery, as an alternative to the above-mentioned pure nickel base,
There has been proposed an iron powder sintered substrate having a three-dimensionally continuous space whose surface is nickel-plated and filled with an active material.

[0005] Further, the method for producing the iron powder sintered substrate is as follows.
After applying an iron powder slurry to a synthetic resin core having a three-dimensionally continuous space, for example, a foamed polyurethane resin core,
The heat treatment was performed to remove the urethane foam core and to sinter the remaining iron powder.

[0006]

However, the iron powder sintered substrate as described above has its surface plated with nickel, but because of its complicated three-dimensional structure, it cannot be completely covered with an iron substrate. And there is a portion (pinhole portion) where no nickel plating is applied.

For this reason, in an alkaline storage battery constituted by using this iron powder sintered substrate, iron is eluted into the alkaline electrolyte from a portion of the substrate not subjected to nickel plating, that is, an exposed portion of iron. It adversely affects the initial charge and discharge of the battery and the battery characteristics after long-term storage.

Further, in order to form an oxide of iron as a protective film in the electrode of the battery, it is necessary to reduce the oxygen overvoltage during charging to lower the charging efficiency. There is a problem that the output cannot be sufficiently output as a battery because the utilization factor is also reduced.

[0009]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides an iron powder sintered substrate having a three-dimensionally continuous space, which is subjected to nickel plating. An electrode for a filled alkaline storage battery,
An alloy layer of iron and nickel is formed on a surface portion of the iron base of the base. Of these alloy layers, those formed below the nickel plating layer have a higher nickel concentration than iron, and Those formed on the iron base without the plating layer were assumed to have a lower nickel concentration than iron.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION
It is directed to the electrode of the above-mentioned contents, and in particular, an alloy layer of iron and nickel is formed on the surface portion of the iron base material of the base, and the alloy layer is formed under the nickel plating layer of the alloy layer. Those having a higher nickel concentration than iron had a lower nickel concentration than iron formed on an iron base without a nickel plating layer.

[0011] This is because the surface portion of the iron powder sintered substrate has
An iron-nickel alloy layer is formed regardless of the presence or absence of a nickel plating layer by solid solution diffusion of the iron base and nickel obtained by nickel plating, thereby improving corrosion resistance. When an alkaline storage battery is constructed using this electrode, the surface portion of the iron sintered substrate constituting this electrode is always protected by a nickel plating layer or an alloy layer of iron and nickel having high corrosion resistance.
Even when the battery is charged and discharged or stored for a long period of time, iron does not elute from the sintered iron substrate into the alkaline electrolyte.

For this reason, this iron sintered substrate can be used for an electrode of an alkaline storage battery instead of a nickel sintered substrate, and can obtain the same characteristics as a battery using a conventional nickel powder sintered substrate. In addition, since iron is used, an inexpensive substrate and an alkaline storage battery can be provided.

According to a second aspect of the present invention, in the above-mentioned electrode, the thickness of the nickel plating layer formed on the surface portion of the iron powder sintered substrate is defined, which is defined by the diameter of the iron skeleton. The range of 1/10 to 1/2 is preferable for protecting the iron base.

According to a fifth aspect of the present invention, there is provided a method for manufacturing an electrode for an alkaline storage battery in which a nickel powder is applied to a sintered iron powder substrate having a three-dimensionally continuous space, and a space portion of the substrate is filled with an active material powder. In this method, an iron powder sintered base having a three-dimensionally continuous space is nickel-plated to a thickness of 1/10 to 1/2 of the iron skeleton diameter, and the base is coated with 650 to 650. Under a reducing atmosphere at 720 ° C.,
By heating for 20 minutes, the surface of the iron substrate and nickel are dissolved and diffused with each other, and an alloy layer of iron and nickel is formed on the surface portion of the iron sintered powder. The condition of this alloy layer is that the one formed under the nickel plating layer has a higher nickel concentration than iron, and the one formed on the iron base where nickel is not applied has a lower nickel concentration than iron. Are formed. In this way, an iron-nickel alloy layer having high corrosion resistance is formed on the surface of the iron base using the nickel plating layer and the iron base to protect the sintered iron base.

[0015]

Next, specific examples of the present invention will be described.

First, the method for producing the iron powder sintered body in the embodiment of the present invention was divided into the following first to third steps.

In the first step, a polyurethane resin core having three-dimensionally continuous pores of about 600 μm was prepared. Separately Fe ₂ 0 ₃ powder and metallic iron 7 were mixed with phenolic resin in 3 ratio (weight ratio). Prepare this slurry and apply it to the foamed polyurethane resin surface by 20 μm.
And dried at 90 ° C.

In a second step, the foamed polyurethane resin coated with the iron slurry on its surface is heated to 110
Heat treatment at 0 ° C. for 30 minutes to remove the polyurethane resin core and sinter the iron powders to form a sintered iron powder 1
Was formed. The diameter of the iron skeleton at this time is about 20 μm.

As a third step, the sintered body 1 was immersed in an aqueous hydrochloric acid solution to perform a pretreatment for removing impurities, and then subjected to nickel plating of 5 μm in a nickel sulfate bath at a current density of 10 A / dm ² . Then, the substrate was washed with water, and the substrate was subjected to a heat treatment at 700 ° C. for 10 minutes in a reducing atmosphere of hydrogen to diffuse iron and nickel to each other, thereby forming an alloy layer of iron and nickel on the surface portion of the iron substrate. The substrate a of the example was produced. FIG. 1 shows a schematic sectional view of the substrate surface. In FIG. 1, 1 is a sintered iron powder, 2 is a nickel plating layer, 3a is an alloy layer of iron and nickel formed under the nickel plating layer, and 3b is formed on an iron base without nickel plating. 3 shows an alloy layer of iron and nickel.

This alloy layer was analyzed using an Auger electron spectrometer to confirm that it was an alloy layer of iron and nickel. Also, of this alloy layer, the one formed under the nickel plating layer has a higher nickel concentration than iron, and the one formed on the iron base without the nickel plating layer has a nickel concentration higher than iron. It was confirmed that it was low.

The alloy layer of iron and nickel is stable in an alkaline aqueous solution, and does not elute into an alkaline electrolyte even when a potential changes due to charging and discharging of a battery.

Using the above-mentioned substrate a, a positive electrode a for an alkaline storage battery of an example was produced by the following method. First, a paste-like active material is prepared by mixing an active material mainly composed of nickel hydroxide and water, and the paste-like active material is filled and dried.
It was press-molded and cut into predetermined dimensions. Then, one end of the lead piece was welded to produce a positive electrode a for an alkaline storage battery of the example.

[0023] Separately, the foamed polyurethane resin core body having a pore similar three-dimensionally continuous about 600 .mu.m, Fe ₂ 0 ₃ powder and metallic iron 7: phenol 3 ratio (by weight) Apply the slurry mixed with the resin,
Heat treatment was performed at 1100 ° C. for 30 minutes in a hydrogen atmosphere to remove the polyurethane resin core and to produce an iron sintered substrate in which iron powder was sintered. This iron sintered substrate was also subjected to nickel plating with a thickness of 5 μm in the same manner as described above, and was subjected to a heat treatment at 500 ° C. to produce an iron sintered substrate b of a comparative example.

At this time, the portion of the substrate b not subjected to nickel plating was analyzed using an Auger electron spectrometer. As a result, no alloy layer of nickel and iron was formed, and metallic iron, that is, It was confirmed that it was exposed.

The substrate b was filled with an active material mainly composed of nickel hydroxide, dried, pressed, and cut into a predetermined size. Thereafter, one end of the lead piece was welded to produce a positive electrode b for an alkaline storage battery of a comparative example.

The negative electrode 4 was produced by applying a paste mainly composed of cadmium oxide to a punched metal core material obtained by plating nickel on iron, drying, washing with water, drying, and cutting to a predetermined size.

The positive electrode a and the negative electrode 4 produced as described above, and a polypropylene separator 5 interposed therebetween, are spirally wound to form an electrode plate group, which is formed in a nickel-plated iron battery case 6. After inserting a predetermined amount of the alkaline electrolyte into the case 6, the upper portion of the case 6 is sealed with a sealing plate 7 also serving as a positive electrode terminal, and has a nominal capacity of 1400 mA.
Thus, an A-size cylindrical nickel-cadmium storage battery A having a length h was constructed. FIG. 2 shows a half sectional view of the battery A.

A battery B of a comparative example was constructed in the same manner as the battery A except that the positive electrode b was used instead of the positive electrode A.

Next, the utilization rates of the positive electrode active materials of the battery A of the example and the battery B of the comparative example were determined. This test method was performed for Battery A,
B at 20 ° C. in an atmosphere of 0.1 C (140
The battery is charged for 12 hours at a current of
The discharge capacity when discharging was performed at a current magnitude of (280 mA) until the terminal voltage dropped to 1 V was determined. The filling capacity of the positive electrode active material in each battery (nickel hydroxide is 29
The ratio of the discharge capacity to 8 mAh / g) was determined as the utilization rate of the positive electrode active material. The results are shown in (Table 1).

[0030]

[Table 1]

As shown in Table 1, in the battery A of the example, the utilization rate of the positive electrode active material was 95% or more, and 90% or more.
It is more than 5% higher than the weak battery B.

Next, in a 20 ° C. atmosphere, each of the batteries A and B was discharged and stored at a current of 0.2 C (280 mA) in a state of being discharged, and then was charged. The charge recovery characteristics were measured. The test conditions for the recovery characteristics were as follows: charging was performed at 20 ° C. with a current of 0.1 C (140 mA) for 12 hours;
The discharge capacity at the time of discharging until the terminal voltage is reduced to 1 V with the current of the magnitude of A) is obtained, and the initial nominal capacity is set to 1
The discharge capacity ratio at the time of being set to 00% was taken as the recovery characteristic. The result is shown in FIG.

As shown in FIG. 3, even after being stored for about one year, the capacity of the battery A of the embodiment has recovered to about 90% of the initial capacity, and the recovery characteristics of the battery B of the comparative example are more than 30%. Is improving.

Subsequently, each of the batteries A and B is
The charging was performed at a current of 1 C (1400 mA) at 1.2 ° C. for 1.2 hours, and the discharging was performed until the terminal voltage decreased to 1 V at a current of 1 C (1400 mA). The capacity retention ratio with respect to the initial capacity when the battery was repeatedly charged and discharged was determined, and this was taken as the battery life characteristic. FIG. 4 shows the results.

As shown in FIG. 4, even after 800 cycles of charge / discharge, the battery A of the embodiment had 90% of the initial capacity.
Capacity is secured. However, battery B has 10 charge / discharge cycles.
The capacity has already been reduced to 80% of the initial capacity when 0 cycles have been performed, and has significantly decreased to about 30% of the initial capacity when charging and discharging have been performed up to 800 cycles.

The reason for this is that, in the battery B of the comparative example, the base b has a portion not subjected to nickel plating, that is, an exposed portion of the iron base, and this portion is directly exposed to the alkaline electrolyte inside the battery. At the time of charge and discharge, iron is easily eluted into the alkaline electrolyte and further taken into the active material of the positive electrode to form FeOOH, which is an insulating material. Therefore, the battery B causes a decrease in the utilization efficiency of the positive electrode active material and a decrease in the charging efficiency due to a decrease in the oxygen overvoltage. As a result, the discharge characteristics, the life characteristics, and the capacity recovery characteristics after the discharge standing are larger than those of the battery A. It has fallen.

On the other hand, in the battery A, all parts of the surface of the iron sintered substrate, that is, the lower side of the nickel plating layer and the iron base part on which the nickel plating is not applied are also provided with the highly corrosion-resistant iron and nickel. Since the alloy layer is formed, the battery A is not affected by a change in the potential of the battery, and since the iron base of the base does not elute into the alkaline electrolyte, the utilization rate of the positive electrode active material decreases and There is almost no decrease in charging efficiency due to a decrease in oxygen overvoltage, and discharge characteristics as a battery,
The life characteristics and the capacity recovery characteristics after being left for discharge are improved.

In the above-described embodiment, a nickel plating layer having a thickness of about 5 μm was formed on the surface of the iron sintered body as the base body with respect to the iron skeleton diameter of 20 μm. Here, in order to diffuse iron and nickel to each other and form an alloy layer of iron and nickel having a high corrosion resistance to a sufficient thickness on the surface portion of the iron sintered substrate, the thickness of the initial nickel plating layer is as follows. It is preferable to keep the iron skeleton diameter in the range of 1/10 to 1/2.

The above-mentioned substrate a is formed by applying nickel plating to a sintered iron powder substrate having a three-dimensionally continuous space, and heating the substrate in a reducing atmosphere of hydrogen at 700 ° C. for 10 minutes. An alloy layer of iron and nickel was formed on the surface of the substrate. According to the study of the inventors, by heating the substrate after nickel plating in a reducing atmosphere at 650 to 720 ° C. for 5 to 20 minutes, the surface portion of the iron base is made of substantially the same iron as the example. A nickel alloy layer could be formed.

Further, in the examples, the positive electrode A was produced using the substrate a. However, the substrate a may be used as the negative electrode, and the substrate a may be used as both the positive electrode and the negative electrode.

[0041]

As described above, the present invention relates to an electrode for an alkaline storage battery in which a nickel powder is applied to a sintered iron powder substrate having a three-dimensionally continuous space and a space portion of the substrate is filled with an active material powder. An alloy layer of iron and nickel is formed on the surface portion of the iron base of the base. Of these alloy layers, those formed under the nickel plating layer have a nickel concentration higher than that of iron. Those formed on an iron base portion which was high and had no nickel plating layer were assumed to have a lower nickel concentration than iron. By constructing an alkaline storage battery using these electrodes, iron does not elute from the substrate in contact with the alkaline electrolyte, so that a good utilization rate of the positive electrode active material and an improvement in reliability over a long period of time are obtained. Thus, an inexpensive alkaline storage battery can be provided.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view showing a surface of a sintered iron substrate according to an embodiment of the present invention.

FIG. 2 is a half sectional view of the nickel-cadmium storage battery.

FIG. 3 is a diagram showing a relationship between a storage period and a capacity recovery rate of the battery.

FIG. 4 is a diagram showing a relationship between a charge / discharge cycle and a capacity retention ratio of the battery.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Iron powder sintered body 2 Nickel plating layer 3a Iron-nickel alloy layer 3b Iron-nickel alloy layer 4 Negative electrode 5 Separator 6 Battery case 7 Sealing plate

Claims (5)

[Claims] 1. An electrode for an alkaline storage battery in which a nickel powder is applied to a sintered iron powder base having a three-dimensionally continuous space and a space portion of the base is filled with an active material powder,
An alloy layer of iron and nickel is formed on the surface portion of the iron base of the base, and among these alloy layers, those formed under the nickel plating layer have a higher nickel concentration than iron, and The electrode formed on the iron base without the plating layer is an electrode for an alkaline storage battery having a lower nickel concentration than iron. 2. The electrode for an alkaline storage battery according to claim 1, wherein the thickness of the nickel plating layer is 1/10 to 1/2 with respect to the skeleton diameter of iron. 3. A nickel positive electrode, a negative electrode, a separator,
An alkaline storage battery comprising: an alkaline electrolyte; wherein the positive electrode and / or the negative electrode are formed by applying nickel plating to an iron powder sintered substrate having a three-dimensionally continuous space, and filling the space with an active material powder. Electrode, wherein an alloy layer of iron and nickel is formed on a surface portion of the iron base of the base, and an alloy layer formed under the nickel plating layer is more nickel than iron. An alkaline storage battery having a high concentration of nickel and having a nickel concentration lower than that of iron formed on a portion having no nickel plating layer. 4. The electrode for an alkaline storage battery according to claim 3, wherein the thickness of the nickel plating layer is 1/10 to 1/2 with respect to the iron skeleton diameter. 5. A method for producing an electrode for an alkaline storage battery in which a nickel powder is applied to a sintered iron powder substrate having a three-dimensionally continuous space and a space portion of the substrate is filled with an active material powder. Is an iron powder sintered substrate having a three-dimensionally continuous space, which is 1/10 to 1/2 of the iron skeleton diameter.
This substrate is subjected to nickel plating having a thickness of
A method for producing an electrode for an alkaline storage battery, wherein an alloy layer of iron and nickel is formed on a surface portion of an iron substrate by heating in a reducing atmosphere at 20 ° C. for 5 to 20 minutes.