JPH11288725A - 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 filling an active material powder into a space part of an iron powder sintered substrate 1 having three-dimensionally continuous space. Here, a nickel-iron alloy layer 2 is provided on the whole surface of the substrate 1, and the alloy layer 2 is obtained by mutual solution and diffusion of the nickel and the iron formed by nickel plating.

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 electrode for an alkaline storage battery in which a space portion of an iron powder sintered base having a three-dimensionally continuous space is filled with an active material powder. An alloy layer of nickel and iron was provided on all of the surface portions of the substrate, and the alloy layer was obtained by solid solution diffusion of nickel and iron formed by nickel plating. .

[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 nickel and iron is provided on the entire surface portion of the iron sintered substrate, and this alloy layer is formed by nickel and iron formed by nickel plating. It is obtained by solid solution diffusion. An iron-nickel alloy layer is provided on all of the surface portions of the iron powder sintered substrate regardless of the presence or absence of nickel plating, so that corrosion resistance can be improved. When an alkaline storage battery is formed using this electrode, the surface of the iron sintered substrate forming the electrode is always protected by a nickel-iron alloy layer having high corrosion resistance. Even if stored for a long period of time, iron does not elute from the iron sintered substrate into the alkaline electrolyte.

For this reason, the iron sintered substrate can be used for an electrode of an alkaline storage battery instead of the nickel sintered substrate, and the same characteristics as those of a battery using a conventional nickel powder sintered substrate can be obtained. 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, the thickness of the alloy layer of nickel and iron provided on the surface portion of the sintered iron powder substrate is defined, and this thickness is preferably in the range of 1 to 7 μm. .

According to a fifth aspect of the present invention, there is provided an alkali filling a space portion of an iron powder sintered substrate having a three-dimensionally continuous space and having a nickel-iron alloy layer on a surface thereof, with an active material powder. A method for producing an electrode for a storage battery, wherein the substrate is formed by plating a surface of an iron powder sintered substrate having a three-dimensionally continuous space with nickel plating having a thickness of 1 to 5 μm, and then heating the substrate at 750 to 900 ° C. Under a reducing atmosphere for 5 to 20 minutes to form an alloy layer of nickel and iron on the entire surface of the substrate regardless of the presence or absence of nickel plating.

In this manufacturing method, nickel-plated nickel powder is applied to the sintered body of the iron powder, and then heat-treated in a reducing atmosphere at 750 to 900 ° C., so that nickel of nickel-plated metal and the surface of the iron base material are dissolved and diffused. The alloy layer of nickel and iron is formed on the entire surface of the iron sintered powder.

[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 foamed polyurethane resin core having three-dimensionally continuous pores of about 600 μm was prepared. Separately Fe ₂ 0 ₃ powder and metallic iron 7: mixed with phenolic resin in 3 ratio (weight ratio), and coating the slurry foamed polyurethane resin surface in a thickness of 20 [mu] m, dried at 90 ° C. did.

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.

As a third step, the sintered body 1 was immersed in a hydrochloric acid aqueous solution to perform a pretreatment for removing impurities, and then subjected to nickel plating of 3 μm in a nickel sulfate bath at a current density of 10 A / dm ² . Then, the substrate is washed with water, and the substrate is heated at 800 ° C. under a reducing atmosphere of hydrogen.
The base a of the example in which nickel and iron alloy layers were formed on the entire surface portion of the iron base material by solid-solution diffusion of nickel and iron to each other was produced. FIG. 1 shows a schematic sectional view of the substrate surface. In FIG. 1, 1 indicates a sintered iron powder, and 2 indicates an alloy layer of nickel and iron.

This alloy layer was analyzed using an Auger electron spectrometer to confirm that it was an alloy layer of nickel and iron. The thickness was confirmed to be about 2 to 5 μm by observation using a transmission electron microscope.

The nickel-iron alloy layer 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.

At this time, when the above-mentioned heat treatment is performed at a temperature higher than 900 ° C. or in an air atmosphere, decomposition and oxidation occur, and the substrate strength is reduced to about の of the above-mentioned value. Level.

Using the above 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.

On the other hand, as to prepare a foamed polyurethane resin core body having pores of a three-dimensionally continuous about 600 .mu.m, this fine powder and metallic iron Fe ₂ 0 ₃ 7: 3 ratio (by weight) A slurry mixed with a phenolic resin was applied and heat-treated at 1100 ° C. for 30 minutes in a hydrogen atmosphere to remove the polyurethane resin core and produce an iron-sintered substrate in which iron powder was sintered. This iron sintered substrate is also subjected to nickel plating with a thickness of 3 μm in the same manner as described above,
An annealing process was performed by heating at 500 ° C. to prepare an iron sintered substrate b of a comparative example.

At this time, the portion of the base 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 3 was prepared by applying a paste mainly composed of cadmium oxide to a core of a punched metal plated with nickel on iron, drying, washing with water, drying, and cutting to a predetermined size.

The positive electrode a and the negative electrode 3 produced as described above, and a polypropylene separator 4 interposed therebetween, are spirally wound to form an electrode plate group, which is formed in a nickel-plated iron battery case 5. After inserting a predetermined amount of the alkaline electrolyte into the case 5, the upper portion of the case 5 is sealed with a sealing plate 6 also serving as a positive electrode terminal to have 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).

[0031]

[Table 1]

As shown in (Table 1), the battery A of the example shows that the utilization rate of the positive electrode active material is 96%, which is 7% higher than the battery B of 89%.

Next, in a 20 ° C. atmosphere, each of the batteries A and B was stored and discharged in a state of discharging at a current of 0.2 C (280 mA), and then charged to a two-month initial capacity. 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 directly contacts 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, since the nickel-iron alloy layer having high corrosion resistance is provided on the entire surface portion of the iron sintered body of the base, the battery A is affected by the potential change of the battery. In Battery A, since the iron base of the base did not elute into the alkaline electrolyte, there was almost no decrease in the charge efficiency due to a decrease in the utilization rate of the positive electrode active material and a decrease in the oxygen overvoltage. In addition, the capacity recovery characteristics after leaving for discharge have been improved.

In the above embodiment, an iron-nickel alloy layer having a thickness of about 2 to 5 μm was formed on the entire surface of the iron sintered body of the substrate. If the range is 1 to 7 μm, the same effect as in the embodiment can be obtained.

Further, in the embodiment, the positive electrode A
Was prepared, but 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 space portion of an iron powder sintered base having a three-dimensionally continuous space is filled with an active material powder, and a surface portion of the base. Are provided with an alloy layer of nickel and iron, and this alloy layer is obtained by the solid solution diffusion of nickel and iron formed by nickel plating. In addition, by constructing an alkaline storage battery using this electrode, the base in the battery does not elute iron even when it comes into contact with the alkaline electrolyte, so that a good utilization rate of the positive electrode active material and a long-term reliability can be obtained. It is possible to provide an inexpensive alkaline storage battery which is improved.

[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 and iron alloy layer 3 Negative electrode 4 Separator 5 Battery case 6 Sealing plate

Claims (5)

[Claims] 1. An electrode for an alkaline storage battery in which a space portion of an iron powder sintered base having a three-dimensionally continuous space is filled with an active material powder, and the entire surface of the base is formed of nickel and iron. An electrode for an alkaline storage battery, comprising an alloy layer, wherein the alloy layer is obtained by solid solution diffusion of nickel and iron formed by nickel plating. 2. The thickness of said alloy layer of nickel and iron is from 1 to 1.
The electrode for an alkaline storage battery according to claim 1, which has a thickness of 7 µm. 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 electrodes in which a space portion of an iron powder sintered substrate having a three-dimensionally continuous space is filled with an active material powder, An alloy layer of nickel and iron is provided on all of the surface portion of the base, and this alloy layer is an alkali layer obtained by solid solution diffusion of nickel and iron formed by nickel plating. Storage battery. 4. The nickel-iron alloy layer has a thickness of 1 to 4.
The electrode for an alkaline storage battery according to claim 3, which has a thickness of 7 µm. 5. A method for manufacturing an electrode for an alkaline storage battery, comprising a three-dimensionally continuous space, and a space portion of an iron powder sintered substrate having a nickel-iron alloy layer on the surface and filling a space portion with an active material powder. The substrate is formed by plating a surface of an iron powder sintered substrate having a three-dimensionally continuous space with nickel plating having a thickness of 1 to 5 μm, and then subjecting the substrate to a reducing atmosphere of 750 to 900 ° C. for 5 to 5 μm. A method for manufacturing an electrode for an alkaline storage battery, wherein a heat treatment is performed for 20 minutes to form an alloy layer of nickel and iron on the entire surface of the substrate regardless of the presence or absence of nickel plating.