JPS61216244A - Manufacture of sintered nickel substrate of alkaline storage battery - Google Patents

Abstract

PURPOSE:To restrain the nickel corrosion during the impregnation procedure of active materials, so as to prevent the decrease of mechanical strength of the pole plates and to make, free of occurrence, variation or decrease of the utility factor of active materials, by producing passive membrane composed of very thin oxide layers uniformly on the surface of sintered nickel plates. CONSTITUTION:Nickel powder is kneaded with organic water-soluble macromolecule and water to produce nickel slurry, and after the slurry is applied to porous electro- collectors and dried, the nickel powder is sintered in an atmosphere containing more than ten times equivalent weight of water vapor for carbon content contained in the nickel to produce sintered nickel plates. Further, the sintered nickel plates are heat-treated in an atmosphere containing oxygen at 160-300 deg.C, and the passive membrane composed of nickel oxide layers is produced on the surface of the sintered nickel plates. By this, passive membrane composed of very thin uniform oxide layers can be produced on the surface of the sintered nickel plates, and so the nickel corrosion during the impregnation procedure of active materials can be restrained, and thus the decrease of mechanical strength of pole plates can be prevented, and the pole plates having no or little decrease of utility factor of active materials can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a nickel sintered substrate for use in alkaline storage batteries such as nickel-cadmium storage batteries.

Conventional technology Conventionally, sintered substrates for alkaline storage batteries have been made by kneading nickel powder, such as carbonyl nickel powder, with a binder solution in which a water-soluble organic polymer, such as methylcellulose or carboxymethylcellulose, is dissolved in water. slurry and pear,
This nickel slurry is applied to a porous current collector, such as a nickel-plated perforated steel plate. It was manufactured by drying and then sintering in a reducing atmosphere. Since such a nickel sintered body has high activity, a portion of the nickel body is corroded by the acidic active material solution during the subsequent active material impregnation step.

In other words, the nickel sintered body is corroded by the impregnating liquid for the positive electrode, such as a nickel nitrate solution, and the impregnating liquid for the negative electrode, such as a cadmium nitrate solution. Therefore, the mechanical strength of the electrode plate decreases. Furthermore, in cadmium negative electrode plates, nickel hydroxide, which is a corrosion product of the nickel sintered body, mixes into the active material cadmium hydroxide, and when subjected to long-term trickle charging at high temperatures, the aggregate (support) alloy is formed. This has caused a two-stage phenomenon (hereinafter referred to as two-stage discharge) in which the voltage at the end of the next discharge decreases.

As a means to solve these problems, it is possible to form a passive film made of a nickel oxide layer (hereinafter simply referred to as an oxide layer) on the surface of the nickel sintered body to prevent corrosion of the nickel sintered body during the active material impregnation process. Proposed. (For example, JP-A-59
-96659 Publication) Problems to be Solved by the Invention When a pure nickel sintered body is heat-treated in an oxygen-containing atmosphere to form an oxide layer on its surface, due to the difference in specific volume with the underlying metal, Compressive stress is generated in the oxide layer, forming a dense passive film. Even if the nickel sintered body with the passive film formed thereon is immersed in an acidic active material solution in the active material impregnation step, almost no corrosion of nickel occurs and the mechanical strength of the electrode plate does not decrease. Roughly speaking, the cadmium negative electrode plate suppresses the formation of nickel hydroxide, and has the effect of preventing the phenomenon of two-stage discharge due to Ni--Cd content.

However, on the other hand, an electrode plate made from a nickel sintered substrate with a passive film formed on it is unprecedented! , 7 A new problem arises in which the utilization rate of active materials varies and decreases.
It was difficult to solve these problems at the same time.

The present invention aims to solve the above-mentioned problems of the prior art.

Means for Solving the Problems The present invention applies a nickel slurry to a porous current collector, dries it, and then sintering it. Sinter the nickel powder in an atmosphere 1), and further heat the nickel sintered body to 160~
After the first heat treatment in an oxygen-containing atmosphere at 300° C., a passive film consisting of an extremely thin oxide layer is uniformly formed on the surface of the nickel sintered body. Furthermore, in order to precisely control the thickness of the oxide layer, one nonionic substance is used as the water-soluble organic polymer when preparing the nickel slurry.

In an electrode plate made from a nickel sintered substrate with an oxide layer formed on its working surface, there is a tendency that the active material utilization rate of the electrode plate decreases as the thickness of the oxide layer increases. The reason for this is that NIO, which is an oxide of nickel, is originally a semiconductor close to an insulator at room temperature, and as the oxide layer becomes thicker, its insulating properties appear, inhibiting the electron conductivity of the electrode plate. This is thought to be due to the

Furthermore, in order to passivate nickel, it is generally necessary to form an oxide layer of several atomic layers or more, but the thickness of this film is thought to be about 30, which is extremely thin.

Based on these facts, we investigated a method for forming an extremely thin and uniform oxide layer on the surface of the nickel sintered body, and found that the temperature conditions during heat treatment and the removal of impurities mixed in the nickel sintered body are important for controlling the process. It turned out to be important.

The rate of oxidation of pure nickel by oxygen is determined by the rate of movement of the reaction components in the oxide=5 layer, and this rate of movement increases gradually as the temperature increases. In other words, in the case of low-temperature oxidation where the heat treatment temperature is 300°C or less, the oxidation rate is probably determined by the movement of electrons, and the number of electrons passing through the oxide layer due to the tunnel effect decreases exponentially with the thickness of the oxide layer. . A logarithm exists between the thickness of the oxide layer and the oxidation time, and the thickness of the oxide layer is substantially no thicker than several tens of nanometers, which is suitable for forming a thin oxide layer. Further, in this case, the oxidation rate of nickel does not depend on the oxygen partial pressure.

On the other hand, in oxidation at medium to high temperatures of 400°C or higher, a straightening agent or parabolic agent is established between the thickness of the oxide layer and the oxidation time, and compared to low-temperature oxidation, the oxidation of the oxide layer is The growth rate increases significantly. Therefore, although such high-temperature oxidation is advantageous for forming an oxide layer with a thickness of several hundred angstroms or more, it is extremely difficult to control and is not suitable for forming a thin oxide layer.

From these facts, in order to form an extremely thin oxide layer on the surface of the nickel sintered body, heat treatment at a temperature of 300°C or less is required.
I! However, since it takes a very long time to form the necessary oxide layer at temperatures lower than 160°C, it is not practical, and in reality heat treatment at 160-300°C is necessary. desirable.

Next, among the impurities mixed into the nickel sintered body, carbon is the main factor that inhibits the desired formation of the oxide layer described above. This is because the carbon in the carbonyl nickel used to prepare the nickel slurry and the water-soluble organic polymer as a binder cannot be completely removed during the sintering process and remain in the nickel sintered body. However, when such a nickel sintered body is used, even if heat treatment is performed in an atmosphere containing oxygen, corrosion of the nickel cannot be sufficiently suppressed in the subsequent active material impregnation step. The reason for this is that an oxide layer is formed on the surface of the nickel sintered body during heat treatment, but at the same time carbon oxidation also occurs, and the pressure associated with the volume change when solid carbon becomes gaseous carbon oxide. This is thought to be due to the fact that the oxide layer is destroyed and the nickel surface of the metal is exposed.

What is the method of removing carbon mixed in nickel?
It is effective to sinter nickel in a reducing atmosphere containing water vapor, and the reaction is thought to be based on equation (1). In this case, as shown in FIG. 1, the amount of water vapor added must be about 10 times the amount of carbon mixed in the nickel immediately before sintering, so that carbon is almost completely removed.

C+H20→CO+ 112... (1) From the two things mentioned above, it is possible to sinter nickel in a reducing atmosphere containing more than 10 times as much water vapor as the carbon mixed in the nickel just before sintering. As long as the heat treatment for the purpose of forming a passive film consisting of an oxide layer on the surface of the nickel sintered body is carried out at a temperature of 160 to 300°C, the performance of the produced electrode plate will be normal. , is in an acceptable range in most cases, but for even better control of the oxide layer thickness, 1(jli metal ions,
Mainly 11! The problem is that I+ ions are mixed into the nickel sintered body before heat treatment.

If a nickel sintered body contains monovalent metal ions such as Na+ ions, when heat-treated in an atmosphere containing oxygen, the oxidation rate of nickel will be lower than that of pure nickel based on the theory of valence control. Maro becomes smaller. Since it is considered that the amount of 11 ions mixed into the nickel sintered body is not always constant, the thickness of the produced oxide layer has low reproducibility. One of the reasons why Na + ions are mixed into the nickel sintered body is that a substance in the form of a metal salt such as sodium salt of carboxymethyl cellulose or sodium alginate is used as the water-soluble organic polymer used to prepare the nickel slurry.

For this reason, nonionic compounds such as methylcellulose, hydroxyethylcellulose, and hydroxypropylcellulose should be used as the water-soluble organic polymer used in preparing the nickel slurry.

Example Hereinafter, the present invention will be explained in detail with reference to Examples.

1. Knead carbonyl nickel powder with methyl cellulose and water to make nickel slurry, apply the nickel slurry to a nickel-plated perforated steel plate, dry it, and remove 20 (8 equivalents) of the carbon mixed in the nickel. A nickel sintered substrate was produced by sintering at 900°C in a reducing atmosphere containing water vapor.Next, the nickel sintered substrate was sintered at 200°C.
0 minutes (A-1) and 1 minute (A-1) in an electric furnace in an air atmosphere of
A-2).

3 minutes (A-3>, 10 minutes (Δ-4), 30 minutes (A-3)
-5), 100 minutes (A-6), 300 minutes (
A-7) After heat treatment, a cadmium negative electrode plate was prepared by a normal chemical impregnation method, and this was used as samples A-1 to A.
−7 (product of the present invention).

2. The heat treatment conditions in Example 1 were changed to 0 seconds (1'3-1>, 10 seconds (1'3-1>) and 10 seconds (
B-2), 20 seconds (B-3), 30 seconds (B-4),
Cadmium negative electrode plates were prepared in the same manner as in Example 1 using Ig for 40 seconds (B-5), 50 seconds (B-6), and 60 seconds (B-7), and these were used for samples B-1 to B. -7 (conventional product)
And so.

3. A cadmium negative electrode was prepared in the same manner as in Example 1, except that the sintering of nickel in Example 1 was carried out as normal sintering in a reducing atmosphere that does not contain water vapor, and the subsequent heat treatment was performed at 200°C for 30 minutes. A plate was prepared and designated as Sample C (conventional product).

4. Carboxymethylcellulose was used instead of methylcellulose in Example 1, and the heat treatment conditions were set to 200%
A cadmium negative electrode plate was prepared in the same manner as in Example 1, except that the temperature was increased for 30 minutes, and this was designated as Sample D (conventional product).

5. The sintering in Example 1 above was performed as normal sintering in a reducing atmosphere that does not contain water vapor, and a cadmium negative electrode plate was produced by a normal chemical impregnation method without heat treatment. ).

6. The heat treatment conditions in Example 1 above were changed to 200°C x 30
A nickel positive electrode plate was prepared in the same manner as in Example 1, except that the heating time was 10 minutes, and this was designated as Sample F (product of the present invention).

7. A nickel positive electrode plate was produced in the same manner as in Example 5 above, and this was designated as Sample G (conventional product).

Figure 2 shows samples A-1 to A-7 heat-treated at 200°C after sintering with addition of water vapor in Example 1, cut into 40 x 40 mm dimensions, and then cut into KOL with a specific gravity of 1.250 (20°C).
When two nickel plates of the same size as the sample are used as counter electrodes in a solution of R1, and the theoretical capacity of the test R1 is charged and discharged at a current flow rate of 5 hours, 3 circles are discharged? l! i1! The active material utilization rate of I and the amount of nickel corrosion (%) after the active material impregnation process are shown. Sample E, which was impregnated with an active material without heat treatment after normal sintering in Example 5, is also shown as a target product.

Figure 3 shows the same test content as Figure 2, with pretreatment 1 after sintering with the addition of water vapor in Example 2! I] Test where only the aging temperature was 400°C) Shows the unity of '31 B-' 1 to B-7.

When comparing these two figures with different heat treatments nFm,
For example, the heat treatment time range in which the amount of nickel corrosion is 1% or less and the active material utilization rate is 72% or more, which is 2% lower than the conventional sample E, is the present invention heat-treated at 200°C as shown in Figure 2. In the case of heat treatment, the time is approximately 18 minutes to 100 minutes, whereas in the case of heat treatment at 400°C as shown in Figure 3, such a range is very narrow and short, 30 seconds to 32 seconds. It turns out that its control is difficult. A similar phenomenon is observed in a nickel positive electrode plate using nickel hydroxide as an active material.

Figure 4 shows the effects of water vapor addition during sintering. Sample "C" was heat-treated at 200°C for 30 minutes after normal sintering in Example 3, and Sample "C" was heat-treated at 200°C for 30 minutes after normal sintering in Example 1. -5 high temperature trickle charge (charging current 30 hours rate, charging time 1 month, electrolyte temperature 4 months)
5° C.) is shown. Regarding sample A-5, the discharge curve did not become two steps, and consistent with the results shown in Figure 2, nickel corrosion did not occur during the active material impregnation process.
On the other hand, Sample C, in which no water vapor was added during sintering, had a two-stage discharge curve, indicating that the corrosion of nickel was not suppressed. This shows that unless nickel is sintered in a reducing atmosphere containing water vapor, an effective defective film consisting of an oxide layer cannot be formed in the subsequent heat treatment.

Next, in order to investigate the influence of molecules on water-soluble organic compounds for preparing nickel slurry, we conducted a sample sample using the carboxymethyl cellulose of Example 4 and a trial II using the methyl cell mouthpiece.
When the amount of corrosion of nickel of each 100 rimple of A-5 was investigated, the average corrosion m of the sample was about 2.3 times that of sample A-5, and the difference in standard tHQ was about 2.8 times, and the amount of corrosion was It can be seen that the variation is smaller when nonionic methylhirulose is used, and the reproducibility is better.

Also, regarding the mechanical strength of the electrode plate, test 1!1. A comparison was made between F and G. The defect rate was 2.1% for Sample G, which was not heat-treated after normal sintering, whereas it was 0% for Sample 1, which was heat-treated after sintering with the addition of water vapor. In the trial rIF in which water vapor was added before sintering, corrosion of the nickel sintered body, which is the framework of the electrode plate, was suppressed during the active material impregnation process, and the mechanical strength of the electrode plate was clearly improved. Note that the same tendency was observed for the cadmium-cum negative electrode plate.

Effects of the Invention As described above, according to the manufacturing method of the present invention, an immobile WA film consisting of an extremely thin and uniform oxide layer can be formed on the surface of a nickel sintered body, and this also allows the active material to It is possible to suppress the loss of nickel in the impregnation process, prevent a decrease in the strength of the electrode plate, and obtain an electrode plate with almost no decrease in the utilization rate of the active material. Furthermore, especially in the case of a cadmium negative electrode plate, the phenomenon of two-stage discharge due to the N1-Cd alloy can be prevented by suppressing the formation of nickel hydroxide. Furthermore, when a nonionic compound is used as a water-soluble organic polymer for preparing nickel slurry and a passive film consisting of an oxide layer is formed on the surface of a nickel sintered body using the method according to the present invention, the thickness of the passive film can be reproduced. It becomes a sexual thing.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the degree of reduction of carbon in nickel depending on the amount of water vapor added in the sintering process, and Figures 2 and 3 are graphs of nickel sintered substrates produced using the manufacturing method of the present invention. Figure 4 is a diagram comparing the active material utilization rate during discharge of the cadmium negative electrode plate at the third N3 cycle and the amount of nickel corrosion after the active material impregnation process. FIG. 3 is a diagram comparing the discharge curves of cadmium negative electrode plates produced using the method after high-temperature trickle charging. 1) Concubine, **Ipponryo Kenji Q (J<t-: ('/,) ban etc. wIN (da) Tsubo - voice Rin Hitsuji house

Claims (2)

[Claims] (1) Knead nickel powder with a water-soluble organic polymer and water to make a nickel slurry, apply the nickel slurry to a porous current collector, dry it, and then apply the nickel slurry to a porous current collector that has an equivalent amount of at least 10 times the amount of carbon mixed in the nickel. The nickel powder is sintered in a reducing atmosphere containing water vapor to form a nickel sintered body, and the nickel sintered body is further heat-treated in an atmosphere containing oxygen at 160 to 300°C to form a surface of the nickel sintered body. A method for producing a sintered nickel substrate for an alkaline storage battery, which comprises forming a passive film made of a nickel oxide layer. (2) The method for producing a nickel sintered substrate for an alkaline storage battery according to claim (1), wherein the water-soluble organic polymer used for preparing the nickel slurry is nonionic.