JPH0613076A - Nickel hydroxyde positive electrode plate for alkaline battery and its manufacture - Google Patents

Abstract

PURPOSE:To suppress electrode plate swelling in a nickel hydroxide positive electrode plate for alkaline battery by providing cobalt-contained nickel base, nickel hydroxide having cobalt solid solution formed thereon, and cadmium hydroxide never forming a solid solution with them. CONSTITUTION:Carbonyl nickel powder, metal cobalt powder and methyl cellulose aqueous solution are kneaded together to form a slurry. This is applied to a nickel-plated punched plate, dried, and sintered in hydrogen atmosphere to form a nickel base having a porosity of about 85%. The base is dipped in sodium hydroxide aqueous solution. The resulting base is dipped in sodium hydroxide aqueous solution after sufficient washing with water and drying. Thereafter, washing with hot water and drying are conducted to complete a positive electrode plate. According to this constitution, the swelling of the positive electrode plate by charge and discharge is suppressed, and a long-lived and high energy density battery or quick charging battery can be provided. It is effective that the cobalt content to be solid-dissolved in nickel hydroxide is set larger than the cobalt content of the nickel base.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a positive electrode plate comprising a nickel substrate containing cobalt, nickel hydroxide forming a solid solution with cobalt, and nickel or cadmium hydroxide not forming a solid solution with cobalt, and a method for producing the same. Is.

[0002]

2. Description of the Related Art In recent years, with the development of electronic equipment, the emergence of new high-performance secondary batteries is expected. Currently, nickel-cadmium batteries, nickel-zinc batteries, nickel-based batteries such as nickel-hydride batteries, and lead batteries are used as power sources for electronic devices. These secondary batteries are required to have high capacity as well as rapid charging performance. Among them, nickel-based secondary batteries use a nickel hydroxide electrode as a positive electrode plate. The electrode reaction of this positive electrode plate is diffusion of H ⁺ ions, and because it does not have a dissolution / precipitation mechanism unlike the electrode reaction of the positive electrode of lead batteries, it is expensive, but it is used as a long-life and high-performance electrode. There is. When this electrode is charged, nickel hydroxide becomes nickel oxyhydroxide (NiOOH). This nickel oxyhydroxide has β type and γ type, but if γ-NiOOH is generated during charging
Volume expansion of 31% occurs, and when it becomes α-NiOOH which is a discharge product of γ-NiOOH, it expands by 59%. In recent years, in order to increase the energy density of a battery, when the active material is filled in a large amount, the residual porosity of the electrode becomes small, and when the active material expands, the electrode becomes thick, and the electrolytic solution of the separator moves to the electrode. So-called "dry-up" in which internal resistance increases
A phenomenon may occur or the electrode may collapse to cause a short circuit. Furthermore, in applications requiring a shortened charging time, that is, in the case of performing rapid charging, the production of γ-NiOOH is particularly likely to occur, and a countermeasure for it has become necessary.

Conventionally, a method of adding cobalt hydroxide to an active material for the purpose of improving the utilization rate of the nickel hydroxide active material (for example, Electrochemistry 31,47 (1936), Patent Publication 50-1).
32441), and after filling the nickel substrate with the active material, Co (O
H) ₂ forming method (for example, Japanese Patent Publication No. 57-005018)
A method of forming a binary system of Cd (OH) ₂ -Ni (OH) ₂ (for example, Japanese Patent Publication No. 2-39063, USP4603094 (1984), Japanese Patent Publication No. Sho 56)
_{-36796) · Ni (OH) 2} -Co (OH) 2 - Cd (OH) method of forming a ₂ ternary (e.g. Patent Publication Rights 3-20860, USP395686 (19
76)) etc. have been proposed. Further, a method of incorporating metallic cobalt into a sintered nickel substrate which is a holder of an active material has also been proposed (for example, Japanese Patent Publication No. 54-1010). However, it was insufficient from the viewpoint of suppressing the production of γ-NiOOH.

[0004]

SUMMARY OF THE INVENTION Nickel-based batteries such as nickel-cadmium batteries, nickel-zinc batteries, and nickel-hydride batteries are required to have high energy density and rapid charging. However, the nickel hydroxide positive electrode plate used in high energy density batteries and batteries for rapid charging swells and becomes thicker as the charge and discharge cycle progresses, and the electrolyte solution of the separator moves to the electrodes and increases the internal resistance. There is a drawback that the battery life is shortened due to an up phenomenon. In particular, when a nickel substrate that is an active material holder having a nickel substrate of 85% or more is used, there is a problem that the swelling of the positive electrode plate becomes large because the strength of the substrate is weak.

[0005]

The present invention provides a nickel substrate containing cobalt in a nickel hydroxide positive electrode plate for an alkaline battery, nickel hydroxide which forms a solid solution with cobalt, and nickel or cadmium hydroxide which does not form a solid solution with cobalt. By including the above, the swelling of the positive electrode plate due to charging and discharging is suppressed, and a long-life high energy density battery and a battery for rapid charging are provided. Particularly, it is more effective if the content rate of cobalt which is solid-dissolved in nickel hydroxide is higher than the content rate of cobalt of the nickel substrate.
The present invention also provides that the nickel substrate has a porosity of 85 to 98%.
It is possible to extend the life of the high energy density positive electrode plate using the above. The manufacturing method is as follows.After holding nickel hydroxide forming a solid solution with cobalt on a nickel substrate containing cobalt, the content of cadmium is 10 to 80.
It is simple to immerse a mixed solution of mol% of cobalt and cadmium, then treat with an alkaline aqueous solution and dry.

[0006]

[Function] As a means for improving the utilization rate of the active material of the nickel hydroxide positive electrode plate, the active material holder such as a nickel porous body is filled with the active material, and then an aqueous cobalt solution such as cobalt nitrate or cobalt sulfate is impregnated with water. A method is generally used in which a layer of cobalt hydroxide is formed on the surface of the active material by neutralizing with an alkaline aqueous solution such as sodium oxide, and then charged to change to a layer of conductive cobalt oxyhydroxide. There is. Further, as an active material, cobalt hydroxide is added to the active material to form a solid solution with nickel hydroxide, or cadmium hydroxide is added to form a solid solution, thereby suppressing the production of γ-NiOOH. Therefore, a means for improving the utilization rate is also known as a universal technology. Further, a means for forming cadmium hydroxide that does not form a solid solution in addition to nickel hydroxide which is a positive electrode active material is a means known as a measure against over-discharge.

According to the present invention, the nickel hydroxide positive electrode plate used in a high energy density battery or a battery for rapid charging swells and becomes thicker as the charging / discharging cycle progresses, and the electrolytic solution of the separator moves to the electrode. Although it has been known that the cause of the increase in internal resistance, the dry-up phenomenon, and the shortening of battery life is that γ-NiOOH is produced as a charge product of the nickel hydroxide active material. In addition, the nickel porous body used as the active material holder is oxidized by charge and discharge to become nickel hydroxide, which becomes γ-NiOOH, so that the positive electrode plate swells and becomes thicker,
It is based on the finding that a major cause is that the electrolytic solution of the separator moves to the electrode plate. As a countermeasure, nickel is added to the active material holder, and cobalt is added to the active material. Further, by optimizing the active material and adding nickel hydroxide or cadmium hydroxide that does not form a solid solution with cobalt hydroxide, oxidation of the substrate can be prevented. It provides a means for suppressing the further oxidation of the nickel hydroxide produced to γ-NiOOH.

[0008]

The preferred embodiments of the present invention will be described below. [Example 1] Carbonyl nickel powder and 2 wt% metallic cobalt powder were mixed and then kneaded with a 0.1 wt% methylcellulose aqueous solution to form a slurry. This slurry was applied to a nickel plated 0.1 mm perforated plate, dried with a heater and then sintered at 950 ° C in a hydrogen reducing atmosphere to produce a sintered nickel substrate with a porosity of 85%. did. Next,
This sintered nickel substrate contains 2 mol% cobalt nitrate and 5M
Impregnated with nickel nitrate aqueous solution at 80 ℃,
Immerse in an aqueous solution of sodium hydroxide. After that,
After performing the operation of drying 8 times, at the end 10mo
After impregnating with a 1.5 M aqueous solution of cobalt nitrate containing 1% of cadmium, it is immersed in a 5 M aqueous solution of sodium hydroxide at 80 ° C. (hereinafter, this operation is referred to as “postcoat”). After that, it is washed with hot water and dried to have a theoretical capacity of 300 mAh and dimensions of 0.
A positive electrode plate of the present invention having a size of 8 × 14 × 52 (mm) was manufactured.

In Example 1, the content of metallic cobalt powder was set to 0,
Two positive electrode plates with 1,2,3,5,10 wt% were changed, and three conventionally known cadmium negative electrode plates with theoretical capacity of 500 mAh and dimensions of 0.7 x 15 x 52 (mm) were manufactured.

Next, the positive electrode plate was wrapped with a 0.12 mm polyamide nonwoven fabric separator and then heat-sealed.
Subsequently, a positive electrode plate and a negative electrode plate were alternately stacked to form an electrode plate group. Using this electrode group and 2.5 ml of 8.5 M potassium hydroxide aqueous solution as an electrolyte, a prismatic nickel-cadmium battery was manufactured using a nickel-plated iron battery case with a nominal capacity of 500 mAh. The external dimensions are 67 x 16.5 x 8 (mm),
The battery is equipped with a safety valve that operates at 0.5 kg / cm ² . The codes of the batteries containing 0,1,2,3,5,10 wt% of metallic cobalt are A, B, C, D, E, and F, respectively.

A cycle test was conducted in which these batteries were charged at 25 ° C. and 1 C for 70 minutes and then discharged to 1.0 V at a current of 0.5 C. FIG. 1 shows the change in the value of the internal resistance with the progress of cycles. From the figure, it can be seen that A with a metal cobalt content of 0% has an internal resistance value of 300 mΩ when the charge / discharge cycle reaches about 300 times. Thus, when the value of the internal resistance rapidly increased, the discharge capacity of the battery also decreased and the charging voltage also increased. On the other hand, the increase in internal resistance of B, C, D, E, and F having a metallic cobalt content of 1% or more is extremely small. When battery A was disassembled and the elements of the battery were examined, the separator electrolyte was depleted and the positive electrode plate was swollen thickly. Since there was almost no decrease in the weight of the battery, it is considered that a metal cobalt content of 0% means that γ-NiOOH was generated due to the oxidation of the nickel substrate. The formula of this γ-NiOOH is K _0.33 NiO ₂ · 0.67H ₂ O,
This means that the electrolytic solution is absorbed by the positive electrode.

The optimum content of metallic cobalt depends on the porosity of the sintered nickel substrate and the residual porosity after filling the active material. In Example 1, a positive electrode plate having residual porosity of 30% and metallic cobalt content of 1,2,3 wt% (G, H, and I, respectively) was prepared, and 8 MKOH was used as an electrolyte and a nickel plate was used as a counter electrode. Using two sheets, after charging 200% of the nominal capacity at a charge rate of 2C, discharge to 0V (Hg / Hg0) at 0.5C, and then change the thickness of the electrode plate after charging under the same conditions. As shown in FIG.
It has been empirically found that the internal resistance value of the battery rises when the increase rate of the electrode thickness exceeds 15%. From the figure, in order to set the increase rate of the thickness of the electrode plate to 15% or less, if the porosity of the nickel substrate is 80%, the content value of metallic cobalt is 1 wt% and the porosity is 85%. It is understood that the addition amount is required to be 2 wt% in the case of, and 3 wt% or more when the porosity is 90%.

Next, 5M containing 6 mol% cobalt nitrate on a nickel substrate having a metal cobalt content of 2% and a porosity of 80%.
Impregnated with nickel nitrate aqueous solution at 80 ℃,
Immerse in an aqueous solution of sodium hydroxide. After that,
After the drying operation was repeated 8 times, 1.5M containing 0,5,10,20,30,60,70,80mol% cadmium as post-coat.
After being impregnated with the cobalt nitrate aqueous solution of, it is immersed in a 5M aqueous sodium hydroxide solution at 80 ° C. Then, it was washed with hot water and dried to manufacture a positive electrode plate of the present invention having a theoretical capacity of 300 mAh and dimensions of 0.8 × 14 × 52 (mm).

These positive plates were used with 8 MKOH as the electrolyte and two nickel plates as the counter electrodes, and after charging 200% of the nominal capacity at a charging rate of 2 C, they were discharged to 0 V (Hg / Hg0) at 0.5 C. After charging under the same conditions, the material was washed with hot water and dried, and the active material was subjected to X-ray diffraction analysis. γ-NiOOH
The amount of γ-NiOOH (003) peak / (β-NiOOH (001) peak + γ-NiOOH (003) peak) is shown in FIG. From the figure, it can be seen that the production of γ-NiOOH is suppressed when the cadmium content of the postcoat is 10 mol% or more, and the production amount thereof is small particularly when it is 50 mol% or more. Practically, the cadmium content is preferably 10 to 80 mol%. Even if the cobalt-containing solution and the cadmium-containing solution were separated by post-coating, the same effect was obtained, but using a mixed solution of cobalt and cadmium requires only one process and is simple and easy. is there.

Next, two positive electrode plates and three conventionally known cadmium negative electrode plates having a theoretical capacity of 500 mAh and dimensions of 0.7 × 15 × 52 (mm) were manufactured.

The positive electrode plate was wrapped with a 0.12 mm polyamide nonwoven fabric separator and then heat-sealed. Subsequently, a positive electrode plate and a negative electrode plate were alternately stacked to form an electrode plate group. Using this electrode group and 2.5 ml of 8.5 M potassium hydroxide aqueous solution as an electrolyte, a prismatic nickel-cadmium battery was manufactured using a nickel-plated iron battery case with a nominal capacity of 500 mAh. The external dimensions are 67 × 16.5 × 8 (mm), and the battery is equipped with a safety valve that operates at 0.5 kg / cm ² . The batteries using post-coating positive electrode plates with cadmium content of 2,5,10,15 mol% are J, K, L and M. Figure 4 shows the change in capacity when a cycle test was performed in which this battery was charged at 1C for 1.2 hours and then discharged at 0.2C to 0.5V. From the figure, those with a cadmium content of 2 mol% (J) and 5 mol% (K)
When the number of charge / discharge cycles exceeds 600, the discharge capacity decreases, but the cadmium content is 10 mol% (L) and 15 mol%.
It can be seen that the capacity of the battery (M) according to the present invention is stable and good.

Thus, the content of cadmium is 10 mol%
In the above cases, the charge / discharge cycle life is improved because the nickel hydroxide formed by the oxidation of nickel on the active material and the nickel substrate changes to a state in which γ-NiOOH does not easily become γ-NiOOH during charging as the charge / discharge cycle progresses. It is thought to be due to the reason. The mechanism is considered as follows. That is, the content rate of cadmium in the post-coat liquid is
When the content is 10 mol% or more, hydroxides formed in the neutralization step form cadmium hydroxide that does not form a solid solution, in addition to cobalt hydroxide that forms a solid solution with cobalt hydroxide.
Nickel hydroxide becomes γ-NiOOH during charging, and its discharge product becomes α-Ni (OH) ₂ , but this α-Ni (OH) ₂ dissolves in an alkaline aqueous solution to form β-Ni (OH) 2. Phase change to ₂ . At that time, cadmium hydroxide that does not form a solid solution is incorporated into the crystal as a solid solution in the active material. Then, in the subsequent charging, it is considered that the generation of γ-Ni (OH) ₂ is suppressed, the swelling of the electrode plate is reduced, and the life is extended. The relationship between the content of cobalt in the nickel substrate and the content of cobalt in solid solution in nickel hydroxide is that the content of cobalt in solid solution in nickel hydroxide is higher than the content of cobalt in the nickel substrate. Was good. This is because when the amount of cobalt contained in nickel hydroxide produced by the oxidation of the nickel substrate is large, it becomes more active than the active material,
It is considered that during discharge, the active material in the bulk is discharged preferentially, and the discharge product thereof becomes a resistance to deteriorate the discharge performance of the positive electrode.

[0018]

As described above, in the nickel hydroxide positive electrode plate for alkaline batteries, the nickel substrate containing cobalt, nickel hydroxide forming a solid solution with cobalt, and nickel or cobalt and cadmium hydroxide not forming a solid solution are provided. As a result, the swelling of the positive electrode plate due to charging and discharging is suppressed, and a long-life high energy density battery and a battery for rapid charging are provided. Particularly, it is more effective if the content rate of cobalt which is solid-dissolved in nickel hydroxide is higher than the content rate of cobalt of the nickel substrate. Further, according to the present invention, a positive electrode plate having a high energy density using a nickel substrate having a porosity of 85 to 98% can have a long life.

[Brief description of drawings]

FIG. 1 is a diagram comparing changes in internal resistance of a conventional battery and a sealed nickel-cadmium battery using a positive electrode plate according to the present invention with progress of charge / discharge cycles.

FIG. 2 is a diagram showing the relationship between the increase rate of the electrode plate thickness of the positive electrode plate of the present invention and the porosity of the substrate.

FIG. 3 is a diagram showing a relationship between a production state of γ-NiOOH in a charged state and a cadmium content rate.

FIG. 4 is a diagram comparing the capacity retention ratios of a sealed nickel-cadmium battery using the positive electrode plate according to the present invention and a conventional battery with charge / discharge cycles.

Claims (4)

[Claims] 1. A nickel hydroxide positive electrode plate for an alkaline battery, comprising a nickel substrate containing cobalt, nickel hydroxide forming a solid solution with cobalt, and nickel or cadmium hydroxide not forming a solid solution with cobalt. 2. The nickel hydroxide positive electrode plate for an alkaline battery according to claim 1, wherein the content of cobalt dissolved in nickel hydroxide is higher than the content of cobalt in the nickel substrate. 3. The nickel hydroxide positive electrode plate for an alkaline battery according to claim 1, wherein the nickel substrate has a porosity of 85 to 98%. 4. A nickel substrate containing cobalt, which holds nickel hydroxide forming a solid solution with cobalt, is dipped in a mixed solution of cobalt and cadmium having a cadmium content of 10 to 80 mol%, and then an alkaline aqueous solution. A method for producing a positive electrode plate for an alkaline battery, which is characterized in that it is treated with and dried.