JPH02103859A - Nickel electrode for alkaline battery and its manufacture - Google Patents

Abstract

PURPOSE:To improve the utilization factor of active material and to prevent electrode swelling by making cobalthydroxide, existing at the surface of the pole plate of a nickel electrode, alpha-CO(OH)2. CONSTITUTION:Before filling nickel hydroxide being main ingredient active material, cobalthydroxide is filled singly, and next a specific amount of nickel hydroxide being main ingredient active material is filled, and then further cobalthydroxide existing at the surface of the pole plate of a nickel electrode wherein cobalthyhydroxide is filled singly is made alpha-CO(OH)2. By making cobalthyhydroxide alpha-CO(OH)2 so as to cover the nickel active material this way, the utilization factor of active material is improved, and also the place of action becomes uniform, and even before charge the generation of gamma-NiOOH being higher order oxide of nickel is suppressed, so electrode swelling attendant upon the crystal density change can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a nickel electrode for alkaline storage batteries and a method for manufacturing the same.

Conventional technology and its problems Nickel-cadmium! Alkaline storage represented by oil wt.
As is well known, nickel flEm used in oil is produced by impregnating a nickel nitrate aqueous solution under reduced pressure into the pores of a porous substrate obtained by sintering niranal powder etc. on a nickel-plated copper plate, and then chemically It is manufactured using the so-called chemical impregnation method, which converts it into nickel hydroxide.

Addition of cobalt has been used for a long time as a method for improving the characteristics of nickel electrodes. Cobalt added by the conventional method forms a solid solution state with disocyl hydroxide and has the effect of improving charging characteristics. On the other hand, it has become clear that cobalt, which does not form a solid solution with nickel hydroxide, that is, is added in a free state, exhibits very interesting behavior in improving electrode performance. From this point of view, for example, as described in Japanese Patent Publication No. 57-5018, nickel hydroxide, which is an active material, is added to nickel plaque by using an impregnating solution containing more cobalt salt than nickel salt. A method of forming a cobalt hydroxide layer in a free state has been proposed.

However, in this method, cobalt, which is at the solid solubility limit, is liberated, and since about 20% of cobalt relative to nickel is within the solid solubility limit, it becomes a solid solution with nickel hydroxide.

That is, a cobalt hydroxide layer in a free state and a layer in a solid solution state with nickel hydroxide coexist. It has been found that this nickel hydroxide layer in a solid solution with cobalt hydroxide has a drawback that causes a large drop in discharge voltage.

Therefore, it is necessary to cover the nickel active material layer with only a layer of free pure cobalt compound, and as one method for this, an invention as described in JP-A-65-40255 has been proposed. . According to this publication, it is described that a single layer of cobalt is formed on a sintered nickel substrate, then impregnated with a nickel active material, and then a single layer of cobalt is formed again to cover the active material. .

By the way, cobalt in a single layer is effective as an additive because the β-Go(OH)2 wall precipitated between the current collector and the active material particles and between the active material particles is oxidized by charging and discharging. It has been reported that the utilization rate can be improved by forming a conductive OOOOH layer. Therefore, based on the above findings, it can be said that a high-performance nickel electrode can be obtained by coating nickel hydroxide particles, which are active materials, with a free layer of cobalt hydroxide.

By the way, it has been found that the cobalt hydroxide present on the tV produced by the above method is easily oxidized in the air and easily converted into an inert substance. This is due to the fact that the cobalt hydroxide produced by the above method is a substance that is unstable in air and is crystallographically classified as β-Co(OH)2, as described in the above literature. and this β-Co(
OH)2 undergoes air oxidation to become inert, low conductive CO
This is because it changes to HO2. For this reason, the added cobalt cannot form highly conductive and effective 0oOOH, so for the purpose of obtaining high-performance nickel electrodes, β-
It can be said that preventing oxidation of CfO(OH)2 is an essential factor. Furthermore, 0OHO2 and 00, which have low conductivity,
When 304 is interposed between the current collector and the active material, non-uniformity occurs in the charging/discharging reaction field, and the current density locally increases.
This also induces the disadvantage that OH is more likely to be generated.

For these reasons, at present, the effects of cobalt additives have not been fully obtained.

Purpose of the Invention The present invention provides a nickel electrode for alkaline storage batteries that has a high active material utilization rate due to the excellent effects of cobalt, has low wt electrode swelling, has excellent storage stability, has a high capacity, and has excellent cycle characteristics, and a method for producing the same. The purpose is to provide

Structure of the Invention In order to achieve the above-mentioned object, the present invention is to fill cobalt hydroxide alone before filling nickel hydroxide which is the main component active material, and then after filling a predetermined amount of the main component active material, Furthermore, the present invention is a nickel electrode for an alkaline storage battery characterized in that the cobalt hydroxide present on the surface of the electrode plate of the nickel electrode filled with cobalt hydroxide alone is a-00(OH)2.

In the production of the nickel electrode, after impregnating a cobalt salt aqueous solution into a nickel sintered substrate under reduced pressure, the pH is adjusted to 9 to 1.
It is characterized in that it is converted into a hydroxide in a basic bath in step 5.

(1-Go(OH)2, which is generated in a weakly alkaline region, is
It is stable and difficult to oxidize even in the air, while rapidly changing to β-Co(OH)2 in an alkaline electrolyte. Therefore, by coating the nickel active material as a-Co(OH)2, the cobalt additive becomes an inert higher-order cobalt oxide (30HO2) that has an effective 0o00H conductivity even after long-term storage. It is possible to form layers.

The conductivity of the nickel electrode on which the 0o00H layer is formed facilitates the electron movement of the nickel active substance at the end of discharge, and as a result, deep discharge is possible to a region with a low oxidation value.

That is, the active material utilization rate is improved. Also, inert CoHO
2 is not formed, the reaction field becomes uniform, and even during charging, γ-NiOO, which is a higher order oxide of nickel,
Since the generation of H was suppressed, electrode swelling due to changes in crystal density was prevented, and there was a tendency to suppress a decrease in the strength of the electrode plate.

Example Hereinafter, the details of the present invention will be explained with reference to Examples.

Example 1 A sintered nickel substrate with a porosity of 80% cotton and a specific gravity of approximately 1.6.
After impregnation with a cobalt nitrate aqueous solution (20℃) under reduced pressure, it was immersed in a weak alkaline ammonium hydroxide aqueous solution (pH -9) without using the conventional strong alkaline aqueous solutions such as sodium hydroxide and potassium hydroxide. It was washed and dried to form a cobalt hydroxide layer. Next, after impregnating under reduced pressure with a nickel nitrate aqueous solution with a specific gravity of approximately 1.3 (80 °C),
A predetermined amount of nickel hydroxide active material was filled by repeating the steps of neutralizing with an aqueous sodium hydroxide solution at a temperature of 30°F (°C), washing with hot water, and drying several times. Furthermore, the particles were again impregnated with a cobalt nitrate aqueous solution under reduced pressure, immersed in a weak alkaline solution, washed with hot water, and dried to coat the Niracle hydroxide particles with cobalt hydroxide. The thus obtained electrode plate of the present invention was designated as electrode plate A.

This electrode plate is crushed and the crystalline state of the added cobalt is determined by X!
As confirmed by the diffraction characteristic peak, the main product is α-
It was 00(OH)2. Cobalt hydroxide near the substrate is difficult to perform X-ray analysis due to Niracle hydroxide particles, but the following possibilities can be considered. It is thought that the highly concentrated alkaline aqueous solution bath in the process of filling the nickel hydroxide active material changes the previously formed cobalt hydroxide layer to β-Co(OH)2, which is easily oxidized in the air. It is believed that the oxidation of cobalt oxide is inhibited by the active material layer and the generation of inactive Cf0HO2 is avoided. If this assumption is based on this assumption, the cobalt hydroxide layer, which is susceptible to oxidation and easily changes to inert 00HO2, is located on the surface of the nickel hydroxide active material layer, not in the layer between the nickel substrate and the active material layer. layer (copal hydroxide impregnated last), and the latter cobalt hydroxide layer is α
It can be said that the form it takes is important.

Example 2 The same sintered nickel substrate used in Example 1 was impregnated with a cobalt nitrate aqueous solution with a specific gravity of about 1.6 (20°C) under reduced pressure, and then hydroxylated with a specific gravity of about 1.3 (80°C). ) Neutralized with IJum aqueous solution, washed with hot water, and dried to form a cobalt hydroxide layer. Next, the process of impregnating under reduced pressure with a nickel nitrate aqueous solution with a specific gravity of approximately 1.6 (20°C), neutralizing with a sodium hydroxide aqueous solution having a specific gravity of approximately 1.3 (80°C), washing with hot water, and drying is repeated several times. A hydroxide niracle active material layer was formed. Furthermore, the cobalt nitrate aqueous solution was impregnated under reduced pressure, and the specific gravity was approximately 1.3 (
The active material layer was coated with a cobalt hydroxide layer by neutralizing with a sodium hydroxide water bath solution at 80° C., washing with hot water, and drying. The comparative cobalt-added electrode plate thus obtained was designated as electrode plate B.

When the X-ray diffraction peak of this electrode plate was examined in the same manner as for electrode plate A, the main cobalt product was β-Co(OH)2. FIG. 2 shows the results of examining the X-ray diffraction peaks after Plate B was stored at 40° C. for 5 days at a temperature of 80%.

As is clear from the figure, in the electrode plate A of the present invention, there is no generation of inert cobalt higher order oxide C0HO2, but in the electrode plate B, most of the cobalt is changed to C0HO2. Therefore, it is considered that the effect of cobalt addition cannot be sufficiently obtained in the electrode plate B after being left alone.

In order to confirm this, batteries obtained by combining these electrode plates with a known cadmium electrode as shown in FIG. 1 were designated as Battery A and Battery B, respectively.

Both battery A and battery B have a nominal capacity of 1. The capacity of the cadmium electrode was sufficiently larger than that of the nickel electrode, and the electrolyte was potassium hydroxide with a specific gravity of 1.24 (at 20° C.). Further, a battery C similar to battery A and battery B was manufactured using a conventional sintered nickel electrode. Here, a mercury/mercury oxide electrode was used as the reference electrode.

After charging these batteries at 0.1 OA (100 mA) for 14 hours, they were discharged at 1.0 OA (1, OA) and the end-of-discharge voltage was referenced [0. The cycle characteristics at Ov are shown in FIG. 3, and the discharge characteristics are shown in FIG. 4.

Battery A of the present invention exhibits superior cycle characteristics compared to Battery B1 and Battery C, and also has high voltage flatness in discharge characteristics.
It can also be seen that the battery has a large capacity and weight.

Here, the discharge voltage of Battery A1 and Battery B is lower than that of Battery O because, when impregnated again with the cobalt nitrate aqueous solution, the active material layer elutes and re-precipitates, forming a solid solution of nickel and cobalt. This is thought to be due to the fact that

Table 1 shows the results of disassembling the battery after 200 cycles of charging and discharging and examining changes in the thickness of the nickel positive electrode.

There was almost no change in the thickness of the electrode plates of battery B1 and battery C, whereas the electrode plates of battery B1 and battery C swelled, causing so-called blisters in some parts, and even causing some parts to fall off. So, when we investigated the X-ray diffraction of these electrode plates, we found that
It was found that a large amount of γ-NiOOH was produced.

Considering this phenomenon, in the electrode plate B, the added cobalt cannot form an effective conductive 0o00H layer, and as mentioned above, non-uniformity of the charging/discharging reaction field occurs, causing local It is considered that the current density increased and a large amount of γ-NiOOH was generated. Therefore, 1-Ni0
It is thought that stress was generated in the sintered nickel substrate due to a change in crystal density due to the generation of OH, and the stress strain caused the electrode plate to fall off. Therefore, it can be seen that when high-density packing is performed using a nickel substrate with low strength and high porosity, the method according to the present invention can be a very effective means for improving the strength of the electrode plate.

Swelling rate: Plate thickness after 200 cycles relative to the plate thickness before charging and discharging Table 2 shows the changes in the oxidation value of the nickel positive electrode during charging and discharging. Inventive battery A has a low oxidation value at the end of charging, which also indicates that the generation of 1-Ni0OH is suppressed, and the oxidation value at the end of discharge is also low, making deeper discharge possible. You can see that Therefore, Km of the present invention does not require high-density packing.
It is possible to increase the capacity.

Table 2 Oxidation value: X value of NiOx Here again, since the cobalt added to the battery Bt is oxidized in the air and changed to GOHO2 as described above, it cannot become an 0oOOH layer that is effective as an additive. Therefore, it seems that the behavior was almost the same as that of Battery C without cobalt added.

In this example, α
-(3o(OH)2), α-Co(OH)2 can be precipitated in the pH range of 7 to 15. However, if the neutralization step is performed in the pH range of 9 to 15, α-Co(OH)2 can be precipitated efficiently. -Co(OH)2 is obtained.

Effects of the Invention As described above, the present invention provides a nickel electrode for alkaline storage batteries that has a high utilization rate of active material due to the excellent effects of cobalt, has low electrode swelling, has excellent storage stability, and has high capacity and excellent cycle characteristics. Since it is possible to provide a method for producing the same and a method for producing the same, its industrial value is extremely large.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of the test battery, FIG. 2 is a comparison of X-ray diffraction of the electrode plates, FIG. 3 is a comparison of charge/discharge cycle characteristics, and FIG. 4 is a comparison of discharge characteristics.

Claims (2)

[Claims] (1) Before filling with nickel hydroxide, which is the main active material,
Cobalt hydroxide present on the electrode plate surface of a nickel electrode filled with cobalt hydroxide alone, then filled with a predetermined amount of the main component active material, and then filled with cobalt hydroxide alone becomes α-Co(OH). A nickel electrode for an alkaline storage battery characterized by being _2. (2) In the cobalt hydroxide filling step of the nickel electrode for an alkaline storage battery according to claim 1, after impregnating the cobalt salt aqueous solution into the nickel sintered substrate or the like under reduced pressure, the pH is 9 to 15.
A method for producing a nickel electrode for an alkaline storage battery, characterized by converting it into a hydroxide in a basic bath.