JPH07320737A - Non-sintered nickel electrode for alkaline storage battery and manufacture thereof - Google Patents

Abstract

PURPOSE:To enhance conductivity of an electrode plate and active material utilization factor by protecting an unstable inner layer with a relatively stable outer layer. CONSTITUTION:A nickel hydroxide particle or a solid solution particle mainly comprising nickel hydroxide, whose surface is covered with a cobalt hydroxide layer is used as an active material. The cobalt hydroxide layer consists of two layers of an inner layer mainly comprising alpha-Co(OH)2 and an outer layer mainly comprising beta-Co(OH)2. When a nickel electrode is manufactured, the solid solution particle is immersed in a cobalt compound aqueous solution, an alkaline aqueous solution is added to the solution until pH of the solution becomes 9-10, then mixed to produce an active material intermediate product in which a covering layer mainly comprising alpha-Co(OH)2 is formed on the surface of the solid solution particle. The intermediate product is immersed in a cobalt compound aqueous solution, an alkaline aqueous solution is added to the solution until pH of the solution becomes 11-12, then mixed to produce the active material in which a covering layer mainly comprising beta-Co(OH)2 is formed on the surface of the intermediate product particle. The active material obtained is filled in a conductive substrate.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-sintered nickel electrode for alkaline storage batteries having a high utilization rate of active material and a method for producing the same.

[0002]

BACKGROUND OF THE INVENTION A typical nickel electrode for an alkaline storage battery is a solution impregnated into pores of a sintered substrate obtained by sintering nickel powder on a perforated steel plate or the like. Sintered nickel electrode filled with an active material by the method, and an alkali-resistant metal fiber sintered body, or a porous substrate made of carbon fiber nonwoven fabric plated with a metal having excellent alkali resistance such as nickel, There is a non-sintered nickel electrode formed by filling a paste of nickel hydroxide powder.

The sintered nickel electrode has a high utilization ratio of the active material because the sintered substrate has good conductivity. However, since the bonding between the nickel particles of the sintered substrate is weak, the active material is likely to drop out of the sintered substrate when the sintered substrate having high porosity is used. Therefore, the practicable sintered substrates are limited to those having a porosity of about 80% or less. In addition, a cored bar such as a perforated steel plate for holding the nickel sintered body is required. For these reasons, the sintered nickel electrode has a problem that the packing density is low. Moreover, the pores of the nickel sintered body are 10 μm.
Since it is as small as the following, it is necessary to repeat the solution impregnation operation when filling the active material, and there is also a problem that the production of the electrode plate is complicated.

The non-sintered nickel electrode has been proposed to solve the above problems of the sintered nickel electrode. In this non-sintered nickel electrode, since the active material is once filled in the base material such as the alkali-resistant metal fiber sintered body having a large porosity and having no core metal, the nickel electrode having a large packing density can be obtained. Also, the production of the electrode plate is simple.

However, if the substrate is filled with only nickel hydroxide powder, the utilization factor of the active material is remarkably low due to the poor conductivity of the electrode plate, and a practical product cannot be obtained.

In an attempt to improve the utilization rate of the active material of the non-sintered nickel electrode and put it into practical use, divalent cobalt hydroxide (powder) as a conductive agent is added and mixed with nickel hydroxide powder. A method (addition and mixing method) has been proposed (JP-A-61-49374).

By the way, since cobalt hydroxide is apt to be unevenly distributed in the paste and it is difficult to uniformly mix and disperse it with the nickel hydroxide powder, in order to effectively improve the utilization rate of the active material,
It is necessary to add a large amount of cobalt hydroxide. However, when a large amount of cobalt hydroxide is added, the filling amount of nickel hydroxide as an active material is inevitably reduced, so that the electrode plate capacity decreases.

Therefore, in recent years, as an alternative to the above-mentioned addition and mixing method, a method (single coating method) of forming a coating layer (single layer) of cobalt hydroxide on the surface of nickel hydroxide particles has been proposed (special feature). JP-A-62-234867, JP-A-62-237667, and JP-A-62-22256.
No. 6, etc.). In this single coating method, a coating layer of α-Co (OH) ₂ or β-Co (OH) ₂ is formed on the surface of nickel hydroxide particles to enhance the conductivity between the active material particles, thereby increasing the utilization ratio of the active material. It is intended to improve. α
-Co (OH) ₂ or β-Co (OH) ₂ is oxidized during charging to form a conductive matrix made of CoOOH.

By the way, α-Co (OH) ₂ is β-C
Compared to o (OH) ₂ , it forms a dense conductive matrix and is therefore preferable as a coating layer for increasing the conductivity of the active material powder. However, as a result of examination by the present inventors, α
-Co (OH) ₂ is unstable, and when it is immersed in an electrolytic solution (high-concentration alkaline solution), most of it changes to β-Co (OH) ₂ , so in the above conventional coating method, a dense conductive matrix is used. It has been found that it is difficult to obtain a non-sintered nickel electrode having a sufficiently high active material utilization rate.

The present invention has been made on the basis of such findings, and an object of the present invention is to provide non-sintered nickel for an alkaline storage battery, which has a very high utilization ratio of active material due to the high conductivity of the electrode plate. A pole and its manufacturing method are provided.

[0011]

The non-sintered nickel electrode for an alkaline storage battery according to the present invention (hereinafter, referred to as "the electrode of the present invention") for achieving the above object is a cobalt hydroxide layer whose surface is In a non-sintered nickel electrode for an alkaline storage battery having coated nickel hydroxide particles or solid solution particles containing nickel hydroxide as a main component as an active material, the cobalt hydroxide layer is mainly composed of α-Co (OH) ₂ . And an outer layer mainly composed of β-Co (OH) ₂ , forming a two-layer structure.

The inner layer mainly composed of α-Co (OH) ₂ is
a layer containing α-Co (OH) ₂ as a main component,
It may be a layer consisting essentially of α-Co (OH) ₂ . On the other hand, the inner layer mainly composed of β-Co (OH) ₂ is
A layer containing β-Co (OH) ₂ as a main component,
It may be a layer consisting essentially of β-Co (OH) ₂ .

As solid solution particles containing nickel hydroxide as a main component, zinc hydroxide, cobalt hydroxide, cadmium hydroxide, calcium hydroxide, barium hydroxide, manganese hydroxide and the like may be used alone or in combination with nickel hydroxide. Examples of co-precipitated seeds are given.

The method for producing a non-sintered nickel electrode for an alkaline storage battery according to the present invention (hereinafter referred to as "the method of the present invention") comprises nickel hydroxide particles or solid solution particles containing nickel hydroxide as a main component. Is immersed in an aqueous solution of a cobalt compound, an alkaline aqueous solution is added until the pH of the solution becomes 9 to 10, and the mixture is stirred and mixed to deposit α-Co (OH) ₂ on the surface of the nickel hydroxide particles or the solid solution particles. Let me
Α on the surface of the nickel hydroxide particles or the solid solution particles
Step 1 of producing an active material intermediate in which a coating layer mainly containing -Co (OH) ₂ is formed, and the active material intermediate is immersed in an aqueous solution of a cobalt compound, and an alkaline aqueous solution is adjusted to a pH of 11 to 11. 12 to 12 and mixed with stirring to precipitate β-Co (OH) ₂ on the surface of particles of the active material intermediate, and β-Co (O) on the surface of particles of the active material intermediate.
H) ₂ is included in the step 2 of producing an active material having a coating layer formed thereon, and the step 3 of filling the conductive substrate with the active material.

When the pH of the liquid is in the range of 9 to 10, the reaction between the cobalt compound and the alkaline aqueous solution mainly causes α-Co.
(OH) ₂ is deposited on the surface of the nickel hydroxide particles or the solid solution particles. In the region where the pH of the liquid is 11 to 12,
Due to the reaction between the cobalt compound and the alkaline aqueous solution, β-Co (OH) ₂ is mainly deposited.

Examples of the cobalt compound in the method of the present invention include water-soluble cobalt salts such as cobalt nitrate, cobalt hydrochloride and cobalt sulfate, and examples of the alkaline aqueous solution include sodium hydroxide, potassium hydroxide and lithium hydroxide. An aqueous solution is exemplified.

[0017]

In the electrode of the present invention, unstable α-Co (O
Β-Co (O) having a relatively stable inner layer mainly composed of (H) ₂
Since H) ₂ is mainly protected by the outer layer, α-Co (OH) ₂ in the inner layer hardly changes to β-Co (OH) ₂ when the alkaline electrolyte is injected. For this reason, a relatively dense conductive matrix made of CoOOH is formed in the electrode plate during charging, and the conductivity of the nickel electrode is improved.

[0018]

EXAMPLES The present invention will be described in more detail based on the following examples, but the invention is not intended to be limited to the following examples, and various modifications may be made without departing from the scope of the invention. Is possible.

(Example) A nickel solution obtained by mixing aqueous solutions of nickel nitrate, zinc nitrate and cobalt nitrate in a weight ratio of nickel nitrate: zinc nitrate: cobalt nitrate of 95: 2: 3, and 20 An aqueous alkaline solution obtained by mixing a 20% by weight aqueous sodium hydroxide solution and a 20% by weight aqueous ammonia solution at a weight ratio of 5: 1 was simultaneously added to a water tank filled with water, and the coprecipitate formed was filtered. Wash with water, dry,
A solid solution powder containing nickel hydroxide as a main component was prepared.

This solid solution powder is dipped in an aqueous solution of cobalt nitrate, and while measuring the pH of the solution, 1N until pH 9 is reached.
An aqueous solution of sodium hydroxide was added dropwise, and the mixture was reacted for 1 hour while stirring and mixing, then filtered, washed with water, and dried in vacuum to coat the surfaces of nickel hydroxide particles with α-Co (OH) ₂ as a main component. An active material intermediate having a layer was prepared (step 1). For the pH measurement, a glass electrode pH meter equipped with an automatic temperature compensation function was used.
The same thing was used in the measurement. ).

Then, the above active material intermediate is immersed in an aqueous solution of cobalt nitrate, 1N aqueous sodium hydroxide solution is added dropwise until pH 11 while measuring the pH of the solution, and then the mixture is reacted with stirring for 1 hour. , Filtration, washing with water, and vacuum drying, and then β-Co (O
An active material having a coating layer mainly composed of H) ₂ was formed (step 2).

90 parts by weight of the thus obtained active material was kneaded with 20 parts by weight of a 1% by weight methylcellulose aqueous solution to prepare a slurry, and this slurry was filled in a nickel foam to form an electrode A (electrode of the present invention). It was produced (step 3).

Comparative Example A solid solution powder prepared in the same manner as in the example was dipped in an aqueous cobalt nitrate solution, and while measuring the pH of the solution, a 1N sodium hydroxide aqueous solution was added until the pH reached 9, 10, 11, 12 or 13. Was added dropwise, and then the mixture was reacted with stirring and mixing for 1 hour, then filtered, washed with water, and vacuum dried to prepare five types of active materials in which a cobalt hydroxide layer was formed on the surface of solid solution particles.

X-ray diffraction measurement was carried out on the cobalt hydroxide layer of these five kinds of active materials under the following conditions. The X-ray diffraction patterns are shown in FIGS. From FIG. 1, α-Co (OH) ₂ is inactive at pH = 9 and 10, β-Co (OH) ₂ is inactive at pH = 11 and 12 from FIG. 2, and inactive at pH = 13 from FIG. It can be seen that CoHO ₂ is mainly produced.

<Measurement conditions> Anticathode Cu tube voltage 40 kV tube current 100 mA filter Ni scanning speed 2.00 ° / min divergence slit 1 °

Then, the electrode B1 (pH = 9) and the electrode B1 (pH = 9) were sequentially prepared in the same manner as in the example except that these active materials were used.
B2 (pH = 10), B3 (pH = 11), B4 (pH
= 12), B5 (pH = 13) were produced (single coat method). Further, solid solution powder 8 produced in the same manner as in the example.
1 part by weight was kneaded with 9 parts by weight of cobalt hydroxide and 20 parts by weight of a 1% by weight methylcellulose aqueous solution to prepare a slurry, and this slurry was filled in a nickel foam to prepare an electrode B6 (addition and mixing method).

[Preparation of Test Cell] Electrodes A and B1 to B6
One of them as a test electrode, a hydrogen storage alloy electrode having a sufficiently large electrochemical capacity as compared with this test electrode as a counter electrode, and these are laminated through a separator (polyamide non-woven fabric) to form a laminate. Put the body in a polyethylene bag, pressurize with a pressing force of 40 kgf to make an electrode body, inject the electrolyte solution (KOH aqueous solution with a specific gravity of 1.23) into the separator, and test cell (open type single electrode cell) Was produced. As a hydrogen storage alloy electrode, MmNi _3.2 Co
90 parts by weight of _1.0 Mn _0.6 Al _0.2 was kneaded with a 1% by weight aqueous solution of polyvinyl alcohol to prepare a slurry, and this slurry was applied to a punching metal having a porosity of 40% and dried.

[Active Material Utilization Rate of Each Electrode] Each test cell was charged with a current of 0.1 C for 15 hours, then discharged to a voltage of 1.0 V with a current of 1/3 C, and the capacity of each test cell was measured. ,
The active material utilization rate of the test electrode used in each test cell was calculated by the following formula. The results are shown in Table 1.

Utilization rate of active material (%) = discharge capacity of test cell (mAh) × 100 / {weight of active material (g) × theoretical capacity per unit weight of active material (mAh / g)}

[0030]

[Table 1]

As shown in Table 1, the electrodes A and B1 to B5 prepared by the coating method are the electrodes B prepared by the additive mixing method.
6 has a higher utilization rate of the active material, and in particular, the electrode A (invention electrode) produced by the 2-coat method has a much higher utilization rate of the active material than the electrodes B1 to B5 produced by the single-coat method. The reason why the active material utilization rate of the electrode B6 is low is that cobalt hydroxide is likely to be unevenly distributed in the paste and is difficult to be uniformly mixed and dispersed with the nickel hydroxide powder. The active material utilization rate of the electrode A is particularly high because α-Co (OH) ₂ present in a large amount in the inner layer.
So that if protected by an outer layer composed mainly of β-Co (OH) _2, liquid hardly varies β-Co (OH) ₂ to touch the electrolysis, the conductive matrix comprised of dense CoOOH by charge formation Because it is done.

The electrodes B1 to B prepared by the single coating method
In the case of 5, the amount of α-Co (OH) ₂ produced is large.
The electrodes B1 and B2 produced in 9 or 10 are β-Co (O
The active material utilization rate is higher than that of the electrodes B3 and B4 produced at pH = 11 or 12 where a large amount of H) ₂ is produced.

In the above-mentioned embodiment, the method of the present invention has a pH of 9 in step 1 and a pH of 1 in step 2.
Although the case where the pH is set to 1 has been described as an example, the pH in each step may be within the range regulated by the present invention.
It was confirmed that even when H was 12, an electrode having a high utilization ratio of the active material similar to the electrode A was obtained.

Further, in the above-mentioned examples, the case where solid solution particles obtained by coprecipitating nickel hydroxide, zinc hydroxide and cobalt hydroxide and coated with a cobalt hydroxide layer was used as an active material was taken as an example. As described above, when nickel hydroxide particles or other solid solution particles containing nickel hydroxide as a main component are coated with a cobalt hydroxide layer having a two-layer structure regulated by the present invention, the active material is used. It was also confirmed that a nickel electrode having a high utilization rate of the active material can be obtained.

[0035]

The electrode of the present invention is α-Co (OH)₂Wealth
The inner layer is β-Co (OH)₂Protected by a rich outer layer
Therefore, α-Co (OH) in the inner layer₂Is β-Co
(OH) ₂It is difficult to change to
Tricks are formed. Therefore, the electrode of the present invention is
High quality utilization rate.

Further, according to the method of the present invention, the electrode of the present invention having a high utilization rate of the active material can be manufactured.

[Brief description of drawings]

FIG. 1 is an X-ray diffraction diagram of an active material produced at pH = 9 or 10 in Examples.

FIG. 2 is an X-ray diffraction diagram of the active material produced at pH = 11 or 12 in Examples.

FIG. 3 is an X-ray diffraction diagram of the active material prepared in Example at pH = 13.

Front page continuation (72) Inventor Kozo Nogami 2-5-5 Keihan Hon-dori, Moriguchi-shi, Osaka Sanyo Electric Co., Ltd. (72) Inventor Koji Nishio 2-5-5 Keihan-hondori, Moriguchi-shi, Osaka Sanyo Electric Co., Ltd. (72) Inventor Toshihiko Saito 2-5-5 Keihan Hondori, Moriguchi City, Osaka Sanyo Electric Co., Ltd.

Claims (3)

[Claims] 1. A non-sintered nickel electrode for an alkaline storage battery, comprising a nickel hydroxide particle whose surface is coated with a cobalt hydroxide layer or a solid solution particle containing nickel hydroxide as a main component as an active material. The layer is α-Co (O
A non-sintered nickel electrode for an alkaline storage battery, which has a two-layer structure of an inner layer mainly composed of H) ₂ and an outer layer mainly composed of β-Co (OH) ₂ . 2. Nickel hydroxide particles or solid solution particles containing nickel hydroxide as a main component are immersed in an aqueous solution of a cobalt compound, an alkaline aqueous solution is added until the pH of the solution becomes 9 to 10, and the mixture is stirred and mixed. Α-Co (OH) ₂ is deposited on the surface of the nickel hydroxide particles or the solid solution particles,
Α on the surface of the nickel hydroxide particles or the solid solution particles
Step 1 of producing an active material intermediate in which a coating layer mainly composed of —Co (OH) ₂ is formed, and immersing the active material intermediate in an aqueous solution of a cobalt compound,
The alkaline aqueous solution was added until the pH of the solution became 11 to 12, and the mixture was stirred and mixed, and β-C was added to the surface of the particles of the active material intermediate.
Step 2 of producing an active material in which a coating layer mainly composed of β-Co (OH) ₂ is formed by depositing o (OH) ₂ on the particle surface of the active material intermediate, and conducting the active material. 3. A method for manufacturing a non-sintered nickel electrode for an alkaline storage battery, the method comprising: filling a flexible substrate. 3. An alkaline storage battery active material comprising nickel hydroxide particles or solid solution particles mainly comprising nickel hydroxide, the surface of which is coated with a cobalt hydroxide layer, wherein the cobalt hydroxide layer is α- Co (OH) and an inner layer mainly _2, beta-Co (OH) active material for an alkaline storage battery, characterized in that forming a two-layer structure of ₂ mainly outer layer.