JP3515251B2 - Method for producing positive electrode active material for alkaline storage battery - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a positive electrode active material for an alkaline storage battery containing a nickel hydroxide active material as a main component.

[0002]

2. Description of the Related Art In recent years, word processors, mobile phones, personal computers,
Portable electronic devices such as video cameras are
Increasingly smaller and lighter. Further, as for batteries used in these electronic devices, higher performance batteries are required in order to further improve convenience.

Conventionally, as a positive electrode used in an alkaline storage battery, a substrate obtained by applying a slurry containing nickel powder as a main component to a punching metal or the like and then sintering the substrate is impregnated with an active material. So-called sintered nickel positive electrodes are known. However, the electrode of this system is weak in strength when the substrate has high porosity, and nickel powder comes off, so that the practical limit of the porosity of the substrate is 80%. Since a core body such as punching metal is required, the packing density of the active material is small, which is disadvantageous in achieving high energy density.

Further, the pores of the sintered substrate are as small as 10 μm or less, and the method of filling the active material has a drawback that it is limited to the solution impregnation method and the electrodeposition impregnation method which require complicated steps.

As an attempt to improve these drawbacks, for example, a non-sintering type in which a nickel hydroxide active material powder is directly filled with a binder in a metallic porous body such as nickel foam having a porosity of about 95% and having no core body Nickel positive electrodes have been proposed.

As a means for suppressing the swelling of such a non-sintered nickel positive electrode, Japanese Patent Laid-Open No. 3-62457 discloses a solid solution layer composed of nickel hydroxide and cobalt hydroxide on the surface of a nickel hydroxide active material. It is proposed to coat.

[0007]

However, when the surface of nickel hydroxide was coated with a multi-component compound containing cobalt hydroxide as a main component and then dried in air, it was formed on the surface of nickel hydroxide particles. Since the cobalt compound undergoes oxidative deterioration to reduce the conductivity between the active material particles, there is a problem in that the utilization rate of the active material is reduced.

The present invention has been made in view of such problems, and it is an object of the present invention to prevent a decrease in conductivity between active material particles and improve the utilization rate of the active material. It is an issue.

[0009]

A method for producing a positive electrode active material for an alkaline storage battery according to the present invention comprises a step of removing the surface of active material particles containing nickel hydroxide as a main component from nickel, zinc, cadmium,
An active material coating step of coating with a multi-component compound consisting of a cobalt compound and at least one compound selected from the group consisting of magnesium, aluminum and indium; and active material particles coated with the multi-component compound,
Heat treatment in the coexistence of oxywater in the multi-component compound
A heat treatment step for forming cobalt oxide, and the heat treatment
And a drying step of drying the active material particles subjected to the above step under a nitrogen or inert atmosphere or under vacuum.

[0010]

When the cobalt compound is added to the nickel hydroxide active material, the conductivity between the active materials can be improved. In particular, by coating the surface of the particles containing nickel hydroxide as the main component with the cobalt compound, the effect of improving the conductivity of the cobalt compound can be more exerted as compared with the case where the cobalt compound is simply added. However, with the progress of over-discharge and charge / discharge cycle, the cobalt compound coated on the surface of the nickel hydroxide particles diffuses inside the nickel hydroxide, and the phenomenon that the amount of cobalt coated on the surface becomes small occurs. The conductivity improving effect of the cobalt compound decreases.

Therefore, at the same time as the cobalt compound, nickel, zinc, cadmium, magnesium, aluminum,
At least one compound selected from the group consisting of indium is added to form a multi-component compound, and by coating this multi-component compound on the nickel hydroxide surface, the diffusion of the cobalt compound into the nickel hydroxide particles can be prevented. Since it can be suppressed, the effect of improving the conductivity of the cobalt compound is exhibited for a long period of time.

However, when the surface of the nickel hydroxide particles is coated with the multi-component compound as described above and then dried in an atmosphere containing a large amount of oxygen such as in the air, the cobalt particles coated on the surface of the nickel hydroxide particles are coated. The compound undergoes oxidative deterioration to form a low-conductivity cobalt compound such as tricobalt tetroxide (Co ₃ O ₄ ) and the conductivity between the active material particles is reduced, thus improving the conductivity of the cobalt compound. It was found that it would be difficult to take full advantage of.

Therefore, it is possible to suppress the production of a low-conductivity cobalt compound such as tricobalt tetroxide (Co ₃ O ₄ ) by drying in a nitrogen or inert gas atmosphere or under vacuum, and the cobalt compound Since the effect of improving conductivity can be sufficiently exhibited, the utilization factor of the active material is improved.

[0014]

Example ( Reference Example 1) [Preparation of nickel hydroxide active material] Mixing nickel sulfate, zinc sulfate, and cobalt sulfate in a molar ratio of 1 nickel to 0.005 zinc and 0.02 zinc. While stirring the aqueous solution, gradually add ammonia water and an aqueous sodium hydroxide solution, and p
Nickel hydroxide was deposited by controlling the addition amounts of the ammonia water and the sodium hydroxide aqueous solution so that H was 10 to 12. Next, the precipitate was collected, washed with water and dried to prepare active material particles containing nickel hydroxide as a main component.

Next, about 4 times (weight ratio) of water is added to the active material particles containing nickel hydroxide as a main component and mixed and dispersed. The concentration of the dispersion liquid is about 10% by weight in terms of metal amount. A multi-component solution prepared by adding 5% by weight of zinc sulfate to a cobalt sulfate aqueous solution and a sodium hydroxide aqueous solution were added to coat the surfaces of the active material particles with a multi-component compound including a cobalt compound and a zinc compound. Then, the active material coated with the above multi-component compound is washed with water and in a nitrogen atmosphere (oxygen concentration: 0.
5 vol% or below) which was dried at 80 ° C. referred to as Reference Example active material a.

Reference Example 2 In the production of the active material in Example 1, the nitrogen atmosphere was replaced with a helium atmosphere (oxygen concentration 0.5% by volume).
A reference example active material b was prepared in the same manner as in the reference example 1 except that it was dried in the following).

[0017] In the preparation of the active material in Reference Example 3 Reference Example 1, except that dried in vacuo instead of nitrogen atmosphere to prepare Reference Example active material c in the same manner as in Reference Example 1.

[0018] In the preparation of the active material in Comparative Example 1 Reference Example 1, except that dried in air instead of nitrogen atmosphere to prepare a comparison active material x in the same manner as in Reference Example 1.

[Production of Battery] 0.1 wt% of each active material a, b, c, x produced as described above and the active material.
Aqueous solution of hydroxypropyl cellulose
0% by weight was mixed to form a slurry, the foamed nickel having a porosity of 95% was filled, dried and rolled to a predetermined thickness to produce a positive electrode.

The positive electrode thus produced and a known hydrogen storage electrode having a sufficient discharge capacity for the positive electrode were wound around a separator to produce a spiral electrode body. After inserting this spiral electrode body into the battery outer can and injecting the electrolytic solution,
Sealing was performed to manufacture nickel hydrogen batteries having a nominal capacity of 1200 mAh. [Battery test conditions] Using the nickel-hydrogen battery produced as described above, the battery was charged at a current value of 120 mA for 24 hours,
The battery was discharged at a current value of 400 mA until the battery voltage reached 1.0 V, and the discharge capacity was measured. Then, the utilization rate was calculated based on the following formula, and the result is shown in Table 1 below.

Discharge capacity / nominal capacity × 100 However, it is shown by an index when the active material a of the present invention is 100.

[0022]

[Table 1]

As is clear from Table 1, the active materials a, b and c of the reference example have a higher utilization rate than the comparative active material x dried in air.

This is because when excess oxygen is present in a dry atmosphere like air, cobalt hydroxide on the surface of the particles, which is unstable in nature, undergoes oxidative deterioration, and tricobalt tetraoxide (Co ₃
It is considered that a low conductivity cobalt compound such as O ₄ ) is formed and conductivity between the active material particles is reduced, which leads to a decrease in utilization rate of the active material.

Example 1 In this example 1 , the heat treatment in the presence of alkali was examined.

In the preparation of the active materials of Reference Examples 1, 2 and 3, the same procedure as in Reference Examples 1, 2 and 3 was carried out except that an alkali was added before drying and then heat treatment was performed in air. The active material of the present invention was prepared as A, B and C, respectively.

Then, according to the above [Production of Battery] and [Test Conditions of Battery], the utilization rate was obtained and the results are shown in Table 2 below.

[0028] However, it is shown by an index when the Reference Example active material a is 100.

[0029]

[Table 2]

As is clear from Table 2, the utilization factor is dramatically improved by heat treatment in the presence of alkali before the drying step. It is considered that this is because the cobalt compound coated on the surface by the alkali heat treatment was changed to highly conductive cobalt oxyhydroxide, so that the conductivity between the active material particles was improved and the utilization rate was improved.

Reference Example 4 In Reference Example 4 , the drying temperature was examined.

In the preparation of the active material of Reference Example 1, the drying temperatures were 50, 120, 150, 180 and 20, respectively.
Active materials were prepared in the same manner as in Reference Example 1 except that the temperature was changed to 0 ° C.

Then, according to the above [Production of battery] and [Test conditions of battery], the utilization rate was obtained and the results are shown in Table 3 below.

[0034] However, it is shown by an index when the Reference Example active material a is 100.

[0035]

[Table 3]

As is apparent from Table 3, the drying temperature is 18
When the temperature exceeds 0 ° C, the utilization factor of the active material decreases, so that the drying temperature is preferably 180 ° C or lower. this is,
If the drying temperature is excessively increased, the cobalt hydroxide on the surface of the nickel hydroxide particles is oxidatively deteriorated, and a low-conductivity cobalt compound such as tricobalt tetraoxide (Co ₃ O ₄ ) is formed, so that the conductivity between the active material particles is increased. It is considered that this is because the utilization rate of the active material was lowered due to the decrease in the property.

In this embodiment, the component of the coating layer is a two-component compound of a cobalt compound and a zinc compound. The same effect can be obtained by using a binary compound with an indium compound. Also, the same effect can be obtained by forming the coating layer with a multi-component compound of a cobalt compound and two or more of these compounds.

In this embodiment, helium is used as the inert gas, but the present invention is not limited to this, and the same effect can be obtained by using neon, argon or xenon. The same effect can be obtained by using these mixed gases.

[0039]

As described above, according to the manufacturing method of the present invention,
Since the cobalt compound coated on the surface can be effectively prevented from oxidative deterioration and the conductivity improving effect of the cobalt compound can be sufficiently exerted for a long period of time, a high active material utilization rate and a high capacity battery Is obtained.

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yoshitaka Baba 2-5-5 Keihan Hondori, Moriguchi City, Osaka Sanyo Electric Co., Ltd. (56) Reference JP-A-3-62457 (JP, A) JP HEI 5-89876 (JP, A) JP 61-110962 (JP, A) JP 62-222566 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) H01M 4 / 52

Claims (3)

(57) [Claims] 1. A multi-component comprising a cobalt compound and at least one compound selected from the group consisting of nickel, zinc, cadmium, magnesium, aluminum and indium on the surface of active material particles containing nickel hydroxide as a main component. an active material coating step of coating with a compound, the multi
Active material particles coated with component compounds in the presence of alkali
After heat treatment, cobalt oxyhydroxide is added to the multi-component compound.
And a drying step of drying the heat-treated active material particles under a nitrogen or inert gas atmosphere or under a vacuum, the positive electrode active material for an alkaline storage battery. Manufacturing method. 2. The method for producing a positive electrode active material for an alkaline storage battery according to claim 1, wherein the inert gas is at least one selected from helium, neon, argon and xenon. 3. The method for producing a positive electrode active material for an alkaline storage battery according to claim 1, wherein the drying temperature in the drying step is 180 ° C. or lower.