JP3485740B2 - Positive electrode active material for alkaline storage battery, method for producing the same, and positive electrode 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 positive electrode active material used in alkaline storage batteries such as nickel-cadmium batteries, nickel-hydrogen batteries and nickel-zinc batteries, a method for producing the same, and a positive electrode.

[0002]

2. Description of the Related Art As a technique for increasing the energy density of a nickel-hydrogen battery or a nickel-cadmium battery, a nickel electrode as a positive electrode has 95% or more of holes instead of a conventional sintered electrode. A paste electrode formed by filling a nickel metal porous substrate with a nickel hydroxide active material has been used.

However, in the paste type nickel electrode, merely filling the nickel hydroxide particles as an active material can obtain an active material utilization rate of about 60% and cannot be a high capacity electrode. Therefore, a cobalt compound such as cobalt hydroxide is mixed and added to improve the utilization rate of the active material. According to this, the active material utilization rate of 90% or more becomes possible, and the paste type nickel electrode is put into practical use.

The mechanism of action of the cobalt compound added to improve the utilization rate of the active material is considered as follows.
That is, the cobalt compound is once dissolved in the alkaline electrolyte and then re-precipitated as cobalt hydroxide to coat the surface of the nickel hydroxide particles, and the cobalt hydroxide changes into conductive cobalt oxyhydroxide during the initial charging process. Then, the active material particles are connected by a conductive network made of cobalt oxyhydroxide.

Further, in order to increase the capacity of the paste-type nickel electrode, the active material particles themselves are densified into particles having a high apparent density, thereby enabling high-density filling. There is. For example, USP484499
9, USPRE34752 suppresses the development of the internal pore volume of the spherical nickel hydroxide particles to increase the density and uses the above-mentioned cobalt compound to
Electrodes of 00 mAh / ml or more have been obtained.

Further, in order to make the added cobalt compound act effectively, the surface of the nickel hydroxide particles is coated with the cobalt compound in advance to form composite particles, so that the active material particles are more effectively formed by the conductive network. The connection is also done. For example, Japanese Patent Laid-Open No. 62-2348
67, JP-A-62-234868, the surface of nickel hydroxide particles is coated with α-type cobalt hydroxide showing an X-ray diffraction peak at a face spacing of 8Å or β-type cobalt hydroxide showing an X-ray diffraction peak at a face spacing of 4.65Å. Has been shown to
JP-A-3-78965, JP-A-3-62457, and JP-A-5-65988 show that nickel oxyhydroxide particles are coated on the surface of nickel hydroxide particles.

It is very effective to use the composite particles as an active material for a paste type nickel electrode, but there are the following problems in practical use. That is, the conventional composite particles have a problem that the cobalt compound has poor adhesion to the surface of the nickel hydroxide particles, and the cobalt compound is liberated from the nickel hydroxide particles when a paste is prepared by adding an aqueous solvent. Since the cobalt compound adheres to the surface of the nickel hydroxide particles in a coarse state, the apparent density of the composite particles is much lower than that of the nickel hydroxide particles themselves, and even if high density nickel hydroxide particles are used. There is a problem that the characteristics cannot be utilized and the paste cannot be filled at a high density.

The present invention has been made in view of the above problems, and provides a positive electrode active material for an alkaline storage battery, which can increase the apparent density of composite particles and can perform high-density filling in a paste state. It is also an object of the present invention to provide a method for producing the positive electrode active material, and further to provide a positive electrode using the positive electrode active material.

[0009]

In order to achieve the above object, the positive electrode active material for an alkaline storage battery according to claim 1 of the present application is a cobalt compound in which the surface of nickel hydroxide particles is chemically deposited. Or in the positive electrode active material for an alkaline storage battery consisting of partially coated composite particles, the apparent density of the composite particles is a cobalt compound in which the surface of the nickel hydroxide particles is chemically deposited by applying a vibration treatment. It is higher than the case of being entirely or partially coated, and is characterized by 2.0 to 2.3 g / ml.

In the positive electrode active material according to claim 1, since the apparent density of the composite particles is high, it is possible to fill the paste with a high density.

[0011]

[0012]

According to a second aspect of the positive electrode active material for an alkaline storage battery of the present invention, the nickel hydroxide particles contain at least one element belonging to Group 2 of the periodic table in a solid solution state. The nickel hydroxide particles are
The total pore volume is 0.1 ml / g or less, and the apparent density is 1.8 to 2. 4 g / ml.

In the positive electrode active material according to the second aspect, it is possible to fill the paste with a sufficiently high density. Moreover,
Since it contains the Group 2 element in a solid solution state, γ-NiOO
Generation of H is prevented, and the pore structure of the nickel hydroxide particles is maintained. From this point as well, the capacity can be increased.

According to a third aspect of the present invention, in the positive electrode active material for an alkaline storage battery according to the first aspect, the cobalt compound has cobalt hydroxide having a predetermined crystal structure, or a composite hydroxide including a predetermined element and cobalt. The predetermined crystal structure is an α-type that exhibits an X-ray diffraction peak at an interplanar spacing of 8Å or a β-type that exhibits an X-ray diffraction peak at an interplanar spacing of 4.65Å, and the predetermined element is an element other than Co. That is, it is an element belonging to any of 1B group, 2A group, 2B group, 3A group, and 3B group of the periodic table. The positive electrode active material for an alkaline storage battery according to claim 4 is the structure according to claim 1, wherein the cobalt compound is cobalt hydroxide having a predetermined crystal structure, or a composite hydroxide composed of a predetermined element and cobalt. , The predetermined crystal structure is an α-type that exhibits an X-ray diffraction peak at an interplanar spacing of 8Å or a β-type that exhibits an X-ray diffraction peak at an interplanar spacing of 4.65Å, and the predetermined element is an element other than Co, It is an element belonging to Group 7A of the periodic table.

Specific examples of the predetermined element include zinc, magnesium, calcium, cadmium, aluminum, copper, manganese, ytterbium, erbium, lutetium and yttrium.

In the positive electrode active material according to claim 3 or 4, since the solubility of these cobalt compounds in the alkaline electrolyte is excellent, a conductive network is easily formed, and therefore the active material utilization rate is high. Is improved. Moreover, since different elements coexist, charging efficiency is improved.

In the method for producing a positive electrode active material for an alkaline storage battery according to claim 5, nickel hydroxide particles are placed in an aqueous solution containing an ammonia or ammonium ion supplier and an alkali metal hydroxide, and the cobalt compound is added thereto. The first step of obtaining a composite particle in which the salt of the constituent element of (1) is added dropwise while controlling the pH to 8 to 13, whereby the surface of the nickel hydroxide particle is wholly or partially coated with the precipitated cobalt compound. And a second step of placing the composite particles in a shaker and subjecting the composite particles to a vibration treatment having a strength that does not destroy the particles.

In the manufacturing method according to claim 5, the second
The structure of the cobalt compound coating layer becomes dense due to the vibration treatment in the process.

According to a sixth aspect of the present invention, in a positive electrode for an alkaline storage battery in which a positive electrode active material composed of composite particles is filled in a porous substrate with paste, the composite particles have nickel hydroxide particles whose surfaces are chemically deposited. The cobalt particles are wholly or partially coated with a cobalt compound, and the apparent density of the composite particles is wholly or partially coated with a cobalt compound which is chemically deposited on the surface of the nickel hydroxide particles by applying a vibration treatment. It is higher than the case of only being coated, and is characterized in that it is 2.0 to 2.3 g / ml.

In the positive electrode according to the sixth aspect, since the paste is filled at a high density, the capacity and energy density are high.

[0022]

BEST MODE FOR CARRYING OUT THE INVENTION A basic embodiment of the present invention will be described below, but the present invention is not limited to this. The positive electrode active material for alkaline storage batteries of the present invention has the following steps (1) to (3)
Manufactured by
Manufactured according to (4).

(1) Preparation of nickel hydroxide particles: Ammonium sulfate was added to an aqueous solution in which nickel sulfate and zinc sulfate were dissolved at a predetermined ratio to form an ammine metal complex, and then the aqueous sodium hydroxide solution was vigorously stirred. While maintaining the pH at 10 to 13, the mixture was added dropwise to obtain spherical nickel hydroxide particles in which zinc was dissolved in 5% by weight. The obtained nickel hydroxide particles had an apparent density (tapping density) of 2.1 g / ml and an internal pore volume of 0.03 ml.
/ G. In order to fill the paste in a high density, it is desirable to use nickel hydroxide particles having an apparent density of 1.8 to 2.3 g / ml and an internal pore volume of 0.1 ml / g or less. .

(2) Preparation of composite particles (that is, nickel hydroxide particles coated with a cobalt compound): The nickel hydroxide particles obtained in (1) were adjusted to pH 8 to 13 with ammonium sulfate and an aqueous sodium hydroxide solution. The mixture was poured into an aqueous solution, to which a cobalt sulfate aqueous solution and a sodium hydroxide aqueous solution were stirred vigorously and the pH was adjusted to 8
The solution was added dropwise while controlling to ~ 13 to precipitate cobalt hydroxide entirely or partially on the surface of the nickel hydroxide particles.
Note that the partially precipitated state is also referred to as an ordered mixed state. Then, the obtained product is filtered, washed with water,
After drying under reduced pressure, nickel hydroxide particles coated with a cobalt compound, that is, composite particles were obtained.

In order to make the crystal structure of the precipitated cobalt hydroxide into an α-type exhibiting an X-ray diffraction peak at an interplanar spacing of 8Å, the pH during the reaction is controlled to the lower limit, and the interplanar spacing of 4.65Å
It is desirable to control the pH at the time of the reaction to the upper limit in order to obtain β-type which exhibits an X-ray diffraction peak.

If a mixed aqueous solution of a cobalt salt and a salt of another element is used instead of the cobalt sulfate aqueous solution, a multi-component cobalt compound is deposited. As other elements,
1B group, 2A group, 2B group, 3A group, 3B group of the periodic table,
And an element belonging to any of Group 7A are used. For example, zinc, magnesium, calcium, cadmium, aluminum, copper, manganese, ytterbium, erbium, lutetium, yttrium, and the like.

(3) Densification of composite particles: The composite particles obtained in (2) were mixed at 100 mm with a vertical stroke of 5 mm.
The mixture was placed in a shaker vibrating at 0 times / minute and subjected to a vibration treatment for 2 hours to obtain composite particles having an apparent density of 2.2 g / ml. The treatment for increasing the density may be carried out in the reduced pressure drying process in (2), in which case a rotary kiln, a paddle dryer, a kneader, a vibration dryer or the like is used to apply impact or pressure to the particles for drying. It is desirable to use a device.

With these treatments, the apparent density of 2.0 to
It is possible to obtain 2.3 g / ml composite particles. Further, it is presumed that the adhesion of the cobalt compound coating layer to the surface of the nickel hydroxide particles is also increasing.

Table 1 shows the apparent densities of nickel hydroxide particles coated with various cobalt compounds by the above method, before coating (after step (1)), after coating (after step (2)), and after vibration treatment. (After step (3)) is shown.

[0030]

[Table 1] The apparent density shown in Table 1 is 1 when a predetermined amount of particles is put in a graduated cylinder and naturally dropped from a height of 10 cm.
It is the apparent density after repeating 00 times.

As can be seen from Table 1, the particles obtained in the step (2) surely have a high apparent density due to the step (3). That is, the structure of the cobalt compound coating layer is surely made dense by the step (3).

(4) Preparation of paste liquid and positive electrode: To 80 parts by weight of the composite particles obtained in (3), 20 parts by weight of an aqueous solution in which a thickener such as carboxymethyl cellulose is dissolved is added and kneaded to form a paste liquid. It was made. This paste solution was filled in a nickel porous substrate having 95% of pores, dried and pressed to prepare a positive electrode. Table 2 shows the properties of the composite particles obtained in step (2) and step (3).

[0033]

[Table 2]

As can be seen from Table 2, the particles obtained in the step (2) have too high a viscosity and the paste liquid density is 2.4 g /
When it was made into ml, the fluidity of the paste was lost and filling was impossible. However, the particles that have undergone the step (3) have a low viscosity even when such a high-density paste liquid is used,
Since it becomes a fluid paste, it can be filled and achieves a high energy density. Further, the active material utilization rate of the positive electrode of the present invention showed a high value of 95% or more.

[0035]

According to the positive electrode active material for an alkaline storage battery of claim 1, since the composite particles have a high apparent density, even if the paste density is increased, the paste liquid becomes a fluid paste liquid, which enables high-density paste filling. You can

[0036]

According to the positive electrode active material for an alkaline storage battery of claim 2, satisfactory high density paste filling can be achieved. Moreover, since the Group 2 element is contained in a solid solution state, the capacity can be increased from this point as well.

According to the positive electrode active material for an alkaline storage battery of claim 3 or 4, since the solubility of these cobalt compounds in an alkaline electrolyte is excellent, a conductive network can be easily formed to form an active material. The utilization rate can be improved. Moreover, since different elements coexist, charging efficiency can be improved.

According to the method for producing a positive electrode active material for an alkaline storage battery described in claim 5, the structure of the cobalt compound coating layer can be made fine by the vibration treatment in the second step. Therefore, the positive electrode active material according to claim 1 can be obtained.

According to the positive electrode for an alkaline storage battery of the sixth aspect, since the paste is filled at a high density, a high capacity and a high energy density can be achieved.

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Junichi Imaizumi 45 characters, Shirokata-cho, Fukui City, Fukui Prefecture 5-10 Sunamahamawari, Tanaka Chemical Research Institute, Inc. (72) Inventor, Toyoshi Iida 45 characters, Shirakata-cho, Fukui City, Fukui Prefecture Sand beach division 5-10 Tanaka Chemical Laboratory Co., Ltd. (56) Reference JP 62-234867 (JP, A) JP 7-320737 (JP, A) JP 8-102322 (JP, A) Special Kaihei 4-192259 (JP, A) (58) Fields surveyed (Int.Cl. ⁷ , DB name) H01M 4/52 H01M 4/32

Claims (6)

(57) [Claims] 1. A positive electrode active material for an alkaline storage battery, which comprises composite particles in which the surface of nickel hydroxide particles is wholly or partially coated with a chemically deposited cobalt compound, wherein the apparent density of the composite particles is By applying the vibration processing
It is higher than the case where the surface of the nickel hydroxide particles is wholly or partially coated with the chemically deposited cobalt compound, and is 2.0 to 2.3 g / ml. A characteristic positive electrode active material for alkaline storage batteries. 2. Nickel hydroxide particles contain at least one element belonging to Group 2 of the periodic table in a solid solution state, and the nickel hydroxide particles have a total pore volume of 0.1 m.
It is 1 / g or less, and the apparent density is 1.8 to 2. 4 g / m
The positive electrode active material for an alkaline storage battery according to claim 1, which is 1. 3. The cobalt compound is cobalt hydroxide having a predetermined crystal structure, or a composite hydroxide composed of a predetermined element and cobalt, and the predetermined crystal structure has an X-ray diffraction peak at an interplanar spacing of 8Å. Α-type or β-type showing an X-ray diffraction peak at an interplanar spacing of 4.65Å, the predetermined element is an element other than Co, and
The positive electrode active material for an alkaline storage battery according to claim 1, which is an element belonging to any one of Group B, Group 2A, Group 2B, Group 3A, and Group 3B. 4. The cobalt compound is cobalt hydroxide having a predetermined crystal structure, or a composite hydroxide composed of a predetermined element and cobalt, and the predetermined crystal structure has an X-ray diffraction peak at an interplanar spacing of 8 Å. Α-type or β-type showing an X-ray diffraction peak at an interplanar spacing of 4.65Å, the predetermined element is an element other than Co, and
The positive electrode active material for an alkaline storage battery according to claim 1, which is an element belonging to Group A. 5. Nickel hydroxide particles are placed in an aqueous solution containing an ammonia or ammonium ion supplier and an alkali metal hydroxide, and a salt of the constituent element of the cobalt compound is added dropwise thereto while controlling the pH to 8 to 13. The first step of obtaining composite particles in which the surface of nickel hydroxide particles is wholly or partially coated with the cobalt compound deposited, and the composite particles are placed in a shaker to The method for producing a positive electrode active material for an alkaline storage battery, comprising: a second step of subjecting the material to a vibration treatment with a strength that does not destroy the material. 6. A positive electrode for an alkaline storage battery, wherein a positive electrode active material composed of composite particles is filled in a porous substrate with paste, wherein the composite particles are a cobalt compound in which the surface of nickel hydroxide particles is chemically deposited. Or, it is partially coated, and the apparent density of the composite particles is
More, the surface of the nickel hydroxide particles are those higher than simply being wholly or partially coated with a cobalt compound chemically precipitated a 2.0~2.3g / ml Characteristic positive electrode for alkaline storage battery.