JPH10154508A - Alkaline storage battery, its nickel electrode, and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high capacity density alkaline storage battery nickel electrode by forming active material powder through the powder obtained by heat-treating nickel hydroxide powder whose surface is coated through α-Co(OH)2 or by adding heat-treated a type cobalt hydroxide to a main component of spherical nickel hydroxide powder. SOLUTION: Nickel hydroxide powder whose surface is coated by α-Co (OH)2 is heat-treated in temperatures from 100 to 150 deg.C, or the α-CO(OH)2 heat- treated in temperatures from 100 to 150 deg.C is added to nickel hydroxide so as to constitute a nickel electrode. Water of crystallization is eliminated from between α-Co(OH)2 layers by heat-treating so that the cobalt hydroxide having wide layer-to-layer space is formed and the formation of a conductive network can be facilitated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an alkaline storage battery, particularly a nickel / hydrogen storage battery, and a nickel electrode as a positive electrode thereof.

[0002]

2. Description of the Related Art In recent years, there has been a strong demand for higher capacity secondary batteries with the spread of communication equipment and the like. Hitherto, high capacity has been achieved by increasing the capacity of the positive and negative electrodes and reducing the thickness of the separator. In particular, since nickel / hydrogen storage batteries are designed by regulating the positive electrode, it is urgently necessary to increase the capacity of the positive electrode.

Hereinafter, a nickel electrode used as the positive electrode for an alkaline storage battery will be described.

Conventionally, as a positive electrode for an alkaline storage battery,
A porous sintered substrate having a porosity of about 80% obtained by sintering nickel powder is impregnated with a salt solution such as an aqueous solution of nickel nitrate, and then immersed in an aqueous solution of alkali to form a nickel hydroxide on the substrate. There is a sintered electrode plate manufactured by producing an active material. In this type, it is difficult to further improve the porosity of the substrate, and it is not possible to increase the amount of nickel hydroxide to be filled, and is not suitable for increasing the capacity.

A non-sintered positive electrode is disclosed in
The use of spherical nickel hydroxide is proposed in JP-A-131765. This makes it possible to uniformly and densely fill the substrate with the active material, which is an effective method for increasing the capacity as compared with a sintered substrate. The active material used for filling this non-sintered substrate is mainly spherical nickel hydroxide obtained by adding a cobalt compound such as cobalt hydroxide or cobalt monoxide as a conductive agent, metallic cobalt, metallic nickel, or the like. It is widely known that the conductivity of nickel hydroxide is improved by the conductive agent.

[0006]

More recently, measures for further increasing the utilization rate of active materials have been studied. For example, Japanese Patent Application Laid-Open No. 7-320733 discloses α-Co (OH) ₂ and β-Co (OH) _2.
A nickel electrode has been proposed in which nickel hydroxide particles whose surface is coated with a cobalt hydroxide layer composed of a mixture with -Co (OH) ₂ or solid solution particles containing nickel hydroxide as a main component are used as an active material.

However, α-Co (OH) ₂ has a high solubility in alkali, and the dissolution and precipitation reaction of α-Co (OH) ₂ is Co (OH) ₂ ⇒ HCoO ₂ ^- ⇒ CoHO ₂ , or Co
(OH) ₂ ⇒ HCoO ₂ ^- ⇒ β-Co (OH) ₂ can be considered, but it easily progresses to CoHO ₂ , and since CoHO ₂ is inactive, the active material utilization rate decreases. Therefore, it is expected that it is difficult to simply use a mixture of α-Co (OH) ₂ as an additive.

In view of the above problems, the present invention provides a nickel electrode for an alkaline storage battery having a high filling density and a high capacity density.

[0009]

In order to solve the above-mentioned problems, a nickel electrode for an alkaline storage battery according to the present invention has a crystal form close to that of β-Co (OH) ₂ , but does not have water of crystallization. This is a powder obtained by oxidizing nickel hydroxide powder whose surface is coated with cobalt hydroxide composed of (OH) _2. Cobalt hydroxide is converted to cobalt oxyhydroxide by oxidation treatment as a battery. Is converted to Alternatively, a paste prepared by using a spherical nickel hydroxide powder as a main component and adding an α-type cobalt hydroxide which has been heat-treated as an additive to the powder is used.

Α-Co (OH) ₂ coating the surface of the nickel hydroxide powder or α used as an external additive
Crystalline form of -Co (OH) ₂ is has a layered structure with hexagonal in β-Co (OH) ₂ interlayer has a structure containing crystal water. By subjecting the α-Co (OH) ₂ to a heat treatment, the water of crystallization contained between the layers is desorbed and β-C
Cobalt hydroxide having a larger interlayer distance than o (OH) ₂ can be obtained. In addition, cobalt hydroxide having a wide layer between layers has a lower solubility in an alkaline solution than α-Co (OH) ₂ , while it has a higher solubility than β-Co (OH) _2. Since a conductive network connecting the active materials can be easily formed and the spacing between the crystal layers is wide, the binding force of protons between the layers is smaller than that of β-Co (OH) ₂ , and the conductivity is high. From this, it is possible to improve the conductivity between the conductive skeleton of the metal porous substrate and the nickel hydroxide particles or the nickel hydroxide particles as the active material, and to perform deep discharge. Therefore, the amount of external additives can be reduced as compared with the conventional example, and the active material filling density and the capacity density as a nickel electrode can be improved, and stable battery characteristics can be obtained.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The first aspect of the present invention specifies active material particles in a battery state.

According to a third aspect of the present invention, α-Co (O
H) A powder obtained by heat-treating a nickel hydroxide powder whose surface is coated with cobalt hydroxide composed of ₂ is used as active material particles.

In each case, the amount of external additives can be reduced as the nickel electrode, and the packing density of the active material and the capacity density as the electrode plate can be improved.

According to a fourth aspect of the present invention, an α-Co (O
H) defines the heat treatment temperature of the nickel hydroxide powder whose surface is coated with cobalt hydroxide of ₂ ) and the amount of Co added. If the heat treatment is performed at a temperature higher than 150 ° C., cobalt hydroxide and nickel hydroxide as a base are oxidized.
50 ° C. is preferred. If the compounding ratio of Co to nickel hydroxide in cobalt hydroxide is less than 2% by weight, it is insufficient to form a dense conductive network.
If the content is more than the weight percentage, the filling amount of nickel hydroxide as an active material is reduced. From these facts, the ratio of Co in cobalt hydroxide to spherical nickel hydroxide is 2 to 1
It is desirably 0% by weight.

According to a fifth aspect of the present invention, a spherical nickel hydroxide powder is used as a main component, and the additive is added at 100 to 150 ° C.
Is a nickel electrode for an alkaline storage battery using α-type cobalt hydroxide heat-treated at a temperature of α-Co (OH) ₂ , which is oxidized when heat-treated at a temperature higher than 150 ° C.
The heat treatment is preferably performed at a temperature of 150 ° C. or lower and 100 ° C. or less.
Cobalt hydroxide having a wider interlayer distance than β-Co (OH) ₂ can be obtained. This cobalt hydroxide having a wide layer between layers has a higher solubility in alkali than regular β-Co (OH) ₂ , can easily form a conductive network, and has a binding force of protons between crystal layers. , The conductivity is also high. Therefore, the amount of the external additive used as the conductive agent can be reduced, and the packing density of the active material and the capacity density of the electrode plate can be improved.

According to a sixth aspect of the present invention, the ratio of Co in cobalt hydroxide to the weight of the active material particles is defined. If the ratio is less than 1% by weight, a dense conductive network is formed. On the other hand, if it is more than 15% by weight, the filling amount of the nickel hydroxide active material will decrease. From these, it is desirable that the ratio of Co in cobalt hydroxide to spherical nickel hydroxide is 1 to 15% by weight.

The invention according to claim 7 is characterized in that the heat-treated α-
It defines the particle size of nickel hydroxide particles whose surface is coated with a layer of cobalt hydroxide composed of Co (OH) ₂ ,
By setting this to an appropriate range, the packing density of the active material and the capacity density of the electrode plate are improved.

According to the present invention, the packing density of the active material and the capacity density of the electrode plate are improved by a combination of the particle size of the nickel hydroxide powder as the main component and the α-type cobalt hydroxide.

According to a ninth or tenth aspect of the present invention, the powder obtained by heat-treating the nickel hydroxide particles whose surface is coated with cobalt hydroxide is used as an active material,
A nickel / hydrogen storage battery is obtained by combining a heat-treated positive electrode made of nickel hydroxide to which α-type cobalt hydroxide is added, a negative electrode made of a hydrogen storage alloy, a separator, and an alkaline electrolyte.

Hereinafter, the nickel electrode for an alkaline storage battery of the present invention will be described.

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, a cobalt hydroxide layer of powder obtained by heat-treating nickel hydroxide particles whose surface is coated with cobalt hydroxide composed of α-Co (OH) ₂ , or α-Co ( OH) ₂ powder obtained by heat treatment is α-Co (O
Water of crystallization contained between the crystal layers of H) ₂ is eliminated, and cobalt hydroxide having a wider interlayer distance than regular β-Co (OH) ₂ is obtained. This wide cobalt hydroxide between the layers
Compared with —Co (OH) ₂ , it has higher solubility in alkali and can easily form a conductive network, and has high conductivity due to a small proton binding force between layers. Therefore, the amount of the external additive as the conductive agent can be reduced, and the packing density of the active material and the capacity density as the electrode plate can be improved accordingly.

[0022]

EXAMPLES The method for producing this nickel positive electrode and the nickel-metal hydride storage battery using this positive electrode will be described in more detail below.

(Embodiment 1) First, in the first step, α-C
A spherical nickel hydroxide powder whose surface is coated with cobalt hydroxide composed of o (OH) ₂ is heat-treated. The mixing ratio of Co to nickel hydroxide in cobalt hydroxide was 7% by weight.

The heat treatment temperature is 100, 130, 150,
Carried out in four different 180 ° C., respectively _{A 1, A 2, A 3} ,
It was A _4. Also those not heat-treated for comparison were the A _0. In the second step, 2 parts by weight of zinc oxide was added to 100 parts of the obtained powder, and the water content was adjusted with pure water to form a paste. And By combining this positive electrode and a negative electrode made of a hydrogen storage alloy powder, a well-known cylindrical sealed nickel-metal hydride battery was formed.

With respect to the five types of batteries A _{0 to} A ₄ configured as described above, charging is performed at 0.1 CmA for 15 hours, and discharging is performed at 0.2 CmA to discharge to a final voltage of 1.0. Was performed 5 times, and the battery capacity was measured.
The utilization factor obtained by dividing each battery capacity by the theoretical capacity (a value obtained by multiplying the weight of the active material filled in the positive electrode by the amount of electricity of 289 mAh / g when one-electron reaction is caused by nickel hydroxide) is shown in (Table 1). .

[0026]

[Table 1]

As described above, according to this embodiment, α-Co
By subjecting the nickel hydroxide particles whose surface is coated with cobalt hydroxide composed of (OH) ₂ to a heat treatment at 150 ° C. or lower, water of crystallization contained between the layers of α-Co (OH) ₂ is desorbed, and β- Cobalt hydroxide having a wider interlayer distance than Co (OH) ₂ can be obtained.

The cobalt hydroxide having a wide interlayer has a β-C
Compared to o (OH) ₂ , it has higher solubility in alkalis and facilitates formation of a conductive network. In addition, since the binding force of protons between layers is small, the conductivity is high and the capacity density of the electrode plate is improved. And stable battery characteristics were obtained.

In the examples, those having a cobalt ratio of 7% by weight in cobalt hydroxide were used. However, if the ratio of Co in cobalt hydroxide was less than 2% by weight, a dense conductive network was used. It is not sufficient to form a crack, and if it is more than 10% by weight, the filling amount of the nickel hydroxide active material is reduced. Therefore, it is desirable that the compounding ratio of Co in the cobalt hydroxide to the spherical nickel hydroxide is 2 to 10% by weight.

(Embodiment 2) In the first step, α-Co
(OH)_TwoHeat treat the powder. Heat treatment temperature is 100,1
Perform at 30, 150, 180, 200 ° C in 5 ways
B each₁, B_Two, B _Three, B_Four, B_FiveAnd Also heat treatment
B that did not do₀And The second step is hydroxylation
Hydroxide obtained in the first step with respect to 100 parts of nickel powder
10% by weight of cobalt oxide powder and 2% by weight of zinc oxide
Then, adjust the water content with pure water to make a paste,
The nickel-containing positive electrode was filled in a hollow porous substrate. This
Combination of positive electrode and negative electrode made of hydrogen storage alloy powder
To form a well-known cylindrical sealed nickel / hydrogen storage battery.
Done.

The above six batteries B _{0 to} B ₅ were charged at 0.1 CmA for 15 hours, and discharged at 0.2 CmA for 5 cycles of discharging to a final voltage of 1.0. The battery capacity at the time of the test was measured. The utilization rate obtained by dividing each battery capacity by the theoretical capacity (a value obtained by multiplying the weight of the hydroxide active material filled in the positive electrode by the amount of electricity of 289 mAh / g when nickel hydroxide performs a one-electron reaction) (Table 2) Shown in

[0032]

[Table 2]

As described above, according to this embodiment, α-Co
By adding cobalt hydroxide consisting of (OH) ₂ and heat-treated at 150 ° C. or lower to the paste, the capacity density as an electrode plate was improved, and a high utilization factor and stable battery characteristics were obtained.

In the examples, the ratio of Co of cobalt hydroxide to the weight of the nickel hydroxide active material was set to 10% by weight. If the ratio was less than 1% by weight, a dense conductive network was formed. Not enough, and 1
When the content is more than 5% by weight, even though the construction of the network is sufficient, the filling amount of the nickel hydroxide active material is relatively reduced. From these facts, the ratio of Co in cobalt hydroxide to spherical nickel hydroxide is 1 to 15% by weight.
Is desirable.

[0035]

As described above, the present invention relates to α-Co (O
H) A powder obtained by oxidizing nickel hydroxide powder whose surface is coated with cobalt hydroxide composed of ₂ is used as active material particles, or spherical nickel hydroxide powder is used as a main component and added to this. 100-150 ° C
By using a nickel electrode to which α-type cobalt hydroxide added with the heat treatment is applied, the capacity density of the positive electrode plate can be improved and stable battery characteristics can be obtained.

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Hideo Kaiya 1006 Kadoma Kadoma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (10)

[Claims] (1) A crystalline form close to β-Co (OH) ₂ , and at least a part of the surface is coated with cobalt oxyhydroxide obtained from α-Co (OH) ₂ having no water of crystallization as a starting material. Electrode for alkaline storage batteries using nickel hydroxide powder as active material particles. 2. The nickel electrode for an alkaline storage battery according to claim 1, wherein substantially all of the surface of said nickel hydroxide powder is coated with cobalt oxyhydroxide. 3. A heat treatment of a nickel hydroxide powder having a surface coated with cobalt hydroxide comprising α-Co (OH) ₂ ,
A method for producing a nickel electrode for an alkaline storage battery, comprising removing water of crystallization from the cobalt hydroxide. 4. The heat treatment temperature of the nickel hydroxide powder is as follows:
The method for producing a non-sintered nickel electrode for an alkaline storage battery according to claim 3, wherein the temperature is 100 to 150 ° C, and the weight ratio of Co in the cobalt hydroxide to nickel hydroxide is 2 to 10% by weight. 5. A method for producing a nickel electrode for an alkaline storage battery, comprising a spherical nickel hydroxide powder as a main component, and adding an α-type cobalt hydroxide heat-treated at 100 to 150 ° C. as an additive to prepare a paste. 6. The method according to claim 5, wherein the weight ratio of Co in the cobalt hydroxide to the nickel hydroxide powder is 1 to 15% by weight. 7. The nickel electrode for an alkaline storage battery according to claim 3, wherein the nickel hydroxide powder whose surface is coated with cobalt hydroxide composed of α-Co (OH) ₂ has a particle size of about 5 to 50 μm. Manufacturing method. 8. The method for producing a nickel electrode for an alkaline storage battery according to claim 5, wherein the nickel hydroxide powder as a main component of the nickel electrode has a particle size of about 5 to 50 μm. 9. A positive electrode comprising, as an active material, a powder obtained by heat-treating nickel hydroxide particles having a surface coated with cobalt hydroxide comprising α-Co (OH) _2, and a hydrogen storage alloy powder. An alkaline storage battery composed of a combination of a negative electrode, a separator, and an alkaline electrolyte. 10. A composition comprising a spherical nickel hydroxide powder as a main component,
An alkaline storage battery comprising a combination of a positive electrode to which heat-treated α-type cobalt hydroxide is added as an additive, a negative electrode made of a hydrogen storage alloy powder, a separator, and an alkaline electrolyte.