JPH0422065A - Manufacture of cadmium negative electrode for alkaline storage battery - Google Patents

Abstract

PURPOSE:To enhance the utilization factor of a negative electrode by blending cadmium oxide as an active material, and blending metal cadmium obtained by wet method with the active material in a wet state to form a paste, and applying the paste on a conductive base, and drying the paste. CONSTITUTION:A metal oxide serving as an active material is blended with a paste and metal cadmium obtained by wet method is mixed with the paste in a wet state and the paste is adjusted and applied on a conductive base and dried. As the metal oxide, cadmium oxide can be mentioned and the water content of the metal cadmium in its wet state is preferably more than 5wt.%. The surface of the metal cadmium in the paste is thus avoided from making direct contact with air, and so when the paste is applied on the conductive base and dried, the metal cadmium can be maintained in its highly active state together with the active material and the capacity factor of the electrode material including the metal cadmium which functions well as a discharge spare without inhibiting conductivity between active materials is enhanced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Field of Application) The present invention relates to a method for manufacturing a cadmium negative electrode for an alkaline storage battery.

(Prior Art) In recent years, cadmium negative electrodes have been used in alkaline storage batteries. In particular, paste-type cadmium negative electrodes are widely used because they have advantages such as a simpler manufacturing process, lower cost, and higher energy density than sintered-type ones.

Conventionally, alkaline storage batteries with paste-type cadmium negative electrodes have a discharged capacity of the cadmium negative electrode larger than the capacity of the positive electrode, so that the positive electrode is fully charged first during charging, and the oxygen gas generated from the positive electrode is absorbed by the cadmium negative electrode. The cadmium negative electrode is designed to prevent the generation of hydrogen gas that would lead to full charge. For example, in a sealed nickel-cadmium storage battery, the discharged capacity of the cadmium negative electrode is generally about twice the capacity of the nickel positive electrode. On the other hand, during discharge, if the cadmium negative electrode is regulated, the high rate discharge characteristics and cycle characteristics will be significantly deteriorated, so by performing chemical formation that places part of the cadmium negative electrode in a charged state, a part of the cadmium oxide, which is the active material, is charged. It is designed to convert into metallic cadmium in the state (discharge reserve) and become a positive electrode regulation.

However, the above-mentioned chemical conversion process requires a large amount of power and is a complicated process, and there are also problems in processing cleaning waste liquid, and furthermore, it is difficult to uniformly distribute metallic cadmium in a charged state. .

In order to solve this problem, a manufacturing method has been proposed in which metallic cadmium is added in advance as a discharge reserve into the cadmium negative electrode, and the chemical formation step is omitted.

However, the cadmium negative electrode manufactured by the above method has a problem in that the utilization rate of the electrode cannot be sufficiently improved for the following reasons. That is, the method is a method in which a paste is prepared by blending metal cadmium with cadmium oxide as an active material, and a cadmium negative electrode is obtained by applying this paste to a conductive substrate such as punched metal and drying it. The metal cadmium used here includes metal cadmium powder obtained by a wet method or a dry method, and the metal cadmium powder obtained by the wet method is used after washing with water and drying. The metal cadmium powder produced by the wet process is generally spongy and has a large surface area, so compared to the spherical metal cadmium powder produced by the dry process which has a small surface area, it has the advantage of being highly active as a discharge reserve. However, the surface of any metal cadmium powder reacts with oxygen or moisture in the air before the paste is prepared, and an electrochemically stable oxide or hydroxide film is formed on the surface. Therefore, the obtained cadmium negative electrode is
Despite the inclusion of metallic cadmium as a discharge reserve, there was a problem in that the original activity as a discharge reserve was lost, there was no conductive path, and the conductivity of the active material was reduced, resulting in a lower utilization rate.

On the other hand, a method has also been proposed in which the surface of the cadmium negative electrode is plated to form a conductive layer of nickel, carbon, etc. to improve the conductivity of the electrode surface and increase the utilization rate, but this method complicates the manufacturing process. Therefore, there was a problem in that it was disadvantageous in terms of cost.

(Problems to be Solved by the Invention) The present invention has been made in order to solve the conventional problems, and aims to provide a method for easily manufacturing a cadmium negative electrode for alkaline storage batteries with improved utilization rate. It is.

[Structure of the Invention (Means for Solving the Problems) The present invention comprises a step of preparing a paste by blending cadmium oxide as an active material and blending metallic cadmium obtained by a wet method in a wet state. A method for producing a cadmium negative electrode for an alkaline storage battery, comprising the steps of applying the paste on a conductive substrate and drying it.

Another invention according to the present invention includes a step of preparing a first paste by blending cadmium oxide as an active material;
a step of applying and drying the paste on a conductive substrate to form an active material layer; a step of preparing a second paste by blending metal cadmium obtained by a wet method in a wet state; This is a method for producing a cadmium negative electrode for an alkaline storage battery, comprising the steps of applying the second paste on the layer and drying it.

Examples of the cadmium oxide include cadmium oxide and cadmium hydroxide.

The wet method is a method for obtaining metal cadmium by a substitution reaction in a solution containing cadmium ions. In such a wet method, for example, zinc and nickel powder or nickel ions are added to a cadmium salt solution such as cadmium sulfate or cadmium acetate, and the cadmium ions in the cadmium salt solution are replaced with zinc ions to remove metallic nickel. A method for obtaining the metal cadmium contained therein is mentioned.

As for the wet state of the metal cadmium, it is desirable that the moisture content (the amount of water relative to the amount of metal cadmium) be 5% by weight or more. The reason for this is that if the water content is less than 5% by weight, the surface of the metal cadmium will be oxidized, the activity will decrease, and there is a risk that the utilization rate of the electrode will decrease. Further, from the viewpoint of preventing ignition, it is suitable to set the lower limit of the water content to 5% by weight. Note that the upper limit of the water content may be appropriately set according to the components of the paste so that a paste with the desired viscosity can be obtained.

Examples of the conductive substrate include those with a two-dimensional structure such as punched metal, expanded metal, and wire mesh, and those with a three-dimensional structure such as foamed metal and reticulated sintered metal fiber.

The paste is usually prepared by blending a polymer binder, a conductive material, etc. in water or an organic solvent in addition to the cadmium oxide and metal cadmium.

Examples of the polymer binder include carboxymethyl cellulose, short acrylic fibers, polyvinyl alcohol, and sodium polyacrylate.

Examples of the conductive material include conductive materials such as carbonyl nickel, carbon black, and graphite.

(Function) According to the present invention, by preparing a paste by blending cadmium oxide as an active material and blending metallic cadmium obtained by a wet method in a wet state, the surface of metallic cadmium in the paste is Since direct contact with air can be avoided, formation of an oxide or hydroxide film on the surface of metal cadmium can be prevented.

Therefore, by applying the paste onto a conductive substrate and drying it, metal cadmium can be maintained at a high level of activity together with the active material. As a result, it is possible to easily produce a cadmium negative electrode for an alkaline storage battery that contains metal cadmium that functions well as a discharge reserve without impeding the conductivity of the living material and has an improved utilization rate.

On the other hand, according to another invention related to the present invention, by preparing a paste by blending metal cadmium obtained by a wet method in a wet state, the surface of metal cadmium in the paste is directly exposed to air. Since contact with metal cadmium can be avoided, formation of an oxide or hydroxide film on the surface of metal cadmium can be prevented. Therefore, by applying and drying the paste on an active material layer formed on a conductive substrate and containing cadmium oxide as an active material, metal cadmium can be maintained in a highly active state together with the active material. As a result, it is possible to easily produce a cadmium negative electrode for an alkaline storage battery, which contains metal cadmium that functions well as a discharge reserve without impeding the conductivity of the living material, and which has an improved utilization rate.

(Example) Examples of the present invention will be described in detail below.

Example 1 Metal cadmium powder in a solution obtained by a wet method was adjusted to have a moisture content of 30% by weight by suction filtration. The moisture content was adjusted by adjusting the size of the funnel and the suction time. The resulting metal cadmium 1 with a water content of 30 and a weight of 9o
A water solvent vest was prepared by dispersing and mixing 0 parts by weight with 90 parts by weight of cadmium oxide, 5 parts by weight of carbonyl nickel, 0.5 parts by weight of carboxymethyl cellulose, and 0.5 parts by weight of acrylic short fibers. This paste was applied to a conductive support, ie, punched metal, and dried at 120° C. for 2 hours to produce a cadmium negative electrode.

Example 2 A first paste was prepared by adding cadmium oxide, carbonyl nickel, and short acrylic fibers to an ethylene glycol solution containing carboxymethyl cellulose. This paste was applied to punched metal and dried at 120° C. for 2 hours to form an active material layer. Next, metal cadmium 10 with a water content of 30% by weight prepared in the same manner as in Example 1.
A second paste was prepared by adding 0 parts by weight to an aqueous solution containing 0.5 parts by weight of polyvinyl alcohol and 0.5 parts by weight of carboxymethylcellulose. This second paste was applied to the active material layer and dried at 120° C. for 2 hours to produce a cadmium negative electrode.

Comparative example 1 Metal cadmium powder obtained by wet method is washed with water.

A cadmium negative electrode was produced in the same manner as in Example 1, except that a paste having the same composition as in Example 1 was prepared using this metal cadmium.

Comparative Example 2 Example 1 using metal cadmium powder obtained by dry method
A cadmium negative electrode was produced in the same manner as in Example 1, except that a paste having the same composition as in Example 1 was prepared.

Comparative Example 3 After producing an electrode in the same manner as in Comparative Example 1, the surface of the electrode was subjected to nickel plating to produce a di-Sokel plated cadmium negative electrode. In the nickel plating process, nickel was plated at a current density of 100 mA/cmF with nickel as the counter electrode at a temperature of 30°C in a commercially available bath for electrolytic metal plating mainly containing nickel sulfate or nickel chloride. A method was adopted in which the parts were heated with electricity for a few minutes, then washed with water and dried.

The cadmium negative electrodes of Examples 1 and 2 and Comparative Examples 1 to 3 were combined with a known paste-type nickel positive electrode to achieve a nominal capacity of 50
Five types of battery type test cells of 0+nAh were assembled. These five types of test cells were charged at a temperature of 20° C. with a current of 2 C for a certain period of time, and then discharged with an IC current.

At this time, the internal pressure of each test cell was measured. The results are shown in FIG.

As is clear from FIG. 1, each test cell becomes fully charged after 30 minutes of charging, and the internal pressure increases.

It can be seen that the test cells of Example 1.2 and Comparative Example 3 after being fully charged have a smaller increase in internal pressure than the battery of Comparative Example 1.2. The reason for this is that the cadmium negative electrodes of Examples 1 and 2 and Comparative Example 3 have better conductivity and higher utilization rate of metal cadmium inside the electrodes than the cadmium negative electrodes of Comparative Example 1.2. This is due to consuming (absorbing) a large amount of oxygen gas. In the test cell of Comparative Example 3, a small amount of hydrogen was generated during charging because the nickel on the surface of the negative electrode lowered the hydrogen generation overvoltage value of the negative electrode, and this hydrogen remained inside even after the discharge was completed.

Example 3 The metal cadmium powder in the solution obtained by the wet method was suction-filtered to adjust the water content in the same manner as in Example 1,
Metallic cadmium having a water content of 2.5, 20, 50, 70, and 100% by weight was obtained, respectively. A paste was prepared and applied to punched metal in the same manner as in Example 1 using each of the obtained cadmium metals.

Six types of cadmium negative electrodes were manufactured by drying.

Six types of storage batteries were assembled by combining each of the obtained cadmium negative electrodes with a known paste-type nickel positive electrode.

For each storage battery, 0. After charging with the IC current for 15 hours, the discharge capacity when discharging with the IC current was measured, and the ratio of the above-mentioned 711] constant value to the theoretical capacity of the negative electrode was determined as the utilization rate. The results are shown in FIG.

As is clear from Figure 2, from the perspective of improving the utilization rate,
It can be seen that it is desirable to use metal cadmium with a water content of 5% by weight or more. In addition, the moisture content is 70% fit 0
When metallic cadmium exceeding 6 was used, the viscosity of the paste decreased and it became difficult to apply it to punched metal.

[Effects of the Invention] As detailed above, according to the present invention, it is possible to provide a method for easily producing a cadmium negative electrode for an alkaline storage battery that has improved utilization rate and excellent oxygen gas absorption performance during charging. can.

[Brief explanation of the drawing]

Figure 1 is a characteristic diagram showing changes in internal pressure during charging and discharging in the test cells of Examples 1 and 2 and Comparative Examples 1 to 3. FIG. 3 is a characteristic diagram showing a change in the utilization rate of the negative electrode with respect to the water content. Applicant's agent Patent attorney Takehiko Suzue

Claims (2)

[Claims] (1) A step of preparing a paste by blending cadmium oxide as an active material and blending metallic cadmium obtained by a wet method in a wet state, and a step of applying the paste on a conductive substrate and drying it. A method for producing a cadmium negative electrode for an alkaline storage battery, comprising: (2) A step of preparing a first paste by blending cadmium oxide as an active material, a step of applying the paste on a conductive substrate and drying it to form an active material layer, and a step of forming an active material layer by a wet method. A cadmium for alkaline storage battery comprising the steps of preparing a second paste by blending cadmium metal in a wet state, and applying and drying the second paste on the active material layer. Manufacturing method of negative electrode.