JP2968813B2 - Method for producing cadmium negative electrode for alkaline storage battery - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial application field) The present invention relates to a method for producing a paste-type cadmium negative electrode used for an alkaline storage battery (prior art). Paste-type cadmium negative electrodes, which have advantages such as simpler production, lower cost and higher energy density than conventional cadmium negative electrodes, have been widely used.

By the way, in a sealed nickel-cadmium storage battery, generally, the capacity of a cadmium negative electrode in a discharged state is about twice as large as the capacity of a nickel positive electrode. Is consumed by the cadmium negative electrode, and the cadmium negative electrode is designed so that it does not reach full charge and does not generate hydrogen gas. Also, since the utilization rate of the cadmium negative electrode is lower than that of the nickel positive electrode, the battery capacity is regulated by the cadmium negative electrode if the charge amount is the same. However, when the cadmium negative electrode is regulated during discharge, high-rate discharge and cycle characteristics are significantly degraded, so that the negative electrode is partially charged to prevent the cadmium negative electrode regulation, so-called formation of the nickel positive electrode is performed. It is designed to be. Chemical formation is generally performed by partially charging a cadmium negative electrode in a discharged state in an electrolytic solution. However, there are problems such as complicated processes, discharge of a cleaning solution, and variation in the amount of charge.

For this reason, a paste-type cadmium negative electrode in which an active material mainly composed of, for example, cadmium oxide and metal cadmium are used in a fixed ratio, that is, a so-called unformed one is being studied. However, when the active material mainly composed of cadmium oxide and metal cadmium are mixed, the added metal cadmium powder is covered with cadmium oxide, which is an insulator, and is not efficiently used as a conductive matrix. There was a problem of lowering. When an organic solvent is used as the solvent for the paste, the metal cadmium itself has good affinity for alcohols, so that it cannot be dried by a usual method, and the alcohols remain. The remaining alcohols have the advantage of providing a reserve for discharge by anodizing the cadmium negative electrode, but ultimately generate carbon dioxide gas, causing a problem that adversely affects battery performance.

On the other hand, Japanese Patent Application Laid-Open No. 54-50843 discloses a method of forming a layer of an active material mainly composed of cadmium oxide on a conductive substrate, and further forming a metal cadmium layer on this layer. As a method of forming the cadmium oxide layer, a method is described in which a paste is prepared using water as a solvent, and the paste is applied and dried, or a method in which a fluororesin such as polytetrafluoroethylene is mixed to form a sheet. I have. However, when water is used as the solvent, cadmium oxide is changed to cadmium hydroxide to lower the density, thereby impairing the high density filling of the conductive substrate, which is an advantage of the paste method.
Although phosphate is added to avoid this, the change to cadmium hydroxide is somewhat suppressed, but the production of cadmium hydroxide cannot be completely suppressed. Further, in the method of mixing the fluororesin to form a sheet, not only the process becomes complicated, but also the adhesion to the metal cadmium layer is reduced, and the strength for producing an electrode group together with the nickel positive electrode and the separator is reduced.

In JP-A-61-10857, a layer of an active material mainly composed of cadmium oxide is formed on a conductive substrate, and a paste composed of metal cadmium and an aqueous solution of polyvinyl alcohol is applied on this layer and dried. A method for forming a metal cadmium layer is disclosed. However, in order to prepare a paste using metal cadmium and an aqueous solution of polyvinyl alcohol, if the concentration of the polyvinyl alcohol is not increased, solid-liquid separation will not be possible unless polyvinyl alcohol is used. There is a problem that triggers a rise.

(Problems to be Solved by the Invention) The present invention has been made to solve the above-mentioned conventional problems, and a first negative electrode mixture layer containing high-density cadmium oxide is formed on a conductive substrate, It is still another object of the present invention to provide a method for producing a cadmium negative electrode for an alkaline storage battery in which a second negative electrode mixture layer containing metal cadmium having high density and good gas permeability is formed on the first negative electrode mixture layer. .

[Means for Solving the Problems] The method for producing a cadmium negative electrode for an alkaline storage battery according to the present invention is directed to an organic solvent comprising an active material mainly composed of cadmium oxide and a binder comprising ethylene glycol or propylene glycol. Forming a first negative electrode mixture layer by applying the first paste dissolved and kneaded in the conductive substrate to a conductive substrate, and then drying until the organic solvent in the paste is completely evaporated and removed; A second paste obtained by kneading an aqueous solution obtained by dissolving or dispersing a binder consisting of cadmium-based active material and carboxymethylcellulose is applied onto the negative electrode mixture layer, and then dried to form a second negative electrode mixture. And a step of forming an agent layer.

Another method for producing a cadmium negative electrode for an alkaline storage battery according to the present invention is to dissolve an active material mainly composed of cadmium oxide and a binder in an organic solvent composed of ethylene glycol or propylene glycol, and knead the first paste. Preparing a first negative electrode mixture layer by applying the first paste to a conductive substrate, and then drying until the organic solvent in the paste is completely evaporated and removed; and forming a first negative electrode mixture layer. Active material and its active material 100
An aqueous solution obtained by dissolving or dispersing a mixed binder composed of carboxymethyl cellulose and polyvinyl alcohol (provided that the polyvinyl alcohol is 2 parts by weight or less) is kneaded in an amount of 0.5 to 5 parts by weight based on the weight of the second binder. Preparing a second paste, applying the second paste on the negative electrode mixture layer, and then drying the paste to form a second negative electrode mixture layer. .

Examples of the conductive substrate include punched metal, wire mesh, lath metal, and the like.

Examples of the binder constituting the first paste include polytetrafluoroethylene, carboxymethylcellulose, and polyvinyl alcohol.

The amounts of the active material and the binder constituting the first and second pastes are desirably 0.5 to 5 parts by weight of the binder with respect to 100 parts by weight of the active material.

In addition, synthetic resin short fibers serving as a reinforcing material may be added to the first paste as needed.

(Action) According to the present invention, an active material mainly composed of cadmium oxide and a binder are dissolved in an organic solvent composed of ethylene glycol or propylene glycol as a first paste,
By using the kneaded material, it is possible to prevent cadmium oxide from being converted into cadmium hydroxide as when water is used as a solvent. Therefore, by applying the first paste on the conductive substrate and then drying the first paste, a high-density first negative electrode mixture layer can be formed.

In addition, the first paste is dried until the organic solvent composed of ethylene glycol or propylene glycol, which is relatively difficult to evaporate and remove by natural drying, is completely evaporated and removed. When applying the second paste containing metal cadmium on the first negative electrode mixture layer, since no organic solvent is present in the first negative electrode mixture layer, the organic solvent in the second paste A high-density second negative electrode mixture layer can be formed while avoiding adverse effects on metal cadmium, and the utilization efficiency of metal cadmium can be improved.

Further, the second paste is prepared by kneading an aqueous solution in which an active material mainly composed of metal cadmium and a binder made of carboxymethylcellulose are dissolved or dispersed, whereby the second negative electrode having good gas permeability is kneaded. An agent layer can be formed.

As a second paste, an active material mainly composed of cadmium metal and a mixed binder of carboxymethylcellulose and polyvinyl alcohol blended in an amount of 0.5 to 5 parts by weight with respect to 100 parts by weight of the active material (provided that polyvinyl alcohol is 2% by weight). Parts or less) is kneaded with an aqueous solution obtained by dissolving or dispersing the second negative electrode mixture having a good gas permeability almost the same as that obtained when using only carboxymethyl cellulose as the binder. Layers can be formed.

Therefore, according to the present invention, the first and second negative electrode mixture layers described above have a higher density, an improved utilization rate of metal cadmium,
By forming the second negative electrode mixture containing metal cadmium having good gas permeability, a cadmium negative electrode having excellent discharge efficiency and good gas absorption characteristics can be manufactured.

(Example) Hereinafter, an example of the present invention will be described in detail.

Example 1 First, 100 parts by weight of cadmium oxide and 0.5 parts by weight of short fibers of a vinyl chloride-acrylonitrile copolymer were kneaded in a kneading solution in which 1 part by weight of carboxymethyl cellulose was dissolved in 30 parts by weight of ethylene glycol at 120 ° C. One paste was prepared. In addition, carboxymethyl cellulose 0.
After dissolving 5 parts by weight in 100 parts by weight of ion-exchanged water at 90 ° C,
Allow to cool to form a kneading solution.
A second paste was prepared by kneading parts by weight.

Next, the first paste is applied to both sides of a nickel-plated 0.06 mm-thick punched metal plate having a porosity of 58% and dried with hot air at 150 ° C. for 3 hours to completely evaporate ethylene glycol. Thickness including cadmium oxide removed
A first negative electrode mixture layer of 0.7 mm was formed. Subsequently, the second paste is applied to both surfaces of the first negative electrode mixture layer,
After drying to form a second negative electrode mixture layer containing cadmium metal, the resultant was pressed and cut to produce a cadmium negative electrode.

Example 2 First, 100 parts by weight of cadmium oxide and 0.5 part by weight of short fibers of a vinyl chloride-acrylonitrile copolymer were kneaded with a kneading solution in which 1 part by weight of carboxymethyl cellulose was dissolved in 30 parts by weight of ethylene glycol at 120 ° C. One paste was prepared. Also, 2 parts by weight of polyvinyl alcohol and 0.5 part by weight of carboxymethyl cellulose were dissolved in 100 parts by weight of ion-exchanged water at 90 ° C., and then allowed to cool to form a kneading liquid. The kneading liquid was kneaded with 100 parts by weight of metal cadmium. A second paste was prepared.

Next, the first paste was applied to both sides of a punched metal plate as in Example 1, dried for 3 hours with hot air at 150 ° C., and dried to a thickness of 0.7 containing cadmium oxide from which ethylene glycol was completely evaporated and removed. The first negative electrode mixture layer of mm was formed. Subsequently, the second paste is applied to both surfaces of the first negative electrode mixture layer, dried to form a second negative electrode mixture layer containing metal cadmium, and then pressed and cut to form a cadmium negative electrode. Was manufactured.

Comparative Example 1 First, 100 parts by weight of cadmium oxide, 17 parts by weight of metal cadmium, and 0.5 parts by weight of short fibers of a vinyl chloride-acrylonitrile copolymer were mixed in a kneading solution in which 1 part by weight of carboxymethyl cellulose was dissolved in 30 parts by weight of ethylene glycol at 120 ° C. The parts were kneaded to prepare a paste. Subsequently, this paste was applied to both sides of a punched metal plate as in Example 1 and dried with hot air at 150 ° C. for 3 hours to form a 0.8 mm thick negative electrode mixture layer in which cadmium oxide and metal cadmium were mixed. After the formation, the cadmium negative electrode was manufactured by pressing and cutting.

Comparative Example 2 First, 1 part by weight of carboxymethylcellulose was dissolved in 30 parts by weight of ion-exchanged water at 90 ° C., and then allowed to cool to form a kneading liquid. 100 parts by weight of cadmium oxide and a vinyl chloride-acrylonitrile copolymer were added to the kneading liquid. Was kneaded with 0.5 part by weight of the short fiber of No. 1 to prepare a first paste. Subsequently, the first paste was applied to both sides of a punched metal plate as in Example 1, dried with hot air at 150 ° C. for 3 hours, and contained 0.7 mm in thickness containing cadmium oxide from which water was completely evaporated and removed. The first negative electrode mixture layer was formed. Next, a second paste having the same composition as in Example 1 was applied to both surfaces of the first negative electrode mixture layer and dried to form a second negative electrode mixture layer containing metal cadmium. Then, a cadmium negative electrode was manufactured.

Comparative Example 3 First, 100 parts by weight of cadmium oxide and 0.5 part by weight of a short fiber of a vinyl chloride-acrylonitrile copolymer were kneaded with a kneading solution in which 1 part by weight of carboxymethyl cellulose was dissolved in 30 parts by weight of ethylene glycol at 120 ° C. One paste was prepared. After dissolving 5 parts by weight of polyvinyl alcohol in 100 parts by weight of ion-exchanged water at 90 ° C., the mixture was allowed to cool to obtain a kneading liquid, and 100 parts by weight of metal cadmium was kneaded with the kneading liquid to prepare a second paste. .

Next, the first paste was applied to both sides of a punched metal plate as in Example 1, dried for 3 hours with hot air at 150 ° C., and dried to a thickness of 0.7 containing cadmium oxide from which ethylene glycol was completely evaporated and removed. The first negative electrode mixture layer of mm was formed. Subsequently, the second paste is applied to both surfaces of the first negative electrode mixture layer, dried to form a second negative electrode mixture layer containing metal cadmium, and then pressed and cut to form a cadmium negative electrode. Was manufactured.

Thus, AA size batteries (nominal capacity 500 mAh) were assembled using the cadmium negative electrodes of Examples 1 and 2 and Comparative Examples 1 to 3 and a known sintered nickel positive electrode. These batteries were charged at 0.3C for 5 hours and then discharged at 0.2C to 1V. FIG. 1 shows the discharge characteristics at this time, and FIG. 2 shows the change in the internal pressure of the battery.

As is clear from FIGS. 1 and 2, in the battery of Comparative Example 1, the nickel positive electrode was not charged due to the influence of ethylene glycol adsorbed on metal cadmium, and the discharge duration was short. In the battery of Comparative Example 2, since the packing density of the negative electrode mixture layer could not be sufficiently obtained, hydrogen was generated, and the internal pressure increased. In the battery of Comparative Example 3, since the second negative electrode mixture layer containing metal cadmium was hindered by the polyvinyl alcohol film and gas absorption characteristics were inferior, the internal pressure rise was the largest. On the other hand, it can be seen that the batteries of Examples 1 and 2 have a long discharge duration and a low battery internal pressure. In this method, a first paste containing cadmium oxide containing ethylene glycol is used, while a second paste containing metal cadmium does not contain an organic solvent such as ethylene glycol and is in an aqueous solution state. This is because the paste is dried by completely evaporating and removing ethylene glycol after application of the paste. Also,
In Example 2, since the mixture of carboxymethylcellulose having a polyvinyl alcohol content of 2% or less was used as the binder of the second paste, the gas absorption characteristics could be improved.

[Effects of the Invention] As described above in detail, according to the present invention, a first negative electrode mixture layer containing high-density cadmium oxide is formed on a conductive substrate, and further, on the first negative electrode mixture layer. A method for producing a cadmium negative electrode for an alkaline storage battery, which is excellent in efficient discharge by forming a second negative electrode mixture layer containing metal cadmium having high density and good gas permeability and has good gas absorption characteristics, can be provided.

[Brief description of the drawings]

FIG. 1 is a characteristic diagram showing the discharge duration during charging and discharging of the batteries provided with the cadmium negative electrodes of Examples 1 and 2 and Comparative Examples 1 to 3, and FIG. 2 is Examples 1 and 2 and Comparative Examples 1 to 3. FIG. 4 is a characteristic diagram showing a change in internal pressure during charging and discharging of a battery including the cadmium negative electrode of FIG.

──────────────────────────────────────────────────続 き Continuation of front page (72) Inventor Dr. Suzuki 3-4-10 Minamishinagawa, Shinagawa-ku, Tokyo Toshiba Battery Corporation (56) References JP-A-61-10857 (JP, A) JP-A-61-10857 JP-A 64-35859 (JP, A) JP-A-1-260760 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) H01M 4/26

Claims (2)

(57) [Claims] 1. A first paste obtained by dissolving an active material mainly composed of cadmium oxide and a binder in an organic solvent composed of ethylene glycol or propylene glycol, and kneading the first paste.
A step of forming a first negative electrode mixture layer by applying the organic solvent in the paste until the organic solvent in the paste is completely evaporated and removed, and applying an active material mainly composed of cadmium metal and carboxymethyl cellulose. Applying a second paste obtained by kneading an aqueous solution obtained by dissolving or dispersing a binder onto the negative electrode mixture layer, followed by drying to form a second negative electrode mixture layer. A method for producing a cadmium negative electrode for an alkaline storage battery. 2. A step of dissolving an active material mainly composed of cadmium oxide and a binder with an organic solvent composed of ethylene glycol or propylene glycol, and kneading the mixture to prepare a first paste; A step of forming a first negative electrode mixture layer by applying the composition to a conductive substrate and then drying the organic solvent in the paste until the organic solvent in the paste is completely removed; and forming an active material mainly composed of cadmium metal and the active material 100 An aqueous solution obtained by dissolving or dispersing a mixed binder composed of carboxymethyl cellulose and polyvinyl alcohol (provided that the content of polyvinyl alcohol is 2 parts by weight or less) in an amount of 0.5 to 5 parts by weight based on the weight of the second binder is kneaded. A step of preparing a paste, after applying the second paste on the negative electrode mixture layer,
Drying to form a second negative electrode mixture layer. A method for producing a cadmium negative electrode for an alkaline storage battery.