JPH09115520A - Manufacture of paste type cadmium negative electrode for alkaline storage battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high performance paste type cadmium negative electrode whose partial charging process is ovbiated by agitating paste by adding collected carbon fiber to an active material mainly composed of prescribed cadmium type powder, and forming the negative electrode by sticking it to a core material. SOLUTION: Paste is formed by adding carbon fiber collected by low molecular nylon to an active material mainly composed of one or more kinds among metallic cadmium powder, cadmium oxide powder and cadmium hydroxide powder. When this paste is agitated, the collected carbon fiber is uniformly dispersed, and when it is painted on a core material, a negative electrode in which a conductive matrix skeleton of mrtallic cadimium powder is formed can be provided. Therefore, a high performance paste type negative electrode whose partial charging process is obviated and short circuit occurrence rate is low can be provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in a method for producing a paste type cadmium negative electrode used in nickel cadmium storage batteries and the like.

[0002]

2. Description of the Related Art In alkaline storage batteries used as various power sources, a cadmium electrode is used as a negative electrode in nickel-cadmium storage batteries and the like. There are a sintering method and a pasting method in the manufacturing method of this cadmium electrode. The paste-type electrode is obtained by adding an active material, a conductive agent, and a binder to form a paste, and applying it to a support in a sheet shape, so that the process is simple and the cost can be reduced. Specifically, the paste-type cadmium negative electrode contains cadmium oxide or cadmium hydroxide as a main component, and conductive powder such as carbon nickel and graphite, a binder such as polyvinyl alcohol and carboxymethyl cellulose, and water and ethylene glycol. It is obtained by adding a solvent and kneading to form a paste, which is applied to a conductive core body such as a nickel-plated perforated steel sheet. However, compared with the sintering method, the high-rate discharge characteristic is inferior because the active material is less in contact with the conductive support. Therefore, a method has been proposed in which metal fibers or metal-plated fibers are mixed in the paste in order to increase the strength as an electrode and improve the electron conductivity (Japanese Patent Laid-Open No. 58-75771).

Further, in the case of a cadmium negative electrode, regardless of whether it is a sintering type or a paste type, a step of partially charging in an alkaline solution after manufacturing the electrode is added. The purpose of this partial charge is to convert a part of the discharged cadmium compound such as cadmium oxide and cadmium hydroxide used as the active material material into charged metal cadmium to provide a precharged portion in the negative electrode. When there is no pre-charged portion in the negative electrode, the utilization factor of the negative electrode is lower than that of the positive electrode, so that the discharge becomes dominant in the negative electrode and the high rate discharge characteristic of the battery deteriorates. Further, since the negative electrode is completely discharged, the characteristics of the battery are significantly deteriorated. For this reason, partial charging is performed and the negative electrode capacity of 15 to
25% charged.

However, this process requires extra electric power, complicates the process, and it is not easy to evenly distribute the metal cadmium in the electrode by partial charging, and variations in characteristics are likely to occur. In order to solve such a problem, a method of eliminating a partial charging step by adding an active metal cadmium powder as shown in Japanese Patent Publication No. 57-37986 in a kneading amount of an active material corresponding to a preliminary charge amount. Is proposed.

[0005]

However, the paste-type cadmium negative electrode produced by the method of adding the metal cadmium powder in an amount corresponding to the pre-charge amount during the kneading of the active material has a problem that the metal cadmium powder is added to the metal cadmium powder in the initial stage of battery construction. There is a phenomenon that the formation of the conductive matrix in cadmium is insufficient and does not work as an active material during discharge, resulting in poor discharge characteristics.

Even when the method of adding metal fibers or the like is used, since the dispersibility at the time of kneading is poor, the fibers are entangled with each other and are not uniformly mixed with the active material to form a lump or a protrusion, and There are drawbacks in that fibers come out on the surface and are easily short-circuited with the counter electrode through the separator, and because the dispersibility is poor, the conductive matrix becomes insufficient and discharge characteristics deteriorate. It is an object of the present invention to solve the above problems and provide a means for producing a high performance paste type cadmium negative electrode that does not require a partial charging step.

[0007]

To achieve the above object, the present invention provides a carbon fiber bundled with a metal cadmium powder and an active material mainly containing cadmium oxide powder or cadmium hydroxide powder. Is added to form a paste, which is stirred and then applied to the core material. In order to enhance conductivity, the carbon fibers may be plated with nickel and then bundled and used.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The purpose of incorporating fibers into a paste of an active material is to strengthen the binding property between the active materials and between the active material and the support by the same principle as that of using straw for the soil wall of a house. To do. Furthermore, the use of conductive fibers as in the present application is, of course, to form a conductive network thereby.

Therefore, it is premised that the fibers are dispersed in the active material as uniformly as possible. Therefore, the fibers to be added are also dispersed to add the active material. However, even if fibers in such a state are added to the binder solution in advance and stirred, or even if added to the active material and agitated, the fibers are entangled with each other, so that the dispersibility at the time of kneading is poor. The fibers are entangled with each other, and the fibers are not uniformly mixed with the active material, and the fibers become fluffy and hardened or protruded. In an extreme case, fibers will come out on the surface of the electrode, which will short-circuit with the counter electrode through the separator.

Contrary to the general idea, however, when carbon fibers in a pre-focused state are added to the active material and stirred, the fibers do not become fluffy in this state, so most of the fibers are focused by simple stirring. It was found that evenly dispersed in the paste. After that, when the stirring is continued, the dispersed fiber group is dispersed in a state close to a single fiber. In this case, it has been found that the fiber group is small in scale, and thus it is easy to mix with the active material. The present application is based on this phenomenon.

That is, if the carbon fibers, which are conductive fibers, are uniformly dispersed in the active material, it is possible to improve the utilization rate of the metal cadmium powder without isolation of the added metal cadmium powder.

In order to further improve the conductivity of the fiber and make it advantageous for high discharge, it is preferable to nickel plate the surface of the carbon fiber.

[0013]

【Example】

(Embodiment 1) Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

The metal cadmium powder having an average particle diameter of 10 μm and the cadmium powder having an average particle diameter of 1 μm are in a weight ratio of 10:90.
0.2% of "Vesphite MC" manufactured by Toho Rayon Co., Ltd., which is a carbon fiber obtained by mixing 1.0% by weight of low molecular weight nylon and bundling the mixture, and adding ethylene glycol solution of polyvinyl alcohol. Was thoroughly kneaded in a paste form and applied to a perforated steel sheet and dried. Next, the coated plate was immersed in a KOH aqueous solution having a specific gravity of 1.20 and a temperature of 20 ° C. for 15 minutes to convert a part of cadmium oxide in the electrode plate into cadmium hydroxide, followed by washing with water and drying. This electrode plate is referred to as a cadmium negative electrode a according to the embodiment of the present invention. Next, as a comparative example, an electrode plate prepared by adding the same amount of acrylonitrile-based fibers in place of "Vesphite MC" was used as a conventional example cadmium negative electrode b. Further, an electrode plate prepared by adding the same amount of carbon fiber without a sizing agent was used as a second conventional example cadmium negative electrode c.

Cadmium negative electrodes a, b and c were combined with an existing sintered nickel positive electrode to manufacture sealed storage batteries A, B and C having a nominal capacity of 600 mAh. A discharge rate characteristic test was conducted to evaluate the discharge characteristic of the negative electrode. FIG. 1 shows the relationship between the discharge rate and the discharge capacity ratio. That is, the discharge characteristics were evaluated by the ratio of the discharge capacity at the time of discharging the battery at various discharge rates and the discharge capacity at a current equivalent to 0.2 CmAh.

A, B and C in the figure are the characteristics of the respective batteries. The negative electrode a, in which a uniform conductive network is formed in the electrode plate, has good discharge characteristics, but the negative electrodes b and c have insufficient conductive networks, and thus have poor discharge characteristics. Further, the average voltage when discharged to 1.0 V at 1 CmA was 1.23 V for A, 1.20 V for B, and 1.21 V for C. From this, battery A
However, it is considered that the discharge voltage is improved because a conductive matrix of metal cadmium is formed in the negative electrode.

Next, 1000 batteries were prepared for each battery, and an internal micro short circuit of the battery group was investigated. (Table 1)
The occurrence rates of internal micro short circuits of batteries A, B, and C are shown in FIG.

[0018]

[Table 1]

As is clear from (Table 1), since the battery group A using the negative electrode a according to this embodiment uses the bundled carbon fibers, the internal micro short circuit is greatly reduced. By attaching the sizing agent to the carbon fiber, it is possible to suppress the fluffing of the fiber, and the fibers do not become entangled with each other after the addition. Then, by controlling the addition amount of the sizing agent to 0.5 to 3%, the sizing agent is easily dispersed at the time of kneading. As a result, it became clear that a smooth electrode plate can be created and internal micro-short circuits can be greatly reduced.

(Example 2) In the same manner as in Example 1, 1.0% by weight of low molecular weight nylon was attached to nickel-plated carbon fibers to be bundled, and then 0.2% by weight in the active material.
The mixture was added, and sufficiently kneaded with an ethylene glycol solution of polyvinyl alcohol to form a paste, which was applied to a perforated steel sheet and dried. Next, the coated plate was subjected to KO with a specific gravity of 1.20 and a temperature of 20 ° C.
It was immersed in an aqueous solution of H for 15 minutes to convert a part of the cadmium oxide in the electrode plate into cadmium hydroxide, followed by washing with water and drying. This electrode plate is used as a cadmium negative electrode d according to an embodiment of the present invention.
And As a comparative example, a cadmium negative electrode e according to the comparative example is a plate prepared by adding the same amount of nickel-plated carbon fibers without a sizing agent to the paste. Each of these cadmium negative electrodes d and e is combined with a sintered nickel positive electrode to form a sealed storage battery D having a nominal capacity of 600 mAh.
E was prototyped and a discharge rate characteristic test was conducted to evaluate the discharge characteristic of each negative electrode. FIG. 2 shows a discharge curve at 3C discharge at 0 ° C. As is apparent from FIG. 2, the battery D using the negative electrode d of the example has a final voltage of 0.7 V and a
In contrast to 0 mAh, the battery E using the negative electrode e of the comparative example showed only 450 mAh with a final voltage of 0.7 V. In the battery using the negative electrode e of the comparative example, the cadmium negative electrode was rate-controlled and the capacity decreased.

Next, the cadmium negative electrodes d and e were combined with a sintered nickel positive electrode and wound through a separator to produce 1000 electrode groups, and an internal micro short circuit of the electrode group was investigated.

Table 2 shows the occurrence rates of internal minute short circuits in the electrode group using the negative electrode d and the electrode group using the negative electrode e in D and E, respectively.

[0023]

[Table 2]

As is clear from (Table 2), by plating the comparative battery E as well, fluffing was suppressed and the number of micro short circuits was reduced as compared with the battery B of (Table 1), but it was still much higher than that of the battery D. The effect of the sizing agent is clear. That is, in the electrode group D using the negative electrode d, the internal micro-short circuit is greatly reduced by the metal-plated carbon fiber using the sizing agent, and the effect of suppressing the fluffing of the fiber is sufficiently exerted.

[0025]

INDUSTRIAL APPLICABILITY As described above, the present invention forms a conductive matrix skeleton of metal cadmium powder by adding focused carbon fibers to a paste containing metal cadmium powder and cadmium oxide powder as a main active material. In addition, it is possible to reduce the minute short circuit which was frequently generated when the carbon fiber is used for the cadmium negative electrode, and to provide the production of the paste type cadmium negative electrode which does not require the partial charge / discharge step.

[Brief description of the drawings]

FIG. 1 is a diagram showing a relationship between a discharge rate and a discharge capacity ratio of a battery using a cadmium negative electrode according to a first embodiment of the present invention and a conventional example.

FIG. 2 is a discharge curve (0 ° C., 1 CmA) of a battery using a cadmium negative electrode according to a second embodiment of the present invention and its comparative example.
Figure showing

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hiroki Takeshima 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (2)

[Claims] 1. A core material after adding concentrated carbon fibers to an active material containing, as a main component, at least one of a metal cadmium powder and a cadmium oxide powder or a cadmium hydroxide powder to form a paste and stirring the core material. A method for producing a paste-type cadmium negative electrode, which is characterized in that it is applied to 2. A nickel-plated carbon fiber is focused on an active material containing at least one of a metal cadmium powder and a cadmium oxide powder or a cadmium hydroxide powder as a main component, and the carbon fiber is stirred with the added paste, followed by a core. A method for producing a paste-type cadmium negative electrode, which comprises applying it to a material.