JP2855754B2 - Nickel / cadmium storage battery - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement of a paste-type cadmium electrode for a nickel-cadmium storage battery.

Conventional technology Conventionally, as electrodes for nickel-cadmium storage batteries,
A so-called sintered electrode plate in which nickel powder is sintered and metal cadmium or cadmium hydroxide as an active material is held in the pores has been used.

On the other hand, from the viewpoint of increasing the capacity of a battery, a paste-type cadmium electrode having a high packing density in which cadmium oxide powder or cadmium hydroxide powder is bound with an organic binder has come to be used in many cases. However, since the cadmium electrode does not have a conductor such as a sintered body, it has a drawback that the charge / discharge utilization rate is poor.

Problems to be Solved by the Invention Therefore, it is conceivable to improve charging and discharging efficiency by adding nickel powder, carbon powder, metal cadmium, and the like to the electrode.

However, the addition of nickel powder to the paste-type cadmium electrode has little effect because a small amount of nickel powder particles are not continuously connected. For this reason,
In order to obtain the effect, a large amount must be added, and it is difficult to increase the capacity, which is the original purpose of the paste method.

Also, the addition of carbon powder requires only a very small amount compared to nickel powder. However, polyvinyl alcohol, which is generally used as a binder, acts on carbon powder to gel and paste a gelled paste, and the strength of the dried electrode is extremely weak. On the other hand, when a carbon powder having a large specific surface area is added, the initial charge / discharge efficiency is very good, but there is a problem that the active material is coarsened as the charge / discharge cycle proceeds, and the discharge utilization rate is rapidly deteriorated. .

Further, the addition of metal cadmium is hardly used at first because it is inactive compared to metal cadmium generated by charging, but is gradually activated as charging / discharging proceeds and participates in discharging. Further, similarly to nickel powder, metal cadmium has a problem that a large amount of metal cadmium must be added because the particles are not continuous.

Means for Solving the Problems The present invention has a specific surface area of 900 m ² /
g or more of carbon powder is added to the active material of the cadmium electrode.

Effect It has the original continuous structure of carbon, and it is effective for conductivity even if it is added in a small amount to the active material. It is also very effective for the life of charging and discharging.

Example An example of the present invention will be described.

Example 1 A paste containing cadmium oxide as a main component was prepared as follows.

i 95% by weight of cadmium oxide, polyvinyl alcohol 3
Parts by weight, 2 parts by weight nylon short fiber.

ii 94 parts by weight of cadmium oxide, polyvinyl alcohol 3
Parts by weight, nylon short fiber 2 parts by weight, furnace carbon black (specific surface area 900 m ² / g).

iii 92 parts by weight of cadmium oxide, 3 parts by weight of polyvinyl alcohol, 2 parts by weight of nylon short fibers, and 3 parts by weight of a conductive material obtained by nickel-plating furnace-based carbon black (specific surface area: 900 m ² / g) with a commercially available nickel electroless plating solution.

Here, for the electroless plating of nickel on carbon, 10 g of carbon black was placed alongside the electroless solution plating of SUMMER S-680 manufactured by Kanigen Japan Co., Ltd. and held at 40 ° C. for 2 minutes. After that, it was washed with water and hot water, dried at 100 ° C., pulverized and used.

Ethylene glycol was added to each of the above mixtures to iii to form a paste, which was applied to a punching metal obtained by plating nickel on iron and dried. This is ^l 50
× cut into ^W 30, and Kaee repeated charge and discharge cycles with 30% potassium hydroxide solution. FIG. 1 shows the change in the utilization at that time.

In FIG. 1, A is an electrode obtained by applying the above-mentioned i (without adding a conductive material), but the initial utilization rate is low and gradually decreases. B is an electrode obtained by applying the above ii (addition of carbon powder), but the initial utilization rate is high. However, the decrease accompanying the charge / discharge cycle is large. As a result of observation with a scanning electron microscope, it is considered that the crystal becomes coarse. C is an electrode obtained by applying the above iii (addition of nickel-plated carbon powder), and has a high initial utilization rate and a small tendency to deteriorate in charge and discharge.

Next, the peel strength of the active material with respect to the electrode compositions of these electrodes A, B, and C was measured. The measuring method was performed by applying an adhesive to the surface of nickel having an area of 1 cm ² , bonding the adhesive to the electrode surface in this state, drying and pulling. The results are as shown in Table 1.

As is clear from Table 1 above, the electrode C added in the nickel-plated carbon active material has the same strength as the electrode A in which no carbon is added in the active material. It was very effective compared to the electrode B added in the substance.

Example 2 Powders of 92 parts by weight of cadmium oxide, 3 parts by weight of polyvinyl alcohol, 2 parts by weight of nylon short fiber, and 3 parts by weight of nickel-plated carbon were mixed, and ethylene glycol was added to form a paste. In this case, the plated carbon is 200 m ² / g, 500 m ² / g, 900 m ² / g, 1200 m ² / g carbon. The plating was performed using a nickel electroless plating solution as in Example 1. FIG. 2 shows the initial utilization rate at that time. As described above, the electrode plated on carbon having a specific surface area of 900 m ² / g or more is higher than the electrode plated on carbon having a specific surface area of 500 m ² / g or less. The reason is considered that carbon having a large specific surface area has a structure in which particles generally called a structure are connected.
And it seems that this structure is not destroyed by kneading.

In the embodiment of the present invention, by coating the carbon powder with nickel, when polyvinyl alcohol is used as a binder, the gelation that occurs in the case of the carbon powder does not occur, and the strength of the obtained electrode is high. . In addition, only by coating the carbon powder with nickel, the original continuous structure of carbon is maintained, and even if the addition is small, it is extremely effective for conductivity. Furthermore, since the electrode surface is nickel, there is almost no change due to charging and discharging,
The active material does not become coarse as seen when carbon powder is added, and is extremely effective for the life of charge and discharge.

Effect of the Invention As described above, the present invention prevents the deterioration of the early utilization rate at the time of adding carbon to the active material while taking advantage of the high capacity characteristic of the paste-type cadmium electrode. The industrial value is extremely large, for example, the utilization rate is improved.

[Brief description of the drawings]

FIG. 1 is a curve diagram showing a change in utilization rate during discharge accompanying a charge / discharge cycle, and FIG. 2 is a curve diagram showing the effect of the utilization rate on the specific surface area of carbon to be plated.

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-1-304661 (JP, A) JP-A-63-170852 (JP, A) JP-A-61-240576 (JP, A) (58) Investigation Field (Int.Cl. ⁶ , DB name) H01M 4 / 62,4 / 24

Claims (2)

(57) [Claims] 1. A nickel-cadmium storage battery using a paste-type cadmium electrode in which carbon powder whose surface is coated with nickel is added to an active material of the electrode. 2. The carbon powder to be coated has a specific surface area of 900 m.
^2. The nickel-cadmium storage battery according to claim 1, wherein the storage capacity is ² / g or more.