JPH10275619A - Paste type cadmium electrode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To retard the generation of hydrogen gas and enhance charging characteristics at low temperature by containing cadmium, β type cadmium hydroxide, γ type cadmium hydroxide in an electrode, separating the β type cadmium hydroxide from the γ type cadmium hydroxide so as not to come in contact with each other, and holding them with one kind of polymer binder selected from two and three kinds. SOLUTION: A paste type cadmium electrode is manufactured with paste prepared by dispersing β type cadmium hydroxide, metallic cadmium, and nylon fibers in an aqueous solution of one of PVP, PTFE in the specified solid composition ratio. Another paste is prepared by dispersing γ type cadmium hydroxide, metallic cadmium, and nylon fibers in an aqueous solution of one of CMC, MC, and PVA in the specified solid composition ratio, and applied to the cadmium electrode. The viscosity of the later paste is made lower than the that of the former paste. The drying temperature of both paste after coating is preferable to set to 150-200 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a paste-type cadmium electrode which is a negative electrode of a sealed nickel-cadmium storage battery used for a small device or the like, and more particularly, to a case where a sealed nickel-cadmium storage battery is charged at a low temperature. The present invention relates to the suppression of generation of hydrogen gas from a paste-type cadmium electrode.

[0002]

2. Description of the Related Art As a cadmium electrode used in a sealed alkaline storage battery such as the above-mentioned sealed nickel-cadmium storage battery, a paste type electrode whose process is relatively simple and whose production cost is low is widely used. As a method of manufacturing this paste-type cadmium electrode, an active material such as cadmium oxide is kneaded together with a polymer binder solution as a binder until a paste is formed, and the paste is applied to a conductive core material. A method of drying to obtain a paste-type cadmium electrode is generally used. The paste-type cadmium electrode requires a larger amount of active material than the nickel electrode mainly composed of nickel hydroxide, which is the positive electrode of the sealed nickel-cadmium storage battery. This is because the utilization rate of the paste-type cadmium electrode is lower than that of the nickel electrode, and charging is performed so that hydrogen gas is not generated from the paste-type cadmium electrode when the sealed nickel-cadmium storage battery is charged beyond full charge. This is because an uncharged portion is left as a reserve. Oxygen gas generated at the nickel electrode is reduced by the paste-type cadmium electrode, and metal cadmium, which is a charge product, changes to cadmium hydroxide, which is a discharge product, so that the amount of charge reserve does not decrease. As a result, the charging of the paste-type cadmium electrode proceeds even after full charge, and no hydrogen gas is generated.

However, since the utilization rate of the paste-type cadmium electrode is lower than that of the nickel electrode, particularly in the case of overcharging of a sealed nickel-cadmium storage battery at a low temperature,
Hydrogen gas is generated from the paste-type cadmium electrode, and the internal pressure of the battery increases. When the internal pressure of the battery rises, a safety valve provided on the battery lid eventually opens, causing leakage of the electrolytic solution, resulting in a problem such as a reduction in battery life or contamination of peripheral devices. Therefore, it has been proposed to add nickel powder as a conductive agent for the paste cadmium electrode. For example, in JP-A-58-35870, a conductive agent composed of a nickel powder having a nickel hydroxide layer on the surface obtained by dispersing a nickel powder in an acidic solution of a nickel salt is added to a paste-type cadmium electrode. It is thought that. However, since nickel powder reduces hydrogen overvoltage, the situation where hydrogen gas is easily generated remains unchanged. In JP-A-58-186163, generation of hydrogen gas is suppressed by reducing the amount of carbonyl nickel powder added to 1% by weight or less based on the main active material, and a metal nickel layer and a metal cadmium layer are formed on the active material surface layer. Are sequentially formed so that the nickel layer is not directly exposed on the surface of the active material to secure the conductivity of the paste-type cadmium electrode. In this case, when the charged amount is about 200%, the generation of hydrogen gas is suppressed, but when the battery is continuously charged, the effect of suppressing the generation of hydrogen gas is reduced, and the internal pressure of the battery eventually increases.

[0004] As another method, it has been proposed to suppress the rise in battery internal pressure by consuming generated hydrogen gas in the battery. For example, Japanese Patent Application Laid-Open No. 52-58827 discloses that a gas-absorbing electrode in which a current collector holds cobalt hydroxide containing 60% by weight or less of nickel or a nickel compound with respect to cobalt is connected to a positive electrode or a negative electrode. It is considered that the absorbed hydrogen gas is absorbed by the gas absorbing electrode. Also, Japanese Patent Application Laid-Open No. 61-179070
In the publication, it is considered that a hydrogen storage alloy electrode is inserted into a sealed nickel-cadmium storage battery and connected to a positive electrode, and the generated hydrogen gas is absorbed by the hydrogen storage alloy electrode. However, these methods have a complicated battery structure and are difficult to manufacture.

[0005]

SUMMARY OF THE INVENTION Nickel powder, which is a conductive agent, is in a state where hydrogen gas is easily generated because hydrogen overvoltage is reduced, and addition of nickel powder is not preferable. In addition, when nickel powder is added, the volume energy density of the paste-type cadmium electrode is reduced, which is not suitable for increasing the capacity of a sealed nickel-cadmium storage battery. Further, when the auxiliary electrode is provided in the battery, the structure of the battery becomes complicated and manufacturing becomes difficult.

[0006]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention relates to a paste type cadmium electrode used in a sealed alkaline storage battery, for example, a sealed nickel-cadmium storage battery. Cadmium hydroxide and γ-type cadmium hydroxide are contained, and β-type cadmium hydroxide and γ-type cadmium hydroxide in the electrode are not in contact with each other, and β-type cadmium hydroxide in the electrode is polyvinylpyrrolidone (hereinafter referred to as polyvinylpyrrolidone). "PVP"), polytetrafluoroethylene (hereinafter "PTFE")
Γ-cadmium hydroxide (hereinafter referred to as “CMC”) and methylcellulose (hereinafter referred to as “MC”). ) And polyvinyl alcohol (hereinafter referred to as "PVA"), and is held by only one kind of binder selected from the group consisting of polyvinyl alcohol (hereinafter referred to as "PVA"). The binder binds the active materials or the active material and the conductive core material by surrounding cadmium, β-type cadmium hydroxide, and γ-type cadmium hydroxide, which are active materials, thereby preventing the active material from falling off. . Since the active material is surrounded by the binder, the performance of the paste-type cadmium electrode is affected by the type of the binder. For example, the charging potential when charging the paste-type cadmium electrode also differs depending on the type of the binder.

[0007] β-type cadmium hydroxide is PVP, PTFE
Paste-type cadmium electrode produced by kneading with one kind of binder selected from the group consisting of: CMC, MC, PVA
When the paste-type cadmium electrode prepared by kneading with one kind of binder selected from the above is charged at a low temperature, the former paste-type cadmium electrode has a higher charging potential than that of the latter. This is PVP, PTF
It is considered that E has better wettability with the electrolytic solution than CMC, MC, and PVA, so that the diffusion overvoltage of the electrolytic solution becomes smaller, and as a result, the charging potential becomes more noble. On the other hand, among β-cadmium hydroxide and γ-cadmium hydroxide, γ-cadmium hydroxide has a more noble charging potential,
Easy to charge. In the case of a sealed nickel-cadmium storage battery, the paste-type cadmium electrode is provided with an uncharged portion called a charging reserve, so that the charging of the paste-type cadmium electrode proceeds even after the battery is fully charged, and no hydrogen gas is generated. Oxygen generated from the nickel electrode is reduced on the paste-type cadmium electrode, and at that time, the metal cadmium returns to cadmium hydroxide, so that apparently the charging of the paste-type cadmium electrode does not proceed, and the charge reserve amount Does not decrease. After the battery is fully charged,
If charging does not proceed to the charging reserve, decomposition of the electrolytic solution starts, and hydrogen gas is generated. At a low temperature, the charging of the paste-type cadmium electrode becomes difficult to progress, the utilization rate decreases, and the charge reserve decreases or becomes inactive.

Therefore, it is conceivable to use γ-cadmium hydroxide, which is more easily charged than β-cadmium hydroxide, as a charge reserve. That is, the paste-type cadmium electrode holds β-cadmium hydroxide only with the binder having a more noble charge potential, and the paste-type cadmium electrode holds gamma-type cadmium hydroxide with only the lower-potential binder. It is. Therefore, β-type cadmium hydroxide is held only by one kind of binder selected from PVP and PTFE, and γ-type cadmium hydroxide is held only by one kind of binder selected from CMC, MC and PVA. PVP,
Β-cadmium hydroxide held by only one kind of binder selected from PTFE has a higher charging potential than γ-type cadmium hydroxide held by only one kind of binder selected from CMC, MC and PVA. Therefore, when charging is started, charging starts from β-type cadmium hydroxide. afterwards,
When the potential of the paste-type cadmium electrode is lowered and hydrogen gas starts to be generated, charging starts in the γ-type cadmium hydroxide, which has a more negative charging potential due to the binder. Since γ-type cadmium hydroxide is easier to charge than β-type cadmium hydroxide, the charge reserve is active and hydrogen gas generation can be suppressed.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below.

(Example) PVP was prepared at the following solid content ratio.
A paste-type cadmium electrode (A) is prepared from a paste (a) in which β-type cadmium hydroxide, metal cadmium, and nylon fibers are put into an aqueous solution. Preferably, the drying temperature after applying the paste to the conductive core material is 150-2.
Dry at 00 ° C. β-type cadmium hydroxide: 500 metal cadmium: 100 Nylon fiber: 5 PVP powder: 2.5 Then, γ-type cadmium hydroxide, metal cadmium, and nylon fiber are put into a CMC aqueous solution at the following solid content composition ratio, Another paste (b) is prepared and applied to the paste-type cadmium electrode (A). At this time, the viscosity of the paste (b) is set lower than the viscosity of the paste (a). Paste (b) is replaced with a paste-type cadmium electrode (A)
The drying temperature after coating is preferably in the range of 150 to 200 ° C. Thus, a cadmium electrode (1) is obtained. Gamma-type cadmium hydroxide: 50 Metal cadmium: 10 Nylon fiber: 0.5 CMC powder: 0.25 Similarly, the paste type cadmium electrode shown in Table 1 was changed by changing only the binder type of the pastes (a) and (b). (2)-
(6) is produced.

[0011]

[Table 1]

(Comparative Example) A paste-type cadmium electrode to which nickel powder is added at the following solid composition ratio is prepared by a usual method. This paste-type cadmium electrode is referred to as a paste-type cadmium electrode (7). The paste-type cadmium electrode produced using only CMC as a binder was used as a paste-type cadmium electrode (8). β-type cadmium hydroxide: 500 γ-type cadmium hydroxide: 50 Metal cadmium: 110 Nylon fiber: 5.5 PVA powder or CMC powder: 2.75 Nickel powder having nickel hydroxide on the surface: 40 A paste-type cadmium electrode was produced at a composition ratio. Thereafter, negative electrolysis is performed in a nickel salt aqueous solution, then impregnated in a cadmium salt aqueous solution, and then negative electrolysis is performed in an alkaline aqueous solution, thereby sequentially forming a metal nickel layer and a metal cadmium or cadmium hydroxide layer on the surface of the active material. A paste-type cadmium electrode (8) in which the nickel layer was not directly exposed on the surface was produced. β-type cadmium hydroxide: 500 γ-type cadmium hydroxide: 50 Metal cadmium: 110 Nylon fiber: 5.5 PVA powder or CMC powder: 2.75 Carbonyl nickel powder: 1 Next, paste-type cadmium electrodes (1) to (8) ), And cut into predetermined dimensions to form a completed negative electrode plate, and a sealed nickel-cadmium storage battery having a nominal capacity of 800 mAh was produced using a known paste-type nickel electrode as a positive electrode. Here, the paste type cadmium electrodes (1), (2),
The sealed nickel-cadmium storage batteries using (3), (4), (5), (6), (7), and (8) are replaced with batteries (1), (2), (3), and (4), respectively. , (5), (6),
(7) and (8). The batteries (1) to (8) were activated, and the next test was started.

The battery was kept at an ambient temperature of 0 ° C. and charged continuously at a current of 0.3 C for one week. At this time, a hole with a diameter of 1 mm was made in the bottom of the battery can, and a pressure sensor was attached.
The internal pressure of the battery during charging was measured. Table 2 shows the internal pressure of the battery at the end of charging. As is clear from Table 2, the batteries (1) to (6) of the present invention were the batteries (7) and (8) of the conventional comparative examples.
As compared with, the internal pressure of the battery could be kept low. That is, the batteries (1) to (6) of the present invention have a greater effect of suppressing the generation of hydrogen gas during one week of continuous charging than the batteries (7) and (8) of the conventional comparative examples. became. From the above test, the batteries (1) to (6) of the present invention have an excellent effect of suppressing hydrogen gas generation during low-temperature charging as compared with the conventional batteries (7) and (8) of the comparative example. You can see that. This is because β-cadmium hydroxide held by only one kind of binder selected from PVP and PTFE is C
Since the charging potential is more noble than γ-type cadmium hydroxide held by only one kind of binder selected from MC, MC, and PVA, when charging starts, charging starts from β-type cadmium hydroxide. After that, the potential of the cadmium electrode decreases,
When the hydrogen gas starts to be generated, the γ-type cadmium hydroxide whose charging potential is made more negative by the binder is charged. Since γ-type cadmium hydroxide is more easily charged than β-type cadmium hydroxide, the charge reserve is active and hydrogen gas generation can be suppressed.

[0014]

[Table 2]

[0015]

As described above, in the paste-type cadmium electrode of the present invention, the electrode contains cadmium, β-type cadmium hydroxide, and γ-type cadmium hydroxide. The γ-cadmium hydroxide does not touch each other, the β-cadmium hydroxide in the electrode is held only by one kind of binder selected from PVP and PTFE, and the γ-cadmium hydroxide is CMC. , MC, PVA
By being held only by the type of binder, it is possible to suppress the generation of hydrogen gas from the paste-type cadmium electrode when a sealed alkaline storage battery such as a sealed nickel-cadmium storage battery is charged at a low temperature. The charging characteristics of the sealed battery are greatly improved as compared with the conventional battery.

Claims (1)

[Claims] 1. A paste type cadmium electrode, wherein the electrode contains cadmium, β-type cadmium hydroxide and γ-type cadmium hydroxide, and the β-type cadmium hydroxide and the γ-type cadmium hydroxide in the electrode are in contact with each other. Without
And the β-type cadmium hydroxide in the electrode is PVP, PTF
E is held only by one kind of binder selected from E, and γ-type cadmium hydroxide is CMC, MC,
A paste-type cadmium electrode which is held only by one kind of binder selected from PVA.