JPH0680585B2 - Method for producing paste type cadmium negative electrode - Google Patents

Description

TECHNICAL FIELD The present invention relates to a paste type cadmium negative electrode used in an alkaline storage battery.

2. Description of the Related Art Generally, a method for producing a paste-type cadmium negative electrode for an alkaline storage battery includes a cadmium active material powder mainly composed of cadmium oxide or cadmium hydroxide, a conductive powder such as carbonyl nickel or braphite, polyvinyl alcohol or carboxymethyl cellulose, etc. A paste prepared by kneading a binder and a solvent such as water or utylene glycol is applied to a conductive core body such as a nickel-plated perforated steel sheet and dried, and then formed into an alkaline solution. The purpose of the chemical conversion step is to convert one of the cadmium compounds in the discharged state (cadmium oxide, cadmium hydroxide) into metallic cadmium in the charged state to provide a precharged portion in the negative electrode. When there is no pre-charged part in the negative electrode, the negative electrode utilization rate is lower than that of the positive electrode, so the discharge is dominant in the negative electrode, the high rate discharge characteristics of the battery are poor, and the negative electrode receives a complete discharge. Markedly deteriorated. The formation is performed for the above reasons.

Problems to be Solved by the Invention However, in the chemical conversion process, a large amount of electric power is used to charge 20-50% of the negative electrode capacity. Also, in the chemical conversion process,
It is not easy to evenly distribute the charged metal cadmium in the electrode plate, and variations in the electrode plate characteristics are likely to occur.
Particularly in the case of the paste type cadmium negative electrode, the tendency is larger than that in the sinter type. In order to solve such a problem, in recent years, for example, as shown in JP-B-57-37986 or JP-A-58-32744, an active metal cadmium powder is used as a precharge amount when an active material is mixed. A paste-type cadmium negative electrode plate has been proposed which does not require a chemical conversion step by adding. The metal cadmium powder added as a precharge amount is preferably one having a high activity, that is, one having a high utilization rate of the active material, in order to efficiently contribute to the battery charge / discharge reaction.

However, since the metal cadmium powder produced by the dry method as proposed in Japanese Patent Publication No. 57-37986 has a spherical particle shape, it has a small surface area and a low utilization rate of the active material. In addition, even if a mixture of metal cadmium and metal nickel is used to chemically substitute zinc in a cadmium salt containing metal nickel powder as proposed in Japanese Patent Publication No. 58-32744, it is possible to prevent cadmium from aggregating. The metallic nickel powder added in advance for the purpose of improving conductivity becomes a form covered with the generated metallic cadmium, and when it changes to insulating cadmium hydroxide, which is the discharge state of metallic cadmium, metallic nickel functions sufficiently. There was a need for improvement such as disappearance.

The present invention solves the above problems and provides a method for producing a high-performance metal cadmium powder, and a method for producing a high-performance paste-type cadmium negative electrode to which this is applied, which does not require a chemical conversion step. Is.

Means for Solving the Problems The present invention relates to a paste type cadmium negative electrode that does not require a chemical conversion step, and contains cadmium oxide powder, an active material mainly composed of metal cadmium powder as a precharge amount, and a binder. In a method of kneading and drying a paste obtained by kneading the solvent with a conductive core body such as an open-hole nickel plate, the metal cadmium powder as a precharge amount is a general method such as a wet type or a dry type. Immersing the metal cadmium powder produced by in a solution containing nickel ions,
It is characterized in that a part of cadmium metal is converted into nickel metal by a substitution reaction and deposited on the cadmium metal.

Operation The principle of the present invention will be described below.

There are the following items that affect the utilization rate of metallic cadmium alone or the utilization rate of a mixture of metallic cadmium and cadmium oxide as the main active material.

1 Surface area The larger the surface area, the higher the contact rate between the active materials and the contact with the electrolytic solution.

2 Shape The utilization rate is higher when the surface area is large or there are many contacts due to the entanglement of the active materials and the conductivity is high.
Therefore, the shape is preferably an irregular shape having more irregularities than a spherical shape.

3 Conductive metal cadmium easily reacts with oxygen and moisture in the air, and easily forms an oxide or hydroxide film on the surface thereof. Since these coatings are chemically and electrochemically stable, when the metal cadmium powder having such coatings is used for the electrodes, the conductivity between the active materials is lowered,
The active material utilization rate decreases. Therefore, it is desirable that the metal cadmium powder be coated with a metal that is stable in the battery electrolyte or in the air, such as metal nickel.

The present invention has the above items, metal cadmium powder,
This is satisfied by a method of precipitating metallic nickel on a part of the surface of metallic cadmium by a substitution reaction by immersion treatment in a solution containing nickel ions.

When the metal cadmium powder is immersed in a nickel salt solution such as an aqueous solution of nickel sulfate, the substitution reaction dissolves the metal cadmium and deposits nickel metal. When this reaction is allowed to proceed appropriately and then stopped by washing with water or the like, the surface layer of the metal cadmium powder is in a state of being coated with metal nickel.

The surface of the metal cadmium powder becomes rough due to melting, and since fine metal nickel is present thereon, the surface area becomes very large, and the metal cadmium active material has high activity. In this case, the metal cadmium powder as a raw material may be one obtained by a wet method or one having a small surface area obtained by a dry method. When the wet method is used, a higher activity is obtained. Moreover, even if a powder produced by a dry method which is easy to handle but has low activity is used, it is sufficiently activated.

Cadmium powder, which has a large surface area and high activity, is easily oxidized in air or water as described above, and is easily inactivated by handling during electrode plate manufacturing or treatment such as the drying process, resulting in poor performance. Easy to invite.

However, according to the present invention, when the surface of the metal cadmium powder is covered with metal nickel, it is less susceptible to oxidation, and even if a partially oxidized film is formed on the metal cadmium, the battery activity is reduced. When used as a substance,
An electric current flows through the metallic nickel existing on the metallic cadmium, and the charging / discharging reaction of the active material proceeds, so that the deterioration of the characteristics is less likely to occur.

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

The metal cadmium powder used as a raw material had a mean particle size of about 2 μm manufactured by a wet method. This metal cadmium powder was immersed in a 0.5 molar aqueous solution of nickel sulfate at 20 ° C. for about 10 seconds, then taken out, washed with water and dried. This was used as an active material as a preliminary charge of the electrode plate.

To 100 parts by weight of the cadmium oxide powder as the main active material, 20 parts by weight of the metal cadmium powder as the above-mentioned precharge amount was added and mixed, and an ethylene glycol solution of polyvinyl alcohol was added thereto, and kneaded into a paste form. To do. This paste was applied on a nickel-plated iron plate having a thickness of 0.1 mm and dried to obtain an electrode plate having a thickness of about 0.5 mm. The above cadmium negative electrode, and a cadmium negative electrode using a metal cadmium powder that is not subjected to immersion treatment in a nickel salt solution are combined with a sintered nickel positive electrode to prototype a sealed storage battery,
The discharge rate characteristics and the battery internal pressure test at the time of overcharging were performed. The discharge rate characteristic is that the battery is at a current equivalent to 0.1C at 20 ° C.
It was evaluated by the ratio of the discharge capacity when it was charged for 15 hours and discharged at a current equivalent to 1 to 3 C and the discharge capacity when discharged at a current equivalent to 0.2 C. Also, the internal pressure characteristics during overcharging are 1 / at 20 ° C.
The peak value of the battery internal pressure when overcharged with a current equivalent to 3 to 3 C was evaluated.

FIG. 1 shows the relationship between the discharge rate and the discharge capacity ratio. a
Indicates a battery using the negative electrode according to the present invention, and b indicates a battery using the negative electrode of the comparative example. Generally, the discharge rate characteristic improves with an increase in the amount of metal cadmium as a precharge amount, but the difference in the characteristic when the above negative electrode having the same amount of metal cadmium is used contributes to the electrochemical reaction of charge and discharge. It is considered that this is due to the difference in the rate of metal cadmium, that is, the utilization rate. In the negative electrode according to the present invention, it is considered that the utilization rate is improved and the discharge rate characteristics are improved because the activity of metal cadmium is high. FIG. 2 shows the relationship between the charging rate and the battery internal pressure. The effect of the present invention is exhibited even in the battery internal pressure.

When the battery is overcharged, oxygen is generated from the positive electrode, and this oxygen is absorbed by the metal cadmium of the negative electrode. In this case, if the negative electrode metal cadmium is active, the oxygen gas absorption capacity becomes high and the internal pressure of the battery becomes low. In a sealed storage battery, this oxygen gas absorption capacity is important. Usually, in order to improve the oxygen gas absorption capacity, a method of increasing the amount of metal cadmium is used, but it is more advantageous to improve the oxygen gas absorption capacity by increasing the activity with the same amount of metal cadmium. Many. The negative electrode according to the present invention has a high activity of metal cadmium added as a precharge amount, and the metal nickel present on the surface thereof acts as a catalyst for absorbing oxygen gas, so that the oxygen gas absorption capacity is high and the internal pressure of the battery is high. Is considered to be low.

EFFECTS OF THE INVENTION As described above, according to the present invention, a highly active pre-charged amount of metal cadmium can be obtained, and a paste type cadmium negative electrode having excellent characteristics and requiring no chemical conversion can be obtained.

[Brief description of drawings]

FIG. 1 is a diagram showing the relationship between the discharge rate and the discharge capacity ratio of a sealed nickel-cadmium storage battery, and FIG. 2 is a diagram showing the relationship between the charge rate and the peak value of the battery internal pressure.

Claims (1)

[Claims] 1. A conductive core is kneaded and dried with a paste obtained by kneading cadmium oxide powder, an active material mainly composed of metal cadmium powder as a precharge amount, a binder, and a solvent thereof. A method for producing a cadmium negative electrode, wherein the metal cadmium powder as the precharge amount is obtained by immersing a raw material cadmium powder in a solution containing nickel ions, and by a substitution reaction, nickel metal is partially deposited on the cadmium powder. A method for producing a paste-type cadmium negative electrode, characterized in that