JPS60258854A - Method of manufacturing paste type cadmium negative pole - Google Patents

Abstract

PURPOSE:To manufacture a paste type cadmium negative pole with high performance by immersing a plate into solution containing nickel oil after giving metal cadmium as a preliminary charging volume to the plate in the formation process, and permitting the nickel to deposit on the plate. CONSTITUTION:When a plate, in which paste of active material mainly composed by cadmium oxide etc. is applied to the core, is negatively electrolyzed in alkaline solution, metal cadmium is electrochemically generated in the plate. This process is carried out so as to give a preliminary charging volume. When the plate, in which the formation has been completed, is immersed into solution containing nickel ions, the cadmium is dissolved and the substitution reaction which deposits the nickel in the plate is generated, because the metal cadmium in the plate has lower potential than that of the nickel. The metal nickel is deposited in surface layers of the plate and in holes within the plate to form a conductive matrix. Whereby, it is possible to manufacture a paste type cadmium negative pole with high performance which can be charged in a short time.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for producing a paste-type cadmium negative electrode for alkaline storage batteries.

Structure of conventional examples and their problems Paste-type cadmium negative electrodes for alkaline storage batteries generally consist of cadmium oxide or cadmium hydroxide,
In addition, carbonyl nickel, conductive powder such as graphite, and polyvinyl alcohol.

Add a binder such as carboxymethyl cellulose and a solvent such as water or ethylene glycol, knead to make a paste,
It is manufactured by applying this to a conductive core material such as a nickel-plated perforated steel plate, drying it, and then chemically converting it in an alkaline solution.

The purpose of the above chemical conversion process is to convert part or all of the cadmium compound in the discharged state with cadmium oxide and cadmium hydroxide used for each active material phase into metallic cadmium in the charged state, and to provide a pre-charged portion in the negative electrode. It's about doing.

Paste-type cadmium negative electrodes have the advantage of being easier to manufacture and providing higher capacity density than sintered-type ones, but because they do not have a conductive matrix like sintered-type cadmium negative electrodes, metal cadmium produced during battery charging is Growth occurs near the core material and is difficult to reach the surface layer of the electrode plate. For this reason, the reaction with oxygen gas generated from the positive electrode during overcharging does not occur efficiently, and when used in a sealed battery, there is a drawback that the internal pressure of the battery increases. Furthermore, if the battery is left in a high-temperature atmosphere or repeatedly charged and discharged, the active material particles on the surface of the negative electrode will become coarser, resulting in the deterioration of charge-discharge characteristics. Such coarsening of active material particles is a phenomenon that is unlikely to occur in a sintered type having a skeleton that holds the active material.

In order to solve these problems, a method has been proposed in which the electrode plate before chemical formation is subjected to negative electrolysis in a solution containing nickel ions to form a nickel layer on the electrode plate surface (Japanese Patent Laid-Open No. 58-32).
363) has the disadvantage that the process is complicated.

OBJECTS OF THE INVENTION It is an object of the present invention to eliminate the above-mentioned conventional disadvantages and provide a high-performance paste-type cadmium negative electrode.

Structure of the Invention The present invention involves applying an active material paste mainly composed of cadmium oxide powder or cadmium hydroxide powder to a conductive core material, and then adding metallic cadmium as a precharge amount in a chemical formation process. This is a method for producing a paste-type cadmium negative electrode in which nickel is immersed in a solution containing nickel and nickel is deposited on the electrode plate by reaction with cadmium at a degree of substitution of 1'.

The present invention will be explained in detail below.

When an electrode plate whose core material is coated with an active material paste containing cadmium oxide or cadmium hydroxide is subjected to negative electrolysis in an alkaline solution, metallic cadmium is electrochemically generated in the electrode plate. This process is a chemical conversion process that is generally performed to provide a preliminary charge amount. When this chemically formed electrode plate is immersed in a solution containing nickel ions, the metal cadmium in the electrode plate has a lower potential than nickel, so a substitution reaction occurs in which the cadmium dissolves and nickel is deposited on the electrode plate. Metallic nickel is deposited in the plate surface layer and in the pores in the plate to form a conductive matrix.

When the above electrode plate is used in a sealed storage battery, the metal cadmium generated in the negative electrode during battery charging grows uniformly on the electrode plate surface layer 1 along the conductive matrix of applied metal nickel. On the other hand, in an electrode plate that undergoes only a chemical conversion process and does not have a conductive matrix like the one of the present invention, the generation of metallic cadmium during charging is concentrated near the core material, and the proportion of metal cadmium reaching the surface layer is small. In sealed batteries, the absorption reaction at the negative electrode of oxygen gas generated from the positive electrode during overcharging is important.

If this oxygen absorption is poor, the internal pressure of the battery will rise during overcharging, making it impossible to charge with a large current. In other words, it cannot be charged for a short period of time. Since oxygen gas is absorbed by the metal cadmium of the negative electrode, it is advantageous for the metal cadmium to be distributed in large amounts on the electrode plate surface, as in the case of the present invention.

Further, as described above, the paste-type cadmium negative electrode has the drawback that the active material particles become coarse at high temperatures. Since the coarse active material particles are electrochemically inactive,
This results in deterioration of charge/discharge characteristics. Further, as this phenomenon progresses further, the cadmium compound that has grown in the form of a dendrite penetrates the separator and reaches the positive electrode, causing an internal short circuit. This phenomenon of active material coarsening is
This is particularly noticeable in paste types that do not have a skeleton that physically holds the active material, such as the sintered type, and is more likely to occur on the surface of the electrode plate. According to the present invention, a matrix of metallic nickel is formed on the electrode plate, which physically suppresses the coarsening of the active material on the surface of the electrode plate 6, and is effective in preventing the above-mentioned characteristic deterioration.

Description of Examples Cadmium oxide powder with an average particle size of about 1 μm is kneaded with a polyvinyl alcohol ethylene glycol solution to make a paste, which is applied to a nickel-plated perforated iron plate and dried to a thickness of about 0.25 mm. It was used as a pole plate. Next, this electrode plate was subjected to negative electrolysis in a sodium hydroxide aqueous solution with a specific gravity of 1.20,
Chemical conversion was performed to add metal cadmium, followed by washing with water and drying. Thereafter, it was immersed for about 20 seconds in a 1 mol/l aqueous solution of nickel sulfate adjusted to a pH of 3.6 and a liquid temperature of 50'C to cause a substitution reaction between part of the metal cadmium and nickel ions.

The metallic nickel produced by this treatment forms a film on the surface of the electrode plate, and also precipitates in the pores within the electrode plate, forming a conductive matrix. In the case of the example, the analytical results showed that about 6-10% of the metallic cadmium was replaced by metallic nickel.

After washing and drying this electrode plate, cut it to the specified size,
In combination with a sintered nickel positive electrode, a sealed storage battery equivalent to 1200 mAh was constructed and the battery characteristics were tested.

The tests included a battery internal pressure test during overcharging to evaluate the oxygen gas absorption of the negative electrode, and a high-temperature charge-discharge cycle test to evaluate the high-temperature characteristics. Battery internal pressure test is 20'
Evaluation was made at the peak of the battery internal pressure when charged at a current equivalent to 1 to 3C at 46°C.
Evaluation was made based on the discharge time when charging and discharging were repeated at a current equivalent to 10%.

FIG. 1 shows the relationship between the charging rate and the peak of the battery internal pressure. A shows a battery using the negative electrode of the above example, and b shows a battery using a negative electrode of a comparative example in which the chemical conversion process of the example was performed. In the negative electrode according to the present invention, metal cadmium is easily distributed on the electrode plate surface during charging, and the oxygen gas absorption capacity is high. Therefore, battery a has a low internal pressure and can be charged at a high rate.

! 1 Figure 2 shows the change in discharge time associated with the charge/discharge cycle.There were many Japanese dog crystals that grew in a flat plate shape, but there were fewer of them in battery a. As described above, in the negative electrode of the present invention, coarsening of the crystals is less likely to occur, so that in battery a, there is little deterioration in characteristics due to charging/discharging cycles at high temperatures.

Effects of the Invention As described above, according to the present invention, the characteristics of a paste-type cadmium negative electrode can be significantly improved with simple processing.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the relationship between the charging rate of a nickel-cadmium storage battery and the peak pressure inside the battery, and FIG. 2 is a diagram showing the relationship between the number of times of charging and discharging and the discharge time.

Claims (1)

[Claims] A process of applying a paste mainly containing cadmium oxide or cadmium hydroxide to a conductive core material, a chemical conversion process of applying a preliminary charge amount by electrolyzing the applied electrode plate in an alkaline electrolyte, and a process of applying a pre-charge amount to the conductive core material. A method for producing a paste-type cadmium negative electrode, which includes the step of immersing the subsequent electrode plate in a solution containing nickel ions to deposit nickel on the electrode plate.