JPS63308870A - Manufacture of paste type cadmium negative electrode - Google Patents

Abstract

PURPOSE:To improve negative electrode's capability of absorbing an oxygen gas and to prevent a charge-and-discharge characteristic from being deteriorated, by dipping a formation-finished negative electrode plate into a solution containing copper ions so that copper is precipitated on the electrode plate. CONSTITUTION:After a conductive core material is coated with paste of an active material consisting of cadmium oxide powder or cadmium hydroxide powder mainly, this negative plate is negatively electrolyzed in an alkaline solution so that formation is performed to provide this plate with metallic cadmium as a material for auxiliary charge. Next the formation-finished electrode plate is dipped into a solution containing copper ions so as to precipitate copper on the electrode plate by the use of substitution reaction with cadmium, so that a conductive matrix of copper is formed on a surface of the electrode plate and inside the electrode plate. Hence, negative electrode plate's capability of absorbing an oxygen gas is improved and also a charge-and-discharge characteristic can be prevented from being deteriorated due to charge-and-discharge repetition.

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.

Conventional technology 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 carboxymethylcellulose and a solvent such as water or ethylene glycol, knead to make a paste, apply this to a conductive core material such as a nickel-plated perforated steel plate, dry it, and then apply an alkaline solution. It is manufactured by chemical conversion inside.

The purpose of the above chemical conversion step is to convert part or all of the cadmium compound in a discharged state, such as cadmium oxide or cadmium hydroxide, used for the active material into metallic cadmium in a charged state, and to provide a pre-charged portion within the negative electrode. There is a particular thing.

Problems to be Solved by the Invention Paste-type cadmium negative electrodes have the advantage of being easier to manufacture than sintered-type cadmium negative electrodes and can provide higher capacity density, but because they do not have a conductive matrix like sintered-type ones, The growth of metallic cadmium generated during battery charging occurs near the core material, making it 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, leading to deterioration of charge and 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 this problem, a method has been proposed in which electrolytic nickel plating is applied to the surface of a paste-type negative electrode (Japanese Patent Publication No. 61-61227), but this method has the disadvantage that the process is complicated. Additionally, a method has been proposed in which a conductive layer made of carbon powder is provided on the surface of a paste-type negative electrode (Japanese Patent Laid-Open No. 60-63875), but according to this method,
There is a problem in that the carbon powder exists only on the surface of the electrode plate, making it difficult to form a conductive matrix within the active material, and there is still room for further improvement. In addition, a method has been proposed in which the electrode plate after the chemical formation process is immersed in a solution containing nickel ions, and a nickel layer is formed on the electrode plate surface by a substitution reaction with the metal cadmium generated in the chemical formation process (% Kaisho 60-258854
Publication No.).

However, the method using electrolytic nickel plating
Regarding methods of forming a nickel layer, including ``61227 Publication,'' ``nickel has a low hydrogen generation overvoltage;
Hydrogen is generated when charging the battery.

The problem is that it becomes easier. Hydrogen generated during charging is not consumed within the battery, which is an important problem, especially for sealed batteries.

An object of the present invention is to solve the above-mentioned problems and provide a high-performance paste-type cadmium negative electrode.

Means for Solving the Problems The present invention applies an active material paste mainly composed of cadmium oxide powder or cadmium hydroxide powder to a conductive core material, and then electrolyzes the electrode plate in an alkaline solution. , conducts chemical formation to impart metallic cadmium as a pre-charge amount, immerses the chemically formed electrode plate in a solution containing copper ions, and deposits copper on the electrode plate through a substitution reaction with cadmium. By forming a conductive matrix of copper within the electrode plate, the oxygen gas absorption ability of the negative electrode is improved, and
This prevents deterioration of charging and discharging characteristics due to repeated charging and discharging.

Function When an electrode plate whose core material is coated with an active material paste mainly composed of 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 copper ions, the metal cadmium in the electrode plate has a lower potential than copper, so a substitution reaction occurs in which the cadmium dissolves and copper is deposited on the electrode plate. Copper precipitates in the surface layer of the seed plate and in the pores in the electrode plate, forming 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 to the electrode plate surface layer along the applied conductive marx of metal steel. 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 the case with 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 copper matrix is formed on the electrode plate, and this physically suppresses the coarsening of the active material on the electrode plate surface, which is effective in preventing the above-mentioned characteristic deterioration.

In addition, although copper is soluble in alkaline liquid, it has a higher potential than metal cadmium, so if metal cadmium is present in the negative electrode, copper exists as a metal and cannot be eluted into alkaline liquid. stable characteristics can be obtained.

Further, since copper has a higher hydrogen generation overvoltage than nickel or the like, hydrogen generation during charging is also reduced.

Further, when copper or nickel is deposited on the negative electrode by a substitution reaction using the method described above, copper is superior to nickel in terms of deposition efficiency. It is known that when nickel is plated by chemical plating, cadmium acts as a desolative poison and reduces the efficiency of nickel precipitation. It is thought that when Sinisokel is deposited on the negative electrode by a substitution reaction, the deposition efficiency decreases due to the same effect as in chemical plating. However, in the case of copper, there is no such effect and the precipitation efficiency is approximately 100%.

The precipitation efficiency of nickel is about 60% or less, and there are problems in the process, such as a loss of cadmium material to be dissolved or a long precipitation time in order to ensure the necessary amount of nickel precipitation.

Details will be explained below using examples.

Example: Cadmium oxide powder with an average particle size of about 1 μm was kneaded with polyvinyl alcohol dissolved in ethylene glycol to make a paste, which was applied to a nickel-plated perforated iron plate and dried to form a paste with a thickness of about 0.5 nm. It was used as a pole plate. Next, this electrode plate was subjected to negative electrolysis in an aqueous solution of thorium hydroxide having a specific gravity of 1.20 to perform chemical conversion to impart metal cadmium, and was washed with water and dried.

Thereafter, it was immersed for about 20 seconds in a 1 mol/l aqueous solution of copper sulfate adjusted to a pH of 3 and a liquid temperature of 30°C to cause a substitution reaction between a portion of the metal cadmium and copper ions. The copper produced by this treatment forms a film on the surface of the electrode plate, and is deposited in the holes within the electrode plate, forming a conductive matrix. In the case of the example, the analytical results showed that about 5 to 10% of the metallic cadmium was replaced by metallic copper.

After washing and drying this electrode plate, it was cut into a predetermined size and combined with a sintered nickel positive electrode to form a sealed storage battery equivalent to 120 mA h, 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 is made at the peak of the battery internal pressure when charged at a current equivalent to 1 to 3C at 45°C.
Evaluation was made based on the discharge time when charging and discharging were repeated at a current equivalent to 1C.

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.

FIG. 2 shows the change in discharge time associated with charge and discharge cycles.

A is a battery using the negative electrode of the above example, and b is a battery using a negative electrode of a comparative example that has been subjected to the chemical conversion step of the example.

The reason why the charge/discharge cycle characteristics of battery a using the negative electrode according to the present invention is improved is that the conductive matrix of copper provided in the negative electrode suppresses the deterioration of the discharge characteristics due to coarsening of the active material. Conceivable.

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 the drawing]

FIG. 1 is a diagram showing the relationship between the charging rate and the peak pressure inside the battery of a 2Y Quell cadmium storage 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 composed of 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; A method for producing a paste-type cadmium negative electrode, which includes the step of immersing the subsequent electrode plate in a solution containing copper ions to deposit copper on the electrode plate.