JPS61208755A - Pasted negative cadmium plate for sealed alkaline storage battery - Google Patents

Abstract

PURPOSE:To increase the ability of a pasted negative cadmium plat to absorb oxygen by mixing carbon particles into the active material layer and coating the active material layer with a thin conductive layer principally composed of carbon particles. CONSTITUTION:A mixture principally composed of an active material such as metallic Cd, CdO or Cd(OH)2 is applied to a conductive core to form a paint film used as the active material layer. Carbon particles are dispersed in the active material layer and its surface is coated with a thin conductive layer principally composed of carbon particles. Due to the above thin layer formed on the active material layer, highly conductive metallic Cd is deposited near the conductive core during charging. The thin layer and the core are connected electrically by excess metallic Cd and metallic Cd is deposited rapidly on the surface of the negative plate which easily becomes in contact with oxygen produced from a positive plate. As a result, oxygen can be chemically consumed and the thin layer can electrochemically consume oxygen, thereby increasing the ability of the negative plate to absorb oxygen.

Description

DETAILED DESCRIPTION OF THE INVENTION (1) Field of Industrial Application The present invention relates to a paste-type cadmium cathode plate for use in sealed alkaline power storage, etc., which improves oxygen gas absorption ability and suppresses hydrogen gas generation during charging.

(b) Compared to the conventional paste-type cadmium cathode plate, the manufacturing process is simpler, 8V, and the manufacturing cost is lower than that of the sintered-type force dolum cathode plate.
Although it has the advantage of obtaining high energy density, the electron conductivity of the electrode plate is poor, so the ability to absorb oxygen gas generated from the anode plate during overcharging is poor, and when used in a sealed battery, the internal gas pressure The disadvantage is that it is easy to put it on and take it off. The oxygen gas absorption reaction by this cadmium cathode plate is expressed by the following equation.

Cd+hOz+H20-CdtOH)z-11 This is a reaction at the interface of six phases: air, liquid, and solid.

The more the metal cadmium and oxygen gas come into contact, the more active the reaction is. In the case of a sintered electrode plate, a conductive matrix of Niel-Kel sintered body as a base exists, and the charging reaction proceeds uniformly over the entire electrode plate through this conductive matrix, and metal cadmium is likely to be generated near the surface of the i-plate. However, in paste-type electrode plates, the active material 1@ has low conductivity, and the charging reaction progresses gradually from the vicinity of the core toward the surface of the electrode plate. Therefore, the metal cadmium leaves the conductive core and moves near the surface of the electrode plate. It is becoming harder to generate. Therefore, a! The elementary gas is absorbed only after passing through the entire surface layer of the electrode plate, which has poor air permeability.
Oxygen gas absorption capacity decreases.

In Japanese Patent Application Laid-Open No. 54-109134, metal cadmium is generated in advance on the surface of a paste-type cadmium cathode plate, which is easily contacted by oxygen generated from the anode plate during charging, and the amount of metal cadmium is secured as a pre-charge amount. Improvement in oxygen gas absorption ability? It is proposed to do so. However, is there metallic cadmium on the surface of the cathode plate? It is necessary to perform chemical conversion to produce the metal, and this chemical conversion significantly increases the number of man-hours and equipment. In addition, metal cadmium as a pre-charge amount can be secured by directly mixing metal cadmium powder when preparing the paste, so chemical formation is not practical. The metal cadmium that has been used for this purpose helps absorb oxygen gas during the early stages of charging and discharging. If this is repeated, it will become involved in charging and discharging, and the metal cadmium will change to cadmium hydroxide, making it impossible to maintain the oxygen gas absorption ability of the cathode plate for a long period of time.

(9) When the 1TFI electrode plate is overcharged after being fully charged, it reaches the hydrogen generation potential and begins to generate all hydrogen. That is, this is an electrolytic reaction of water, and the following reaction occurs.

2H20+26 -20H+H2? -t21 Unlike oxygen, the hydrogen thus generated cannot be consumed within the battery, and is accumulated in the battery. For this reason, in order to suppress the generation of hydrogen gas, the cathode capacity is generally set to a large anode capacity 9 and incorporated into the battery to prevent the cathode plate from becoming fully charged. However, is it a paste-type cadmium cathode plate? For example, if the cathode plate is charged at a very low temperature such as O''C, hydrogen gas will be generated before the cathode plate is fully charged.This is because the paste-type cadmium cathode plate is The charging reaction inside the cathode plate is delayed and the charging reaction inside the cathode plate is delayed at low temperatures such as zero, and the charging reaction inside the cathode plate is delayed. This is thought to be because the overvoltage on the surface increases and hydrogen gas is more likely to be generated.

However, a paste-type rechargeable battery with a complete cadmium cathode plate cannot be used particularly at low temperatures, and its range of use is limited.

el Problems to be Solved by the Invention The present invention aims to improve the oxygen gas absorption capacity of a paste-type cadmium cathode plate and to suppress the generation of hydrogen scum during low-temperature charging. The aim is to expand the scope of use.

(b) Means for solving the problem The paste-type cadmium cathode plate of the present invention is made of metal cadmium or cadmium oxide formed by coating on a conductive core. Along with mixing carbon powder such as acetylene black or graphite inside the material layer.

Carbon powder on the surface of the active material layer? A conductive thin layer is formed as the main component.

(e) Effect If a conductive thin layer made of carbon powder exists on the surface of the active material layer of a paste-type cadmium cathode plate, highly conductive metal cadmium is generated from near the conductive core during charging. When the cadmium produced in a certain area reaches the conductive thin layer on the surface of the active material layer, the conductive thin layer and the conductive core work on the metal cadmium, which is a charged product, and generate electricity. Since metallic cadmium is generated early on the surface of the cathode plate that is easily connected to the oxygen gas generated from the anode plate, the oxygen gas can be chemically consumed, and the oxygen gas? The ability to absorb oxygen gas, which can be consumed electrochemically, is improved.

Moreover, if carbon powder is further mixed into the active material.

A conductive layer made of carbon powder is formed in the active material layer, and a conductive thin layer made of carbon powder is present on the surface of the active material layer, so there are many charging reaction points.

The charging reaction proceeds smoothly even at low temperatures, and hydrogen gas generation is suppressed.

(F) Example: Cadmium oxide powder, metal cadmium powder, and acetylene black were mixed in a total weight ratio of 90:10:4.Then, methyl cellulose was used as a sizing agent, nylon fiber was used as a reinforcing material, and water was used as a dispersion medium. ? The mixture is then kneaded and applied to a conductive core made of punched metal.

After drying, the surface is further immersed in a liquid containing acetylene black and polyvinyl alcohol in a proportion of 50% to form carbon powder within the active material layer. The electrode plate of the present invention contains a conductive spring layer mainly composed of carbon powder on the surface of the active material layer. 7'c.

As a comparison, there is a comparative electrode plate A1 in which the active material layer is made of carbon powder on the surface of the electrode plate of the present invention without any conductive thin metal molding, and a comparative electrode plate A1 in which the active material layer is not formed with carbon in the electrode plate of the present invention. Comparative electrode plates Bf to which no powder was added were each produced.

Next, the #1 electrode was attached to each of these electrode plates, and a separator was placed between each sintered nickel anode plate, and the separator was wound spirally into a sealed nickel-cadmium battery case.
10 hours rate current at 0 (0, IC current)
After charging the battery for one hour, the internal gas pressure of the battery (
Total pressure) The H2 partial pressure was measured and the results are shown in the table below, corresponding to the cathode plates used in all the above batteries.

(7 cm) As is clear from the table, the T battery using the electrode plate of the present invention has a higher internal gas pressure, that is, the total of oxygen gas and hydrogen gas 'I, than the battery using the comparative electrode plates A and B-i. It can be seen that both the pressure and the partial pressure of hydrogen gas are kept low.

The reason for this? Presumably, the electrode plate of the present invention has a conductive thin layer made of carbon powder on the surface of the active material layer, and metal cadmium is generated early in the parts that easily come into contact with oxygen gas, and the oxygen gas generated from the anode plate. Due to the presence of Mayuko's conductive thin layer and the carbon powder in the active material layer, there are many charging reaction points and charging proceeds smoothly, suppressing the rise in overvoltage and suppressing hydrogen gas generation. Considered a friend. On the other hand, comparative plates A and B do not have either the conductive thin layer made of carbon powder on the surface of the active material layer or the carbon powder inside the active material layer. The carbon powder that forms the conductive layer on the surface of the layer is
Stable in alkaline electrolyte, does not participate in charge/discharge reactions and has no adverse effect on battery performance.

It has the following characteristics: it does not cause significant hydrogen gas generation due to a reduction in hydrogen overvoltage, it is inexpensive, etc. However, when a metal powder is used in place of the carbon powder, it is not preferred because of the following problems.

■ When using cadmium, the effect cannot be sustained because the metal cadmium as a conductive layer is directly involved in charging and discharging.

■ When aluminum, zinc, tin% lead, copper, etc. are used, the conductive layer disappears as it dissolves into the alkaline electrolyte.
loses its effect. In addition, zinc completely forms acicular crystals on the surface of the cathode during the charging and discharging reaction, causing internal interactions and reducing battery life. Hook Cu ”” C
The u''(i') reaction promotes the complete self-discharge of the battery.

■ When used with iron, nickel, cobal), platinum, etc., the hydrogen overvoltage is small, so when overcharged, the cathode plate causes significant hydrogen gas generation, causing the battery to become airtight and destroy the threads inside the battery.

■ Gold, silver, and other metals that are less available are much more expensive than carbon powder, making it difficult to put them into practical use.

■ Other sin Metals that are close to metal elements and substances called conductive metal oxides are also not effective because they have low conductivity and little effect, and are also expensive.

one! t, as carbon mixed into the active material layer.

A fibrous material is also possible, but a fibrous material is difficult to disperse uniformly in the active material, and carbon fibers are expensive compared to carbon powder, so a powdered material is preferred.

(G) Effects of the Invention The sealed paste-type cadmium cathode plate for use in alkaline power storage, etc. of the present invention has carbon powder completely mixed inside the active material layer formed on the cadmium active material formed by coating on a conductive core. In addition, a conductive thin layer mainly composed of carbon powder is formed on the surface of the active material layer. Since metal cadmium is easily generated, the oxygen gas absorption ability is improved, and the conductivity of the F cathode plate is improved due to the conductive thin layer and the carbon powder inside the active material layer, and charging progresses smoothly. This suppresses the increase in overvoltage and suppresses the generation of hydrogen gas. In addition, in a battery that uses all of the cathode plates, the increase in gas pressure inside the battery can be suppressed to a low level even during low-temperature charging, making it possible to expand the range of use of the battery.

Claims (1)

[Claims] (1) Carbon powder is mixed inside an active material layer mainly composed of cadmium active material formed by coating on a conductive core, and a conductive thin film mainly composed of carbon powder is applied to the surface of the active material layer. Paste-type cadmium cathode plate for sealed alkaline power storage and other applications.