JPH01239766A - Manufacture of cadmium negative plate - Google Patents

Abstract

PURPOSE:To obtain a cadmium negative plate having high oxygen-gas absorbing capability by filling active material paste in a metal substrate having continuous three-dimensional pores, drying, and pressing in the thickness direction while the paste on the surface is peeling off. CONSTITUTION:A paste-state active material containing cadmium oxide or cadmium hydroxide is filled in a metal substrate having continuous pores such as foamed metal, and dried. The active material only on the surface of the filled plate is peeled off with a brush. The filled plate is pressed in the thickness direction and only the surface is made dense because of low mechanical strength. Current easily flows on the surface compared with the inside, and the active material on the surface is quickly, sharply converted into metallic cadmium to increase oxygen gas absorbing capability. Increase in internal pressure in a battery is retarded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for manufacturing a paste-type cadmium negative electrode plate used in an alkaline storage battery.

[Prior Art] A sealed nickel-cadmium storage battery, which is a type of alkaline storage battery, usually has a cadmium negative plate with a larger capacity than a nickel positive plate, and a portion of each plate is exposed from the electrolyte. Each electrode plate is impregnated with an electrolytic solution to a certain extent. This is because oxygen gas is generated only from the positive electrode plate side at the end of charging the storage battery, and this generated oxygen gas is absorbed by the metal cadmium of the negative electrode plate, thereby suppressing an increase in battery internal pressure. The cadmium negative electrode plate of such a sealed nickel-cadmium storage battery is manufactured by a paste method, which is a relatively simple process. The conventional paste manufacturing method involves kneading active materials such as cadmium oxide powder or cadmium hydroxide powder with a binder such as methylcellulose or CMC (carboxymethylcellulose) to form a paste, and then applying this paste to a nickel-plated porous It is applied to a conductive core such as a steel plate, dried, and then subjected to a chemical conversion treatment in an alkaline solution to impart a precharge m.

[Problems to be Solved by the Invention] However, since the cadmium negative electrode plate obtained by the conventional paste method does not have a dense conductive matrix like the negative electrode plate obtained by the sintering method, metal cadmium on the surface of the negative electrode plate during charging. The progress of hydrogenation is slow, the ability to absorb oxygen gas generated from the positive electrode plate is small, and the internal pressure of the battery increases due to overcharging.

For this reason, charging with a large current of 0.5C or more is not possible, for example.

The present invention has been made in consideration of the above circumstances, and it is an object of the present invention to provide a method for manufacturing a cadmium negative electrode plate that increases the oxygen gas absorption capacity and is suitable for charging with a large current.

[Means for Solving the Problems] In order to achieve the above object, the manufacturing method according to the present invention involves filling a metal structural plate having continuous three-dimensional pores with a paste in which cadmium oxide or cadmium hydroxide is kneaded, and drying the paste. a step of removing the paste so that the surface of the filling plate is exposed; a step of pressurizing the filling plate in the thickness direction; and a step of subjecting the pressurized filling plate to alkaline electrolysis. The present invention is characterized in that it includes a step of applying a preliminary charge amount by negative electrolysis, and a step of immersing the filling plate in a fluororesin dispersion to form a fluororesin film.

The metal structure plate having continuous three-dimensional pores is a metal plate having so-called sponge-like pores, and for example, a foamed metal thin plate or a mat-like thin plate made of an aggregate of short metal fibers can be used. This metal structure plate has a large porosity and the amount of active material paste supported increases, so the amount of cadmium metallized is large and the oxygen gas absorption capacity is increased. The active material paste filled in such a metal structural plate is prepared by kneading cadmium oxide or cadmium hydroxide powder and a binder.

As a binder, polyvinyl alcohol (PVA), methylcellulose, carboxymethylcellulose (CMC)
These resins or mixtures of these resins with fibers are selected. A paste is produced by kneading cadmium oxide or the like with a binder, and the filled plate is formed by kneading this paste into the metal structural plate or by immersing the metal structural plate in the paste and drying it.

Next, the paste is removed so that both the front and back sides of the filling plate are exposed, and after the paste is removed, the filling plate is pressurized in the thickness direction. Removal of the paste on the front and back surfaces of the filling plate is performed so that compression in the subsequent pressurizing operation acts only on the surface layer portion of the filling plate. In other words, if the paste on the front and back surfaces is not removed, the pressure will be applied uniformly to the entire filling plate, and the entire filling plate will be compressed uniformly in the thickness direction, whereas if the paste on the front and back surfaces is removed, the paste will This is because the mechanical strength of the surface layer of the filling plate becomes smaller compared to the inside of the filling plate in which the filling plate is supported, and when this is pressurized, only the surface layer of the filling plate is compressed so as to become dense. Since current flows through the dense surface layer more easily than inside the filling plate, the surface layer is charged from the surface layer during charging.

Therefore, the active material in the surface layer is rapidly and smoothly converted into metal cadmium, and the oxygen gas absorption capacity is increased.

Note that the active material paste on the front and back surfaces of the filling plate can be removed using a brush,
This can be easily done by scraping off using a spatula, roller, etc. Further, the pressure after the active material paste is removed is applied at such a pressure that only the surface layer portion of the filling plate has a dense structure.

After such pressurization, the filling plate is chemically formed to provide a precharge amount. Chemical formation is performed by removing electrolysis in an alkaline electrolyte using the pressurized packed plate as a cathode. Potassium hydroxide solution, sodium hydroxide solution, etc. can be used as the alkaline electrolyte. This chemical conversion activates cadmium oxide or cadmium hydroxide, leaving a part of it as metallic cadmium, and providing a pre-charge amount. In this case, the amount of preliminary charging is performed to be a predetermined percentage of the negative electrode plate capacity. The metal cadmium produced through chemical formation absorbs oxygen gas generated during charging of storage batteries. After this chemical formation, the filling plate is washed with water and dried.

The fluororesin film forming step is carried out by immersing the filling plate in a fluororesin dispersion and then drying it. As the fluororesin, for example, polytetrofluoroethylene (PTFE) is used.
) (trade name: Teflon) can be used. In this case, the immersion in the fluororesin dispersion may be performed immediately after the above-mentioned chemical conversion treatment, after washing with water after chemical conversion, after drying after washing with water, or even after the filling plate is lowered before chemical conversion. This may be done after applying pressure. By dipping and drying the fluororesin dispersion, the surface of the filling plate is covered with a fluororesin film, which provides lyophobicity with the electrolyte in the battery can of the storage battery, facilitating the formation of a three-phase interface. In other words, oxygen gas generated by charging the storage battery is absorbed by the metal cadmium of the negative electrode plate, but this absorption reaction occurs between the metal cadmium of the negative electrode plate, which is in the same phase, and the electrolytic solution impregnated in the electrode plate, which is in the liquid phase. It is carried out at a three-phase interface consisting of oxygen gas, which is a gas phase. In the present invention, the fluororesin coating increases the lyophobicity of the negative electrode plate to the electrolyte, making it easier for the electrolyte to disperse, thereby ensuring a three-phase interface, which significantly improves oxygen gas absorption ability. It is something to do. Therefore, even if a large amount of oxygen gas is generated, an increase in the internal pressure of the battery can can be suppressed, making it possible to charge with a large current, thereby increasing the rapid charging ability of the storage battery.

[Function] Since the present invention is configured as described above, the oxygen gas absorption capacity of the cadmium negative electrode plate is increased.

[Example] Hereinafter, the present invention will be explained in more detail with reference to Examples.

A paste was prepared by kneading cadmium oxide powder into an ethylene glycol solution of polyvinyl alcohol. next,
This paste was kneaded and filled into a metal structural plate made of metal fiber mat with an average pore diameter of 200 μm and a thickness of 0.7 mm.
Dry. Then, the front and back surfaces of this filling plate were scraped off with a nylon brush to expose the surface. Thereafter, the filling plate was pressurized to a thickness of 0.55 mm. After pressurization, negative electrolysis was performed in an aqueous potassium hydroxide solution having a specific gravity of 1.20 to perform chemical conversion to impart metal cadmium. After this, the filling plate was washed with water and 3%
It was immersed for a minute and then dried to obtain a cadmium negative electrode plate of the present invention. Next, this negative electrode plate is cut to a predetermined size and combined with a nickel positive electrode plate obtained by sintering.
A sealed alkaline storage battery equivalent to 8705KR-AA 500mAh was manufactured and the battery characteristics were examined. The test was carried out by measuring the internal pressure peak of the battery can during overcharging with respect to the charging rate, and the results are shown in FIG. In FIG. 1, the characteristic curve a shows the product of the present invention obtained by the above method. 1) shows a storage battery using a cadmium negative electrode plate that was subjected to the same treatment without removing the active material paste and 1) immersing it in a TFE dispersion.As shown in the figure, a cadmium negative electrode plate according to the present invention was used. It can be seen that the increase in internal pressure of the storage battery is suppressed and the oxygen gas absorption capacity is increased. This is thought to be because metal cadmium is easily distributed on the surface of the scraper during charging, and the three-phase interface is well formed by the fluororesin film, resulting in an increase in oxygen gas absorption capacity.

[Effects of the Invention] As explained above, the present invention provides a method for obtaining a filled plate by filling an active material paste into a metal structural plate having continuous three-dimensional pores.
Since only the surface layer of this filling plate was pressurized to be dense and a fluorine fNt fat film was formed, the oxygen gas absorption capacity was increased. Therefore, the storage battery using the cadmium negative electrode plate according to the present invention can be easily charged with a large current.
Rapid charging capacity increases.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the charging rate of a sealed nickel-cadmium storage battery and the peak of battery internal pressure during overcharging. Patent applicant: Furukawa Battery Co., Ltd. Representative Patent attorney: Hideaki Sato

Claims (1)

[Claims] A step of filling a metal structure plate having continuous three-dimensional holes with a paste in which cadmium oxide or cadmium hydroxide is kneaded and drying it to form a filled plate, and removing the paste so that the surface of the filled plate is exposed. a step of pressurizing the filling plate in the thickness direction; and a step of negative electrolyzing the pressurized filling plate in an alkaline electrolyte to provide a preliminary charge amount;
A method for manufacturing a cadmium negative electrode plate, comprising the step of immersing the filling plate in a fluororesin dispersion to form a fluororesin film.