JPH04249067A - Manufacture of hydrogen storage electrode - Google Patents

Abstract

PURPOSE:To enhance the absorptivity for hydrogen gas by mixing an electroconductivity agent and resin binder with a powder of hydrogen storage alloy, coating a porous sheet with slurry to which a water solution of consistency increasing agent is added and kneaded, drying the resultant and impregnating with a solution containing dispersed fibrous plastics, and subjecting it to pressurizing and baking process. CONSTITUTION:A water solution of consistency increasing agent is added to a mixture consisting of a powder of hydrogen storage alloy or its H compound, a powder of electroconductivity agent, and a resin binder and the resultant is kneaded to ed turned into slurry. The slurry is applied to a porous sheet and dried, and a dry plate obtained is directly pressurized or subjected to preliminary pressurization. and is impregnated with a solution containing dispersed fibrous plastics, followed by drying process, The dry plate as resultant is subjected to one run or more of pressurization to give it a certain specified thickness, which is followed by baking process. This allows good performance including the resin having trend to be turned fibrous, and the resin is turned fibrous by pressurization so as to increase the hydrophobic property and H gas absorptivity.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a hydrogen storage electrode.

0002

[Prior Art] Conventionally, in the production of hydrogen storage electrodes, a hydrogen storage alloy powder or its hydride powder, a mixture of a conductive agent powder and a resin binder powder made of polyfluorovinylidene or polyethylene, and a mixture of CMC, etc. The method used was to add an aqueous thickener solution, knead to form a slurry, apply this slurry to a porous sheet such as a wire mesh or perforated plate, dry it, pressurize it, and fire it. The resin binder powder used here is melted by firing and used for bonding the alloy powder or its hydride powder to the conductive agent powder and to the porous sheet. The above-described resin binder has a low melt viscosity, excellent bonding properties, and alkali resistance, so it is suitable for manufacturing hydrogen storage alloy electrodes.

The electrode produced in this way is used as a negative electrode, and this is combined with, for example, a nickel oxide electrode as a positive electrode to form a sealed nickel-metal hydride battery. The Neumann method is adopted in which the capacity of the negative electrode is larger than that of the positive electrode in order to consume oxygen gas at the negative electrode and prevent generation of hydrogen gas from the negative electrode.

However, when the internal pressure of the Neumann type sealed battery is measured, it is found to be higher than that of a nickel-cadmium battery, and an analysis of the internal pressure gas components reveals that the same amount of oxygen is present. It turns out that hydrogen exists. This occurs because the potential at which the charging reaction of the hydrogen storage electrode occurs is close to the electrolytic potential of water. In order to reduce the generation of hydrogen gas, the problem can be alleviated to some extent by increasing the capacity of the negative electrode, but the energy density of the battery decreases accordingly, which is not preferable.

[0005] Hydrogen gas once generated is reabsorbed from the hydrophobic portion on the surface of the negative electrode, but the hydrophobic portion formed from the resin binder described above does not have sufficient absorption performance. Regarding the formation of the absorbent part, it is known that the presence of sufficiently fibrous polytetrafluoroethylene is very effective. It is conceivable to knead it into a slurry and apply this slurry to a porous sheet.
When made into a slurry, the viscosity becomes extremely high,
Since it is extremely difficult to apply it, it is extremely difficult to manufacture a hydrogen storage electrode by applying it, drying it, and sintering it.

[Problem to be solved by the invention]

Therefore, it is desirable to be able to easily incorporate such a fibrous resin, which has been difficult to manufacture in the past, and to make it possible to manufacture a hydrogen storage electrode with improved hydrogen gas absorption.

[Means to solve the problem]

The present invention provides a method for manufacturing a hydrogen storage electrode that satisfies the above-mentioned requirements, and is composed of a hydrogen storage alloy powder or its hydride powder, a conductive agent powder, and a resin binder powder. A thickener aqueous solution is added to the mixture and kneaded to form a slurry, and the resulting slurry is applied to a porous sheet and dried, and then the fibrous synthetic resin is applied to the resulting dry plate immediately or after pre-pressing. It is characterized in that it is impregnated with a dispersion liquid, then dried, the obtained dry plate is pressurized at least once to give the dry plate a predetermined thickness, and then it is fired.

[0008]

[Operation] Apply the above slurry to a porous sheet, dry it, impregnate the resulting dry board with a fibrous resin dispersion, and dry it. Pressurize the dry board at least once. As a result, the fibrous resin becomes fibrous and mixed in the dry plate. Therefore, the hydrophobicity of the hydrogen storage electrode obtained by pressurizing to a predetermined thickness and firing is increased by the fibrous resin, and the absorbability of hydrogen gas is improved. In this case, by setting the pre-pressurization to a range of about 90 to 50% of the original thickness of the dry plate, the dry plate can be smoothly and satisfactorily impregnated with the fibrous resin dispersion.

[0009]

EXAMPLE An example of the method for manufacturing a hydrogen storage electrode of the present invention will be described in detail below. Commercially available La, Ni, Co, and Al were weighed and mixed at a constant composition ratio, and heated and melted using an arc melting method. Thus, as an example, the alloy composition was selected to be LaNi4.0Co0.7Al0.3, and a hydrogen storage alloy for a negative electrode was manufactured. The solid mass of the alloy composition is pulverized into a powder of 250 mesh or less, and 3 wt. % polyfluorovinylidene powder and 15 wt.% as a conductive agent. % of carbonyl nickel powder was added and mixed thoroughly. To this mixture, 1 wt. A thickener aqueous solution consisting of a carboxymethylcellulose aqueous solution having a concentration of 1.5% was added and kneaded to form a slurry. A 0.1 mm thick porous sheet with a nickel plated surface, similar to that used in sintered nickel-cadmium batteries, was used as the porous substrate, and the slurry-like material described above was applied to this porous sheet. , dried. The thickness of this dry coating layer was 0.9 mm. Next, the dry plate is pressed by passing it through a pressure roll, etc., to an extent that does not reach a predetermined thickness, for example, to a thickness of 0.7 mm,
Next, the dry plate is treated with a fiber-forming synthetic resin dispersion, for example, 10%
wt. The dry plate is impregnated with the dispersion by dipping it in a polytetrafluoroethylene dispersion with a concentration of In this example, a dried plate with a uniform mixture of fiberized polytetrafluoroethylene with a thickness of 0.5 mm is obtained, and then this is baked at 170°C in a vacuum to form the hydrogen absorbing material of the present invention. An alloy electrode was obtained.

This hydrogen storage electrode was used as a negative electrode, a known paste type nickel electrode was used as a positive electrode, and 7N was used as an electrolyte.
AA size 300 with positive electrode capacity regulation using KOH aqueous solution
A mAh sealed battery was manufactured.

[0011] For comparison, the slurry was
A dry plate obtained by coating and drying a porous sheet of the same material with a thickness of Next, a conventional hydrogen storage electrode was manufactured by firing in the same manner, and this was used as a negative electrode, and a conventional sealed battery was manufactured in the same manner as above.

After a pressure sensor was attached to these batteries, an overcharge test was conducted to compare the internal pressure and gas composition. The conditions for the overcharge test were 1.0C current for 5 hours (500
%) Charged. As a result of this test, the internal pressure of the battery incorporating the electrode of the present invention was approximately 5 Kgf/cm2, and more than 95% of this was oxygen gas. On the other hand, in a battery incorporating the above reference electrode, the internal pressure is approximately 10 kg.
f/cm2, and about 50% of this was hydrogen gas. As is clear from this, the electrode of the present invention can satisfactorily absorb the hydrogen gas generated within the battery, and has the effect of significantly reducing the internal pressure.

[0013] As mentioned above, the reason why pressure is applied in advance when the dry plate is immersed in the dispersion for impregnation treatment is that when the dry plate is immersed in the dispersion, the dry plate This is to prevent part of the slurry coating layer from flowing out, but if impregnation treatment is performed by spraying instead of impregnation treatment by dipping, it is not necessary to pressurize the dry plate in advance as described above. Immediately, the dry plate can be impregnated by spraying, and the dry plate can be impregnated with good quality. Therefore, the pre-pressurization described above is not necessarily necessary. As a result of the study, the degree of pre-pressurization was determined to be approximately 90% of the thickness of the dry plate (that is, the degree of compression is approximately 10%) in order to prevent the slurry from flowing out during immersion impregnation. On the other hand, it has been found that when pressure is applied to a thickness exceeding about 50% of the thickness, the porosity of the dry plate decreases and impregnation with the dispersion liquid cannot be performed satisfactorily. Therefore, the degree of pressurization is
It is preferable to limit the thickness to approximately 90 to 50% of the thickness of the dry plate.

In the production method of the present invention, in the above example, the dried plate obtained by impregnating the dispersion and drying the dispersion is
Although the pressure was applied once to a predetermined thickness, the pressure may be applied several times. For example, as described above, a dry plate obtained by impregnating and drying the pre-pressurized dispersion to a thickness of 0.7 mm is pressurized to a thickness of 0.6 mm, and then this is heated to a predetermined thickness of 0.7 mm. Apply pressure in two batches so that the pressure reaches 5 mm. By applying pressure in stages, the polytetrafluoroethylene mixed in the drying plate can be more effectively fiberized and the fibers can be dispersed. It goes without saying that instead of using hydrogen storage alloy powder as a raw material, its hydride powder can be used.

[0015]

Effects of the Invention As described above, according to the present invention, a slurry-like product prepared by adding and kneading a thickener aqueous solution to a mixture of hydrogen storage alloy powder or hydride powder, conductive agent powder, and resin binder powder was applied to a porous sheet and dried, and the resulting dry plate was impregnated with the fiber-forming synthetic resin dispersion immediately or after being subjected to pressure treatment, so that the fiber-forming resin was well mixed in. Then, the drying plate is pressurized at least once, so that the fibrous resin mixed in the drying plate can be turned into fibers by the pressurization, and then the fiber-forming resin mixed in the drying plate can be fiberized. Since the hydrogen storage alloy electrode is mixed with the hydrophobic fibers, its hydrophobicity and hydrogen gas absorption properties are increased, which increases the absorption of hydrogen gas in a sealed storage battery that incorporates this as a negative electrode. It has effects such as reducing pressure. In addition, when performing preliminary pressurization, the degree of pressurization should be approximately 4
By keeping the amount in the range of 0 to 50%, there is an effect that the slurry is not washed away when the dispersion is immersed and impregnated, and the impregnation can be carried out.

Claims (2)

[Claims] Claim 1: A thickener aqueous solution is added to a mixture of a hydrogen storage alloy powder or its hydride powder, a conductive agent powder, and a resin binder powder, and the mixture is kneaded to form a slurry, and the resulting slurry is used as a porous sheet. Immediately or after pre-pressurization, the obtained dry plate is impregnated with a fiber-forming synthetic resin dispersion, which is then dried, and the obtained dry plate is applied at least once. 1. A method for manufacturing a hydrogen storage electrode, which comprises applying pressure to make the dry plate a predetermined thickness, and then firing it. 2. The method of manufacturing a hydrogen storage electrode according to claim 1, wherein the pre-pressurization ranges from about 90% to 50% of the thickness of the original dry plate.