JP2925591B2 - Method for producing hydrogen storage electrode - Google Patents

Description

The present invention relates to a method for producing a hydrogen storage electrode used as a negative electrode of an alkaline storage battery and capable of reversibly storing and releasing hydrogen.

(B) Conventional technology Conventionally used storage batteries include nickel-cadmium storage batteries and lead storage batteries. In recent years, there is a possibility that these batteries are lighter, have higher capacity and higher energy density than these batteries. Therefore, a metal-hydrogen alkaline storage battery having a negative electrode provided with a hydrogen storage electrode using a hydrogen storage alloy has attracted attention.

By the way, in this kind of hydrogen storage electrode, by repeating the charge and discharge cycle, the hydrogen storage alloy is pulverized and drops from the electrode to cause a decrease in capacity, and also causes a decrease in the mechanical strength of the electrode, and the electrode capacity is reduced for a long time. There was a problem that it was difficult to maintain. For this reason, JP
Japanese Patent Application Publication No. 66366/1999 proposes a method for increasing the mechanical strength of the electrode plate and solving the above-mentioned problems. That is, a plurality of binders such as polytetrafluoroethylene and polyethylene oxide are used in combination, and a paste obtained by kneading these with a hydrogen storage alloy powder is applied to a conductive support such as a punching metal to form an electrode. By manufacturing, the hydrogen storage alloy can be held firmly by the binder.

However, in order to increase the capacity of the electrode, the smaller the additive of the insulating impurity such as the binder, the better,
If the total amount of the binder added is 6% as shown in the examples of the above publication, the capacity of the electrode cannot be sufficiently increased.

On the other hand, regarding the binding effect of holding the alloy on the conductive support in the hydrogen storage electrode, a water-soluble polymer binding agent such as hydroxypropylcellulose and polyethylene oxide is compared with a fluorine resin binding agent such as polytetrafluoroethylene. The effect of the adhesive can be obtained with a small amount of addition. However, in the past-type cadmium electrode conventionally manufactured using a binder as a paste-type electrode for an alkaline storage battery, the addition of polyethylene oxide as the water-soluble polymer binder reduces the overvoltage of hydrogen generation. ,
Hydrogen gas is easily generated, which lowers the charging efficiency of the cadmium electrode. In this way, the paste-type cadmium electrode
Battery performance may be affected by the type of binder,
Generally, hydroxypropyl cellulose or the like is often used as a binder, and polyethylene oxide has not been used.

(C) Problems to be Solved by the Invention The present invention aims to provide a method for producing a hydrogen storage electrode that has a large electrode capacity and can maintain sufficient mechanical strength.

(D) Means for Solving the Problems The method for producing a hydrogen storage electrode according to the present invention comprises preparing a slurry in which a hydrogen storage alloy powder, a binder containing at least polyethylene oxide, and a dispersion medium are kneaded, and Is applied onto a planar conductive support and held, wherein the total amount of the binder is 2% by weight or less based on the alloy, and the polyethylene oxide is used. At least 0.5% by weight or more based on the alloy, and the viscosity of the slurry is 10,000 to 100,
It is characterized in that it is regulated to 000 mPa · s.

(E) Function In the hydrogen storage electrode, the hydrogen atoms adsorbed on the hydrogen storage alloy during charging are diffused and absorbed into the hydrogen storage alloy immediately before generating gas as hydrogen molecules, so that the electrode connection Even when polyethylene oxide is used as the adhesive, the amount of hydrogen gas generated does not increase as compared with the case where other viscous agents are used, and therefore, the charging efficiency due to the charging current being used for hydrogen gas generation Is unlikely to decrease.

In addition, polyethylene oxide has a higher viscosity and a higher binding effect than human hydroxypropylcellulose and the like, so that it is possible to obtain a sufficient slurry viscosity and binding power with a small amount of addition. Since it is a molecule, the active group only exists at the terminal of the polymer, and it is chemically very stable and advantageous.

When this polyethylene oxide is used as a binder for the electrode and the amount added to the hydrogen storage alloy is 0.5% by weight or more, the electrode strength can be sufficiently maintained. Also,
As the binder, polyethylene oxide alone or a combination of polyethylene oxide and another binder may be used. However, when the total amount of the binder exceeds 2% by weight with respect to the hydrogen storage alloy, the conductivity of the electrode is reduced. At the same time, the binder needs to be 2% by weight or less because the binder covers the surface of the hydrogen storage alloy to lower the hydrogen storage efficiency. Further, by setting the viscosity of the slurry in the range of 10,000 to 100,000 mPa · s, the slurry can be uniformly held on the conductive support.

(F) Examples Examples of the present invention will be described below, and reference will be made to comparisons with comparative examples.

[Example 1] misch commercially available metal (Mm), nickel, cobalt, manganese raw material was weighed into a predetermined composition ratio, the alloy represented by the composition formula MmNi ₃ Co _1.4 Mn _0.6 using an arc melting furnace After the preparation, it was pulverized mechanically to obtain a hydrogen storage alloy powder having an average particle diameter of 50 μm. Next, 1% by weight of polyethylene oxide and water as a dispersion medium were added to the hydrogen-absorbing alloy and kneaded, and a slurry having a viscosity of 30,000 mPa · s was produced. Here, the viscosity of the slurry is a value measured using a B-type viscometer B8U manufactured by Tokyo Keiki Co., Ltd. at a spindle TB and a rotation speed of 20 rpm.

The slurry thus prepared is put in a container, and the container is passed through a conductive support made of punched metal plated with nickel and pulled up.
The slurry was applied to the surface of a support, dried and pressed to obtain a hydrogen storage electrode according to the present invention.

This electrode was used as a negative electrode, a sintered nickel electrode was used as a positive electrode, and a spiral electrode body was obtained by winding the positive electrode and the negative electrode with a separator made of a nonwoven fabric interposed therebetween. Then, the spiral electrode body was inserted into a battery outer can, a 30% by weight aqueous solution of potassium hydroxide was injected as an electrolytic solution, and then sealed to assemble a sealed nickel-hydrogen alkaline storage battery having a nominal capacity of 1200 mAH. The battery thus manufactured is referred to as Battery A of the present invention.

In the above example, a battery was prepared under the same conditions except that the amount of polyethylene oxide was 0.5% by weight, and the other conditions were exactly the same as the battery B of the present invention. The battery was manufactured to be Battery C of the present invention.

Example 2 In Example 1 described above, the amount of polyethylene oxide was set to 1% by weight, and
In the same manner as above, a slurry was obtained by adding the same by weight, and a battery was prepared under the same conditions as the other conditions, and this battery was designated as Battery D of the present invention.

Comparative Example 1 A battery was prepared under the same conditions as in Example 1 except that the amount of polyethylene oxide was 0.3% by weight, and the other conditions were exactly the same as Comparative Battery E. Similarly, the amount of polyethylene oxide was 3% by weight. As a comparative battery F
And

[Comparative Example 2] In the above example, the amount of polyethylene oxide was set to 1% by weight, polytetrafluoroethylene was further added by 5% by weight, and a slurry was obtained in the same manner. This battery is referred to as Comparative Battery G.

Each of the batteries thus produced was charged at a current of 120 mA for 16 hours, then discharged at a current of 240 mA, and a charge / discharge cycle test was performed under a cycle condition in which the discharge was stopped when the battery voltage reached 1.0 V. The result is shown in FIG. In the drawing, the battery capacity is shown assuming that the initial capacity of the battery A is 100%.

As is clear from FIG. 1, the batteries A to D of the present invention have better cycle characteristics than the comparative batteries EG.

Thus, the battery of the present invention was excellent in characteristics because the amount of polyethylene oxide added as a binder was 0.5% by weight or more based on the hydrogen storage alloy, and the total amount of the binder was 2% by weight. %, The decrease in the conductivity of the electrode and the decrease in the hydrogen storage efficiency can be suppressed to a minimum while maintaining the strength of the hydrogen storage electrode.

On the other hand, in the comparative battery E, only 0.3% by weight of polyethylene oxide was added, and the strength of the hydrogen storage electrode could not be sufficiently maintained. Fall off,
Battery capacity is low. In Comparative Battery F, polyethylene oxide was added in an amount of 3% by weight, and the strength of the hydrogen storage electrode was sufficient. However, since the amount of polyethylene oxide added was large, the conductivity of the electrode was lowered, and at the same time, the polyethylene oxide stored hydrogen. Covers the alloy surface and reduces hydrogen storage efficiency. Therefore, the battery capacity becomes lower than at the beginning of the cycle, and the internal gas pressure of the battery increases due to the hydrogen gas generated from the negative electrode as the cycle progresses, and the electrolyte leaks due to the operation of the battery safety valve. Occurs and the battery capacity decreases. In addition, the comparative battery G
Although only 1% by weight of polyethylene oxide is added, 5% by weight of polytetrafluoroethylene is added.
Since it is added, the conductivity of the hydrogen storage electrode is reduced similarly to the comparative battery E, so that sufficient performance cannot be obtained.

The viscosity of the slurry was 30,0 in the above example.
It was used as 00 mPas, but as a result of detailed tests by the present inventors, when the viscosity exceeded 100,000 mPas,
When it was lower than 00 mPa · s, the slurry could not be uniformly applied to and held on the conductive support made of punched metal. This is due to the fact that the hydrogen storage alloy powder has a wedge shape, so that the slip is very poor and the true specific gravity is 8.0 g / cc or more, which is very heavy. From the above results, the viscosity of the slurry is 1
Desirably, it is not less than 0,000 mPa · s and not less than 100,000 mPa · s.

(G) Effect of the Invention The method for producing a hydrogen storage electrode of the present invention is characterized in that polyethylene oxide is used in an amount of at least 0.5% by weight based on the hydrogen storage alloy.
The binder contained above is used, and the total amount of the binder is set to 2% by weight or less based on the alloy, and the viscosity of the active material slurry is regulated to 10,000 to 100,000 mPa · s, so that the planar conductive property is controlled. Since the slurry is coated on the porous support, it is possible to suppress a decrease in the conductivity of the electrode and a decrease in the hydrogen storage efficiency while maintaining the electrode strength, and to obtain a high-capacity and long-life hydrogen storage electrode. Further, since the active material slurry can be uniformly held on the conductive support, the productivity of the hydrogen storage electrode can be improved.

[Brief description of the drawings]

FIG. 1 is a cycle characteristic comparison diagram of a battery having an electrode according to the present invention and a comparative battery.

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Claims (1)

(57) [Claims] 1. A slurry is prepared by kneading a hydrogen storage alloy powder, a binder containing at least polyethylene oxide, and a dispersion medium, and the slurry is applied on a planar conductive support and held. A method for manufacturing an electrode, wherein the total amount of the binder is 2% by weight or less based on the alloy, and the polyethylene oxide contains at least 0.5% by weight or more based on the alloy, and the slurry A method for producing a hydrogen storage electrode, wherein the viscosity of the hydrogen storage electrode is regulated to 10,000 to 100,000 mPa · s.