JP3521585B2 - Hydrogen storage alloy plates for sealed nickel-hydrogen storage batteries - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sealed type nickel using a hydrogen storage alloy which stores and releases hydrogen as a negative electrode active material.
The present invention relates to a hydrogen storage alloy electrode plate for a Kel-hydrogen storage battery. 2. Description of the Related Art In an alkaline storage battery such as a nickel-hydrogen storage battery, a hydrogen storage alloy electrode plate using a hydrogen storage alloy that stores and releases hydrogen as an active material is used as a negative electrode plate. This negative electrode plate (hydrogen storage alloy electrode plate) is formed by filling a current collector with a paste obtained by kneading a hydrogen storage alloy powder and a binder to form a paste-type active material layer. As the binder, cellulose derivatives such as methylcellulose, hydroxypropylmethylcellulose and carboxymethylcellulose, water-soluble polymers such as polyvinyl alcohol and polyethylene oxide, and polytetrafluoroethylene are used. [0003] In this type of battery, oxygen gas generated from the positive electrode plate at the end of charging is absorbed by the negative electrode plate (hydrogen storage alloy electrode plate) by both the electrochemical catalytic reaction and the chemical reaction shown below. , Making the battery hermetically sealed. [0004] Usually, oxygen gas is absorbed by both the reaction formulas (1) and (2), but when the above-mentioned conventional binder is used,
Since the electrochemical catalytic reaction of the above (1) is slowed down, the electrochemical catalytic reaction becomes the rate-limiting of the oxygen gas absorption reaction. Therefore, there was a problem that the oxygen gas absorption performance was reduced. Therefore, it has been proposed to form a carbon layer containing carbon powder on a paste-type active material layer to promote an electrochemical catalytic reaction as shown in Japanese Patent Publication No. 6-77450. [0005] However, when a carbon layer is formed on the paste-type active material layer, the oxygen gas absorption performance is improved, but the carbon layer reduces the wettability of the hydrogen storage alloy with respect to the electrolytic solution. And the capacity of the battery decreases. Further, in the conventional hydrogen storage alloy electrode plate using a binder, there is a problem that the active material is easily dropped from the current collector. SUMMARY OF THE INVENTION It is an object of the present invention to provide a sealed nickel alloy capable of improving oxygen gas absorption performance and suppressing a decrease in battery capacity.
- to provide a hydrogen storage alloy electrode plate for hydrogen storage battery. Another object of the present invention is to provide a hydrogen-absorbing alloy electrode plate for a sealed nickel-hydrogen storage battery which can prevent the paste-type active material layer from falling off the current collector. [0008] In order to solve the above problems, the present invention mainly comprises an alloy of misch metal and nickel.
Paste containing hydrogen storage alloy and binder
An active material layer is formed on the current collector, and the paste-type active material is
Closed nickel with a carbon layer formed on the layer
In the hydrogen storage alloy electrode plate for a hydrogen storage battery, the binder
Ethylene-vinyl acetate-long chain vinyl ester copolymer
The paste-type active material layer has a
The weight of the carbon layer is 0.05 to 5 mg / cm ² der to
The ethylene-vinyl acetate-long chain vinyl ester
The weight ratio of the polymer to the hydrogen storage alloy is 0.1 to
It is characterized by 3%. In the present invention, the binder
Ethylene-a kind of ethylene-vinyl acetate resin
A vinyl acetate-long chain vinyl ester copolymer is used. Since a conventionally used binder such as a cellulose derivative covers the surface of the hydrogen storage alloy, if the wettability of the hydrogen storage alloy to the electrolytic solution is reduced by the carbon layer, activation of the hydrogen storage alloy is significantly inhibited. In contrast, ethylene-acetic acid
Since the vinyl-long-chain vinyl ester copolymer does not cover the surface of the hydrogen storage alloy, as in the present invention, ethylene-vinyl acetate-long-chain vinyl ester copolymer is used as a binder.
The use of a body can prevent the activation of the hydrogen storage alloy from being hindered. Therefore, even if the carbon layer is formed, a decrease in the capacity of the battery can be suppressed. Also ethylene-vinyl acetate
-When the long-chain vinyl ester copolymer is used as the binder, the flexibility of the electrode plate can be increased, so that the active material can be prevented from falling off the current collector. DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a paste type active material layer containing a hydrogen storage alloy and a binder formed on a current collector, and a carbon layer formed on the paste type active material layer. The present invention is directed to a hydrogen-absorbing alloy electrode plate for a sealed nickel-metal hydride storage battery in which is formed. Here, the paste-type active material layer is a layer formed from the active material paste or a layer formed by drying the active material paste. The carbon layer is a layer containing carbon or carbon as a main component. For example, a layer formed of carbon powder or a layer formed of a paste obtained by kneading carbon powder and a binder is used. In the present invention, ethylene-vinyl acetate-long-chain vinyl ether is used as a binder.
A steal copolymer is used. Ethylene-vinyl acetate-long chain
The vinyl ester copolymer is a copolymer containing ethylene and vinyl acetate, and has a vinyl acetate content of 50% or more . The weight of the carbon layer per unit surface area of the paste type active material layer is preferably 0.05 to 5 mg / cm ² . If the amount is less than 0.05 mg / cm ² , the oxygen gas absorption performance is reduced. If it exceeds 5 mg / cm ² , the activation of the hydrogen storage alloy is inhibited, and the capacity of the battery decreases. Also, ethylene-vinyl acetate-long chain vinyl
The weight ratio of the ester copolymer to the hydrogen storage alloy is preferably 0.1 to 3%. When the content is less than 0.1% by weight , the binding property is reduced and the active material is easily peeled off from the current collector.
If the content exceeds 3% by weight , the oxygen gas absorption performance is reduced, and the internal pressure of the battery tends to increase. EXAMPLES (Examples 1 to 8) The hydrogen-absorbing alloy electrodes of Examples 1 to 8 were produced as follows. First, an alloy of Mm (mish metal) mainly composed of lanthanum and Ni and a predetermined amount of Co, Al, and Mn were heated and melted by arc melting, and then cooled. This was mechanically pulverized into a powder having an average diameter of about 100 μm using a ball mill to obtain a hydrogen storage alloy. Next, a hydrogen storage alloy powder, 0.5% by weight of nickel powder with respect to the hydrogen storage alloy powder, and 1.06% with respect to the hydrogen storage alloy powder
% By weight of a binder solution consisting of an ethylene-vinyl acetate-long chain vinyl ester copolymer emulsion and 0.5% by weight of methylcellulose based on the hydrogen storage alloy powder, and having a viscosity of 30,000 mPa · s. I made a paste.
The ethylene-vinyl acetate-long chain vinyl ester copolymer emulsion is an emulsion in which an ethylene-vinyl acetate-long chain vinyl ester copolymer is dispersed in water, and has a glass transition temperature (Tg) of -30 ° C. In this example, an ethylene-vinyl acetate-long chain vinyl ester copolymer emulsion sold by Sumitomo Chemical Co., Ltd. under the trade name of Sumikaflex was used. Further, by using 1.06% by weight of the emulsion with respect to the hydrogen storage alloy powder, 0.5% by weight of the binder (ethylene-vinyl acetate-long chain vinyl ester copolymer) with respect to the hydrogen storage alloy powder. Will be added. Next, the paste was applied to both surfaces of a current collector made of a conductive support substrate having a thickness of 60 μm by a doctor blade method, and then dried and pressed to obtain an electrode plate material. Next, a dispersion was prepared by dispersing carbon powder consisting of 50 parts by weight of Ketjen black (carbon powder) and 50 parts by weight of methylcellulose. Next, this dispersion was applied on the surface of the electrode plate material by the loin transfer method, and dried to form a carbon layer. As a result, the electrode plates of Examples 1 to 8 having different weights of the carbon layer with respect to the unit surface area of the paste-type active material layer in the range of 0.04 to 7.0 mg / cm ² as shown in Table 1 were completed. Comparative Example 1 A hydrogen storage alloy electrode plate of this comparative example was produced in the same manner as the electrode plates of Examples 1 to 8, except that no carbon layer was formed on the surface of the electrode plate material. Comparative Example 2 The hydrogen-absorbing alloy electrode plate of this comparative example uses polyvinyl alcohol as a binder instead of ethylene-vinyl acetate-long chain vinyl ester copolymer, and the binder absorbs hydrogen. 1% by weight was added to the alloy powder. The weight of the carbon layer per unit surface area of the paste-type active material layer was 0.1 mg / cm.
^{And 2} . The others were made in the same manner as the electrode plates of Examples 1 to 8. Comparative Example 3 The hydrogen-absorbing alloy electrode plate of this comparative example uses polyethylene oxide as a binder instead of ethylene-vinyl acetate-long-chain vinyl ester copolymer, and uses the binder to absorb hydrogen. 1% by weight was added to the alloy powder. The weight of the carbon layer per unit surface area of the paste-type active material layer was 0.1 mg /
cm ² . The others were made in the same manner as the electrode plates of Examples 1 to 8. [Table 1] Next , the degree of dropping of the active material from the current collector in each electrode plate was examined. Specifically, after each of the above-mentioned electrode plates was wound around a shaft having a diameter of 3 mm, the electrodes were rewound and the rate of dropping of the active material of each electrode plate from the current collector (winding drop rate) was measured. The winding drop-off rate is a value obtained by subtracting the electrode plate weight after the winding test from the electrode weight before the winding test and dividing the value by the electrode weight before the winding test. Table 1 shows the measurement results. From this table, ethylene-acetic acid
The electrode plates of Examples 1 to 8 and Comparative Example 1 using a vinyl-long-chain vinyl ester copolymer as a binder were the electrode plates of Comparative Examples 2 and 3 using polyvinyl alcohol and polyethylene oxide as a binder. It can be seen that the rate of falling off the winding is lower than that of. This is an ethylene-vinyl acetate-long chain vinyl ester
This is because the flexibility of the electrode plate has been increased by using the styrene copolymer as the binder. Next, in order to examine the characteristics of each electrode plate, a sealed nickel-hydrogen storage battery was manufactured using each electrode plate. First, while laminating a known positive electrode plate composed of a nickel electrode having a capacity of 1300 mAh using nickel hydroxide as an active material and the respective electrode plates via a separator made of a nonwoven fabric made of nylon, the respective electrode plates become the outermost periphery. To form a wound electrode plate group. Next, after inserting each electrode plate group into the cylindrical battery container, an electrolyte solution consisting of a 31% by weight aqueous solution of potassium hydroxide was poured into each of the electrode plate groups to form a sealed nickel battery having a nominal capacity of 1300 mAh and a regulated capacity. -Make a hydrogen storage battery. First, an initial capacity test was performed using each battery. First, each battery was subjected to a known activation treatment to store hydrogen in the hydrogen storage alloy, then charged at 0.1 CmA for 16 hours, and charged and discharged at 0.2 CmA for 3 cycles. The discharge capacity during the cycle was measured. Table 1 shows the measurement results. From this table, Comparative Example 2 using polyvinyl alcohol and polyethylene oxide as binders
It can be seen that the battery using the No. 3 electrode plate cannot obtain a sufficient capacity even in the third cycle. In contrast, Examples 1 to
It can be seen that the battery using the electrode plate No. 8 has a high battery capacity from the beginning. In particular , it can be seen that the battery capacity can be increased by using an electrode plate (Examples 1 to 7) in which the weight of the carbon layer per unit surface area of the paste-type active material layer is 5.0 mg / cm ² or less. This is because the activation of the negative electrode is inhibited when the electrode plates of Comparative Examples 2 and 3 are used. Since the capacity of the battery is regulated by the positive electrode capacity, the negative electrode capacity hardly affects the battery capacity. However, if the activation of the negative electrode is inhibited , a predetermined positive / negative capacity ratio cannot be obtained, and the capacity of the battery decreases. Next, the internal pressure characteristics of each battery were examined. Specifically, a 1 mm hole was made in the bottom of the can of each battery, and the pressure sensor was arranged inside the battery. Then, each battery was charged at 1 CmA for 90 minutes (150% charge), and the internal pressure of each battery was measured. Table 1 shows the measurement results. From this table, it can be seen that the internal pressure increases when the electrode plate of Comparative Example 1 in which the carbon layer is not formed is used. On the other hand, in the batteries using the electrode plates of Examples 1 to 8 , it can be seen that the increase in battery internal pressure can be suppressed. In particular, when the weight of the carbon layer per unit surface area of the paste Shikikatsu material layer used 0.05 mg / cm ² or more plates (Example 2-8), seen that the battery capacity is increased. Further, polyvinyl alcohol, in plates of Comparative Examples 2 and 3 using a polyethylene oxide as the binder, a relatively pressure is the is seen higher. This is because polyvinyl alcohol and polyethylene oxide cover the hydrogen-absorbing alloy.
It is considered that the oxygen gas absorbing performance of the electrode plate was decreased. In each test, the weight of the carbon layer per unit surface area of the paste-type active material layer was 0.05 to 5 mg / cm.
^It can be seen that the use of the ^second electrode plate can improve both the internal pressure characteristics and the initial capacity characteristics. In this embodiment, an ethylene-vinyl acetate-long chain vinyl ester copolymer was used as the ethylene-vinyl acetate resin, but other ethylene-vinyl acetate such as an ethylene-vinyl acetate-acrylic copolymer was used. A system resin may be used as a binder. Even when an ethylene-vinyl acetate-acrylic copolymer having a different glass transition temperature (Tg) was used, the same test results were obtained as when an ethylene-vinyl acetate-long-chain vinyl ester copolymer was used. confirmed. The configuration of the invention described in the specification will be described below. (1) A paste-type active material layer containing a hydrogen storage alloy mainly composed of an alloy of misch metal and nickel and a binder is formed on a current collector, and a paste-type active material layer is formed on the current collector. In the sealed nickel-hydrogen storage battery hydrogen storage alloy electrode plate having a carbon layer formed thereon, using an ethylene-vinyl acetate-long chain vinyl ester copolymer as the binder, the paste-type active material layer The weight of the carbon layer per unit surface area is 0.05 to 5 mg /
cm ^2, and the ethylene - vinyl acetate - enclosed nickel weight ratio with respect to the hydrogen storage alloy of long-chain vinyl ester copolymer, characterized in that a 0.1% to 3% -
Hydrogen storage alloy plates for hydrogen storage batteries. EFFECT OF THE INVENTION Ethylene-vinyl acetate-long chain vinyl S
The tercopolymer does not cover the surface of the hydrogen storage alloy.
Therefore, as in the present invention, ethylene-vinegar is used as a binder.
When the acid vinyl-long chain vinyl ester copolymer is used, it is possible to prevent the activation of the hydrogen storage alloy from being hindered even when the wettability of the hydrogen storage alloy with the electrolytic solution is reduced by the carbon layer. Therefore, it is possible to enhance the oxygen gas absorption performance by forming a carbon layer, and to suppress a decrease in battery capacity. Also, ethylene-vinyl acetate-long chain vinyl ester
When the copolymer is used as a binder , the flexibility of the electrode plate can be increased, so that the active material can be prevented from falling off the current collector.

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Satoshi Minoura 2-1-1 Shinishijuku, Shinjuku-ku, Tokyo Inside Shin-Kobe Electric Co., Ltd. (56) References JP-A-54-109142 (JP, A) Hei 6-7750 (JP, B2) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01M 4/24 H01M 4/62

Claims (1)

(57) [Claims] [Claim 1] An alloy of misch metal and nickel is mainly used.
Containing a hydrogen storage alloy as a component and a binder
A paste active material layer is formed on the current collector,
Sealed nickel with a carbon layer formed on the porous layer
-In the hydrogen-absorbing alloy electrode plate for a hydrogen storage battery , ethylene-vinyl acetate-long chain vinyl ether as the binder;
Using a stell copolymer, the paste type active material layer
The weight of the carbon layer with respect to the surface area is 0.05 to 5
mg / cm ² , the ethylene-vinyl acetate-long chain vinyl ester copolymer
Weight ratio of the body to the hydrogen storage alloy is 0.1 to 3%
A hydrogen-absorbing alloy electrode plate for a sealed nickel-hydrogen storage battery , characterized in that: