JPH04315768A - Hydrogen storage electrode and manufacture thereof - Google Patents

Abstract

PURPOSE:To maintain a high capacity of a battery over a long period and to achieve high quality by packing powder of a hydrogen storage alloy in a foaming metal porous body in the form of a rectangular plate to form an electrode body, and fixing the peripheral portion of the eletrode body with metal reinforcing bodies of high alkali resistance. CONSTITUTION:The edge portion of a hydrogen storage electrode is protected by a metal reinforcing body 2 surrounding an electrode body 1 comprising powder of a hydrogen storage alloy packed in a foaming metal porous body and the electrode is supported by the body 2: i.e., the reinforcing body 2 serves as an electrode support body functionally and enhances the conductivity of the electrode. The protection property of the edge portion, the electrode supporting function of the body 2 and the conductivity of the electrode are further enhanced by the use of a second metal reinforcing body 3. When the metal reinforcing bodies 4A, B are used in such a way as being laid across the body 1, not only the electrode performance is enhanced, but also expansion of the hydrogen storage electrode due to repeating of charge and discharge can be restrained. When a rectangular battery is used the bodies 2,3 are connected to each other into an integral structure so that the amount of deformation of the whole structure can be reduced to a small one. Thereby high capacity is maintained over a long period and high quality is achieved.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hydrogen storage electrode that reversibly stores and desorbs hydrogen in an electrolytic solution, and a method for manufacturing the same.

0002

2. Description of the Related Art Hydrogen storage electrodes using alloys that reversibly absorb and desorb hydrogen have generally been manufactured by the following method. That is, various metals are weighed to match the alloy composition, the mixture of various metals is melted by high-temperature arc discharge using an arc melting furnace, etc., to produce an alloy with the desired composition, and this alloy is further pulverized. then 30
The powder has a particle size of 0 mesh or less.

[0003] This powder is kneaded to a uniform state with a binder, etc. to form a paste, which is applied to a foamed metal porous body made of nickel, for example, and then dried and pressurized to form a hydrogen storage electrode. there was. A metal oxide-hydrogen storage battery is constructed by using this hydrogen storage electrode as a negative electrode and combining it with a known nickel positive electrode through a separator.

0004

In general, in hydrogen storage alloys, the alloy powder becomes finer due to repeated storage and release of hydrogen, and its particle size becomes smaller. In an electrode using such an alloy, as the charge/discharge cycle progresses, the binding force decreases due to a change in the particle size of the alloy powder. When a foamed metal porous body is used as a substrate of an electrode, alloy powder tends to fall off particularly from the edges. Once the alloy powder falls off, it progresses gradually. As a result, battery capacity continues to decrease.

[0005] In order to eliminate this phenomenon, a method is adopted in which the amount of binder added is increased. However, if too much binder is added, the amount of alloy per unit weight of the electrode decreases, resulting in a problem that the energy density per unit weight decreases.

[0006] As a hydrogen storage electrode that solves the above problems, Japanese Patent Application Laid-Open No. 2-201870 discloses a method in which a flat plate of a porous metal foam is made hollow, and the hollow portion is densely filled with a hydrogen storage alloy coated with a different metal. However, a hydrogen storage electrode has been proposed in which both planes are covered with a metal mesh surface and the three are integrated under high temperature.

The object of the present invention is to lower the amount of binder added to better exhibit the hydrogen storage properties of the alloy. Specifically, the foam metal porous material that surrounds the four circumferences of the electrode prevents the alloy powder from falling off from the edges, and the metal mesh surface plays the role of preventing the alloy powder from falling off from the flat surface of the electrode. This means that the amount of drug used can be significantly reduced.

However, the method of coating dissimilar metals on alloy powder by electroless plating etc. is expensive, and the yield is low because there is no effective way to use the metal porous material in the cutout gap. It is expensive and has problems in industrial practicality.

As described above, a hydrogen storage electrode that eliminates the problem of alloy powder falling off without reducing the energy density of the electrode and is practical in terms of cost has not yet been proposed.

An object of the present invention is to solve the above-mentioned problems and provide a high-quality hydrogen storage electrode that can maintain a high capacity for a long period of time.

[0011]

[Means for Solving the Problems] The hydrogen storage electrode according to the present invention is characterized in that the periphery thereof is fixed with a metal reinforcing body having high alkali resistance in order to prevent alloy powder from falling off, which causes a decrease in capacity.

[0012] Furthermore, the method for manufacturing this hydrogen storage electrode is as follows:
One method is to fill a square plate-shaped foamed metal porous body with hydrogen-absorbing alloy powder to form an electrode body, and to fix the peripheral portion of the electrode body with the metal reinforcing body. This fixing method includes pressure integration and spot welding, but spot welding is preferable in order to reliably prevent the alloy from falling off and to improve the current collecting ability. At this time, a method is adopted in which the periphery of the foamed metal porous body is reduced in porosity by applying pressure or the like so that it is suitable for spot welding.

[0013] Here, the metal reinforcing body preferably covers the electrode body in a U-shape so as to leave the upper side of the electrode body intact. Furthermore, a configuration in which the metal reinforcing body covers all four circumferences of the electrode body can also be exemplified. In this case, it is also shown that one of the preferred embodiments is to further connect and fix the metal reinforcing bodies in the vertical direction, which fix the four circumferences with another metal reinforcing body.

[0014]

[Operation] FIG. 1A is a diagram showing an example of the structure of an electrode according to the present invention. The operation of the present invention will be explained based on this figure.

A metal reinforcing body 2 surrounding the periphery of the electrode body 1, which is made of a porous foamed metal body filled with powder of a hydrogen storage alloy, serves to protect the edges and support the electrode. That is, the metal reinforcement functions as an electrode support. This metal reinforcement also has the function of improving the conductivity of the electrode.

Furthermore, by using the second metal reinforcing body 3, the protection of the edge portion, the electrode support function, and the conductivity are further improved. Also, as shown in FIG. 1B, metal reinforcing bodies 4A and B
When used across the electrode body 1, in addition to further improving the above-mentioned performance, it is also possible to suppress expansion of the hydrogen storage electrode due to repeated charging and discharging.

In the case of a prismatic battery, it is necessary to increase the area of the hydrogen storage electrode, but at this time a major problem is how to suppress deformation of the electrode. In such a case, the amount of overall deformation can be kept to a minimum by connecting the metal reinforcing bodies 2 and 3 with each other by spot welding or the like to create a structure in which a plurality of hydrogen storage electrodes are connected and integrated on one plane. Can be done.

As described above, the present invention can firmly suppress the falling off of the alloy due to its structure, and therefore can provide an electrode that maintains a higher discharge capacity for a longer period of time than the conventional one with the same amount of binder.

[0019]

[Examples] Examples of the present invention will be described below.

[0020]

[Example 1] Lanthanum (La) with a purity of 99.5% or more,
Nickel (Ni), manganese (Mn), aluminum (
Al) and cobalt (Co) are mixed in a predetermined ratio and melted in an arc melting furnace to form LaNi4.0Mn0.3Al0.
．． A 3Co0.4 alloy was produced. This alloy was ground in an inert atmosphere to a powder of 300 mesh or less.

Polyvinyl alcohol (hereinafter abbreviated as PVA) as a binder was added to this alloy powder in an amount of 0.4% by weight and 4% by weight based on the alloy, and the foamed metal porous body of the electrode support was pressurized. A metal oxide-hydrogen storage battery was assembled using the filled hydrogen storage electrode body as a negative electrode, a known nickel electrode as a positive electrode, and 200 ml of a caustic potassium aqueous solution with a specific gravity of 1.3 as an electrolyte. These are batteries A and A, respectively.
'.

Next, a hydrogen storage electrode body made of 0.4% by weight PVA was made in the same manner, and a U-shaped nickel metal reinforcing body 2 shown in FIG. A lead was connected to the side of the metal reinforcing body to form a negative electrode, which was combined with the positive electrode to form a metal oxide-hydrogen storage battery in the same manner as Battery A. This is called battery B.

Subsequently, the periphery of the foamed metal porous body 1 itself is reduced in porosity by applying pressure, and 0.4% by weight of P is added.
An alloy powder containing VA was pressurized and filled to produce a hydrogen storage electrode body. A U-shaped nickel metal reinforcing body 2 shown in FIG. 1A is spot welded to the electrode body with the upper side left intact, and a lead is connected to the side edge of this metal reinforcing body to form a negative electrode.
In combination with the above positive electrode, a metal oxide-hydrogen storage battery was constructed. This is called battery C.

[0024] Furthermore, in the same manner as for battery C, PVA0.4
% by weight, metal reinforcing bodies 2 and 3 are spot welded so as to surround the four peripheries, a lead is connected to this metal reinforcing body to form a negative electrode, and combined with the above positive electrode, a metal oxide - A hydrogen storage battery was constructed. This is battery D
shall be.

In addition, a hydrogen storage electrode body containing 0.4% by weight of PVA was prepared in the same manner as in Battery C, metal reinforcing bodies 2 and 3 were spot welded around the four peripheries, and leads were connected to the metal reinforcing bodies. Further, metal reinforcing bodies 4A and 4B were fixed in the vertical direction to serve as a negative electrode, which was combined with the positive electrode to form a metal oxide-hydrogen storage battery. This is called battery E.

Note that three sintered nickel hydroxide sheets with a capacity of 1.8 Ah were used as the positive electrode, and two sheets with a capacity of 1.8 Ah were used as the negative electrode. The size of the electrodes is 36 cm2 for both positive and negative electrodes,
Approximately 7 to 8 g of the negative electrode alloy was used per sheet.

Five batteries each of A, A', B, C, D and E were charged and discharged at a current of 2A. The charging time was 50% longer than the discharging time, and the discharge end voltage was 1.0V. Figure 2 shows the fluctuation range of the battery discharge capacity in this charge/discharge cycle test, and Table 1 shows the weight change of the negative electrode after the charge/discharge cycle.
Shown below.

[0028]

[Table 1] From FIG. 2, even after 600 cycles of charging and discharging for batteries D and E, the capacity decrease was only a few percent, which was small. Furthermore, the range of variation in capacity has hardly widened. On the other hand, battery C
is approximately 5-10% after 600 cycles of charging and discharging.
Although some capacity reduction and variation were observed, this was within a range that would pose no problem for practical use. Furthermore, although the initial capacity of battery B is about 5% lower than that of the others, the capacity decrease after 600 cycles is only 10 to 15%.

On the other hand, battery A has no difference from C, D, and E up to 200 cycles, but as the number of cycles increases, the remaining discharge capacity becomes 2.2 Ah at 400 cycles, which is approximately 40 % capacity loss, the maximum remaining discharge capacity was 2.0% after 600 cycles.
There is a very large fluctuation range up to 2Ah batteries.

It is believed that this difference in life characteristics is caused by a decrease in capacity due to shedding of the hydrogen-absorbing alloy powder, and that a large variation range occurs depending on the speed at which the shedding progresses. The alloy powder is fragmented by repeated charge/discharge cycles, and as this progresses, the alloy powder falls off mainly from the end of the negative electrode. Since the shedding progresses gradually, it results in a large capacity reduction. In this way, B, C
, D and E are found to have extremely superior charge/discharge cycle life compared to A.

[0031] In addition, in order to prevent the alloy powder from falling off, PVA
Although the battery A' with increased capacity has good life characteristics, its initial discharge capacity is about 20% lower than that of the other batteries. That is, it can be seen that B, C, D, and E have extremely superior discharge capacities compared to A'.

[0032] Also, the reason why the initial capacity of battery B is low is as follows.
An example of this is poor contact between the electrode body and the metal porous body. This is clear from the fact that, as in Battery C, when the connection between the electrode body and the metal reinforcing body is made stronger by spot welding, the initial capacity is improved. When the internal resistance of battery B was actually measured, it was found to be higher than that of battery C.

After 400 to 600 cycles of charging and discharging, batteries A to E were disassembled and changes in the weight of the negative electrodes were examined. As shown in Table 1, the results show that battery A showed a significant weight reduction. This weight loss corresponds to the amount of alloy powder shedding and is evidence of the large capacity loss shown in FIG. It was also confirmed that the fallen alloy powder was deposited on the bottom of the container.

On the other hand, as a result of similar disassembly examination of batteries B to E of the present invention, it is found that the weight decrease decreases as the number of metal reinforcing bodies increases, and that in battery E there is almost no weight loss. This also has a good correlation with the results shown in FIG.

The phenomenon seen in battery A is particularly noticeable in prismatic batteries. Furthermore, this tendency is somewhat observed in sealed storage batteries, so the method of the present invention is effective.

[0036]

[Example 2] P was applied to the alloy in the same manner as in Example 1.
12c of hydrogen storage alloy powder containing 0.4% by weight of VA
A hydrogen storage electrode body was prepared by pressurizing and filling an m square foam metal porous body, and this was used as a negative electrode in combination with the above positive electrode to construct a metal oxide-hydrogen storage battery in the same manner as in Example 1. This is called battery F.

Next, the periphery of the 12 cm square foam metal porous body was pressurized to reduce the porosity, and hydrogen storage alloy powder was filled therewith with 0.4% by weight of PVA to produce a hydrogen storage electrode body. did. Further, metal reinforcing bodies 2 and 3 are spot welded around the four circumferences to form a negative electrode, and metal oxide -
A hydrogen storage battery was constructed. This is called battery G.

Next, a 6 cm square hydrogen storage electrode body was made in the same manner as for battery G, and four units formed by spot welding metal reinforcing bodies 2 and 3 were arranged in a square so as to surround the four circumferences of the electrode body. Adjacent metal reinforcing bodies of the unit were spot welded together to form a negative electrode, and a metal oxide-hydrogen storage battery was constructed. This is called battery H.

[0039] Furthermore, a 4 cm square hydrogen storage electrode body was made in the same manner as for battery G, and metal reinforcing bodies 2 and 3 were spot welded to surround the four circumferences of the 9 units, each of which was arranged in a square. Adjacent metal reinforcing bodies were spot welded together to form a negative electrode, and a metal oxide-hydrogen storage battery was constructed. This is called battery I.

Note that two sintered nickel hydroxide sheets with a capacity of 7.2 Ah were used as the positive electrode, and three sheets of sintered nickel hydroxide with a capacity of 7.2 Ah were used as the negative electrode. The size of the electrodes was 144 cm2 for both the positive and negative electrodes, and about 30 g of the alloy for each negative electrode was used.

5A for each battery F, G, H and I
It was charged and discharged with a current of . The charging time was 50% longer than the discharging time, and the discharge end voltage was 1.0V. The discharge capacity of this battery at the 2nd cycle and the 400th cycle, and the 400
Table 2 shows the deformation of the hydrogen storage electrode after 0 cycles.

[0042]

[Table 2] The electrode deforms into a bowl shape by repeated charging and discharging. Therefore, the deformation of the battery is shown as the distance between the surface formed by the four corners of the electrode and the top of the bowl.

As can be seen from Table 2, Batteries H and I of the present invention retain more than 90% of their initial discharge capacity even after 400 cycles, while Batteries F and G both maintain The discharge capacity is less than 80% of the initial capacity.

This is because, in addition to the alloy powder falling off, the hydrogen storage electrode, which has been deformed into a bowl shape due to repeated charging and discharging, presses the positive electrode through the separator, resulting in a micro short circuit mainly in the center of the electrode. caused by. This means that battery F,
This can be easily understood from the large deformation of the hydrogen storage electrode of G. Another factor contributing to this trend is that batteries H and I have an increased number of metal reinforcing bodies, which improves the current collecting ability of the electrodes.

As described above, by increasing the number of units, a comprehensive improvement in electrode characteristics can be expected. However, it must be taken into consideration that this also increases the weight of the electrode itself and causes a decrease in capacity per unit weight.

[0046]

[Effects of the Invention] As described above, according to the present invention, it is possible to provide a highly reliable hydrogen storage electrode with an extended charge/discharge cycle life and stable quality.

[Brief explanation of drawings]

FIG. 1 (A) Diagram showing the electrode configuration of an embodiment of the present invention (B
) Diagram showing the electrode configuration in another embodiment of the present invention

[Figure 2
] Diagram showing the difference in discharge capacity and cycle characteristics of metal oxide-hydrogen storage batteries depending on the presence or absence of metal reinforcement, its fixing method, and amount of binder

[Explanation of symbols]

1 Electrode body 2 Metal reinforcement 3 Metal reinforcement

Claims (15)

[Claims] Claim 1: A hydrogen storage electrode made of an alloy that absorbs and releases hydrogen electrochemically, the electrode comprising a foamed or fibrous metal porous body filled with a paste made of hydrogen storage alloy powder and a binder. A hydrogen storage electrode in which a metal reinforcing body 2 having a U-shaped cross section is fixed to the periphery of a square plate-shaped electrode body 1. 2. The hydrogen storage electrode according to claim 1, wherein a lead is connected to at least one side of the metal reinforcing body. 3. The hydrogen storage electrode according to claim 1, wherein a plurality of hydrogen storage electrodes are connected and integrated on one plane, and a lead is connected to at least one side of the metal reinforcing body. 4. The hydrogen storage electrode according to claim 1, wherein metal reinforcing bodies 2 and 3 are fixed around the four circumferences of the electrode body 1. 5. Metal reinforcing bodies 2 and 3 fix the four circumferences of the electrode body 1, and furthermore, one or more metal reinforcing bodies 4 are provided in at least one direction.
5. The hydrogen storage electrode according to claim 4, wherein A and 4B are connected and fixed. 6. The hydrogen storage electrode according to claim 4, wherein a plurality of hydrogen storage electrodes are connected and integrated on one plane. 7. The hydrogen storage electrode according to claim 4, wherein a lead is connected to at least one arbitrary side of the metal reinforcing bodies 2, 3. 8. The peripheral part of the square plate-shaped electrode body 1 is formed by filling a paste made of hydrogen-absorbing alloy powder and a binder into a foamed or fibrous metal porous body whose peripheral part has a low porosity. A hydrogen storage electrode fixed with a U-shaped metal reinforcing body 2. 9. The hydrogen storage electrode according to claim 8, wherein a lead is connected to at least one side of the metal reinforcing body. 10. The hydrogen storage electrode according to claim 8, wherein a plurality of hydrogen storage electrodes are connected and integrated on one plane, and a lead is connected to at least one side of the metal reinforcing body. 11. The hydrogen storage electrode according to claim 8, wherein metal reinforcing bodies 2 and 3 are fixed around the four circumferences of the electrode body 1. 12. The hydrogen storage electrode according to claim 11, wherein the metal reinforcing bodies 2 and 3 fix the four circumferences of the electrode body 1, and furthermore, one or more metal reinforcing bodies 4A and 4B are connected and fixed in at least one direction. . 13. The hydrogen storage electrode according to claim 11 or 12, wherein a plurality of hydrogen storage electrodes are connected and integrated on one plane. 14. Claims 11, 12 and 1, wherein a lead is connected to at least one arbitrary side of the metal reinforcing bodies 2, 3.
3. The hydrogen storage electrode according to any one of 3. [Claim 15] A hydrogen storage device in which a hydrogen storage alloy is filled in a foamed or fibrous metal porous body, the surrounding area and a metal reinforcing body are integrated under pressure or fixed by spot welding, and then leads are connected. Electrode manufacturing method.