JPH06302319A - Manufacture of hydrogen storage electrode and metal oxide-hydrogen storage battery having electrode - Google Patents

Abstract

PURPOSE:To obtain a metal oxide-hydrogen storage battery which has higher capacity than that using a sheet type electrode by eliminating the expansion of an electrode producing after immerssion in an alkaline solution to enhance the current collecting capability within the electrode. CONSTITUTION:An electrode element assembled by holding each porous metal base plate which serves as a current collector 3a, 3b, 3c and also acts as an electrode supporter between two hydrogen storage alloy sheets 1a, 1b formed by kneading a mixture of hydrogen storge alloy powder and a fluororesin binder used as a binder, and by press-molding them. The electrode element is then immersed in an alkaline aqueous solution for washing and dried, and pressed again with a roller press or the like or press-united by sandwiching the electrode element between two metal base plates to prepare a sheet type electrode. A metal oxide-hydrogen storage battery is fabricated with this electrode.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a hydrogen storage electrode capable of reversibly storing and releasing hydrogen in an electrolytic solution, and a metal oxide-hydrogen storage battery using this electrode as a negative electrode.

[0002]

2. Description of the Related Art A hydrogen absorbing alloy powder that reversibly absorbs and desorbs hydrogen, an alloy sheet formed by kneading a fluororesin as a binder, and a current collector having a two-dimensional porous structure such as punching metal. A hydrogen storage electrode composed of a body (hereinafter abbreviated as a sheet electrode) may be less expensive than a hydrogen storage electrode having a foamed metal porous body as a current collector (hereinafter abbreviated as a foam electrode). have.

This sheet electrode was generally manufactured by the following method. That is, various metals are weighed to suit the alloy composition, a mixture of various metals is melted by high temperature arc discharge using an arc melting furnace, etc. to produce an alloy having a desired composition, and the alloy is further crushed. Then 3
The powder has a particle size of 00 mesh or less. This powder is kneaded with a binder or the like so as to be in a uniform state, and formed into a sheet. Then, the sheet-like kneaded product was pressed and integrated with an electrode support such as punching metal to form a hydrogen storage electrode.

In this hydrogen storage electrode body, an appropriate amount of a fluororesin which is a binder is added to prevent the constituent alloy powders from falling off. Moreover, the electrode body is pressure-molded by a roller press. The binding force between the components of the electrode was made stronger. However, since the fluororesin, which is the binder, is highly hydrophobic, the sheet-type electrode is immersed in an aqueous alkaline solution (hereinafter abbreviated as alkaline immersion) prior to battery production.
However, with the elution of soluble components in the alloy that occurs during immersion,
The step of removing the excess binder (fluororesin) on the electrode to increase the hydrophilicity of the electrode has been adopted.

[0005]

However, the discharge capacity of the sheet-type electrode obtained through the above-mentioned steps is higher than that of a known foam-type electrode produced by using the same amount of alloy powder.
It becomes about 10 to 20% smaller from the beginning. This is because the alloy sheet absorbs the alkaline aqueous solution during the immersion in alkali and expands, so that the connection between the alloy sheet and the current collector is deteriorated, and such an electrode is used as a negative electrode of a metal oxide-hydrogen storage battery. It was difficult to put it to practical use. In other words, the problem with the conventional sheet-type electrode is that it has been used for battery fabrication in a state where the electrode expanded after immersion in alkali.

The present invention solves this conventional problem,
An object of the present invention is to provide a method for producing a sheet-type electrode having a good connection between an alloy sheet and a current collector, and further to realize a high-capacity metal oxide-hydrogen storage battery including the sheet-type electrode as a negative electrode. Is.

[0007]

In order to solve the above problems, the present invention is an alloy sheet formed by kneading a fluororesin as a binder with a hydrogen storage alloy powder that electrochemically stores and releases hydrogen. The electrode body, which is press-integrated by sandwiching one porous metal substrate that also serves as a collector and an electrode support with two sheets, is immersed in an alkaline aqueous solution, washed and dried, and then pressed again by a roller press or the like. Alternatively, a hydrogen storage electrode is manufactured by a method in which an electrode body is sandwiched between two porous metal substrates and integrated under pressure, and a high capacity metal oxide-hydrogen storage battery is manufactured by using the sheet type electrode as a negative electrode. It is provided.

[0008]

According to the present invention, as described above, the electrode body is immersed in an alkali and then re-pressurized to the electrode body. By this re-pressurization, the electrode body is present in the electrode expanded by the alkali immersion. The holes that are the traces of the alkaline aqueous solution are crushed. Therefore, after re-pressurization, the connection between the alloy sheet and the current collector is improved compared to before re-pressurization, the electrode reaction is performed smoothly, and it has the same energy density and life characteristics as the foamed electrode. Like

The present invention has established a method of manufacturing a sheet type electrode having such an advantage by a simple means of repressurization, and further, a metal oxide-hydrogen storage battery provided with this sheet type electrode. Can have a higher capacity than a battery having a conventional sheet electrode.

[0010]

EXAMPLES Examples of the present invention will be described below.

Example 1 A misch metal (Mm) containing 20% by weight of lanthanum (La) having a purity of 99.5% or more,
Nickel (Ni), manganese (Mn), aluminum (Al), and cobalt (Co) are mixed at a predetermined ratio and melted in an arc melting furnace to obtain MmNi _4.0 Mn _0.2 Al _0.4 C.
o _0.4 alloy was produced. This alloy was crushed in an inert atmosphere to obtain a powder having a particle size of 300 mesh or less. Polytetrafluoroethylene (PTFE), which is a fluororesin, was added to the alloy powder 8 g (corresponding to 2 Ah), and
Two alloy sheets 1a and 1b were manufactured by adding the weight%.
A current collector (punching metal) 3a to which the lead 2 was attached was sandwiched between the two alloy sheets, and pressure integration was performed by a roller press method to form an electrode body. An aqueous solution of potassium hydroxide (hydroxide ion concentration 6 mol / l, 80
The sheet-type electrode was immersed in an alkali solution for 12 hours (° C.), washed with water, dried, and again pressed by a roller press to be B. Further, the sheet-type electrode having the structure shown in FIG. 1 in which the current collectors 3b and 3c are arranged on both outer sides of the electrode body after being washed and dried and which is integrated under pressure is designated as C. In addition, as a comparative example, a sheet-type electrode which is used as it is without pressurizing the electrode body after being washed and dried is referred to as A.

Further, to 8 g (corresponding to 2 Ah) of the same alloy powder as in the sheet type electrodes A to C, PTFE and carbon fine powder as a conductive material were added in varying amounts as shown in Table 1, and the hydrophilic property was obtained. Sheet electrodes of D to L having the same structure as C were produced using a plurality of types of alloy sheets 1a and 1b having different compositions to which 0.3 wt% of carboxymethyl cellulose (CMC) which is a polymer was added.

[0013]

[Table 1]

The negative electrodes A to A produced as described above
Insert one sheet-type electrode of L into a bag-shaped separator and combine it with two known nickel positive electrodes (corresponding to 2 Ah) to form an electrode group. 200 ml of an aqueous potassium hydroxide solution with a specific gravity of 1.25 is used as an electrolytic solution. As a result, nickel-hydrogen storage batteries A to L were assembled.

Each of these batteries was charged and discharged at a constant current of 1A. The charging time was set to 2.4 hours, the final discharge voltage was set to 1 V, and a 300-cycle charge / discharge test was performed. The change in discharge capacity per alloy weight of the battery of this example is shown in Table 1 together with the result of comparative battery A.

As shown in Table 1, the recharged battery B of this example, compared with the comparative battery A which was not repressurized after the alkali immersion, was about 4% in 2 cycles and 300 cycles. In, a capacity increase of about 8% was observed. This is because the re-pressurization crushed the pores that were the traces of the alkaline aqueous solution that were present in the alloy sheet, and improved the connection (current collection) between the alloy powder in the alloy sheet and the current collector. Actually, when the resistance value between the alloy sheet of the battery A and the battery B and the lead was measured, the value of the battery A was 10 mΩ, whereas the value of the battery B was about 3 mΩ, and the current collecting property was remarkably improved. Was.

Further, in the battery C in which punching metal is applied to both outer sides of the electrode body at the time of repressurization,
Furthermore, a capacity increase of about 8% was observed in two cycles. This is because by disposing current collectors on both outer sides of the electrode during re-pressurization, in addition to eliminating traces of the alkaline aqueous solution, the current collector in the electrode was further improved. The resistance value between them was about 1 mΩ, which was lower than that of the battery B.

Regarding the amount of PTFE as a binder, the battery C having an added amount of 0.5% by weight with respect to the alloy has a capacity of 2 cycles which is better than other batteries, but 180 mAh after 300 cycles. / Discharge capacity decreased to about alloy g. In addition, the discharge capacity of the battery G with the addition amount of 20% by weight remained low from the initial stage. When these two batteries were disassembled after 300 cycles, it was confirmed that the alloy sheet of the negative electrode of battery C was about to peel from the current collector. Further, the contact angle of the negative electrode of the battery G with the water droplet was significantly larger than that of the other batteries. That is, it is considered that the battery reaction via the electrolytic solution was not smoothly performed on the surface of the sheet electrode. Therefore, the amount of PTFE added is
It is preferably in the range of 1 to 10% by weight with respect to the alloy. Although PTFE was used as the fluororesin in this example, tetrafluoroethylene-hexafluoropropylene copolymer, polyhexafluoropropylene, or the like may be used instead.

Regarding the addition of carbon as a conductive material,
It was found that the discharge capacity of the battery having a larger amount of addition was larger. However, when the addition amount is 20% by weight, when the carbon is added to the weight of the hydrogen storage alloy and converted, for example, it becomes 240 mAh / alloy g at 300 cycles,
The superiority of carbon addition can no longer be seen. Therefore, considering the discharge capacity per unit weight of the electrode, it is desirable that the amount of the conductive material added be within the range of 0.1 to 10% by weight.
Although carbon is used as the alkali-resistant conductive material in the present embodiment, one or more selected from platinum, silver, palladium, nickel, cobalt and the like may be added.
The same effect can be obtained.

Regarding the addition of CMC, which is a hydrophilic polymer (Battery L), the affinity for the electrolytic solution is higher than that when only PTFE, which is the hydrophobic binder, is used, and therefore the electrolytic solution is used. The battery reaction was easily performed for lubrication, and therefore, the discharge capacity was extended by about 3 to 4% as compared with the battery D using only PTFE. It was found that the combined use of the fluororesin-based binder having a strong binding force and the hydrophilic binder in this manner is effective in improving the battery characteristics. Although CMC was used as the hydrophilic binder in this example, polyvinyl alcohol, polyethylene oxide or the like may be used instead.

(Example 2) 8 g of the same alloy powder as in Example 1
5% by weight of PTFE was added to (corresponding to 2 Ah) to prepare two alloy sheets 1a and 1b. This alloy sheet 2
The current collector 3a was sandwiched between the sheets and pressure-integrated by a roller press method to obtain an electrode body. As shown in Table 2, this electrode body was immersed in an aqueous solution of potassium hydroxide for 12 hours (alkaline immersion) while changing the hydroxide ion concentration and temperature, washed with water and dried. As a result, two punching metals 3b and 3c were arranged, and they were pressure-integrated by a roller press method to prepare sheet electrodes M to R similar to the battery C of Example 1.

[0022]

[Table 2]

The same nickel-hydrogen storage batteries M-R as in Example 1 were assembled using the sheet-type electrodes produced as described above. Each one of these was charged and discharged at a constant current of 1A. The charging time was set to 2.4 hours, the final discharge voltage was set to 1 V, and a 300-cycle charge / discharge test was performed. The change in discharge capacity of the battery per alloy weight in this test is also shown in Table 2.

Regarding the hydroxide ion concentration of the aqueous potassium hydroxide solution, the batteries C and N (hydroxide ion concentration = 1,
Battery M (hydroxide ion concentration = 6 mol / l)
The discharge capacity of 0.1 mol / l) was remarkably small. This is because if the hydroxide ion concentration is too low, elution of the soluble components in the alloy will be insufficient, and along with this, the excess fluororesin on the electrode surface will be insufficiently removed, making the electrode sufficiently hydrophilic. Probably because it was not done. Therefore, it is desirable that the hydroxide ion concentration used for the alkali immersion is 1 mol / l or more.

Regarding the temperature condition of the alkali immersion, the battery O was compared with the batteries P, C, Q (60, 80, 90 ° C.).
The discharge capacity at (45 ° C.) was remarkably small. However, like the battery M, if the temperature is too low, the soluble components in the alloy will be insufficiently eluted, so that the sheet electrode is sufficiently hydrophilic. It is thought that it was not converted. Battery R (95
The decrease in capacity at (° C.) Was large, but this is considered to be because the elution of the alloy components excessively occurred at high temperatures and the deterioration of the alloy proceeded quickly. Therefore, it is desirable that the temperature of the potassium hydroxide aqueous solution used for the alkali immersion is in the range of 60 to 90 ° C.

[0026]

As described above, according to the present invention, since the sheet type electrode has a higher current collecting property than the conventional one, the electrode reaction occurs smoothly, and a high capacity hydrogen storage electrode and a metal oxide provided with this electrode are obtained. A thing-hydrogen storage battery can be provided.

[Brief description of drawings]

FIG. 1 is a schematic view of an electrode according to an embodiment of the present invention.

[Explanation of symbols]

 1a Alloy sheet 1b Alloy sheet 2 Lead 3a Current collector 3b Current collector 3c Current collector

Claims (8)

[Claims] 1. Two alloy sheets formed by kneading a fluorine-containing resin as a binder into a hydrogen-absorbing alloy powder that electrochemically absorbs and releases hydrogen, and porosity that also serves as a current collector and an electrode support. A method of manufacturing a hydrogen storage electrode, wherein one metal substrate is alternately combined, wherein one porous metal substrate is sandwiched between the two alloy sheets to form an electrode body, which is then immersed in an alkaline aqueous solution. A method of manufacturing a hydrogen storage electrode, which comprises washing and drying, and then repressurizing the electrode body. 2. Two alloy sheets formed by kneading a hydrogen storage alloy powder that electrochemically stores and releases hydrogen with a fluororesin as a binder, and porosity that also serves as a current collector and an electrode support. A method of manufacturing a hydrogen storage electrode, wherein one metal substrate is alternately combined, wherein one porous metal substrate is sandwiched between the two alloy sheets to form an electrode body, which is then immersed in an alkaline aqueous solution. A method for producing a hydrogen storage electrode, comprising washing and drying, and then pressing and integrating the electrode body with two porous metal substrates. 3. The method for producing a hydrogen storage electrode according to claim 1, wherein the fluororesin is 1 to 10% by weight based on the hydrogen storage alloy powder. 4. The method for producing a hydrogen storage electrode according to claim 1, wherein 0.1-10 wt% of an alkali-resistant conductive material is added to the hydrogen storage alloy powder during the kneading step. 5. The method for producing a hydrogen storage electrode according to claim 1, wherein a hydrophilic polymer is added during the kneading step. 6. The method for producing a hydrogen storage electrode according to claim 1, wherein a hydroxide ion concentration of the alkaline aqueous solution is 1 mol / l or more. 7. The temperature of the alkaline aqueous solution is 60 to 90.
The method for producing a hydrogen storage electrode according to claim 1 or 2, which is at a temperature of ° C. 8. A metal oxide-hydrogen storage battery using the hydrogen storage electrode according to claim 1 or 2 as a negative electrode.