JP3028622B2 - Method for producing hydrogen storage electrode and metal oxide-hydrogen storage battery - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a metal oxide-hydrogen storage battery having a negative electrode as a negative electrode for storing and removing hydrogen reversibly in an electrolyte.

[0002]

2. Description of the Related Art A hydrogen storage electrode using an alloy that reversibly stores and desorbs hydrogen is generally manufactured by the following method. In other words, various metals are weighed to match the alloy composition, and a mixture of various metals is melted by high-temperature arc discharge using an arc melting furnace or the like to produce an alloy having an intended composition, and this alloy is further pulverized. Then 300
A powder having a particle size equal to or smaller than the mesh is used.

[0003] This powder is kneaded with a binder or the like so as to be in a uniform state, and is made into a paste. For example, after pressure-filled or coated on an electrode support such as a foamed metal porous body or a punching metal, It is dried to form a hydrogen storage electrode body. The metal oxide-hydrogen storage battery is configured by combining this hydrogen storage electrode with a negative electrode and a known nickel positive electrode or the like via a separator.

[0004]

The preferred alloy for the hydrogen storage electrode is produced by an arc melting method or the like. However, the homogeneity of the alloy is important, and it is necessary to produce an alloy in which this heterogeneity is eliminated as much as possible. is there. However, since some of these alloys contain metals that dissolve in alkaline aqueous solutions, if they are not completely alloyed, some of these metals will dissolve in the alkaline solution that is the electrolyte. I do.
Particularly when the temperature becomes high, the dissolution rate and the dissolution amount increase. When such a hydrogen storage electrode is used as a negative electrode to form a battery system rich in an electrolyte, for example, a stationary metal oxide-hydrogen storage battery, as the charge / discharge cycle is repeated, the above-mentioned metal ions are added to the negative electrode in the electrolyte during discharge. And the metal ions are oxidized and deposited, or deposited in a metallic state due to solubility. Many of these fine precipitates adhere to the separator and cause deterioration of the insulation of the separator. Due to this phenomenon, a minute short circuit occurs in the battery, causing a reduction in capacity.

Accordingly, it is an object of the present invention to provide a metal oxide-hydrogen storage battery having a long life and a stable quality by preventing the above-mentioned phenomenon from occurring during a charge / discharge cycle.

[0006]

SUMMARY OF THE INVENTION The present invention aims at preventing the occurrence of a micro short-circuit which causes a reduction in capacity and, in order to suppress the deposition of the above-mentioned metal or metal oxide, a complexing agent, preferably an alkali-resistant one. A battery having a high complex formation constant with the metal in a high alkali region, for example, an ethylenediamine derivative having a carboxylic acid as a functional group dissolved and contained in a battery.

[0007]

The following three methods can be used to dissolve and contain the above-mentioned complexing agent in the battery. First, there is a method in which a complexing agent relating to a solvent of the paste is contained when forming a negative electrode by forming an alloy powder into a paste. At this time, the amount of the complexing agent in the paste solvent is desirably near the saturation amount,
From the viewpoint of increasing the saturation amount, the pH of the solvent is preferably high.

Second, there is a method in which the complexing agent is dissolved and contained in the electrolytic solution. At this time, the amount of the complexing agent dissolved in the electrolytic solution needs to consider the balance between the effect and the battery performance itself.

Third, there is a method in which at least one of the positive electrode, the negative electrode and the separator is impregnated with an aqueous solution of the complexing agent prior to the construction of the battery. At this time, the amount of the complexing agent in the aqueous solution is desirably near the saturation amount as in the first case, and in order to increase the saturation amount, the pH of the solvent is preferably high.

Although the above three methods are effective even if performed independently, it is shown that performing two or all three methods in combination is a preferable embodiment for further improving the effect.

According to these methods, a metal which does not dissolve in the electrolytic solution during a charge / discharge cycle immediately undergoes a complex formation reaction with a complexing agent after dissolution. When the solubility of the reaction product is low, an insulating precipitate is formed, and the metal ions are removed out of the battery reaction system. When the solubility of the reaction product is high, the formed complex ion is stable, and the metal ion is less likely to undergo electrochemical oxidation or reduction, and the precipitation is suppressed. Detoxifying the interfering ion species in this way is called masking. According to the effect, in the present invention, even if the charge / discharge cycle is repeated, the extent to which the metal or metal oxide precipitates on the separator is significantly reduced, and the short circuit phenomenon is prevented. It can be significantly reduced.

[0012]

Embodiments of the present invention will be described below.

(Example 1) Lanthanum (La), nickel (Ni), manganese (Mn), aluminum (Al), and cobalt (Co) having a purity of 99.5% or more were mixed at a predetermined ratio, and an arc melting furnace was used. Dissolved in LaNi _4.0 Mn _0.3
An Al _0.3 Co _0.4 alloy was produced. This alloy was pulverized in an inert atmosphere to obtain a powder of 300 mesh or less. A polymer binder is added to the alloy powder, and the foamed metal porous body of the electrode support is pressurized and filled to form a hydrogen storage electrode. A known nickel electrode is used as a positive electrode, and a caustic potassium aqueous solution having a specific gravity of 1.3 is used. A metal oxide-hydrogen storage battery was assembled using 200 ml.
This is called battery A.

Next, a hydrogen storage electrode is formed in the same manner,
Combined with the positive electrode. A battery A was prepared by dissolving 7 g of EDTA, a tetraacetic acid derivative of ethylenediamine, in an electrolytic solution.
A metal oxide-hydrogen storage battery was constructed in the same manner as described above. This is called battery B.

Subsequently, a hydrogen storage electrode was prepared in the same manner and impregnated with a saturated aqueous solution of EDTA (pH 12) for one day, and then combined with the positive electrode to form a metal oxide-hydrogen storage battery in the same manner as Battery A. . This is called battery C.

Further, a hydrogen storage electrode was prepared in the same manner, and impregnated with a saturated aqueous solution of EDTA (pH 12) for one day, combined with the above positive electrode, and dissolved 7 g of ethylenediaminetetraacetic acid (EDTA) in the electrolyte. A metal oxide-hydrogen storage battery was constructed in the same manner as Battery A. This is called battery D.

Further, the above-mentioned hydrogen storage alloy powder is kneaded together with a polymer binder by using a saturated aqueous solution of EDTA (pH 12) to form a paste, which is then pressed and filled into a foamed metal porous body of an electrode support. Thus, a hydrogen storage electrode was produced. Using this electrode as a negative electrode, a metal oxide-hydrogen storage battery was constructed in the same manner as batteries A, B, C and D. These are referred to as batteries E, F, G and H, respectively.

The positive electrode used was two sheets having a capacity of 1.8 Ah, and the negative electrode was used three sheets having a capacity of 1.8 Ah. The size of the electrode was 36 cm ² for both the positive and negative electrodes, and the alloy of the negative electrode used was about 7 to 8 g per sheet.

Each of the batteries A to H was charged and discharged at a current of 2 A. The charging time was 50% excess of the discharging time, and the discharge end voltage was 1.0 V. Changes in the discharge capacity of the battery in this charge / discharge cycle test are shown in (Table 1).

[0020]

[Table 1]

From Table 1, it can be seen that batteries B, D, F, G and H
However, even when charge and discharge are repeated for 600 cycles, the capacity decrease is as small as about several percent. On the other hand, in the batteries C and E, when the charge and discharge were repeated for 600 cycles, a capacity reduction of about 5 to 10% was observed, but it was within a range in which there was no problem in practical use. On the other hand, the battery A does not differ from the batteries B to H up to 200 cycles, but the capacity decreases as the number of cycles increases, and the remaining discharge capacity becomes 40% at 600 cycles.
To some extent. Accordingly, it can be seen that the batteries B to H have much better charge / discharge cycle life than the battery A.

This difference in life characteristics is attributed to the fact that a part of the metal contained in the hydrogen storage electrode is dissolved, and the dissolved metal precipitates again on the surface or inside of the separator. It is considered that the sexual function was lost, the short circuit was reduced, and the capacity was reduced. By repeating the charge / discharge cycle, the metal is gradually dissolved, the amount of the metal or metal oxide deposited on the separator is increased, and a minute short circuit is caused, leading to a large capacity reduction. Here, when the battery A after the test is disassembled and inspected, it is easy to judge from the fact that black precipitates adhere to the surface and inside of the separator.

On the other hand, in the battery of the present invention, the metal in which the complexing agent is dissolved is masked, so that precipitation of these metals hardly occurs, and the capacity is hardly reduced. This is apparent from the results of the disassembly and examination of the batteries B to H of the present invention after the test in the same manner as the battery A. As a result, there is almost no deposit on the separator surface, and no short-circuit phenomenon is found. is there. Further, from the difference in capacity reduction between the batteries B to H, it is considered that the masking effect correlates not only with the vicinity of the electrode but also with the total amount of complexing agent ions present in the electrolytic solution.

The phenomenon seen in the battery A is particularly prominent as the amount of the electrolyte is increased. This is because when the amount of the electrolytic solution increases, the dissolution rate of the metal in the electrolytic solution increases.
Further, this tendency is slightly observed even in a sealed storage battery having a small amount of electrolyte, so that the method of the present invention is effective.

Example 2 A polymer binder was added to the hydrogen-absorbing alloy powder produced in the same manner as in Example 1, and the foamed metal porous body of the electrode support was pressed and filled to form a hydrogen-absorbing electrode. ,
Combined with a known nickel positive electrode. The amount of EDTA was changed as shown in Table 2 and dissolved in 200 ml of the electrolytic solution, whereby a metal oxide-hydrogen storage battery was constructed in the same manner as in Example 1.

Each of the batteries was charged and discharged at a current of 2 A. Charge time is 50% excess of discharge time,
The discharge end voltage was 1.0 V. The fluctuation of the discharge capacity of this battery in this charge / discharge cycle test is also shown in (Table 2).

[0027]

[Table 2]

As can be seen from (Table 2), batteries J, K,
L, B and M are 80% of the initial value after 600 cycles
Although the above discharge capacity is maintained, A and I are the initial 7
The discharge capacity is 0% or less. This indicates that the effect of masking the dissolved metal ions decreases as the amount of the complexing agent EDTA decreases. The initial capacity of the battery N is low, which indicates that when the amount of the complexing agent added is too large, the capacity is reduced due to a change in pH or the like. Therefore, when EDTA is used as a complexing agent, the addition amount of alloy 1 must be set to achieve the effect of the present invention.
It is desirable that the amount be 10 ^-6 to 10 ^-2 mol per g. This means that the complex formation reaction is almost metal: complexing agent = 1: 1 to 6
Is applied for all complexing agents.

[0029]

As described above, according to the present invention, it is possible to provide a highly reliable metal oxide-hydrogen storage battery having a stable charge / discharge cycle life, stable quality.

Continuation of the front page (56) References JP-A-61-161659 (JP, A) JP-A-4-82161 (JP, A) Patent 2871065 (JP, B2) (58) Fields investigated (Int. Cl. ⁷⁾ H01M 2/24-2/26 H01M 10/24-10/30 H01M 10/34

Claims (12)

(57) [Claims] 1. An electrode manufacturing method comprising: an electrode containing a hydrogen storage alloy powder that electrochemically stores and releases hydrogen and a binder , and an acid dissociation type complexing agent capable of forming a chelate complex with a transition metal. Hydrogen storage electrode contained by adding
(However, if the binder contains polyethylene oxide,
Excluding) manufacturing method. 2. The method according to claim 1, wherein an ethylenediamine derivative having a carboxylic acid as a functional group is used as the complexing agent. 3. A hydrogen-containing hydrogen-absorbing alloy powder comprising a step of kneading a paste with a hydrogen-absorbing alloy powder kneaded with a binder using an aqueous solution of an acid dissociation type complexing agent capable of forming a chelate complex with a transition metal as a solvent. Manufacturing method of occlusion electrode. 4. The method according to claim 3, wherein an ethylenediamine derivative having a carboxylic acid as a possible group is used as the complexing agent. 5. A method for producing a metal oxide-hydrogen storage battery, comprising using a positive electrode comprising at least one metal oxide, an electrolytic solution, and the hydrogen storage electrode according to claim 1 or 2 as a negative electrode. 6. An alkaline storage battery comprising a positive electrode made of at least one metal oxide, a negative electrode made of a hydrogen storage alloy electrochemically storing and releasing hydrogen, a separator, and an electrolytic solution, wherein the positive electrode and the negative electrode are used. And, after impregnating at least one of the separators with an aqueous solution of an acid dissociation complexing agent capable of forming a chelate complex with a transition metal and drying the mixture, a metal oxide-hydrogen storage battery having a battery configuration by combining these is used. Manufacturing method. 7. The method for producing a metal oxide-hydrogen storage battery according to claim 6, wherein an ethylenediamine derivative having a carboxylic acid as a functional group is used as the complexing agent. 8. The metal oxide according to claim 6, wherein the hydrogen storage electrode according to claim 1 or 2 is used as a negative electrode.
Manufacturing method of hydrogen storage battery. 9. An alkaline storage battery comprising a positive electrode comprising at least one metal oxide, a negative electrode comprising a hydrogen storage electrode according to claim 1 or 2, a separator and an electrolyte, wherein a transition metal is contained in the electrolyte. A method for producing a metal oxide-hydrogen storage battery, comprising dissolving an acid dissociation complexing agent capable of forming a chelate complex with an acid. 10. The production of a metal oxide-hydrogen storage battery according to claim 6, wherein an acid dissociation type complexing agent capable of forming a chelate complex with a transition metal is dissolved in the electrolytic solution. Law. 11. The method for producing a metal oxide-hydrogen storage battery according to claim 9, wherein an ethylenediamine derivative having a carboxylic acid as a functional group is used as the complexing agent. 12. The complexing agent is completely dissolved in the electrolytic solution, and 10 ^-6 to 10 ^-2 mol per 1 g of the hydrogen storage alloy.
The method for producing a metal oxide-hydrogen storage battery according to claim 11, wherein