JPH08241712A - Alkaline storage battery and its manufacture - Google Patents

Abstract

PURPOSE: To provide an alkaline storage battery having good conservative characteristic by use of a hydrogen storage alloy negative electrode having a relatively small Co quantity contained in the alloy is used. CONSTITUTION: In an alkaline storage battery consisting of a positive electrode, a negative electrode containing a hydrogen storage alloy as main constituting material, a separator, and an alkaline electrolyte, a hydrogen storage alloy negative electrode alloy is dipped in an alkaline aqueous solution having cobalt element dissolved therein in the state of powder or electrode plate at the formation of the hydrogen storage alloy negative electrode. Thus, an alkaline storage battery in which the eluted concentration of Mn per appearant surface area of the negative electrode is less than 0.2wt.%/m<2> when the negative electrode is dipped in 200ml of a caustic potash aqueous solution with a specific gravity of 1.30 and at 80 deg.C four 36 minutes is constituted.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an alkaline storage battery using a hydrogen storage alloy capable of electrochemically storing and releasing hydrogen as a negative electrode and a method for producing the same.

[0002]

2. Description of the Related Art A nickel-hydrogen storage battery using a hydrogen storage alloy that can store and release a large amount of hydrogen, which is an active material, as an electrode material has a higher energy density than a nickel-cadmium storage battery and has the same reliability. In recent years, the use as a power source for portable devices has rapidly increased because of its possession.

As a negative electrode material for nickel-hydrogen storage batteries, there has been proposed one in which the Ni portion of MmNi ₅ (Mm is a mixture of rare earth elements) is replaced with a metal such as Cu, Co, Mn, Fe or Al. Among these metals, M
A small amount of n can lower the equilibrium pressure at the time of hydrogen absorption and desorption, and plays an important role. On the other hand, however, Mn has a higher vapor pressure than other metals, and evaporates during melting of the alloy to segregate near the surface of the alloy. Therefore, when Mn is contained, it is difficult to form a uniform alloy. In the negative electrode using such a hydrogen storage alloy having poor homogeneity, unalloyed metal is likely to be eluted in the alkaline electrolyte, and the alloy capacity and charge / discharge reaction rate are likely to decrease.
Some metals such as Mn, Al and rare earth elements which are easily dissolved in alkali are precipitated as oxides or hydroxides, and most of these fine precipitates adhere to the negative electrode and the separator. For example, when the deposit has no conductivity like MnO ₂ , the discharge capacity is lowered by causing an increase in internal resistance of the battery, and conversely, when a substance having conductivity is deposited on the separator. Causes a short circuit between the positive electrode and the negative electrode. Therefore, the alkaline storage battery using such a negative electrode has a problem in storage characteristics. Moreover, this phenomenon becomes remarkable especially at high temperatures.

In order to overcome the above drawbacks, Co
Has been added. C in the hydrogen storage alloy in the battery
Since o dissolves in the alkaline electrolyte in the form of cobalt complex ion and is reduced to a metal again during charging, it functions as a conductive network between alloy particles. Further, the higher the Co content in the alloy, the more the corrosion of the hydrogen storage alloy is suppressed.
Therefore, conventionally, by substituting a part of Ni in the hydrogen storage alloy composition with Co, elution and oxidation of soluble components such as Mn in the alloy have been suppressed, and the battery characteristics have been stabilized. However, the replacement of the alloy with Ni by Co tends to lower the capacity density of the hydrogen storage alloy and also lower the discharge characteristics, and since Co is expensive, it is preferable that the replacement amount be as small as possible.

In order to solve the problem of dissolution / precipitation of hydrogen storage alloys by a method other than Co substitution, JP-A-61-6406
No. 9 proposes coating the surface of a hydrogen storage alloy with Ni metal having corrosion resistance. In addition, JP-A-63-
In 175339, it is proposed that the alloy is immersed in a high temperature alkaline aqueous solution to form an oxide film on the surface of the alloy to improve the corrosion resistance.

[0006]

However, when electroless plating of Ni or the like is applied to the surface of the hydrogen storage alloy, a large amount of plating must be applied to improve the corrosion resistance.
As a result, the proportion of substances other than hydrogen storage alloys increases, which impedes the high energy density, which is one of the advantages of nickel-hydrogen storage batteries. Further, the treatment itself is very complicated and time-consuming, and it is difficult to treat a large amount of alloy at once.

The following simple immersion treatment in an alkaline aqueous solution has the effect of removing the unstable leaching component in the electrolytic solution and improves the corrosion resistance of the alloy by reprecipitating the dissolved Co component. It was effective in alloys with high content, but did not have sufficient effect in alloys with relatively low Co content.

The present invention solves the above-mentioned conventional problems. Even when a hydrogen storage alloy negative electrode containing a relatively small amount of Co contained in the alloy is used, the internal resistance during storage is unlikely to rise and the storage characteristics are good. It is intended to provide a stable alkaline storage battery.

[0009]

In order to solve this problem, the alkaline storage battery of the present invention has a positive electrode containing a metal oxide as a main constituent material and an active material, hydrogen, which is occluded and released electrochemically. Of a negative electrode containing a hydrogen storage alloy as a main constituent material, an alkaline electrolyte, and a separator. The negative electrode is apparently immersed in 200 ml of a caustic potash aqueous solution having a specific gravity of 1.30 at 80 ° C. for 30 minutes. Elution concentration of Mn per surface area is 0.2% by weight /
It is characterized by being m ² or less.

Further, in the method for producing an alkaline storage battery of the present invention, in order to obtain the alkaline storage battery, when forming the hydrogen storage alloy negative electrode, the cobalt element is dissolved in a powder state of the hydrogen storage alloy or in a state of being formed as a negative electrode plate. It is characterized by including a step of immersing in the alkaline aqueous solution.

[0011]

With the above structure, even if a hydrogen storage alloy having a relatively low Co content is used, it is immersed in a high-temperature alkaline treatment aqueous solution to remove unstable leaching components in the electrolytic solution, and to further treat the aqueous solution. By depositing Co ions in the hydrogen storage alloy surface as cobalt oxide, which has excellent corrosion resistance, the elution of Mn and other alkaline electrolytes is suppressed, and the internal resistance of the battery does not rise easily during storage, which improves storage characteristics. It is possible to provide an excellent alkaline storage battery.

[0012]

【Example】

(Example 1) The details of the present invention will be described by taking a nickel-hydrogen storage battery as an example.

As an alloy having a low Co content, MmNi
An alloy having a composition formula of _4.1 Mn _0.4 Al _0.3 Co _0.2 was prepared.

Mm (Misch metal), which is a mixture of rare earth metals, and Ni, Mn, Al, and Co samples were weighed and mixed so as to have the above composition ratio. This sample was placed in an arc melting furnace and evacuated to 10 ^-4 to 10 ^-5 torr, then arc-discharged in an argon gas atmosphere, overheated and melted, and then cooled to prepare an alloy. In order to improve the homogeneity of this alloy, heat treatment was performed for 6 hours in an atmosphere of argon gas at 1050 ° C. Then, this alloy was roughly crushed and then crushed by a ball mill to obtain a hydrogen storage alloy powder a having an average particle diameter of 22 μm. Obtained.

Stirring treatment was carried out for 60 minutes in an aqueous solution of caustic potash at 80 ° C. and a specific gravity of 1.30 in which cobalt hydroxide was previously dissolved so that the amount of Co was 0.5 g per 100 g of this hydrogen storage alloy powder a (hereinafter referred to as “Co 10 g of hydrogen storage alloy that has been washed with water and dried,
A 5% by weight aqueous solution of polyvinyl alcohol was used to form a paste, the foamed nickel porous body was filled, dried and pressed to obtain a hydrogen storage alloy negative electrode having a width of 35 mm, a length of 145 mm and a thickness of 0.4 mm.

Next, a foamed nickel positive electrode obtained by a known method was used as a nickel oxide positive electrode, a sulfonated polypropylene nonwoven fabric obtained by subjecting a polypropylene nonwoven fabric to sulfonation treatment was used as a separator, and lithium hydroxide was used as an electrolytic solution at 40 g / l. A 4/5 A size sealed nickel-hydrogen storage battery having a nominal capacity of 1500 mAh was constructed by using a dissolved caustic potash aqueous solution having a specific gravity of 1.30 and combining with the negative electrode. This battery is designated as Example A according to the present invention.

For comparison, the hydrogen storage alloy powder a was replaced with the Co alkali treatment of Example A, and a hydrogen storage alloy electrode having a wet electroless solution Ni plating of about 1 μm thick was used on the surface of the hydrogen storage alloy powder. A battery configured in the same manner as in Example A was used as Comparative Example B. Similarly, instead of the Co alkali treatment, the specific gravity is 1.30 in a caustic potash aqueous solution of 1.30.
A battery using a hydrogen storage alloy electrode that had been agitated for 0 minutes (hereinafter referred to as “alkali treatment”) was designated as Comparative Example C, and a battery that was not treated was designated as Comparative Example D.

Next, as many hydrogen storage alloys Co content, creating the hydrogen storage alloy having the composition formula _{MmNi 3.5 Mn 0.4 Al 0.3 Co 0.8} . A sample mixed so as to have a desired composition ratio was prepared by the same manufacturing method as the hydrogen storage alloy powder a to obtain a hydrogen storage alloy powder b.

Example A using this hydrogen storage alloy powder b
A battery treated with the same alkali treatment as Co. was used in Example E according to the present invention, and a battery subjected to the same electroless Ni plating as Comparative Example B was treated with the same alkali treatment as Comparative Example F and Comparative Example C. In Comparative Example G and Comparative Example D, a battery which was not treated was designated as Comparative Example H.

Examples A, E, obtained by the above method
The batteries of Comparative Examples B, C, D, F, G and H were charged at 20 ° C. to 0.1 CmA to 150% of the positive electrode capacity and discharged to 0.2%.
Charging / discharging to a final voltage of 0.8 V with CmA was performed for 3 cycles. The discharge capacity at the third cycle was defined as the battery capacity.

In order to investigate the storage characteristics of the batteries A to H,
The discharged battery was stored in an environment of 65 ° C. and the changes in the internal resistance of the battery were compared. In addition, when 30 days have passed since the start of storage, at 1C at 0.1 CmA at a temperature of 20 ° C.
A charge / discharge cycle of charging to 50% and discharging to a final voltage of 0.8 V was performed, and the capacity recovery rate with respect to the capacity before storage was measured.

As a result of various investigations by the present inventors, the increase in internal resistance and capacity recovery rate of the battery before and after storage, and the elution concentration of Mn from the hydrogen storage alloy negative electrode were observed in any alloy composition of this example. It was newly found that there is a correlation between the two.

The Mn elution concentration was measured by the following method. First, Examples A and E after the configuration, Comparative Examples B, C, D, F,
Each of the G and H batteries was disassembled and the taken out hydrogen storage alloy negative electrode was cut into a predetermined size. This electrode plate was placed in 200 ml of a caustic potash aqueous solution having a specific gravity of 1.30 kept at 80 ° C. and immersed for 30 minutes. After that, add 3.0m of solution with a syringe.
l was collected and filtered with a syringe filter, and 1 ml of the filtrate was collected in a beaker. At this time, in order to prevent the precipitation of ions in the filtrate, the sample bottle that receives the filtrate should be
It was kept warm at ℃. Hydrochloric acid was added to the filtrate to acidify it, 10 ml of pure water was added, the mixture was heated on a hot plate, allowed to cool, and then adjusted to a constant volume of 50 ml. The solution thus obtained was quantified by ICP emission spectroscopy, and the elution concentration of Mn per apparent surface area of the negative electrode was calculated by the formula shown in (Equation 1) using the area of the negative electrode of the hydrogen storage alloy.

[0024]

[Equation 1]

The calculation results of the increase in battery internal resistance before and after storage, the capacity recovery rate and the Mn elution concentration are shown in (Table 1).

[0026]

[Table 1]

From these results, the batteries of Examples A and E, which were subjected to the Co alkali treatment according to the present invention, were subjected to other treatments or treatments with any of the hydrogen storage alloy powders a and b. Batteries B to D and F not performed
It can be seen that the storage characteristics are improved because the increase in internal resistance is small and the capacity recovery rate is high as compared with the cases of ~ H. As can be understood from the result of the Mn elution concentration, the reason for the treatment according to the present invention is that the unstable elution component is first eluted in advance in the alkaline electrolyte near the surface of the hydrogen-absorbing alloy, and then Co in the treatment solution is used to generate hydrogen. It is considered that the surface of the storage alloy was coated with the oxidation resistant Co compound layer to suppress the elution of Mn and the like in the alkaline electrolyte in the battery and to suppress the formation of precipitates that deteriorate the storage characteristics. To be

Although the storage characteristics were improved by electroless Ni plating and alkali treatment, Co alkali treatment was more effective. Electroless Ni plating also forms a film having corrosion resistance on the surface of the hydrogen storage alloy, but since electroless Ni plating is usually a dipping treatment in an acidic or weakly acidic plating solution, it is used in a strongly alkaline electrolyte. It is considered that this was because there was no effect of removing the unstable eluted components. On the other hand, since the alkali treatment has a large difference due to the difference in Co content, a hydrogen storage alloy having a relatively small Co content has an effect of removing an unstable elution component in the electrolytic solution,
It is considered that the formation of a film having corrosion resistance was insufficient.

The storage characteristics of the battery of Example A was relatively Co
It was equivalent to the battery of Example E using the hydrogen storage alloy powder b having a large content. That is, it was confirmed that the treatment according to the present invention can improve the storage characteristics particularly effectively in the alloy having a small Co content, which has not been so good in the conventional storage characteristics.

FIG. 1 shows the relationship between the elution concentration of Mn from the hydrogen storage alloy negative electrode and the increase in internal resistance during storage and the capacity recovery rate. In any alloy composition of this example, there is a correlation between the amount of Mn eluted from the hydrogen storage alloy negative electrode and the internal resistance and capacity recovery rate of the battery after storage. The smaller the elution of Mn, the less the internal resistance during storage was likely to rise, and the better the capacity recovery after storage was. If the capacity recovery rate is 95% or more, it is estimated that there is no problem in practical use, so the elution concentration of Mn is 0.2% by weight / m.
² or less is desirable.

When the battery after storage was disassembled, a large amount of precipitates, which are thought to be hydroxides of Mn, were deposited so as to fill the pores of the separator in the battery having poor storage characteristics. Also, the amount of the electrolytic solution held in the separator was reduced.

From the above, it was confirmed that the storage characteristics were affected by the elution of Mn from the hydrogen storage alloy into the alkaline electrolyte.

As a result of various examinations as described above, in order to obtain a sufficiently satisfactory storage characteristic, that is, in order to suppress an increase in internal resistance of the battery and to obtain an excellent capacity recovery rate, the hydrogen storage alloy negative electrode is set to 80%. It was found that the elution concentration of Mn when immersed in 200 ml of a caustic potash aqueous solution having a specific gravity of 1.30 at 30 ° C. for 30 minutes is preferably 0.2% by weight / m ² or less.

In this embodiment, the hydrogen storage alloy is M
Although the mNi ₅ type is used, other alloy type containing Mn such as ZrNi ₂ type may be used, and the positive electrode may be MnO ₂ or the like.

Further, in the present embodiment, the one treated in the powder state is taken as an example, but the treatment may be carried out in the electrode plate state. However, the treatment in a powder state is preferable in order to obtain the effect by the treatment in a short time. The Co compound produced on the surface of the hydrogen storage alloy in order to improve the storage characteristics may be formed by any method as long as it is a thin film. Further, although a complex oxide of Co and another metal may be used, various metal elements have been investigated, and the oxidation resistant Co compound layer produced by the treatment of the present invention showed the best result.

[0036]

INDUSTRIAL APPLICABILITY As described above, according to the present invention, a hydrogen storage alloy having a relatively low Co content is treated by treating the hydrogen storage alloy in a powder state or an electrode plate state in a high temperature alkaline aqueous solution containing elemental cobalt. Even if an alloy is used, a Co compound layer having excellent corrosion resistance is formed on the surface of the alloy to suppress the elution of Mn from the hydrogen storage alloy negative electrode, thereby realizing an excellent alkaline storage battery having good storage characteristics.

[Brief description of drawings]

FIG. 1 is a diagram showing the relationship between the amount of Mn eluted from a hydrogen storage alloy negative electrode and the internal resistance and capacity recovery rate of a battery after storage.

Claims (2)

[Claims] 1. A positive electrode whose main constituent material is a metal oxide, a negative electrode whose main constituent material is a hydrogen storage alloy capable of electrochemically storing and releasing hydrogen as an active material, and an alkaline electrolyte. And a separator, and the negative electrode is 80 ° C. and has a specific gravity of 1.30
The alkaline storage battery is characterized in that the elution concentration of Mn per apparent surface area of the negative electrode is 0.2% by weight / m ² or less under the condition of being immersed in the solution for 30 minutes. 2. A positive electrode whose main constituent material is a metal oxide, a negative electrode whose main constituent material is a hydrogen storage alloy capable of electrochemically occluding and releasing hydrogen as an active material, and an alkaline electrolyte. And a separator, and the negative electrode is 80 ° C. and has a specific gravity of 1.30
A method for producing an alkaline storage battery, wherein the elution concentration of Mn per apparent surface area of the negative electrode is 0.2% by weight / m ² or less under the condition of being immersed in the hydrogen storage alloy for 30 minutes. A method for manufacturing an alkaline storage battery, which comprises a step of immersing in a powder state or in a state of being formed as a negative electrode plate in an alkaline aqueous solution in which cobalt element is dissolved.