JP3454600B2 - Method for producing hydrogen storage alloy for alkaline 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 method for producing a hydrogen storage alloy for alkaline storage batteries, and more particularly to an acid treatment and cleaning treatment method for a hydrogen storage alloy.

[0002]

2. Description of the Related Art Conventionally, alkaline secondary batteries such as Ni-Cd batteries have been used as driving power sources and backup power sources for electronic equipment.
The use of Ni-hydrogen batteries, which have higher capacity and longer life than Cd batteries, is expanding. By the way, in an alkaline storage battery such as a Ni-hydrogen battery using a hydrogen storage alloy, the battery performance depends on the superiority or inferiority of the activity of the hydrogen storage alloy. Therefore, in general, the hydrogen storage alloy for alkaline storage batteries is
In order to increase the reaction area and the packing density, crushed powder having a predetermined particle size is used.
However, the hydrogen storage alloy is an extremely active substance and easily reacts with oxygen in the air to form an oxide film on the surface.
This oxide film reduces the electrical conductivity of the alloy and inhibits initial activation. Therefore, in the production of batteries, great care is taken to prevent oxidation of the alloy, and various treatments are carried out to recover the activity of the alloy that has been oxidized in the pulverization process and the like.

As a method for recovering the activity, for example, Japanese Patent Laid-Open No. 3-98259 proposes a method of treating an alloy with heated water at 60 ° C. or higher. In addition, JP-A-4
-179055, JP-A-6-88150, and JP-A-6-223827 propose methods of treating an alloy with an acidic aqueous solution. When the above-mentioned method is applied to an alloy, the oxide layer and hydroxide layer formed on the alloy surface are removed, and the alloy surface becomes Ni-rich. The initial activation due to charging and discharging becomes easy, and the initial activation effect is enhanced, resulting in improved battery performance.

[0004]

However, the technique disclosed in Japanese Unexamined Patent Publication No. 3-98259 has a problem in that it takes a lot of time for processing and it is difficult to sufficiently obtain the effect of removing an oxide film and the like. On the other hand, the techniques of Japanese Patent Laid-Open No. 4-179055 and the like have the advantages that the effect of removing an oxide film is high and the treatment time can be shortened. Reacts with to form compounds such as chlorides. Since this compound cannot be easily removed by washing with water, the anions remain in the alloy, and this residual anion causes a decrease in alloy activity. It also causes a decrease in positive electrode activity. Therefore, the above-mentioned JP-A-4-179055
Even with the technique disclosed in Japanese Patent Publication, there is a problem in that the effect of improving the battery characteristics by removing the oxide film is reduced by the anions remaining in the alloy, so that the battery performance cannot be sufficiently improved.

The present invention has been made in view of the above, and an object thereof is to provide an efficient and highly effective alloy activation treatment method capable of sufficiently enhancing battery performance.

[0006]

In order to achieve the above object, the present invention has the following constitution. The method for producing a hydrogen storage alloy for an alkaline storage battery according to the invention of claim 1 is characterized in that an acid treatment step of treating the hydrogen storage alloy with an acidic aqueous solution and a residual amount of anions taken in the hydrogen storage alloy by the acid treatment are hydrogen. A washing step of washing the storage alloy to 5 × 10 ⁻⁶ mol / g or less, and the washing in the washing step is performed with an antioxidant-containing aqueous solution.
The antioxidant in the solution is dihydrogen phosphate.
Mu, dipotassium hydrogen phosphate, sodium hydrogen carbonate, carbonic acid
Potassium hydrogen, sodium borohydride, boron hydroxide
Potassium, lithium aluminum hydroxide, sodium hypophosphite
From thorium, potassium hypophosphite, formalin, formic acid
It is characterized by being selected .

According to a second aspect of the present invention, in the method for producing a hydrogen storage alloy for alkaline storage batteries according to the first aspect, the acidic aqueous solution has a pH of 0.5 or more and 3.5 or less. The invention of claim 3 is the method for producing a hydrogen storage alloy for alkaline storage batteries according to claim 1 or 2, wherein:
After the cleaning process, the hydrogen absorption
Preservation washing by dipping and storing Kura alloy in aqueous solution containing antioxidant
It is characterized by having a cleaning process .

[0008] claimed invention in claim 4 is the manufacturing method of claims 1 to 3 for alkaline storage battery hydrogen storage alloy according, before
The hydrogen storage alloy has a non-uniform strain of 4.0 × 10 ⁻³ or less.
It is characterized by having.

[0009]

According to the present invention, since the oxide film formed on the surface of the hydrogen storage alloy is removed by the acid treatment step of treating with an acidic aqueous solution, the initial activation of the battery is facilitated. Also,
Use an aqueous solution containing antioxidant during the acid treatment in the washing process .
The anions taken in the alloy (especially on the alloy surface) are washed down to a concentration of 5 × 10 ^-6 mol / alloy-g or less, so it is faster than washing with pure water.
And it is possible to surely reduce the residual anions in the alloy.
Wear. Therefore, it can be manufactured using the manufacturing method of the present invention.
In the hydrogen storage alloy for Lucari battery, residual anions do not adversely affect the battery performance. Therefore, when the hydrogen storage alloy to which the method of the present invention is applied is used, the alloy activity can be easily increased by the initial charge / discharge, and the residual anions do not lower the activity of the positive and negative electrodes. It is possible to obtain an alkaline storage battery having excellent low temperature discharge characteristics and cycle characteristics.

In the above, if a solution having a pH of 0.5 to 3.5 is used as the acidic aqueous solution used in the acid treatment step,
The effect of removing the oxide film is further enhanced. Also, wash in the washing process
The cleaned alloy is immersed and stored in the antioxidant-containing aqueous solution.
Prevents the alloy from blocking the outside air
In addition to the trace amount of residual anion that could not be washed in the washing process,
It is possible to further remove the gas.

Furthermore, the effects of the above acid treatment and cleaning treatment can be obtained regardless of the type of alloy, but especially 4.0 ×
A remarkable effect is obtained when applied to a hydrogen storage alloy having a non-uniform strain of 10 ⁻³ or less. The reason is as follows. An alloy having a small non-uniform strain has a higher resistance to the expansion and contraction energy of the alloy accompanying absorption and desorption of hydrogen, as compared with an alloy having a large non-uniform strain, and thus is less likely to be miniaturized even with the progress of charge and discharge cycles. Therefore, the alloy having a small non-uniform strain, which has been surface-treated by the treatment method of the present invention, maintains the initial suitable surface state (active state) as it is for a long period of time. On the other hand, in an alloy having a large non-uniform strain, alloy cracking occurs as the charge / discharge cycle progresses, and a new alloy surface (non-activated surface) appears. Therefore, it is considered that the treatment effect of the method of the present invention is relatively reduced in the alloy having a large nonuniform strain.

The non-uniform strain is one of the causes of the phenomenon that the Debye ring becomes broad when the Debye ring is measured with a Laue camera or the like, and is a value defined by the following mathematical expression 1. .

[0013]

[Equation 1]

[0014]

EXAMPLES A method for producing a hydrogen storage alloy for alkaline storage batteries of the present invention will be described based on experiments. (Experiment 1) [Preparation of hydrogen storage alloy] Commercially available misch metal Mm (L
a, a mixture of rare earth elements such as Ce, Nd, Pr), Ni,
Co, Al and Mn are contained in an element ratio of 1: 3.4: 0.8:
0.2: 0.6 weighed and mixed so that, MmNi _3.4 Co _0.8 using a high frequency melting furnace of an inert gas atmosphere
Hydrogen storage alloy ingot represented by a composition formula of Al _0.2 Mn _0.6
(Y) was cast. The non-uniform strain of this hydrogen storage alloy ingot (Y) was 5.4 × 10 ⁻³ . This hydrogen storage alloy ingot
(Y) was crushed in an inert gas atmosphere to give an average particle size of 150.
An alloy powder having a size of μm or less was obtained.

On the other hand, the hydrogen-absorbing alloy ingot (Y) is heat-treated at 1000 ° C. for 8 hours in an inert gas atmosphere to obtain an annealed alloy (Z), and this alloy (Z) is subjected to the same conditions as above. It was crushed to obtain an alloy powder having an average particle size of 150 μm or less. The non-uniform strain of the annealed alloy (Z) is 2.
It was 5 × 10 ⁻³ . [Acid treatment and cleaning treatment] The two kinds of alloy powders having different non-uniform strains produced above are immersed in a hydrochloric acid aqueous solution (PH = 1) having a weight approximately equal to the weight of the alloy, and the mixture is stirred for 20 minutes. Acid treatment was performed by a stirring method. afterwards,
The acid-treated alloy powder was washed under various conditions shown in Table 1.

The cleaning treatment was carried out by a method of treating with pure water or a solution in which 1% by weight of disodium hydrogen phosphate was dissolved in pure water (antioxidant-containing aqueous solution). Specifically, the above cleaning solution was put into a stirring type mixer, and approximately equal weight of acid-treated alloy powder was immersed in this cleaning solution and stirred for a predetermined time. Next, the operation of exchanging the cleaning liquid after stirring for a predetermined time and stirring again for a predetermined time was repeated until the chlorine (anion) concentration in the alloy reached a desired value.

Table 1 shows the type of alloy (of non-uniform strain).
Difference), the difference in cleaning conditions₀~ A ₆, B₁~ B₆, C
₀~ C₆, D₁~ D₆It is indicated by. Also, the salts in Table 1
Elementary concentration is the value measured by atomic absorption spectrometry,
The time is shown as one stirring time × repeating times. [Fabrication of electrodes and batteries]
5% by weight based on the alloy powder of polytetrafluoroethylene
Powder and an appropriate amount of water are added and kneaded to form an alloy paste.
Made This paste is a collector made of punching metal
Apply to both sides of the body, dry, then press to absorb hydrogen
An alloy electrode was produced.

Next, the hydrogen storage alloy electrode (negative electrode) and the sintered nickel electrode (positive electrode) were wound with a separator made of non-woven fabric interposed therebetween to produce an electrode group.
This electrode group was inserted into an outer can, and after further injecting a 30 wt% potassium hydroxide aqueous solution, the outer can was sealed. In this way, a sealed nickel-hydrogen storage battery with a theoretical capacity of 1000 mAh, which differs only in the processing conditions of the hydrogen storage alloy, was produced. Furthermore, these batteries were initially activated under the following charge / discharge conditions (3 cycles at room temperature).

Charging: 1000 mA × 16 hours, resting;
Discharge for 1 hour; 200mA, end voltage of discharge 1.0V, pause; 1
It is to be noted that the batteries A _{0 to} A ₆ , B _{1 to} B ₆ , C corresponding to the types of the alloy powder which has been subjected to the cleaning treatment used for the negative electrode are used.
₀ -C _6, referred to as D ₁ to D _6. [Evaluation of Washing Treatment Conditions] Using the batteries prepared above, the washing treatment conditions were mainly evaluated.

Here, the battery performance was evaluated by various characteristics such as high rate charge / discharge characteristics measured under the following conditions. However, regarding the cycle characteristics, the charge / discharge cycle was performed under the following conditions, and the battery life was defined as the time when the battery capacity reached 500 mA. High rate charge / discharge characteristics: Charge; 100 mA x 16 hours (at room temperature), Pause; 1 hour Discharge; 4000 mA / Discharge end voltage 1.0 V (room temperature), Pause; 1 hour Low temperature discharge characteristics: Charge; 100 mA x 16 hours (At room temperature), pause; 1 hour (-10 ° C) discharge; 1000 mA, discharge end voltage 1.0 V (-10
Charging / discharging cycle characteristics: Charging; 1500 mA × 48 minutes (at room temperature) Discharging: 1500 mA / Discharge end voltage 1.0 V (at room temperature), Pause: 1 hour or less, explanation will be made based on the results shown in Table 1.

[0021]

[Table 1]

Remaining Anion Concentration and Battery Characteristics In Table 1, the relationship between the chlorine concentration in the alloy and the battery characteristics is examined. In any of A to D, the chlorine concentration is 5 × 10 ⁻⁶ mol / g or less with respect to the alloy. When, the battery characteristic value was greatly improved. From this, it was found that, when the alloy was treated with an acid, it was more effective to wash the alloy until the residual anion concentration became 5 × 10 ⁻⁶ mol / g or less in order to improve the battery characteristics.

Cleaning Conditions and Cleaning Effects A _{1 to} A ₆ and B _{1 to} B ₆ , and C _{1 to} C ₆ and D _{1 to} D ₆
From the comparison, the cleaning time (stirring time x number of times) required to reduce the chlorine remaining in the alloy to a predetermined concentration is the value when an aqueous solution containing disodium hydrogen phosphate is used as the cleaning solution (antioxidant-containing aqueous solution **). Was shorter than the case of using pure water (*). Further, the battery using the alloy washed with the aqueous solution containing disodium hydrogen phosphate had excellent battery characteristics as compared with the battery composed of the alloy washed with pure water even if the residual chlorine concentration was the same. . In addition,
Although not shown in Table 1, it has been confirmed that similar effects can be obtained when an antioxidant other than disodium hydrogen phosphate (for example, sodium borohydride) is used.

From these results, it was proved that when the alloy was washed with the antioxidant-containing aqueous solution after the acid treatment, the anions could be removed from the alloy in a shorter time and the battery performance could be improved. The reason why the effect of removing anions and the effect of improving battery characteristics are high when an aqueous solution containing disodium hydrogen phosphate is used as the cleaning liquid is considered to be as follows. That is, during the acid treatment, the rare earth elements in the alloy and the anions bound to nickel are not easily eluted with pure water. On the other hand, when an aqueous solution containing disodium hydrogen phosphate is used, anions such as chlorine bound to the alloy components are exchanged for phosphate ions and the like are eluted into the liquid. Therefore, the anions bound to the alloy components can be easily removed.

On the other hand, since the anions such as phosphate ions remaining in the alloy after substituting with the anions such as chlorine have less adverse effects on the alloy activity and other components of the alkaline storage battery than chlorine, the battery characteristics are improved. It is supposed to do. Furthermore, even if the anion concentration was the same, superior battery characteristics were obtained when washed with an antioxidant-containing aqueous solution. It is considered that this is because the antioxidant adsorbed on the surface enhances the liquid content of the alloy surface, and thus the low temperature discharge characteristics and the high rate discharge characteristics are improved. Further, it is considered that the antioxidant adsorbed on the surface suppresses the oxidation due to oxygen and thus the cycle life is improved.

Based on the results of Table 1, the initial pH of the acid treatment liquid
, The effect of non-uniform strain on the alloy and the cleaning effect, and the effect of preservative cleaning were investigated in more detail. (Experiment 2) In Experiment 2, the effect of the pH of the acidic aqueous solution on the battery characteristics when the alloy was acid-treated by the following method was examined.

First, an aqueous solution of hydrochloric acid having various pHs (initial PH) is prepared, and a non-uniform strain of 5.4 × 10 5 is added to the aqueous solution of hydrochloric acid.
^-3 alloy (almost equal weight) was immersed and stirred with the agitator until the pH of the aqueous hydrochloric acid solution reached 7. Then, the acid-treated alloy was washed with pure water until the residual chlorine amount reached 5 × 10 ⁻⁶ mol / g. Next, initial P in acid treatment
Various batteries (E ₁ ~
E _9, F ₁ ~F ₉₎ constitute, it was investigated battery characteristics of this battery. Other conditions such as the method of constructing the battery and the method of measuring the battery characteristics were the same as in Experiment 1.

The results are shown in Table 2. In Table 2, for each of the alloys (E and F) having non-uniform strain, the characteristic values of each battery significantly decreased when the initial pH of the acid treatment liquid was less than 0.5 or more than 3.5. From this, it is preferable to set the initial PH of the acid treatment liquid in the range of 0.5 to 3.5.

[0029]

[Table 2]

(Experiment 3) In Experiment 3, alloy non-uniform strain and
In order to investigate the relationship with the effects of the treatment method of the present invention, various
An alloy with uniform strain was prepared and evaluated in the same manner as in Experiment 1.
It was The results are shown in Table 3. In addition, A and C in Table 3 are experiments
The alloys G to J prepared in Example 1 are
It was prepared by changing the annealing temperature. Also,
Acid treatment is performed using an aqueous solution of hydrochloric acid with PH = 1, and cleaning treatment is performed.
Is pure water and the chlorine concentration is 5 × 10 with respect to the alloy. ^-6mol /
until g.

[0031]

[Table 3]

From Table 3, it was found that the battery characteristics tended to improve as the non-uniform strain became smaller. Particularly, the non-uniform strain was between 5.0 × 10 ⁻³ and 4.0 × 10 ⁻³ . Has changed a lot. From this, the non-uniform strain is 4.0 × 10.
It was found to be more effective to apply the treatment method of the present invention to the alloy ^{No. -3} . (Experiment 4) In Experiment 4, the untreated alloy and the cleaned alloy were immersed and stored in pure water and an aqueous solution containing disodium hydrogen phosphate for 1 week (at room temperature), and then the alloy was used in the same manner as in Experiment 1. The battery was constructed by using the above method, and the influence of the difference in the storage solution on the battery characteristics was investigated.

The alloy used in this experiment was prepared in Experiment 1, and Table 3 shows the corresponding alloy N in Experiment 1.
o. (Table 1) is represented by the K subscript. Further, each characteristic value is shown on the left side of “→” when pure water is stored, and on the right side when stored in a 1 wt% disodium hydrogen phosphate aqueous solution.

[0034]

[Table 4]

From Table 4, for any of KC _{1 to} KD ₆ , the battery made of the alloy stored in the aqueous solution of disodium hydrogen phosphate has various battery characteristics as compared with the battery made of the alloy stored in pure water. Was excellent. From this, it was found that the antioxidant-containing aqueous solution is also useful as an alloy preservation solution. Since hydrogen-absorbing alloys are extremely susceptible to oxidation, generally when manufacturing batteries, a method of immersing the alloy in pure water or the like to temporarily store it just before use is used. When used as a liquid, storage and washing can be realized at the same time.

[Other Matters] In the above-mentioned Examples, an example of an aqueous solution containing disodium hydrogen phosphate was described, but this does not limit the antioxidant that can be used in the method of the present invention. The antioxidant that can be used in the method of the present invention may be any one that can be dissolved in water to the extent that it can exert its function, can suppress the oxidation of the hydrogen storage alloy, or can dissolve and remove the oxide on the alloy surface. As such, in addition to the disodium hydrogen phosphate used in the above examples, for example, dipotassium hydrogen phosphate, sodium hydrogen carbonate, potassium hydrogen carbonate, sodium borohydride, potassium borohydride, lithium aluminum hydride. , Sodium hypophosphite, potassium hypophosphite,
Examples thereof include formalin and formic acid, and other antioxidants or reducing agents can also be used.

In the above embodiment, the acid treatment and the cleaning treatment were carried out by using a treatment liquid of approximately equal weight to the alloy powder, but it goes without saying that the amount of treatment liquid can be increased or decreased. However, considering the ease of processing and the processing efficiency, alloy powder: processing liquid = 1: 0.5 to 6 (weight ratio) is preferable. The method of the present invention is applicable not only to rare earth-based hydrogen storage alloys but also to titanium-based or Laves-based hydrogen storage alloys.

[0038]

EFFECTS OF THE INVENTION According to the method for producing a hydrogen storage alloy for alkaline storage batteries of the present invention, the alloy activation treatment with an acidic aqueous solution that is performed before the battery is constructed can be performed more effectively. A hydrogen storage alloy that can be easily activated can be provided.

Further, in the hydrogen storage alloy produced by the method of the present invention, the adverse effects of acid treatment are removed and the liquid content of the alloy surface is improved, so that the high rate discharge characteristics, the low temperature discharge characteristics and the cycle characteristics are improved. A battery with excellent characteristics can be constructed.

─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-7-73878 (JP, A) JP-A-4-110403 (JP, A) JP-A-7-65828 (JP, A) (58) Field (Int.Cl. ⁷ , DB name) H01M 4/24-4/26 H01M 4/38

Claims (4)

(57) [Claims] 1. An acid treatment step of treating a hydrogen storage alloy with an acidic aqueous solution, and a residual amount of anions taken in the hydrogen storage alloy by the acid treatment is 5 × 10 ⁻⁶ mol / g with ^respect to the hydrogen storage alloy.
And a washing step of washing the following, wherein the washing in the washing step is performed with an antioxidant-containing aqueous solution.
Are those, antioxidants during the aqueous solution is phosphate dibasic isocyanatomethyl
Lithium, dipotassium hydrogen phosphate, sodium hydrogen carbonate,
Potassium bicarbonate, sodium borohydride, sodium hydroxide
Potassium arsenide, lithium aluminum hydroxide, hypophosphorus
Sodium acid salt, potassium hypophosphite, formalin, formic acid
A method for producing a hydrogen storage alloy for alkaline storage batteries, which is selected from the group consisting of: 2. The pH of the acidic aqueous solution is 0.5 or more,
It is 3.5 or less, The manufacturing method of the hydrogen storage alloy for alkaline storage batteries of Claim 1 characterized by the above-mentioned. 3. The method according to claim 1, further comprising, after the cleaning step, a storage cleaning step of immersing and storing the hydrogen storage alloy cleaned in the cleaning step in an antioxidant-containing aqueous solution. A method for producing a hydrogen storage alloy for an alkaline storage battery. 4. The method for producing a hydrogen storage alloy for alkaline storage batteries according to claim 1, wherein the hydrogen storage alloy has a non-uniform strain of 4.0 × 10 ⁻³ or less.