JPH11315301A - Production of hydrogen storage alloy powder and electrode using the hydrogen storage alloy powder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a hydrogen storage alloy easy in production, high in initial characteristics, high in the capacity and having a long service life by treating alloy powder occluded with hydrogen with a soln. contg. at least one kind of organic acid contg. sulfuric acid or the salt thereof. SOLUTION: This hydrogen storage alloy is not particularly limited, the one used for a negative electrode can selectively be used properly and among them, generally, an LnNi5 series alloy is preferable. The hydrogen storage alloy powder is treated with a soln of organic acid or the salt thereof and is washed as necessary. As the organic acid, the one having a sulfur group is preferable, sulfonic acid, sulfinic acid, sulfenic acid are used and for example, it can suitably be selected from sulfamic acid, sulfanilic acid, sulfaminobenzoic acid, sulfosalicylic acid, sulfobenzoic acid and sulfoacetic acid. These organic acids contain isomers and can be used alone or as the mixture and among them, 5-sulfosalicyclic acid and 2-hydroxy-sulfobenzoic acid are preferable in particular.

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 powder for use in a negative electrode of a nickel-metal hydride secondary battery. The present invention relates to a method for producing a hydrogen storage alloy powder capable of obtaining a long-life nickel-hydrogen secondary battery having excellent characteristics.

[0002]

2. Description of the Related Art Since the discovery of a hydrogen storage alloy that stores and releases hydrogen, it has been applied not only to hydrogen storage means but also to batteries and the like. In particular, alkaline secondary batteries have already been put to practical use, and the hydrogen storage alloys used have been successively increased in capacity and life. That is, the LaNi ₅ alloy having the CaCu ₅ type crystal structure initially studied is La
Is replaced by a rare earth element such as Ce, Pr, Nd or the like, and a part of Ni is replaced by a metal element such as A1, Co, Mn, etc., thereby achieving higher capacity and longer life.

As a metal in which La is partially substituted with Ce, Pr, Nd, etc., misch metal (Mm) is commercially available. The misch metal is a mixture of rare earth elements, and is composed of, for example, 20% by weight of other rare earth elements such as 45% by weight of Ce, 30% by weight of La, 20% by weight of Nd, and 5% by weight of Pr. However, when such a hydrogen storage alloy is used as an electrode for a battery, the capacity and the life of the battery can be increased, but the initial characteristics deteriorate.

[0004] The initial characteristics are generally represented by the number of charge / discharge cycles required to reach the maximum capacity, and the smaller the number of cycles, the higher the initial characteristics. Usually, the initial characteristics are evaluated by the capacity in the first cycle. However, when an electrode having low initial characteristics is sealed to form a battery, the balance between the positive electrode and the negative electrode is lost, and there is a disadvantage that the capacity and life of the battery are reduced.

Therefore, in order to solve the above-mentioned drawbacks, conventionally, a hydrogen storage alloy has been treated with a mineral acid solution such as hydrochloric acid or sulfuric acid or an alkaline solution (for example, NaOH or KOH). However, the alkali treatment not only requires the treatment conditions to be high concentration and high temperature, but also makes it difficult to wash after the treatment, and causes a change in the composition of the hydrogen storage alloy after the treatment. There was a disadvantage that the production became complicated. In the case of conventional mineral acid treatment,
Although the life and initial activity are improved, there is a drawback that the internal pressure characteristics and the preservability do not reach the practical range.

[0006]

The inventors of the present invention have conducted intensive studies on a hydrogen storage alloy powder for a negative electrode and a method for producing the same in order to solve the above-mentioned drawbacks. As a result, the hydrogen storage alloy powder contains S. By treating with a solution of an organic acid or a salt thereof, it is possible to easily obtain a hydrogen storage alloy powder having good workability and handleability and excellent stability, and to obtain a battery by using the hydrogen storage alloy powder. The present inventors have found that it is possible to easily produce a negative electrode for use and to improve the initial characteristics without reducing the capacity and life of the battery, and have reached the present invention.
Accordingly, an object of the present invention is to provide a method for producing a hydrogen storage alloy powder which is easy to produce, has high initial characteristics, has a high capacity and long life, and is suitable for a sealed battery having good internal pressure characteristics, and a method for producing the same. To provide a negative electrode for a battery using the obtained hydrogen storage alloy powder.

[0007]

SUMMARY OF THE INVENTION The above objects of the present invention are as follows.
The present invention has been achieved by a method for producing a hydrogen storage alloy powder, comprising a step of treating the hydrogen storage alloy powder with at least one solution of an organic acid or a salt thereof containing S (sulfur).

[0008]

The applied hydrogen storage alloy of the embodiment of the present invention is not limited in particular, known hydrogen storage alloy used in the negative electrode, for example AB, the _{AB 2, AB 5, A 2} B structure It can be appropriately selected and used from among the hydrogen storage alloys. Among them, in the present invention, it is generally preferable to use an LnNi ₅ alloy generally having an AB ₅ structure.

In the present invention, in particular, of the LnNi ₅ -based alloys, La _x R ₁ -xN in terms of battery capacity and cycle life characteristics.
It is preferable to use an alloy represented by i _a M _b. R in the formula is a rare earth metal other than La or, for example, Ce, Pr, N
a mixture of rare earth metals selected from d, Sm, and Y;
In particular, at least one selected from Ce, Pr, and Nd;
M is at least one selected from Mn, A1, Co, Ti, Fe, Zr, and Cr, x is 0.2 to 1, a + b is 4.0 to 6.0, and b is 0 <b ≦ 2.0. Is preferably a positive number. Note that the above X, 1-X, a, b in the formula are:
The content ratio of each atom in such a structural formula is shown.
Is Ce or when R is a mixture containing Ce, the content ratio of Ce atoms in the structural formula is 0.05 to
It is preferably 0.5. Among M, in particular, Mn
A mixture mainly composed of three components of -Al-Co is preferable.

In the present invention, the hydrogen storage alloy powder is treated with a solution of an organic acid or a salt thereof from the viewpoint of improving the initial characteristics of a battery and producing a high capacity and long life hydrogen storage alloy powder. And wash as necessary. The organic acids are sulfur organic acids are preferred to have a group, a sulfonic acid (R ¹ -S0 ₃ H) as the organic acid, sulfinic acid (R ¹ -SO ₂ H) and Surufein acid (R ¹ -SO
H). Here, R ¹ is a monovalent aliphatic hydrocarbon group (preferably having 1 to 10 carbon atoms), an aromatic hydrocarbon group, an amino group, etc., and these are a carboxyl group, an amino group, a hydroxyl group, a sulfonic acid group. And the like. Specific examples of these organic acids can be appropriately selected from, for example, sulfamic acid, sulfanilic acid, sulfaminobenzoic acid, sulfosalicylic acid, sulfobenzoic acid, and sulfoacetic acid. These organic acids can be used irrespective of the position of the substituent (that is, including isomers), and may be used alone or as a mixture.

In the present invention, among these organic acids, it is preferable to use sulfosalicylic acid, sulfamic acid and sulfoacetic acid. In particular, 5-sulfosalicylic acid, 2
-Hydroxy-sulfobenzoic acid is preferred. Examples of the salt of the organic acid include Na salt, K salt, and Ca salt of the above-mentioned organic acid, and in particular, Na salt, K salt, and Ca salt of sulfosalicylic acid, sulfamic acid, and sulfoacetic acid are preferable. As a solvent used to dissolve the organic acid or a salt thereof,
Examples thereof include ketones such as water, ethanol and the like having 1 to 5 carbon atoms such as alcohol, ether, and acetone. In particular, an organic acid or a salt thereof having an aqueous solution is preferable. In the present invention, as described later, an organic acid or the like may be used in an amount of 0.01 to 30 parts by weight based on the alloy.

In the present invention, the temperature of the processing solution using an organic acid containing S or a salt thereof (hereinafter referred to as an organic acid or the like) is as follows:
It is preferably room temperature to 100 ° C., particularly preferably 20 to 6 ° C.
Preferably it is 0 ° C. Also, normal pressure ~
The treatment is preferably performed under a pressure of 10 kgf / cm ² or less. Processing at high temperature or with cooling is
Since it is produced industrially, the equipment cost is too high and it is not economical. In particular, it is not practical to perform the process by cooling, because the process time is too long. 10kgf / cm ²
If the pressure is exceeded, the battery capacity is undesirably reduced.

[0013] The processing time is 0.1 to 0.1 in any processing.
The time is 10 hours, and may be appropriately adjusted so that the temperature is short when the temperature is high and long when the temperature is low. Further, the concentration of the organic acid or the like in the treatment bath is not particularly limited, but may be about 0.1 to 100 parts by weight of the hydrogen storage alloy to be treated.
A solution in which the content is preferably from 0.01 to 30 parts by weight (about 0.01 to 30% by weight), particularly preferably about 0.5 to 10 parts by weight, and 0.01 to 10% by weight of an organic acid. It is good to process with. When the treatment is performed at a concentration exceeding 30 parts by weight, the initial characteristics are improved, but the attainable capacity is reduced. 0.0
If the amount is less than 1 part by weight, the effect of treatment with an organic acid or the like may not be obtained. Further, the alloy powder treated with the S-containing organic acid as described above can form an Ni-rich layer on the surface of the alloy, and can obtain an alloy having a magnetization per specific surface area of 3 emu / m ² or more, thereby improving the initial characteristics. Is achieved.

When the hydrogen storage alloy obtained by the present invention is used as a negative electrode for a battery, the initial characteristics are improved because an oxide film formed on the surface of the hydrogen storage alloy is removed by an organic acid or the like. This is presumed to be due to the fact that the contact between the alloy and the electrolyte solution is improved, and that a layer containing a large amount of Ni is formed on the surface of the alloy particles by treatment with an organic acid or the like.

According to the present invention, a metal mixture having a composition obtained as a hydrogen-absorbing alloy, for example, a mixture of metal elements having the above-described composition is converted into a vacuum or an inert gas such as Ar using a known high-frequency, arc induction furnace or the like. Under the atmosphere, 1,300-1,
By melting and cooling at 600 ° C., a hydrogen storage alloy is obtained, which is pulverized using a ball mill, a jet mill, a pulverizer or the like, preferably having an average particle size of 5 to 50 μm.
The electrode powder is immersed in a solution of an S-containing organic acid or the like, followed by stirring. Further, a hydrogen storage alloy powder obtained by a quenching method such as a roll quenching method or an atomizing method may be used.

The treatment method of the present invention is not particularly limited, and may be carried out by a known method such as immersing the hydrogen storage alloy in the above-mentioned solution. It is preferable to immerse the hydrogen storage alloy in the form of a powder in the treatment solution. Particularly, when the hydrogen storage alloy is stirred, the initial characteristics of the electrode using the obtained powder can be further improved.

After the treatment, water washing and drying are performed, and then a known binder such as polyvinyl alcohol, methyl cellulose, carboxymethyl cellulose, PTFE (polytetrafluoroethylene), or polymer latex is added in an amount of 0.1 to 20 parts by weight based on 100 parts by weight of the alloy. If necessary, 0.5 to 20 parts by weight of a conductive auxiliary such as carbon graphite powder, Ni or Cu powder is added to form a paste. The paste is uniformly filled into a three-dimensional conductor such as a foamed nickel porous body or a Ni fiber body, and a two-dimensional conductor such as a punching metal, and then vacuum-dried and then pressure-formed to form a battery for the battery of the present invention. A negative electrode can be manufactured. Such a negative electrode,
A known nickel positive electrode, a separator such as polypropylene, and an electrolytic solution such as KOH are incorporated in a container, and can be manufactured as an alkaline storage battery. In the present invention, as described above, it can be used as a storage means such as a heat pump as an application other than the electrode.

[0018]

When the hydrogen storage alloy powder obtained by the method of the present invention is used for a negative electrode of an alkaline storage battery, it is excellent in initial characteristics, hardly raises the internal pressure of the battery at the time of charging, and has a long cycle life. A hydrogen storage alloy negative electrode suitable for a storage battery can be manufactured extremely easily.

[0019]

EXAMPLES The present invention will be described in more detail with reference to the following Examples, but it should not be construed that the present invention is limited thereto.

Examples 1 to 16 and Comparative Example 1 As a misch metal, Mm of La 61% by weight, Ce 7% by weight, Pr 23% by weight and Nd 9% by weight was used.
The respective elements were weighed so that A1, Co, Mn, and Ni became 0.3, 0.75, 0.2, and 3.75, respectively, in atomic ratio with respect to 1.00, and were weighed under an argon atmosphere. Melting was performed in a melting furnace to obtain a hydrogen storage alloy. The obtained hydrogen storage alloy was heat-treated at 1020 ° C. for 5 hours and then pulverized to obtain a hydrogen storage alloy powder having an average particle diameter of 32 μm. 20 g of each of the obtained alloy powders was separately collected (16 samples), treated with a 50 ml organic acid aqueous solution under the conditions shown in Table 1, and then filtered, washed with water, and vacuum dried for each sample. Measurement of magnetization and specific surface area The magnetization of the alloy powder was measured using a vibrating sample magnetometer (VSM). The specific surface area was measured using a fluid type specific surface area automatic measuring device. The results are shown in Table 1. Although the specific surface area of the alloy powder subjected to the alkali solution treatment or the mineral acid solution treatment becomes twice or more, almost the same area can be obtained by the organic acid treatment. In addition, the magnetization is increased by the treatment, and the initial characteristics are improved.

4 g of each of the powders prepared and processed for the open battery was collected, and 1 g of a 3% by weight aqueous solution of polyvinyl alcohol (average degree of polymerization: 2,000, degree of saponification: 98 mol%) was added to each and mixed to obtain a paste. In addition, 17 kinds of pastes were prepared together with the case of Comparative Example 1 in which no treatment was performed. The 17 kinds of obtained lists are
0 mm × 40 mm × 1.6 mm, porosity of 94 to 96
After being uniformly filled in a foamed nickel porous material of volume%, vacuum-dried, and then pressure-formed, 17 types of negative electrodes were produced.

On the other hand, sintered nickel produced according to a known method was used as a nickel oxide positive electrode. Using a polypropylene-based non-woven fabric as a separator,
Seventeen types of open-type nickel-metal hydride batteries were formed by combining with seven types of negative electrodes (Examples 1 to 16 and Comparative Example 1) and using a 6 molar aqueous solution of potassium hydroxide as an electrolytic solution. As a reference electrode, a charged positive electrode was used so as not to be affected by the positive electrode.

Evaluation of capacity and cycle performance (1 cycle)
Le, using 5 cycles) each battery obtained, 20 ° C., which charges 5 hours at 0.3 C, then discharged until the battery voltage at 0.2C is 0.8V conditions this condition as one cycle repetition,
Table 1 shows the results of evaluating the initial activity performance by measuring the capacities at the first and fifth cycles.

[0024]

[Table 1] Concentrations are% by weight of alloy and mAh stands for milliamp hours.

Example 17 and Comparative Examples 2 to 5 The magnetization and specific surface area were measured in exactly the same manner as in Examples 1 to 16 except that the treatment was carried out under the conditions shown in Table 2 instead of the conditions shown in Table 1. , An open battery was manufactured, and its capacity was measured to evaluate its performance. The results are as shown in Table 2. In addition, 50 ml of an acid or alkali solution was used for 20 g of the alloy. Sulfosalicylic acid treatment has the most improved initial properties as compared to untreated.

[0026]

[Table 2] Note 1: 0.1 wt% HCl aqueous solution was used. Note 2: The concentration of hydrofluoric acid (46% hydrofluoric acid) was adjusted to a 0.1N aqueous solution. Note 3: Alkaline treatment is for 6.8N-KOH solution. Concentration is% by weight of alloy, and mAh is milliamp hours. The above results demonstrate the effectiveness (initial characteristics) of the present invention.

Production and Evaluation of Sealed Battery 90 parts by weight of the alloy powder obtained in Example 15 were mixed with 10 parts by weight of Ni powder, and the solid content of PTFE (polytetrafluoroethylene) was 3% by weight (with the mixed powder). The PTFE dispersion was added and kneaded so as to obtain a PTFE solid content (based on the total PTFE solid content), and the mixture was formed into a sheet and pressed on both sides of a nickel expanded metal.

As comparative examples, other acid treatments such as hydrochloric acid treatment (concentration of 0.1% by weight, liquid temperature of 50 ° C.) or hydrofluoric acid treatment (concentration of 0.1 N, liquid temperature of 50 ° C.) were performed for 30 minutes each. And KOH aqueous solution (concentration 6-8N, liquid temperature 50
(° C.) for 2 hours, and an electrode which was not treated at all was produced in the same manner as in the above example.

Each of the electrode sheets obtained by the above method was cut into a width of 33 mm and a length of 220 mm to obtain a negative electrode. The thickness is 0.6 mm. This negative electrode was spirally combined with a known sintered nickel positive electrode with a polypropylene nonwoven fabric interposed therebetween as a separator to form a sub C size sealed battery. The prepared battery was charged and discharged at 20 ° C. under the conditions of charging: 0.1 C × 15 hours, discharging: 0.2 C, and 1 V, and the internal pressure of the battery at the end of charging, battery capacity, and The cycle life was examined.
The results are shown in FIGS.

As is clear from FIGS. 1 and 2, the battery using the electrode of this embodiment has a higher internal pressure of the battery at the end of charging than the batteries using other acid-treated or alkali-treated and untreated electrodes. And the internal pressure rise due to repetition of the charge / discharge cycle is small. Therefore, it has been proved that the battery using the electrode of the present invention also shows a better cycle life than the comparative example.

Therefore, it can be seen from FIGS. 1 and 2 that the treatment with a mineral acid and the treatment with an alkali deteriorate the life and the internal pressure. In the case of the hydrochloric acid treatment, the initial characteristics are excellent, but the internal pressure and the life of the sealed battery are poor. In the case of hydrofluoric acid treatment, the life characteristics are excellent. Internal pressure characteristics are not good. In the case of alkali treatment, it is effective for improving the cycle life and suppressing the rise in battery internal pressure up to a certain time, but only removing the heterogeneous part in the alloy composition, the hydroxide layer or oxide layer on the alloy surface It is considered that the battery performance is inferior to the electrode of the present invention since no removal of the electrode was performed.

As described above, if the electrodes of the present invention are used,
It is possible to provide a battery that has excellent initial characteristics, has a small increase in battery internal pressure due to repeated charging and discharging, and has excellent cycle life characteristics.

[Brief description of the drawings]

FIG. 1 is a graph showing the dependence of the internal pressure of a battery on the number of charge / discharge cycles for each electrode obtained from a hydrogen storage alloy treated by different treatment methods.

FIG. 2 is a graph showing the dependence of the battery capacity on the number of charge / discharge cycles for each electrode obtained from a hydrogen storage alloy treated by different treatment methods, where the capacity per cycle is 100 (%); This is a graph showing the rate of decrease when the test is performed.

Claims (4)

[Claims] 1. A method for producing a hydrogen storage alloy powder, comprising a step of treating the hydrogen storage alloy powder with a solution of at least one organic acid containing S or a salt thereof. 2. The method for producing a hydrogen storage alloy powder according to claim 1, wherein the organic acid containing S is at least one organic acid selected from sulfonic acid, sulfinic acid and sulfinic acid. 3. The total amount of the organic acid or organic acid salt containing S is 0.01 to 100 parts by weight of the hydrogen storage alloy.
3. The method for producing a hydrogen storage alloy powder according to claim 1, wherein the amount is 30 parts by weight. 4. An electrode using the hydrogen storage alloy powder obtained by the production method according to claim 1.