JP2013134903A - Hydrogen absorbing alloy for alkaline storage battery, and alkaline storage battery including the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a hydrogen absorbing alloy for an alkaline storage battery, etc., capable of saving cost while maintaining high output.SOLUTION: A hydrogen absorbing alloy for an alkaline storage battery is represented by general formula: (ReY)ZrMgNiAl(where, Re includes only La or at least one element selected from Nd and Sm and including La, and 0<x≤0.60, 0≤y≤0.02, 0.09≤z≤0.13, 3.40≤a≤3.80 and 0.05≤b≤0.20 are satisfied).

Description

  The present invention relates to a hydrogen storage alloy for an alkaline storage battery suitable for applications requiring high current and high current discharge (high power / high current applications) such as a hybrid electric vehicle (HEV).

Alkaline batteries with a hydrogen storage alloy in the negative electrode are used for applications requiring high power and large current discharge (high power / high current applications) such as for HEVs because they are excellent in safety. . By the way, generally, the hydrogen storage alloy used for the negative electrode of an alkaline storage battery is composed of a single phase of AB ₂ type structure or AB ₅ type structure. However, high output and large current discharge performance far exceeding the conventional range have been demanded, and the AB ₂ type structure and the AB ₅ type structure are combined as in the rare earth-Mg—Ni based hydrogen storage alloy. Those having an A ₂ B ₇ type structure or an A ₅ B ₁₉ type structure as a main phase have been proposed. In the AB ₂ type structure, AB ₅ type structure, A ₂ B ₇ type structure, and A ₅ B ₁₉ type structure, the A component represents the sum of the stoichiometric ratios of rare earth, Zr, and Mg, and the B component is the Ni component. Represents the sum of the stoichiometric ratios of components other than rare earth and Zr and Mg.

Here, in the rare earth-Mg—Ni-based hydrogen storage alloy, the structure is transformed by the stoichiometric ratio of the B component (mainly Ni), and the A ₂ B ₇ type increases as the stoichiometric ratio of the B component increases. A ₅ B ₁₉ type structure is easily constructed from the structure. In this case, the A ₅ B ₁₉ type structure is a structure in which the AB ₂ type structure is stacked with one layer of the AB ₂ type structure and three layers of the AB ₅ type structure as a period, so that the nickel ratio per unit crystal lattice can be improved. Is. For this reason, an alkaline storage battery including a rare earth-Mg—Ni-based hydrogen storage alloy having a main phase of A ₅ B ₁₉ type structure (including relatively many) in the negative electrode is a battery exhibiting particularly excellent high output, It has been proposed in Patent Literature 1, Patent Literature 2, Patent Literature 3, and the like.

JP 2008-300108 A JP 2009-054514 A JP 2009-07631 A

Incidentally, in recent years, in HEV applications, in addition to high output exceeding the conventional range, cost reduction is required. Until now, rare earth-Mg-Ni-based hydrogen storage alloys have been widely used in HEV applications.
Among these, rare earth-Mg—Ni hydrogen storage alloys containing a large amount of Nd as a rare earth element are widely used in HEV applications because they can provide good output performance.
However, since Nd is expensive, the rare earth-Mg—Ni-based hydrogen storage alloy containing a large amount of Nd as a rare earth element has a problem that the raw material cost increases.

As a method for reducing the cost of the hydrogen storage alloy, there is a method of replacing a part of Nd with inexpensive La. However, when a part of Nd is replaced by La, the equilibrium hydrogen pressure (hereinafter referred to as equilibrium pressure) of the hydrogen storage alloy is lowered, and the output is lowered.
On the other hand, as another means for reducing the cost, there has been proposed a method of combining Sm which is an intermediate price between Nd and La. With this method, the output performance is improved to some extent, but there is a problem that sufficient output performance cannot be obtained.

In order to solve the above problems, alkali hydrogen-absorbing alloy for battery of the present invention have the general formula _{(Re 1-x Y x)} 1-y-z Zr y Mg z Ni a-b Al b (Re: La only At least one element selected from Nd and Sm, 0 <x ≦ 0.60, 0 ≦ y ≦ 0.02, 0.09 ≦ z ≦ 0.13, 3.40 ≦ a ≦ 3.80, 0.05 ≦ b ≦ 0.20).

  As described above, when Y is included as a rare earth element, Y increases the equilibrium pressure to the same extent as Sm, but the price is about the same between Nd and La as Sm, and the reaction resistance is higher than Sm. To reduce. For this reason, the hydrogen storage alloy for alkaline storage batteries of the present invention can reduce costs while maintaining high output.

However, if x exceeds 0.60, pulverization associated with hydrogen storage and release is accelerated and the corrosion resistance is lowered. Therefore, it is necessary to satisfy 0 <x ≦ 0.60. Since the cycle life is improved when the molar ratio y of Zr is 0.02 or less, it is necessary to satisfy 0 ≦ y ≦ 0.02.
When the molar ratio z of Mg exceeds 0.13, pulverization accompanying hydrogen storage and release is accelerated, resulting in a decrease in corrosion resistance. When the molar ratio z is below 0.09, the pressure change during hydrogen storage is stable due to multistage. Since the hydrogen storage characteristic cannot be obtained, the molar ratio of Mg needs to satisfy 0.09 ≦ z ≦ 0.13.
When the stoichiometric ratio a is less than 3.40, the equilibrium pressure is low, so the output drop is significant. When the stoichiometric ratio a exceeds 3.80, pulverization associated with hydrogen storage and release is accelerated, and the corrosion resistance is reduced. The stoichiometric ratio must satisfy 3.40 ≦ a ≦ 3.80.
Furthermore, when the molar ratio b of Al exceeds 0.20, the amount of Al eluted into the alkaline electrolyte becomes excessive, and the corrosion resistance is lowered. In addition, an increase in the amount of Al entering the positive electrode causes a decrease in output. On the other hand, if it is less than 0.05, the amount of elution into the alkaline electrolyte is reduced, the contact area with the electrolyte is reduced, and sufficient output cannot be obtained. For this reason, the molar ratio of Al needs to satisfy 0.05 ≦ b ≦ 0.20.

  According to the hydrogen storage alloy for an alkaline storage battery of the present invention, the cost can be reduced while maintaining a high output.

It is sectional drawing which shows typically the alkaline storage battery of one Example of this invention.

  Next, embodiments of the present invention will be described in detail below. However, the present invention is not limited to these embodiments, and can be appropriately modified and implemented without departing from the scope of the present invention.

1. Hydrogen storage alloy The hydrogen storage alloy was produced as follows. In this case, first, lanthanum (La), neodymium (Nd), samarium (Sm), yttrium (Y), zirconium (Zr), magnesium (Mg), nickel (Ni), and aluminum (Al) are shown in Table 1. The mixture was dissolved in an argon gas atmosphere, and the molten metal was rapidly cooled to produce hydrogen storage alloys a1 to e1 ingots. Thereafter, the mass of each of the hydrogen storage alloys a1 to e1 is coarsely pulverized and then mechanically pulverized in an inert gas atmosphere to obtain a hydrogen storage having a particle size (D50) of 25 μm at a volume cumulative frequency of 50%. Alloy powder was prepared. In addition, when the composition of these hydrogen storage alloys a1 to e1 is analyzed by high frequency plasma spectroscopy (ICP), the following Table 1 is obtained.
It turned out that it is a composition shown to.

2. Hydrogen Storage Alloy Negative Electrode Next, using the powders of the hydrogen storage alloys a1 to e1 manufactured as described above, a hydrogen storage alloy negative electrode 11 was manufactured as follows.
In this case, first, the hydrogen storage alloy slurry is prepared by mixing and kneading the powders of the hydrogen storage alloys a1 to e1 prepared as described above, the water-soluble binder, the thermoplastic elastomer, and the carbon-based conductive agent. Produced. In this case, as the water-soluble binder, a material composed of 0.1% by mass of CMC (carboxymethyl cellulose) and water (or pure water) was used. Further, styrene butadiene latex (SBR) was used as the thermoplastic elastomer. Further, ketjen black was used as the carbon-based conductive agent.

Next, the hydrogen storage alloy slurry prepared as described above is applied to a negative electrode conductive core (a nickel-plated soft steel porous substrate (punching metal)) with a predetermined filling density (for example, 5.0 g / The active material layer was formed by applying and drying to a thickness of cm ³ ), and then rolling to a predetermined thickness. Thereafter, the hydrogen storage alloy negative electrode capacity is 14 Ah, and the hydrogen storage alloy negative electrode surface area (short axis length × long axis length × 2) is 1000 cm ² (negative electrode surface area / negative electrode capacity = 71 cm ² / Ah). The hydrogen storage alloy negative electrode 11 (a, b, c, d, e) was produced by cutting. The negative electrode surface area is the sum of the areas of the front and back surfaces of the negative electrode.

  In this case, the hydrogen storage alloy negative electrode a was prepared using the hydrogen storage alloy a1 powder. Similarly, a hydrogen storage alloy negative electrode b is prepared using the hydrogen storage alloy b1 powder, a hydrogen storage alloy negative electrode c is prepared using the hydrogen storage alloy c1 powder, and the hydrogen storage alloy d1 powder is prepared. The hydrogen storage alloy negative electrode d was prepared using this, and the hydrogen storage alloy negative electrode e was prepared using the powder of the hydrogen storage alloy e1.

3. Nickel positive electrode The nickel positive electrode 12 was produced as follows.
First, a porous nickel sintered substrate having a porosity of about 85% is immersed in a mixed aqueous solution of nickel nitrate and cobalt nitrate having a specific gravity of 1.75, and nickel salt and cobalt are placed in the pores of the porous nickel sintered substrate. Salt was retained. Thereafter, the porous nickel sintered substrate was immersed in a 25% by mass sodium hydroxide (NaOH) aqueous solution to convert the nickel salt and the cobalt salt into nickel hydroxide and cobalt hydroxide, respectively.
Next, after sufficiently washing with water to remove the alkaline solution, drying was performed, and the active material mainly composed of nickel hydroxide was filled into the pores of the porous nickel sintered substrate. Such an active material filling operation is repeated a predetermined number of times (for example, 6 times) so that the filling density of the active material mainly composed of nickel hydroxide in the pores of the porous sintered substrate becomes 2.5 g / cm ^3. Filled. Then, after making it dry at room temperature, it cut | disconnected to the predetermined dimension and the nickel positive electrode 12 was produced.

4). Nickel-hydrogen storage battery The nickel-hydrogen storage battery 10 was produced as follows.
First, the hydrogen storage alloy negative electrode 11 and the nickel positive electrode 12 manufactured as described above are used, and a separator 13 made of a nonwoven fabric containing polypropylene fibers is interposed between them, and the spiral electrode group is wound. Was made. The core exposed portion 11c of the hydrogen storage alloy negative electrode 11 is exposed at the lower part of the spiral electrode group thus fabricated, and the core exposed part 12c of the nickel positive electrode 12 is exposed at the upper portion thereof. ing. Next, the negative electrode current collector 14 is welded to the core exposed portion 11c exposed at the lower end surface of the obtained spiral electrode group, and the core exposed portion 12c of the nickel positive electrode 12 exposed at the upper end surface of the spiral electrode group. A positive electrode current collector 15 was welded onto the electrode body to obtain an electrode body.

Next, after the obtained electrode body is housed in a bottomed cylindrical outer can 16 in which iron is nickel-plated (the outer surface of the bottom surface becomes a negative electrode external terminal) 16, the negative electrode current collector 14 is attached to the outer can 16. Welded to the inner bottom. On the other hand, a current collecting lead portion 15a extending from the positive electrode current collector 15 and a sealing plate 17 serving as a positive electrode terminal and having an insulating gasket 18 attached to the outer peripheral portion were welded. The sealing plate 17 is provided with a positive electrode cap 17a, and a pressure valve including a valve body 17b and a spring 17c which are deformed when a predetermined pressure is reached is disposed in the positive electrode cap 17a.

  Next, after forming the annular groove portion 16 a on the upper outer peripheral portion of the outer can 16, the electrolytic solution was injected, and the outer peripheral portion of the sealing plate 17 was mounted on the annular groove portion 16 a formed on the upper portion of the outer can 16. An insulating gasket 18 was placed. Thereafter, the opening edge 16b of the outer can 16 is caulked, and an alkaline electrolyte (for example, composed of 30% by mass potassium hydroxide (KOH) aqueous solution) is put in the outer can 16 at 2.5 g per battery capacity (Ah) ( 2.5 g / Ah) was injected to produce a nickel-hydrogen storage battery 10 (A, B, C, D, E) having a battery capacity of 6 Ah.

  In this case, the battery A was prepared using the hydrogen storage alloy negative electrode a, the battery B was manufactured using the hydrogen storage alloy negative electrode b, and the battery C was manufactured using the hydrogen storage alloy negative electrode c. A battery D was prepared using the hydrogen storage alloy negative electrode d, and a battery E was prepared using the hydrogen storage alloy negative electrode e.

5. Battery test (1) Activation Activation was performed as follows. That is, the nickel-hydrogen storage battery 10 (A, B, C, D, E) manufactured as described above is left until the battery voltage reaches 60% of the peak voltage when left, and then in a temperature atmosphere of 25 ° C. The battery is charged up to 120% SOC at a charging current of 1 It and rests at 25 ° C. for 1 hour. Then, after being allowed to stand for 24 hours in a temperature atmosphere at 70 ° C., a cycle in which the battery voltage was 0.3 V with a discharge current of 1 It in a temperature atmosphere of 45 ° C. was repeated two times.

(2) Output characteristics (-10 ° C assist output)
The output characteristics (−10 ° C. assist output) were determined as follows.
First, the nickel-hydrogen storage battery 10 (A, B, C, D, E) activated as described above was charged to SOC 50% at a charging current of 1 It in a temperature atmosphere of 25 ° C., and then a temperature of 25 ° C. It was allowed to rest for 1 hour in the atmosphere. Next, the battery was charged for 20 seconds at an arbitrary charging rate in a temperature atmosphere of −10 ° C., and then rested for 30 minutes in a temperature atmosphere of −10 ° C. Thereafter, the battery was discharged for 10 seconds at an arbitrary discharge rate in a temperature atmosphere of −10 ° C., and then rested in a temperature atmosphere of −10 ° C. for 30 minutes. In such a temperature atmosphere of −10 ° C., charging for 20 seconds at an arbitrary charging rate, pause for 30 minutes, discharging for 10 seconds at an arbitrary discharge rate, and pause for 30 minutes in a temperature atmosphere of −10 ° C. were repeated. .

  In this case, the charging rate is increased in the order of 0.8 It → 1.7 It → 2.5 It → 3.3 It → 4.2 It, and the arbitrary discharging rate is 1.7 It → 3. The discharge current is increased in the order of 3 It → 5.0 It → 6.7 It → 8.3 It so that 0.8 It charge → 1.7 It discharge → 1.7 It charge → 3.3 It discharge → 2.5 It charge → 5.0 It discharge → 3.3 It charge → 6.7 It discharge → 4.2 It charge → 8.3 It discharge / discharge treatment was performed. At this time, the battery voltage (V) of each battery at the time when 10 seconds passed at each discharge rate was measured for each discharge rate. Next, the battery voltage (V) of each of the batteries A, B, C, D, and E when the measured 10 seconds have elapsed is two-dimensionally plotted against the discharge current value for each discharge rate, and the battery voltage and the discharge current are plotted. When an approximate curve indicating the relationship between values is obtained, and the discharge current value at 0.9 V in the approximate curve is obtained as an SOC 50% output characteristic at −10 ° C. (SOC 50% assist output at −10 ° C.), the following table is obtained. Results were as shown in 2.

(3) Cost characteristics When the raw material costs of the hydrogen storage alloys a1 to e1 were determined, the results shown in Table 2 below were obtained.

6). Test results From the results in the above table, the following became clear.
That is, the output characteristics are improved by substituting a part of Nd with Sm as in the battery E for a composition in which the rare earth element is composed only of LaNd as in the battery D. When Y is replaced with Y, the output characteristics are further improved.
This is because, as in battery E, replacing Nd → Sm increases the equilibrium pressure and improves the output. However, as in battery A, replacing Nd → Y increases the equilibrium pressure to the same extent as Sm replacement. In addition to this, it is considered that an output higher than Sm can be obtained because the reaction resistance in the battery is lower than the Sm substitution.
Further, since Y is about the middle price between Nd and La like Sm, the hydrogen storage alloy substituted with Nd → Y has a lower cost than the composition made of LaNd. Therefore, the hydrogen storage alloy substituted with Nd → Y can achieve both high output and cost reduction of the hydrogen storage alloy.
Further, since the output characteristics of the battery B or the battery C in which the Y substitution amount (x) is increased with respect to the battery A are further improved, the Y substitution amount (x) is preferably 0.40 or more. I understand that. In particular, when Nd is replaced only with La and Y as in the battery C, it is possible to achieve both high output and cost reduction.

Furthermore, in an alkaline storage battery using a hydrogen storage alloy for the negative electrode, as the negative electrode capacity X (Ah) and the negative electrode surface area Y are Y / X increases (especially 60 cm ² / Ah or more), the negative electrode Therefore, the area facing the nickel positive electrode is inevitably increased and the battery resistance is reduced, so that high output can be achieved. When such a high-power battery design is employed, the above-described hydrogen storage alloy of the present invention is preferably employed for the negative electrode.

DESCRIPTION OF SYMBOLS 11 ... Hydrogen storage alloy negative electrode, 11c ... Core exposed part, 12 ... Nickel positive electrode, 12c ... Core exposed part, 13 ... Separator, 14 ... Negative electrode collector, 15 ... Positive electrode collector, 15a ... Lead for positive electrode, DESCRIPTION OF SYMBOLS 16 ... Exterior can, 16a ... Circular groove part, 16b ... Opening edge, 17 ... Sealing plate, 17a ... Positive electrode cap, 17b ... Valve plate, 17c ... Spring, 18 ... Insulation gasket

Claims (2)

A hydrogen-absorbing alloy for an alkaline storage battery, the general formula _{(Re 1-x Y x)} 1-y-z Zr y Mg z Ni a-b Al b (Re: La contains only or includes a La, Nd, At least one element selected from Sm, 0 <x ≦ 0.60, 0 ≦ y ≦ 0.02, 0.09 ≦ z ≦ 0.13, 3.40 ≦ a ≦ 3.80, 0.05 <= B <= 0.20) The hydrogen storage alloy for alkaline storage batteries characterized by the above-mentioned. It is an alkaline storage battery containing the hydrogen storage alloy according to claim 1 in the negative electrode, wherein Y / X is 60 cm ² / Ah or more when the electrode plate capacity of the negative electrode is X and the electrode plate surface area of the negative electrode is Y. Characteristic alkaline storage battery.