JP6394955B2 - Hydrogen storage alloy, electrode and nickel metal hydride storage battery - Google Patents

Description

The present invention relates to a novel hydrogen storage alloy, an electrode containing the hydrogen storage alloy, and a nickel metal hydride storage battery including the electrode.

Nickel metal hydride storage batteries have high energy density, so they can be used as power sources for small electronic devices such as digital cameras and laptop computers. Widely used as a power source for hybrid vehicles and the like.

This type of nickel metal hydride storage battery is usually configured to include a nickel electrode including a positive electrode active material mainly composed of nickel hydroxide, a negative electrode mainly composed of a hydrogen storage alloy, a separator, and an alkaline electrolyte. Yes. Among these battery constituent materials, in particular, the hydrogen storage alloy as the main material of the negative electrode has a great influence on the performance of the nickel-metal hydride storage battery such as discharge capacity and energy density. Have been considered.

In particular, studies have been made on the use of rare earth-Mg-Ni-based hydrogen storage alloys for the negative electrode for the purpose of increasing the capacity of nickel-metal hydride storage batteries (see Patent Document 1).

However, the rare earth-Mg-Ni alloy has a problem that the durability is extremely low when used as a negative electrode of a battery. This was caused by the occurrence of strain between a plurality of crystal phases included in the alloy due to the absorption and release of hydrogen accompanying charging and discharging. Further, there is a problem that the pulverization of the hydrogen storage alloy is accelerated by repeated charge and discharge, and the durability is lowered. Furthermore, the hydrogen storage alloy has a problem that it is easily corroded when the battery is stored in a high temperature atmosphere or when charging and discharging are repeated.

In order to solve these problems, investigations for optimizing the ratio of substitutional elements and crystal phases have been repeated so far (for example, see Patent Documents 2 to 8), but they still have satisfactory corrosion resistance and durability. An alloy has not been obtained.

JP-A-11-323469 JP 2007-291474 A JP 2008-71684 A JP 2009-176712 A JP 2011-21262 A JP2011-82129A JP 2012-67357 A JP 2014-114476 A

The present invention is intended to solve the above problems, and it is an object to provide a hydrogen storage alloy excellent in corrosion resistance and durability, and a nickel hydride storage battery excellent in cycle life using the hydrogen storage alloy. And

The present invention employs the following means in order to solve the above problems.
(1) In formula _{(RE 1-a over b Sm a Mg b) (Ni} 1-c-d Al c M d) x
(However, 0.1 ≦ a ≦ 0.25, 0.1 <b <0.2, 0.02 <cx <0.2, 0 ≦ dx ≦ 0.1, 3. 6 ≦ x ≦ 3.7, RE is one or more elements selected from the group consisting of rare earth elements other than Sm and Y, and the content of La in the RE is the sum of RE, Sm, and Mg The molar amount is 0.6 or more with respect to the amount, and M is M is Mn and / or Co).
( 2 ) The hydrogen storage alloy according to (1 ), wherein the RE contains Nd and / or Pr.
( 3 ) The hydrogen storage alloy according to (1) or (2) , wherein the Pr ₅ Co ₁₉ phase and the Ce ₅ Co ₁₉ phase are contained in an amount of 80% by mass or more as a crystal phase of the alloy.
( 4 ) An electrode comprising the hydrogen storage alloy according to any one of (1) to ( 3 ).
( 5 ) A nickel-metal hydride storage battery comprising the electrode of ( 4 ) as a negative electrode.

Since the hydrogen storage alloy according to the present invention has high corrosion resistance (durability) when used as a negative electrode of a nickel hydride storage battery, a nickel hydride storage battery having an excellent cycle life can be obtained.

Hereinafter, embodiments of the present invention will be described in detail.

The hydrogen storage alloy according to the present invention have the general formula _{(RE 1-a over b Sm a Mg b) (Ni} 1-c-d M c) x

It is represented by However, 0.1 ≦ a ≦ 0.25, 0.1 <b <0.2, 0.02 <cx <0.2, 0 ≦ dx ≦ 0.1, 3.6 ≦ x ≦ 3.7, RE is at least one element selected from the group consisting of rare earth elements other than Sm and Y, and La is essential, and M is M is Mn and / or Co.

As shown in the above general formula, the hydrogen storage alloy according to the present invention has a so-called B / A (a numerical range of X) of 3.6 or more and 3.7 or less. By using a hydrogen storage alloy having B / A within this range, the contents of Pr ₅ Co ₁₉ phase and Ce ₅ Co ₁₉ phase become 80 mass% or more, and the corrosion resistance is improved. Even if B / A is smaller than 3.6 or larger than 3.7, the corrosion resistance is deteriorated.

It was found that a hydrogen storage alloy having high corrosion resistance (durability) can be obtained by substituting a predetermined amount of Sm (samarium) for an alloy having a constant B / A ratio as described above. . In order to improve the corrosion resistance, the substitution amount of Sm is a molar amount relative to the total amount of Sm, RE (one or more elements selected from the group consisting of rare earth elements other than Sm and Y) and Mg, 0.1 or more and 0.25 or less. Even if the substitution amount of Sm is less than 0.1 or more than 0.25, the corrosion resistance is deteriorated.

When the substitution amount of Sm is 0.1 or more and 0.25 or less as described above, the mechanism for improving the corrosion resistance is to replace the Sm with a predetermined amount so that the A ₅ B ₁₉ phase (Pr ₅ Co ₁₉ It is presumed that the entire alloy can be prevented from being deformed by the stable formation of the phase and the Ce ₅ Co ₁₉ phase and the specific stabilization of the crystal structure.

In the hydrogen storage alloy according to the present invention, RE is one or more elements selected from the group consisting of rare earth elements other than Sm and Y, and La is an essential and main component. The La content should be 0.6 or more in terms of molar amount relative to the total amount of Sm, RE (one or more elements selected from the group consisting of rare earth elements other than Sm and Y) and Mg. Is preferable, and more preferably 0.7 or more. Examples of RE other than La include Nd, Pr, Ce, Dy, Gd and the like. Among these, inclusion of Nd and / or Pr is preferable because corrosion resistance is improved.

In the hydrogen storage alloy according to the present invention, in order to improve the corrosion resistance, the content of Mg is the sum of Sm, RE (one or more elements selected from the group consisting of rare earth elements other than Sm and Y), and Mg. More than 0.1 and less than 0.2 in molar amounts relative to the amount. Preferably less than 0.17. Even if it is 0.1 or less or 0.2 or more, the corrosion resistance deteriorates.

In the hydrogen storage alloy according to the present invention, the main component constituting B is Ni, but together with Ni, Al is contained in a molar amount multiplied by X by more than 0.02 and less than 0.2. A hydrogen storage alloy with improved corrosion resistance is obtained. Preferably it is more than 0.05. Even if it is 0.02 or less and 0.2 or more, the corrosion resistance deteriorates. Further, in order to improve the corrosion resistance, 0.1 or less of Mn and / or Co can be contained in a molar amount multiplied by X together with Al.

In the hydrogen storage alloy according to the present invention, the crystal phase contains Pr ₅ Co ₁₉ phase and Ce ₅ Co ₁₉ phase in total of 80% by mass or more, thereby improving the corrosion resistance. The total amount of both is more preferably 90% or more. Further, the content of the Ce ₅ Co ₁₉ phase is preferably 80% by mass or more. In addition to the Pr ₅ Co ₁₉ phase and the Ce ₅ Co ₁₉ phase, a Ce ₂ Ni ₇ phase, a Gd ₂ Co ₇ phase, a CaCu ₅ phase, or the like may be contained.

In the method for producing the hydrogen storage alloy of the present embodiment, for example, a melting step of melting an alloy raw material blended so as to have a predetermined composition ratio as described above, a cooling step of solidifying the molten alloy raw material, An annealing process for annealing the cooled alloy and a grinding process for grinding the alloy are performed.

Each step will be described more specifically. First, based on the chemical composition of the target hydrogen storage alloy, a predetermined amount of raw material ingot (alloy raw material) is weighed.

In the melting step, the alloy raw material is put in a crucible and melted at 1000 ° C. or higher in an inert gas atmosphere or vacuum using a high-frequency melting furnace or the like. The upper limit of the melting temperature is about 2000 ° C., for example, it is melted by heating to 1200 to 1600 ° C.

In the cooling step, the molten alloy material is cooled and solidified. The cooling rate may be so-called slow cooling or 1000 K / second or more (also referred to as rapid cooling), but it is preferable to use a rapid cooling method. By rapidly cooling at 1000 K / second or more, there is an effect that the alloy composition is refined and homogenized. The cooling rate can be set in a range of 1000000 K / second or less.

As the cooling method, specifically, a water-cooled mold method, a melt spinning method with a cooling rate of 100000 K / sec or more, a gas atomizing method with a cooling rate of about 10,000 K / sec, or the like can be preferably used.

In the annealing step, heating is performed at 860 ° C. or higher and 1000 ° C. or lower using, for example, an electric furnace in a pressurized state under an inert gas atmosphere. It is preferable to heat to 930-975 degreeC. The pressurizing condition is preferably 0.2 MPa (gauge pressure) or more and 1.0 MPa (gauge pressure) or less. Moreover, it is preferable that the processing time in this annealing process shall be 3 hours or more and 50 hours or less.

The pulverization step may be performed either before or after annealing, but since the surface area is increased by pulverization, it is desirable to perform the pulverization step after the annealing step from the viewpoint of preventing surface oxidation of the alloy. The pulverization is preferably performed in an inert atmosphere to prevent oxidation of the alloy surface.

As the pulverizing means, for example, mechanical pulverization, hydrogenation pulverization, or the like is used, and it is preferable that the particle size of the hydrogen storage alloy particles after pulverization is approximately 20 to 70 μm.

The use of the hydrogen storage alloy according to the present invention is not particularly limited, and can be applied to various uses including nickel-metal hydride storage batteries, fuel cells, fuel tanks for hydrogen automobiles, among others, It is suitably used as a negative electrode active material for nickel-metal hydride storage batteries. Thus, the nickel metal hydride storage battery provided with the negative electrode containing the hydrogen storage alloy according to the present invention is also one aspect of the present invention.

The nickel metal hydride storage battery according to the present invention includes, for example, a positive electrode (nickel electrode) containing a positive electrode active material mainly composed of nickel hydroxide in addition to a negative electrode containing the hydrogen storage alloy according to the present invention as a negative electrode active material. ), A separator, an alkaline electrolyte, and the like.

The negative electrode is one in which the hydrogen storage alloy according to the present invention is blended as a negative electrode active material. The hydrogen storage alloy which concerns on this invention is mix | blended in a negative electrode as powdered hydrogen storage alloy powder, for example.

In addition to the hydrogen storage alloy powder, the negative electrode may contain a conductive agent, a binder (including a thickener), and the like.

Examples of the conductive agent include natural graphite (scale-like graphite, scale-like graphite, earth-like graphite, etc.), artificial graphite, carbon black, acetylene black, ketjen black, carbon whisker, carbon fiber, vapor-grown carbon, etc. Examples of conductive agents include metal conductive agents composed of powders or fibers of metals such as nickel, cobalt, and copper. These electrically conductive agents may be used independently and 2 or more types may be used together. Moreover, you may contain rare earth oxides, such as an yttrium oxide, as a corrosion inhibitor.

The blending amount of the conductive agent is preferably 0.1 to 10 parts by mass, more preferably 0.2 to 5 parts by mass with respect to 100 parts by mass of the hydrogen storage alloy powder. When the blending amount of the conductive agent is less than 0.1 parts by mass, it is difficult to obtain sufficient conductivity. On the other hand, when the blending amount of the conductive agent exceeds 10 parts by mass, the effect of improving the discharge capacity is not good. May be sufficient.

Examples of the binder include polytetrafluoroethylene (PTFE), polyolefin resins such as polyethylene and polypropylene, ethylene-propylene-diene rubber (EPDM), sulfonated EPDM, styrene butadiene rubber (SBR), fluoro rubber, polyvinyl Alcohol, methylcellulose, carboxymethylcellulose, xanthan gum, etc. are mentioned. These binders may be used independently and 2 or more types may be used together.

The blending amount of the binder is preferably 0.1 to 1.0 part by mass, more preferably 0.5 to 1.0 part by mass with respect to 100 parts by mass of the hydrogen storage alloy powder. . When the blending amount of the binder is less than 0.1 parts by mass, sufficient thickening is difficult to be obtained. On the other hand, when the blending amount of the binder exceeds 1.0 parts by mass, the performance of the electrode is improved. May fall.

Examples of the positive electrode include an electrode in which a nickel hydroxide composite oxide obtained by mixing zinc hydroxide or cobalt hydroxide with nickel hydroxide as a main component is blended as a positive electrode active material. As the nickel hydroxide composite oxide, those uniformly dispersed by a coprecipitation method are preferably used.

The positive electrode preferably contains an additive for improving electrode performance in addition to the nickel hydroxide composite oxide. Examples of the additive include conductive modifiers such as cobalt hydroxide and cobalt oxide, and the nickel hydroxide composite oxide coated with cobalt hydroxide, and the nickel hydroxide composite oxide. Part of the product may be oxidized with oxygen or oxygen-containing gas, K ₂ S ₂ O ₈ , hypochlorous acid, or the like.

As the additive, a substance that improves oxygen overvoltage, such as a compound containing a rare earth element such as Y or Yb or a compound containing Ca, can also be used. Since some of rare earth elements such as Y and Yb are dissolved and disposed on the negative electrode surface, an effect of suppressing corrosion of the negative electrode active material is also expected.

The positive electrode may further contain the above-described conductive agent, binder and the like, similarly to the negative electrode.

Such a positive electrode and a negative electrode were obtained by kneading these with water or an organic solvent such as alcohol or toluene after adding the above-mentioned conductive agent, binder, or the like to each active material as necessary. The paste can be produced by applying it to a conductive support and drying it, followed by rolling.

Examples of the conductive support include a steel plate and a plated steel plate obtained by plating a steel plate with a metal material such as nickel. Examples of the shape of the conductive support include a foam, a molded product of a fiber group, a three-dimensional base material subjected to unevenness processing, and a two-dimensional base material such as a punching plate. Of these conductive supports, for the positive electrode, a foam made of nickel having excellent corrosion resistance and oxidation resistance with respect to alkali and having a porous structure having a current collecting property is preferable. On the other hand, for a negative electrode, a perforated steel sheet obtained by applying nickel plating to an iron foil that is inexpensive and excellent in conductivity is preferable.

The thickness of the conductive support is preferably 30 to 100 μm, more preferably 40 to 70 μm. When the thickness of the conductive support is less than 30 μm, the productivity may be reduced. On the other hand, when the thickness of the conductive support exceeds 100 μm, the discharge capacity may be insufficient. .

When the conductive support is porous, the inner diameter is preferably 0.8 to 2 μm, more preferably 1 to 1.5 μm. If the inner diameter is less than 0.8 μm, the productivity may be lowered. On the other hand, if the inner diameter exceeds 2 μm, the holding performance of the hydrogen storage alloy may be insufficient.

Examples of the method for applying each electrode paste to the conductive support include roller coating using an applicator roll or the like, screen coating, blade coating, spin coating, bar coating, and the like.

Examples of the separator include a porous film and a nonwoven fabric made of a polyolefin resin such as polyethylene or polypropylene, acrylic, polyamide, or the like.

The basis weight of the separator is preferably 40 to 100 g / m ² . If the basis weight is less than 40 g / m ² , a short circuit or a decrease in self-discharge performance may occur. On the other hand, if the basis weight exceeds 100 g / m ² , the proportion of the separator per unit volume increases. Tend to go down. The separator preferably has an air permeability of 1 to 50 cm / sec. If the air permeability is less than 1 cm / sec, the internal pressure of the battery may be too high. On the other hand, if the air permeability exceeds 50 cm / sec, a short circuit or a decrease in self-discharge performance may occur. Furthermore, the average fiber diameter of the separator is preferably 1 to 20 μm. When the average fiber diameter is less than 1 μm, the strength of the separator may decrease, and the defect rate in the battery assembling process may increase. On the other hand, when the average fiber diameter exceeds 20 μm, short circuit and self-discharge performance decrease. Sometimes.

The separator is preferably subjected to a hydrophilic treatment on the fiber surface. Examples of the hydrophilization treatment include sulfonation treatment, corona treatment, fluorine gas treatment, and plasma treatment. Among them, the separator whose fiber surface has been sulfonated has a high ability to adsorb impurities such as NO ₃ ⁻ , NO ₂ ⁻ , NH ₃ ^{− and the} like, which cause a shuttle phenomenon, and an elution element from the negative electrode. The suppression effect is high and preferable.

Examples of the alkaline electrolyte include alkaline aqueous solutions containing potassium hydroxide, sodium hydroxide, lithium hydroxide and the like. The said alkaline electrolyte may be used independently and 2 or more types may be used together.

The concentration of the alkaline electrolyte is preferably a total ion concentration of 9.0 M or less, more preferably 5.0 to 8.0 M.

Various additives may be added to the alkaline electrolyte in order to improve oxygen overvoltage at the positive electrode, improve corrosion resistance of the negative electrode, improve self-discharge, and the like. Examples of such additives include oxides and hydroxides such as Y, Yb, Er, Ca, and Zn. These additives may be used independently and 2 or more types may be used together.

When the nickel-metal hydride storage battery according to the present invention is an open-type nickel-metal hydride storage battery, for example, the battery is sandwiched between a negative electrode and a positive electrode via a separator, and the electrodes are fixed so that a predetermined pressure is applied to these electrodes. It can be produced by injecting an alkaline electrolyte and assembling an open cell.

On the other hand, when the nickel-metal hydride storage battery according to the present invention is a sealed nickel-metal hydride storage battery, the battery is injected with an alkaline electrolyte before or after the positive electrode, the separator, and the negative electrode are stacked, and sealed with an exterior material. Can be manufactured. Further, in a sealed nickel-metal hydride storage battery in which a power generation element in which a positive electrode and a negative electrode are stacked via a separator is wound, an alkaline electrolyte is injected into the power generation element before or after the power generation element is wound. Is preferred. The method of injecting the alkaline electrolyte is not particularly limited, and may be injected at normal pressure. For example, a vacuum impregnation method, a pressure impregnation method, a centrifugal impregnation method, or the like may be used. Moreover, as an exterior material of a sealed nickel-metal hydride storage battery, for example, a material made of iron, stainless steel, polyolefin resin, or the like plated with a metal material such as iron or nickel can be cited.

The embodiment of the sealed nickel-metal hydride storage battery is not particularly limited. For example, a battery including a positive electrode such as a coin battery, a button battery, a square battery, and a flat battery, a negative electrode, and a single-layer or multi-layer separator, a roll And a cylindrical battery including a positive electrode, a negative electrode and a separator.

EXAMPLES Next, although an Example is given and this invention is demonstrated in more detail, this invention is not limited to these.

<Method for producing hydrogen storage alloy>

A predetermined amount of the raw material ingot was weighed so as to have the compositions of Examples 1 to 13 and Comparative Examples 1 to 8 described in Table 1, and put in a crucible, and 1500 using a high frequency melting furnace in a reduced pressure argon gas atmosphere. The raw material was melted by heating to ° C. After melting, the alloy was solidified by applying a melt spinning method and quenching at 500000 K / sec.

Next, the obtained alloy was heat-treated for 5 hours in an argon gas atmosphere pressurized to 0.2 MPa (gauge pressure, hereinafter the same), and then the obtained hydrogen storage alloy was pulverized to obtain an average particle size. A hydrogen storage alloy powder having a diameter (D50) of 50 μm was obtained.

Said heat processing was performed at 950 degreeC about the hydrogen storage alloy powder of Examples 1-12 and Comparative Examples 1-8, and was performed at 930 degreeC about the hydrogen storage alloy powder of Example 13.

<Production of open-type nickel metal hydride batteries>

After adding and mixing 3 parts by mass of nickel powder (INCO # 210) to 100 parts by mass of the hydrogen storage alloy powder obtained as described above, an aqueous solution in which a thickener (methyl cellulose) is dissolved is added. A paste made by adding 1 part by weight of a binder (styrene butadiene rubber) is applied to both sides of a 35 μm thick perforated steel sheet (opening ratio 50%), dried, and then pressed to a thickness of 0.33 mm. Thus, a negative electrode plate was obtained.

As the positive electrode plate, a sintered nickel hydroxide electrode having a capacity three times the negative electrode capacity was used.

The negative electrode plate produced as described above is sandwiched between the positive electrode plates through a separator, these electrodes are fixed so that a pressure of 1 kgf is applied, a 7M potassium hydroxide aqueous solution is injected, and an open cell Assembled.

<Evaluation of open nickel metal hydride batteries>

The open-type nickel metal hydride battery produced as described above was charged in 0.1 ItA (31 mA / g) at 150% in a water bath at 20 ° C., and the final potential of the negative electrode was −0.6 V at 0.2 ItA (vs. The discharge of Hg / HgO) was repeated 10 cycles. Furthermore, 105% charge at 1 ItA and discharge at which the end potential of the negative electrode becomes −0.6 V (vs. Hg / HgO) at 1 ItA were repeated 40 cycles. Under these conditions, a total of 50 cycles of charge and discharge were performed.

<Measurement of specific surface area>

The specific surface area of the alloy before and after the cycle test was measured by the following procedure. The negative electrode plate was taken out from each of the batteries before and after the 40 cycles of charging / discharging, washed with water and dried, and then the mixture layer portion and the substrate (punched steel plate in which iron was plated with nickel) were separated. Next, the composite material layer portion was pulverized with a mortar, placed in a specific surface area measuring device (manufactured by QUANTACHROME, MONOSORB), and the specific surface area was measured by the BET method.

<Analysis of crystal phase>

The crystal was analyzed by the following procedure. The alloy powder was subjected to X-ray diffraction measurement using a powder X-ray diffractometer (Rigaku Minifulex II). Cu was used for the X-ray tube, the output was an acceleration voltage of 30 kV and a current of 15 mA, and Cu-Kα was used. In addition, the measurement range was 2θ = 5-90 °, and step scanning with an integration time of 2 seconds at intervals of 0.02. The powder X-ray diffraction pattern obtained by the above measurement was analyzed by the Rietveld method (analysis software: RIETRAN-2000) to calculate the abundance ratio (mass%) of the crystal phase contained in the alloy.

Next, a sealed battery for a charge / discharge cycle test was prepared and a charge / discharge cycle test was performed as follows.

<Preparation of positive electrode plate for nickel metal hydride storage battery>

As the positive electrode active material, a nickel hydroxide surface containing 3% by mass of zinc and 0.6% by mass of cobalt in a solid solution state was coated with 7% by mass of cobalt hydroxide, and then an 18M sodium hydroxide solution was used. Used was air-oxidized at 110 ° C. for 1 hour. Furthermore, after adding 2% by mass of Yb ₂ O ₃ with respect to the positive electrode active material, an aqueous solution in which a thickener (carboxymethyl cellulose) is dissolved is added to prepare a paste, and the substrate surface density is 300 g / m ^2. After being filled in nickel foam and dried, it was pressed to a predetermined thickness to produce a 2000 mAh positive electrode plate.

<Preparation of negative electrode for nickel metal hydride storage battery>

An aqueous solution in which a thickener (methyl cellulose) is dissolved is added to 100 parts by mass of the hydrogen storage alloy powders of Examples 1 to 13 and Comparative Examples 1 to 8 that are pulverized so that the average particle diameter D50 is 50 μm, and further binding is performed. After adding 1 part by weight of an agent (styrene butadiene rubber), it was applied to both sides of a 35 μm thick perforated steel sheet, dried, pressed to a predetermined thickness, and a 2600 mAh negative electrode plate was formed. Produced.

<Production of sealed nickel-metal hydride storage battery>

A separator (polypropylene nonwoven fabric having a thickness of 120 μm) is folded in two from the approximate center in the longitudinal direction, the positive electrode plate is sandwiched therebetween, and the hydrogen storage alloy powders of Examples 1 to 13 and Comparative Examples 1 to 8 are placed on the outside. The electrode plate was configured by stacking the contained negative electrode plates and winding the resulting laminate in a spiral shape so that the negative electrode plates were on the outer peripheral side. The obtained electrode group was housed in a cylindrical metal battery case, and then 2.6 g of an electrolyte containing 5M KOH, 3M NaOH and 0.8M LiOH was injected, and the metal lid with a safety valve was used. The battery was sealed, and an AA size 2100 mAh nickel-metal hydride storage battery was produced as a test battery.

<Initialization>

Each test battery was initialized by the following procedure. At 20 ° C., charging was performed at 200 mA for 16 hours, and then discharging was performed at 400 mA until reaching 1 V, and this was repeated for 2 cycles. Thereafter, it was stored at 40 ° C. for 48 hours. Then, at 20 ° C., charging was carried out at 200 mA for 16 hours, resting for 1 hour, and discharging was carried out at 400 mA until reaching 1 V, and this was repeated for 2 cycles to complete the formation.

<Charge / discharge cycle test>

In the charge / discharge cycle test, -dV = 5 mV was charged at 0.5 ItA, then rested for 30 minutes, and thereafter, 1 V (20 ° C.) was discharged at 0.5 ItA. When the discharge capacity reached 60% of the initial capacity, the cycle life was determined.

Table 1 shows the measurement results of the abundance ratio of the crystal phase, the specific surface area, and the cycle life of the nickel hydride storage battery using the hydrogen storage alloy, along with the alloy compositions of the hydrogen storage alloys of Examples 1 to 13 and Comparative Examples 1 to 8.

As a result of corrosion, rare earth hydroxide and the like are generated on the surface of the hydrogen storage alloy, and the form changes. Therefore, by measuring the specific surface area value, it can be used as an index of the alloy corrosion amount. The smaller the specific surface area value, the smaller the corrosion amount, and the larger the specific surface area, the larger the corrosion amount. Hydrogen-absorbing alloy represented by the general formula (RE _1-ab Sm _a Mg _b ) (Ni _{1-c d} Al _c M _d ) _x (where 0.1 ≦ a ≦ 0.25, 0.1 <B <0.2, 0.02 <cx <0.2, 0 ≦ dx ≦ 0.1, 3.6 ≦ x ≦ 3.7, RE is selected from the group consisting of rare earth elements other than Sm and Y La is essential, and M is M is Mn and / or Co.) In the hydrogen storage alloys of Examples 1 to 13, a (Sm substitution amount) is 0.1. Less than (Comparative Example 1) or more than 0.25 (Comparative Example 2), hydrogen storage alloy having b of 0.1 or less (Comparative Example 3) or 0.2 or more (Comparative Example 4), cx Is a hydrogen storage alloy having a ratio of 0.02 or less (Comparative Example 5) or 0.2 or more (Comparative Example 6), and x (B / A ratio) is less than 3.6 (Comparative Example 7) or more than 3.7 ( Comparison It can be seen that the specific surface area value is small and the amount of corrosion is small compared to the hydrogen storage alloy of Example 8). The specific surface area value is preferably 1.5 m ² / g or less, and more preferably 1.40 m ² / g or less.

In addition, from Table 1, the hydrogen storage alloys of Examples 1 to 13 having a small specific surface area have improved corrosion resistance (durability) as compared with the hydrogen storage alloys of Comparative Examples 1 to 8 having a large specific surface area. It can be seen that the cycle life of the nickel hydride storage batteries using the hydrogen storage alloys of Examples 1 to 13 is significantly improved as compared with the nickel hydride storage batteries using the hydrogen storage alloys of Comparative Examples 1 to 8. In particular, a hydrogen storage alloy (Examples 8 and 9) containing La as RE in a molar amount of 0.6 or more with respect to the total amount of RE, Sm and Mg, and using Nd and / or Pr together, or A hydrogen storage alloy containing Co as M atoms (Example 12) has a small specific surface area and excellent corrosion resistance (durability), and a nickel-metal hydride storage battery using this has improved cycle life.

The hydrogen storage alloys of Examples 1 to 13 have a small specific surface area, and contain 80% by mass or more of the Pr ₅ Co ₁₉ phase and the Ce ₅ Co ₁₉ phase as the crystal phase of the alloy, so that the corrosion resistance (durability) is high. And the cycle life of the nickel metal hydride storage battery is improved. By using hydrogen storage alloys (Examples 1, 2, 4-9, 12, 13) containing 90% by mass or more of both in total, the cycle life of the nickel-metal hydride storage battery is further improved.

According to the present invention, a hydrogen storage alloy having high corrosion resistance (durability) can be obtained. By using this hydrogen storage alloy as a negative electrode of a nickel metal hydride storage battery, a nickel metal hydride storage battery having an excellent cycle life can be provided.

Claims (5)

Formula _{(RE 1-a over b Sm a Mg b) (Ni} 1-c-d Al c M d) x
(However, 0.1 ≦ a ≦ 0.25, 0.1 <b <0.2, 0.02 <cx <0.2, 0 ≦ dx ≦ 0.1, 3. 6 ≦ x ≦ 3.7, RE is one or more elements selected from the group consisting of rare earth elements other than Sm and Y, and the content of La in the RE is the sum of RE, Sm, and Mg The molar amount is 0.6 or more with respect to the amount, and M is M is Mn and / or Co). The hydrogen storage alloy according to claim 1, wherein the RE contains Nd and / or Pr. 3. The hydrogen storage alloy according to claim 1 , wherein the alloy contains a Pr ₅ Co ₁₉ phase and a Ce ₅ Co ₁₉ phase of 80% by mass or more as a crystal phase of the alloy. An electrode comprising the hydrogen storage alloy according to any one of claims 1 to 3 . A nickel-metal hydride storage battery comprising the electrode according to claim 4 as a negative electrode.