JP2009081040A - Hydrogen storing alloy, hydrogen storing alloy electrode using hydrogen storing alloy, and nickel hydrogen secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rare earth-Mg-Ni hydrogen storing alloy having high hydrogen equilibrium pressure while keeping alkali resistance and hydrogen storing amount; and a hydrogen storing alloy electrode using the hydrogen storing alloy; and a nickel hydrogen secondary battery having high capacity, long cycle life, and high working voltage. <P>SOLUTION: The nickel hydrogen secondary battery contains hydrogen storing alloy particles 36 in a negative electrode 26, and the hydrogen storing alloy has a composition represented by general formula: (Nd<SB>a</SB>Dy<SB>b</SB>A<SB>c</SB>)<SB>1-w</SB>Mg<SB>w</SB>Ni<SB>x</SB>Al<SB>y</SB>T<SB>z</SB>. In the formula, A and T each represent at least one element selected from the group comprising La, Pr and the like, and the group comprising V, Nb and the like; subscripts a, b, and c each satisfy the relation represented by a>0, b>0, c>0, a+b+c=1; subscripts w, x, and z each are in the range represented by 0<w<1, 0.05≤y≤0.35, 0≤z≤0.5, and 3.2≤x+y+z≤3.8. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a hydrogen storage alloy, a hydrogen storage alloy electrode using the hydrogen storage alloy, and a nickel hydride secondary battery.

Hydrogen storage alloys are attracting attention as energy conversion materials and energy storage materials because they can store hydrogen safely and easily. In addition, alkaline storage batteries using a hydrogen storage alloy as a negative electrode, particularly nickel hydride secondary batteries, have features such as high capacity and cleanliness, and thus have a great demand as consumer batteries.
Conventionally, as a hydrogen storage alloy for a negative electrode of a nickel-metal hydride secondary battery, a CaCu ₅ type alloy (rare earth-Ni-based hydrogen storage alloy) such as LaNi ₅ has been used. Rare earth-Mg-Ni hydrogen storage alloys have been developed in which some of the rare earth elements in Mg-Ni hydrogen storage alloys are replaced with Mg elements.

The rare earth-Mg-Ni hydrogen storage alloy has a feature that a large amount of hydrogen gas can be stored near room temperature, compared to the rare earth-Ni hydrogen storage alloy. However, rare earth-Mg-Ni hydrogen storage alloys in the early stages of development have a problem that it is difficult to release the stored hydrogen.
Therefore, Patent Document 1 discloses a rare earth-Mg—Ni-based hydrogen storage alloy having a specific composition. By using the rare earth-Mg—Ni-based hydrogen storage alloy, high capacity and charge / discharge cycle life are disclosed. It is said that a nickel hydride secondary battery excellent in the above will be provided.
Japanese Patent Laid-Open No. 11-323469

In recent years, attention has been focused on how to replace a dry battery as a new use of a nickel metal hydride secondary battery. Since a dry battery is a primary battery and is disposable, a nickel metal hydride secondary battery can be used repeatedly. Therefore, if a nickel metal hydride secondary battery is used instead of a dry battery, the environmental load is reduced.
And even in applications that replace such dry batteries, according to nickel-metal hydride secondary batteries using rare earth-Mg-Ni-based hydrogen storage alloys, the drive time of equipment can be extended due to the high capacity. Expected.

However, some devices that are premised on the use of dry cells include devices that are designed with a dry battery operating voltage of 1.5V, and some nickel-metal hydride batteries with an operating voltage of around 1.2V do not work well. For example, when a nickel metal hydride secondary battery is used for a remote control having a liquid crystal display unit for enhancing convenience, the liquid crystal display becomes thin.
In order to solve this problem, it is difficult to increase the operating voltage of the nickel-metal hydride secondary battery when a rare earth-Mg-Ni-based hydrogen storage alloy is used. This is because the rare earth-Mg-Ni hydrogen storage alloy has a lower ratio of B-site elements such as Ni to A-site elements such as rare-earth elements than the conventional rare-earth-Ni hydrogen storage alloys. This is because the hydrogen equilibrium pressure is low.

  The present invention has been made on the basis of the above circumstances, and the object thereof is to provide a rare earth-Mg-Ni hydrogen storage alloy having a high hydrogen equilibrium pressure while maintaining alkali resistance and hydrogen storage capacity, and the related matter. It is an object of the present invention to provide a hydrogen storage alloy electrode using a hydrogen storage alloy, thereby providing a nickel-metal hydride secondary battery having a high capacity, a long cycle life, and a high operating voltage.

In order to achieve the above object, the present inventors have conducted various studies. As a result, even in the rare earth-Mg-Ni-based hydrogen storage alloy, by including Dy in a predetermined composition, alkali resistance and hydrogen The inventors have found that the hydrogen equilibrium pressure is increased while maintaining the occlusion amount, and have arrived at the present invention.
That is, according to the present invention, the general _{formula: (Nd a Dy b A c} ) 1-w Mg w Ni x Al y T z ( In the formula, A is, La, Ce, Pr, Pm , Sm, Eu , Gd, Tb, Ho, Er, Tm, Yb, Lu, Sc, Zr, Hf, Ca and Y represent at least one element selected from the group consisting of V, Nb, Ta, Cr and Mo. , Mn, Fe, Co, Ga, Zn, Sn, In, Cu, Si, P, and B represent at least one element selected from the group consisting of a> 0, b > 0, c ≧ 0, a + b + c = 1 is satisfied, and subscripts w, x, y, z are 0 <w <1, 0.05 ≦ y ≦ 0.35, 0 ≦ z ≦ 0.5, There is provided a hydrogen storage alloy having a composition represented by: 3.2 ≦ x + y + z ≦ 3.8 (Claim 1).

Preferably, the subscript b is in the range of 0 <b <0.15 (claim 2).
Preferably, the subscript c is 0.1 or less (claim 3).
Preferably, the subscript w is in the range of 0.10 ≦ w ≦ 0.25.
Further, according to the present invention, a hydrogen storage alloy comprising the particles made of the hydrogen storage alloy according to any one of claims 1 to 4 and a conductive core holding the particles. An electrode is provided (claim 5).

  Furthermore, according to the present invention, there is provided a nickel-metal hydride secondary battery comprising the hydrogen storage alloy electrode according to claim 5 as a negative electrode (claim 6).

The hydrogen storage alloy according to claim 1 of the present invention has high hydrogen equilibrium pressure while maintaining alkali resistance and hydrogen storage amount by containing Dy in a predetermined composition. For this reason, when the said hydrogen storage alloy is applied to a nickel-hydrogen secondary battery etc., high capacity | capacitance, the improvement of a cycle life, and high operating voltage are achieved.
In the hydrogen storage alloy of claim 2, the subscript b is in the range of 0 <b <0.15. Thereby, when the said hydrogen storage alloy is applied to a nickel hydride secondary battery etc., the improvement of a cycle life is achieved further.

In the hydrogen storage alloy of claim 3, the subscript c is 0.1 or less. Thereby, when the hydrogen storage alloy is applied to a nickel metal hydride secondary battery or the like, the cycle life is improved and the operating voltage is further increased.
In the hydrogen storage alloy of claim 4, the subscript w is in the range of 0.10 ≦ w ≦ 0.25. Thereby, when the hydrogen storage alloy is applied to a nickel metal hydride secondary battery or the like, the cycle life is improved and the operating voltage is further increased.

According to a fifth aspect of the present invention, there is provided a hydrogen storage alloy electrode comprising the aforementioned hydrogen storage alloy particles. As a result, when the hydrogen storage alloy electrode is applied to a nickel metal hydride secondary battery or the like, it is possible to increase the capacity, improve the cycle life, and increase the operating voltage.
The nickel metal hydride secondary battery according to claim 6 has a high capacity, a long cycle life, and a high operating voltage due to the provision of the hydrogen storage alloy electrode described above. For this reason, the nickel hydride secondary battery can replace, for example, a dry battery, and has high industrial value.

Hereinafter, a nickel metal hydride secondary battery according to an embodiment of the present invention will be described in detail.
The nickel metal hydride secondary battery is an AA size cylindrical battery, for example, and includes an outer can 10 having a bottomed cylindrical shape with an upper end opened as shown in FIG. The bottom wall of the outer can 10 has conductivity and functions as a negative electrode terminal. Inside the opening of the outer can 10, a disc-shaped cover plate 14 having conductivity is arranged via a ring-shaped insulating packing 12, and the cover plate 14 and the insulating packing 12 caulk the opening edge of the outer can 10. It is fixed to the opening edge of the outer can 10 by processing.

  The lid plate 14 has a gas vent hole 16 in the center, and a rubber valve element 18 is disposed on the outer surface of the lid plate 14 so as to close the gas vent hole 16. Furthermore, a flanged cylindrical positive electrode terminal 20 covering the valve body 18 is fixed on the outer surface of the lid plate 14, and the positive electrode terminal 20 presses the valve body 18 against the lid plate 14. Therefore, the outer can 10 is normally airtightly closed by the lid plate 14 via the insulating packing 12 and the valve body 18. On the other hand, when gas is generated in the outer can 10 and the internal pressure increases, the valve body 18 is compressed, and the gas is released from the outer can 10 through the gas vent hole 16. That is, the cover plate 14, the valve body 18, and the positive electrode terminal 20 form a safety valve.

  An electrode group 22 is accommodated in the outer can 10. The electrode group 22 includes a belt-like positive electrode 24, a negative electrode 26, and a separator 28, respectively, and a separator is sandwiched between the positive electrode 24 and the negative electrode 26 wound in a spiral shape. That is, the positive electrode 24 and the negative electrode 26 are overlapped with each other via the separator 28. The outermost periphery of the electrode group 22 is formed by a part of the negative electrode 26 (outermost peripheral portion), and the outermost peripheral portion of the negative electrode 26 is in contact with the inner peripheral wall of the outer can 10 so that the negative electrode 26 and the outer can 10 are electrically connected to each other. Connected. The positive electrode 24, the negative electrode 26, and the separator 28 will be described later.

  In the outer can 10, a positive electrode lead 30 is disposed between one end of the electrode group 22 and the cover plate 14, and both ends of the positive electrode lead 30 are connected to the positive electrode 24 and the cover plate 14, respectively. Therefore, the positive electrode terminal 20 and the positive electrode 24 are electrically connected via the positive electrode lead 30 and the lid plate 14. A circular insulating member 32 is disposed between the cover plate 14 and the electrode group 22, and the positive electrode lead 30 extends through a slit provided in the insulating member 32. A circular insulating member 34 is also arranged between the electrode group 22 and the bottom of the outer can 10.

  Furthermore, a predetermined amount of alkaline electrolyte (not shown) is injected into the outer can 10, and a charge / discharge reaction occurs between the positive electrode 24 and the negative electrode 26 via the alkaline electrolyte contained in the separator 28. proceed. In addition, although it does not specifically limit as a kind of alkaline electrolyte, For example, sodium hydroxide aqueous solution, lithium hydroxide aqueous solution, potassium hydroxide aqueous solution, the aqueous solution which mixed 2 or more of these, etc. can be mention | raise | lifted, Further, the concentration of the alkaline electrolyte is not particularly limited, and for example, 8N one can be used.

As a material for the separator 28, for example, a polyamide fiber nonwoven fabric or a polyolefin fiber nonwoven fabric such as polyethylene or polypropylene provided with a hydrophilic functional group can be used.
The positive electrode 24 includes a conductive positive electrode substrate having a porous structure and a positive electrode mixture held in the pores of the positive electrode substrate. The positive electrode mixture includes positive electrode active material particles and, if necessary, the positive electrode 24 These are various additive particles for improving the characteristics and a binder for binding the mixed particles of these positive electrode active material particles and additive particles to the positive electrode substrate.

  The positive electrode active material particles are nickel hydroxide particles because this battery is a nickel-hydrogen secondary battery. However, the nickel hydroxide particles may be dissolved in cobalt, zinc, cadmium or the like, or the surface is alkaline. You may coat | cover with the heat-treated cobalt compound. In addition, although there is no particular limitation, additives include, in addition to yttrium oxide, cobalt compounds such as cobalt oxide, metal cobalt, and cobalt hydroxide, zinc such as metal zinc, zinc oxide, and zinc hydroxide. Compounds, rare earth compounds such as erbium oxide, etc., and hydrophilic or hydrophobic polymers can be used as binders.

  The negative electrode 26 has a conductive negative electrode substrate (core body) having a strip shape, and a negative electrode mixture is held on the negative electrode substrate. The negative electrode substrate is made of a sheet-like metal material in which through-holes are distributed. For example, a punching metal or a metal powder sintered body substrate that is sintered after molding metal powder can be used. Therefore, the negative electrode mixture is filled in the through holes of the negative electrode substrate and is held in layers on both surfaces of the negative electrode substrate.

  Although the negative electrode mixture is schematically shown in a circle in FIG. 1, the hydrogen storage alloy particles 36 capable of occluding and releasing hydrogen as a negative electrode active material, and a conductive auxiliary agent such as carbon (for example, carbon as necessary) And a binder 38 that binds the hydrogen storage alloy and the conductive additive to the negative electrode substrate. A hydrophilic or hydrophobic polymer or the like can be used as the binder 38, and carbon black or graphite can be used as the conductive assistant. Note that when the active material is hydrogen, the negative electrode capacity is defined by the amount of the hydrogen storage alloy. Therefore, in the present invention, the hydrogen storage alloy is also referred to as a negative electrode active material. The negative electrode 24 is also referred to as a hydrogen storage alloy electrode.

The hydrogen storage alloy in the hydrogen storage alloy particles 36 of this battery is a rare earth-Mg-Ni hydrogen storage alloy, and the main crystal structure is not CaCu ₅ type, but is combined with AB ₅ type structure and AB ₂ type structure. The superlattice structure has a general formula:
_{(Nd a Dy b A c)} 1-w Mg w Ni x Al y T z ... (1)
Indicated by

  However, in Formula (1), A is from the group which consists of La, Ce, Pr, Pm, Sm, Eu, Gd, Tb, Ho, Er, Tm, Yb, Lu, Sc, Zr, Hf, Ca, and Y. Represents at least one element selected, and T is selected from the group consisting of V, Nb, Ta, Cr, Mo, Mn, Fe, Co, Ga, Zn, Sn, In, Cu, Si, P, and B Represents at least one element, subscripts a, b, and c satisfy the relationship represented by a> 0, b> 0, c ≧ 0, a + b + c = 1, and subscripts w, x, y, and z 0 <w <1, 0.05 ≦ y ≦ 0.35, 0 ≦ z ≦ 0.5, and 3.2 ≦ x + y + z ≦ 3.8.

The hydrogen storage alloy particles 36 can be obtained, for example, as follows.
First, metal raw materials are weighed and mixed so as to have the above-described composition, and this mixture is melted in, for example, a high-frequency melting furnace to form an ingot. The obtained ingot was subjected to heat treatment in an inert gas atmosphere at a temperature of 900 to 1200 ° C. for 5 to 24 hours, and the metal structure of the ingot was combined with the AB ₅ type structure and the AB ₂ type structure. Use superlattice structure. Thereafter, the ingot is pulverized and classified to a desired particle size by sieving, whereby the hydrogen storage alloy particles 36 can be obtained.

The nickel hydride secondary battery described above has a high capacity because the hydrogen storage alloy particles 36 are mainly composed of a rare earth-Mg-Ni hydrogen storage alloy.
Further, in this nickel metal hydride secondary battery, the rare earth-Mg—Ni-based hydrogen storage alloy constituting the hydrogen storage alloy particles 36 has the composition represented by the above formula (1) and contains Dy. High hydrogen equilibrium pressure while maintaining alkali resistance and hydrogen storage capacity. For this reason, this nickel metal hydride secondary battery has a high capacity, a long cycle life, and a high operating voltage.

1. Battery assembly Example 1
(1) Fabrication of negative electrode Prepare the rare earth component raw material so that the breakdown of the rare earth component is 20% Pr, 40% Nd, and 40% Dy in terms of the number of atoms, and the rare earth component raw material A mass of a hydrogen storage alloy containing Mg, Ni and Al in an atomic ratio of 0.85: 0.15: 3.3: 0.20: 0.10 was prepared using an induction melting furnace. This alloy was heat-treated at 1000 ° C. for 10 hours in an argon atmosphere, and the composition was (Pr _0.20 Nd _0.40 Dy _0.40 ) _0.85 Mg _0.15 Ni _3.3 Al _0.2 Zn _0.1 An ingot of storage alloy was obtained.

The rare earth-Mg-Ni hydrogen storage alloy ingot was mechanically pulverized in an inert gas atmosphere, and alloy particles having a particle size in the range of 400 to 200 mesh were selected by sieving. When the particle size distribution of the alloy particles was measured using a laser diffraction / scattering type particle size distribution measuring apparatus, the average particle size corresponding to 50% by weight integral was 30 μm, and the maximum particle size was 45 μm.
After adding 0.4 parts by weight of sodium polyacrylate, 0.1 parts by weight of carboxymethylcellulose, and 2.5 parts by weight of polytetrafluoroethylene dispersion (dispersion medium: water, solid content 60 parts by weight) to 100 parts by weight of the alloy particles And kneading to obtain a slurry of the negative electrode mixture.

This slurry was applied evenly and uniformly on both surfaces of a 60 μm thick Fe punching metal plated with Ni. After the slurry was dried, the punching metal was pressed and cut to prepare a negative electrode for an AA size nickel-hydrogen secondary battery.
(2) Preparation of positive electrode A mixed aqueous solution of nickel sulfate, zinc sulfate and cobalt sulfate was prepared so that Zn was 3% by mass and Co was 1% by mass with respect to metal Ni, and this mixed aqueous solution was stirred. While adding sodium hydroxide aqueous solution gradually. At this time, the pH during the reaction was maintained at 13 to 14 to precipitate nickel hydroxide particles. The nickel hydroxide particles were washed three times with 10 times the amount of pure water, and then dehydrated and dried.

The obtained nickel hydroxide particles were mixed with 40% by mass of an HPC dispersion liquid to prepare a slurry of a positive electrode mixture. The slurry was filled in a nickel substrate having a porous structure and dried, and then the substrate was rolled and cut to produce a positive electrode for an AA size nickel metal hydride secondary battery.
(3) Assembly of nickel-metal hydride secondary battery The negative electrode and the positive electrode obtained as described above are spirally wound through a separator made of polypropylene or nylon nonwoven fabric to form an electrode group, and this electrode group Is contained in an outer can, and a 30% by weight potassium hydroxide aqueous solution containing lithium and sodium is injected into the outer can and has the configuration shown in FIG. 1 and has a nominal capacity of 2500 mAh. An AA size nickel metal hydride secondary battery was assembled.

Example 2
A nickel-metal hydride secondary battery was assembled in the same manner as in Example 1 except that the composition of the hydrogen storage alloy was (Pr _0.35 Nd _0.50 Dy _0.15 ) _0.85 Mg _0.15 Ni _3.3 Al _0.2 Zn _0.1 .
Example 3
A nickel hydrogen secondary battery was assembled in the same manner as in Example 1 except that the composition of the hydrogen storage alloy was changed to (Pr _0.30 Nd _0.60 Dy _0.10 ) _0.85 Mg _0.15 Ni _3.3 Al _0.2 Zn _0.1 .

Example 4
A nickel-hydrogen secondary battery was assembled in the same manner as in Example 1 except that the composition of the hydrogen storage alloy was changed to (Pr _0.30 Nd _0.60 Dy _0.10 ) _0.85 Mg _0.15 Ni _2.9 Al _0.2 Zn _0.1 .
Example 5
A nickel metal hydride secondary battery was assembled in the same manner as in Example 1 except that the composition of the hydrogen storage alloy was changed to (Pr _0.30 Nd _0.60 Dy _0.10 ) _0.85 Mg _0.15 Ni _3.5 Al _0.2 Zn _0.1 .

Example 6
A nickel-hydrogen secondary battery was assembled in the same manner as in Example 1 except that the composition of the hydrogen storage alloy was changed to (Pr _0.10 Nd _0.80 Dy _0.10 ) _0.85 Mg _0.15 Ni _3.3 Al _0.2 Zn _0.1 .
Example 7
A nickel-metal hydride secondary battery was assembled in the same manner as in Example 1 except that the composition of the hydrogen storage alloy was changed to (Pr _0.20 Nd _0.40 Dy _0.40 ) _0.75 Mg _0.25 Ni _3.3 Al _0.2 Zn _0.1 .

Example 8
A nickel hydrogen secondary battery was assembled in the same manner as in Example 1 except that the composition of the hydrogen storage alloy was (Pr _0.20 Nd _0.40 Dy _0.40 ) _0.90 Mg _0.10 Ni _3.3 Al _0.2 Zn _0.1 .
Comparative Example 1
A nickel metal hydride secondary battery was assembled in the same manner as in Example 1 except that the composition of the hydrogen storage alloy was (Pr _0.30 Nd _0.70 ) _0.85 Mg _0.15 Ni _3.3 Al _0.2 Zn _0.1 .

Comparative Example 2
A nickel-metal hydride secondary battery was assembled in the same manner as in Example 1 except that the composition of the hydrogen storage alloy was (Pr _0.20 Nd _0.40 Dy _0.40 ) _0.85 Mg _0.15 Ni _3.5 Zn _0.1 .
Comparative Example 3
A nickel metal hydride secondary battery was assembled in the same manner as in Example 1 except that the composition of the hydrogen storage alloy was (Pr _0.20 Nd _0.40 Dy _0.40 ) _0.85 Mg _0.15 Ni _3.1 Al _0.4 Zn _0.1 .

Comparative Example 4
A nickel hydrogen secondary battery was assembled in the same manner as in Example 1 except that the composition of the hydrogen storage alloy was changed to (Pr _0.30 Nd _0.60 Dy _0.10 ) _0.85 Mg _0.15 Ni _3.6 Al _0.2 Zn _0.1 .
Comparative Example 5
A nickel metal hydride secondary battery was assembled in the same manner as in Example 1 except that the composition of the hydrogen storage alloy was changed to (Pr _0.30 Nd _0.60 Dy _0.10 ) _0.85 Mg _0.15 Ni _2.8 Al _0.2 Zn _0.1 .

Comparative Example 6
A nickel-metal hydride secondary battery was assembled in the same manner as in Example 1 except that the composition of the hydrogen storage alloy was changed to (Pr _0.20 Nd _0.40 Dy _0.40 ) _0.70 Mg _0.30 Ni _3.3 Al _0.2 Zn _0.1 .
Comparative Example 7
A nickel-metal hydride secondary battery was assembled in the same manner as in Example 1 except that the composition of the hydrogen storage alloy was (Pr _0.20 Nd _0.40 Dy _0.40 ) _0.95 Mg _0.05 Ni _3.3 Al _0.2 Zn _0.1 .

In Examples 1-8 and Comparative Examples 1-7, when producing hydrogen storage alloys, Pr and Nd as raw materials were based on didymium (mixed metal of Pr and Nd), and Pr as a single metal. May be added. In general, didymium is cheaper than single metals of Pr and Nd, so a hydrogen storage alloy can be produced at a lower cost.
2. Battery Evaluation (1) Operating Voltage For each battery of Examples 1-8 and Comparative Examples 1-7, measure the intermediate operating voltage when charged at a current of 0.1C for 16 hours and then discharged at a current of 0.2C. did. These results are shown in Table 1 as the difference (unit: mV) from the intermediate operating voltage of Comparative Example 1.

In Table 1, subscripts a, b, c, w, x, y, and z are shown, and the ratio of the number of elements at the B site to the number of elements at the A site (B / A ratio) is also shown.
(2) Cycle life For each of the batteries of Examples 1 to 8 and Comparative Examples 1 to 7, the battery capacity measurement was repeated for 1 hour at a current of 1.0 C and then discharged to a final voltage of 0.8 V at a current of 1.0 C. The number of cycles (cycle life) until the battery could not be discharged was counted. These results are shown in Table 1 as relative values with the result of Comparative Example 1 as 100.

(3) Evaluation results Table 1 clearly shows the following.
(I) The working voltage is greatly improved in Example 1 (b = 0.4) containing Dy compared to Comparative Example 1 (b = 0) containing no Dy. In Example 1, the cycle life is also improved, and the inclusion of Dy in the rare earth-Mg-Ni-based hydrogen storage alloy is an elemental technology that achieves both higher operating voltage and improved cycle life. Recognize.

(Ii) The contents of Dy are examined by comparing Examples 1 to 3. In Example 2 in which the subscript b of Dy was 0.15, the operating voltage was lower than that in Example 1 in which the subscript b was 0.4, but the cycle life was comparable. In Example 3 in which the subscript b of Dy is 0.10, the operating voltage is further reduced, but the cycle life is improved. Thus, from the viewpoint of improving the cycle life, the subscript b is preferably set to less than 0.15 (b <0.15).
However, since the operating voltage decreases when the Dy content is reduced, the subscript b is more preferably in the range of 0.10 ≦ b <0.15 considering the balance between the cycle life and the operating voltage.

(Iii) Example 1 and Comparative Examples 2 and 3 are compared to examine the Al content. From Comparative Example 2 (y = 0), when the rare earth-Mg—Ni-based hydrogen storage alloy does not contain Al and contains Dy, the operating voltage is improved compared to Example 1 (y = 0.2), but the cycle The service life is drastically reduced. On the other hand, in Comparative Example 3 (y = 0.4) having a large Al content, the cycle life was improved compared to Example 1 (y = 0.2), but the operating voltage was greatly reduced. Therefore, the subscript y of Al is set in the range of 0.05 ≦ y ≦ 0.35. Preferably, the subscript y is set in a range of 0.10 ≦ y ≦ 0.20.

(Iv) Compare Examples 3 to 5 and Comparative Examples 4 and 5 to examine the B / A ratio. From Example 4 and Comparative Example 4, it can be seen that when the B / A ratio is increased, the operating voltage is improved, but when the B / A ratio exceeds 3.8, the cycle life is decreased.
On the other hand, from Example 5 and Comparative Example 5, it can be seen that when the B / A ratio is lowered below 3.2, the operating voltage rapidly decreases. Accordingly, the B / A ratio, that is, x + y + z is set in a range of 3.2 ≦ x + y + z ≦ 3.8. Preferably, x + y + z is set in a range of 3.3 ≦ x + y + z ≦ 3.5.

(V) Examples 1, 7, 8 and Comparative Examples 6 and 7 are compared to examine the Mg content. From Example 7 and Comparative Example 6, it can be seen that the cycle life decreases when the subscript w exceeds 0.25. On the other hand, from Example 8 and Comparative Example 7, it can be seen that when the subscript w is smaller than 0.1, the operating voltage rapidly decreases. From this, it is understood that the subscript w is preferably in the range of 0.10 ≦ w ≦ 0.25. The subscript w is more preferably in the range of 0.10 ≦ w ≦ 0.20.

(Vi) Compare the Examples 3 and 6 to examine the Pr content. In Example 6 where the subscript c is 0.10, the operating voltage and the cycle life are remarkably improved as compared with Example 3 where the subscript c is 0.3. From this, it is understood that the subscript c is desirably 0.10 or less.
(Vii) In Examples 1 to 8, the subscript z was 0.1, but the subscript z is set in the range of 0 ≦ z ≦ 0.5. The reason why the subscript z is set to 0.5 or less is that when Ni is replaced with another element, the alloy capacity is reduced, and when Al is replaced with another element, the corrosion resistance is reduced.
(Viii) In Examples 1-8, although the rare earth-Mg-Ni hydrogen storage alloy contained Nd, the Nd subscript a is set larger than 0 because it is a relatively easily available rare earth element. This is because the effect of increasing the equilibrium pressure is high and the oxidation resistance is high.

The present invention is not limited to the above-described embodiment and examples, and various modifications are possible. For example, the nickel-hydrogen secondary battery may be a prismatic battery, and the mechanical structure is particularly limited. Never happen.
Finally, it goes without saying that the hydrogen storage alloy and the hydrogen storage alloy electrode of the present invention can be applied to other articles other than nickel-hydrogen secondary batteries.

1 is a partially cutaway perspective view showing a nickel metal hydride secondary battery according to an embodiment of the present invention, schematically showing an enlarged part of a negative electrode in a circle.

Explanation of symbols

26 Negative electrode
36 Hydrogen storage alloy particles

Claims (6)

General _{formula: (Nd a Dy b A c} ) 1-w Mg w Ni x Al y T z
(In the formula, A is selected from the group consisting of La, Ce, Pr, Pm, Sm, Eu, Gd, Tb, Ho, Er, Tm, Yb, Lu, Sc, Zr, Hf, Ca, and Y. T represents at least one element, and T is at least one selected from the group consisting of V, Nb, Ta, Cr, Mo, Mn, Fe, Co, Ga, Zn, Sn, In, Cu, Si, P, and B The subscripts a, b, and c satisfy the relationship indicated by a> 0, b> 0, c ≧ 0, a + b + c = 1, and the subscripts w, x, y, and z (The ranges are 0 <w <1, 0.05 ≦ y ≦ 0.35, 0 ≦ z ≦ 0.5, and 3.2 ≦ x + y + z ≦ 3.8, respectively.)
The hydrogen storage alloy which has a composition represented by these.   2. The hydrogen storage alloy according to claim 1, wherein the subscript b is in the range of 0 <b <0.15.   The hydrogen storage alloy according to claim 1 or 2, wherein the subscript c is 0.1 or less.   The hydrogen storage alloy according to any one of claims 1 to 3, wherein the subscript w is in a range of 0.10 ≤ w ≤ 0.25.   5. A hydrogen storage alloy electrode comprising: a particle made of the hydrogen storage alloy according to claim 1; and a conductive core body that holds the particle.   A nickel metal hydride secondary battery comprising the hydrogen storage alloy electrode according to claim 5 as a negative electrode.

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