JP2008208428A - Hydrogen storage alloy, and hydrogen storage alloy electrode and nickel-hydrogen secondary battery both using this alloy - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rare earth-Mg-Ni-based hydrogen storage alloy containing inexpensive La as a main component and hardly causing pulverization by charge/discharge and a hydrogen storage alloy electrode using this alloy and hereby to provide a high-capacity nickel-hydrogen secondary battery excellent in cycle characteristics using the rare earth-Mg-Ni-based hydrogen storage alloy at a low cost. <P>SOLUTION: The nickel-hydrogen secondary battery contains particles of a hydrogen storage alloy in a negative pole, and this hydrogen storage alloy has a composition represented by general formula (La<SB>a</SB>Pr<SB>b</SB>Nd<SB>c</SB>A<SB>d</SB>)<SB>1-x</SB>Mg<SB>x</SB>Ni<SB>y</SB>T<SB>z</SB>(wherein, A represents at least one element selected from the group consisting of Sm, Eu, etc.; T represents at least one element selected from the group consisting of V, Nb, etc.; subscripts a, b, c and d satisfy relations represented by a≥0.4, b>0, c≥0, d≥0, a≥b>c and a+b+c+d=1, respectively; and subscripts x, y and z are within the ranges represented by 0.10≤x≤0.25, 0.05≤z≤0.35 and 3.0≤y+z≤4.0, respectively). <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a hydrogen storage alloy, a hydrogen storage alloy electrode using the 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.
As a hydrogen storage alloy for the negative electrode of a nickel metal hydride secondary battery, an AB ₅ type (CaCu ₅ type) alloy such as LaNi ₅ is conventionally used. However, in order to increase the capacity of the battery, an AB ₅ type alloy is used. Rare earth-Mg-Ni alloys have been developed in which some of the rare earth elements are replaced with Mg elements.

Rare earth-Mg-Ni alloys have a feature that they can occlude a large amount of hydrogen gas at around room temperature, compared to AB ₅ type alloys. However, rare earth-Mg-Ni alloys in the early stages of development have low alkali resistance, and the sealed alkaline storage battery to which this alloy is applied has a problem that the cycle life of the battery is shortened.
Therefore, Patent Document 1 discloses a rare earth-Mg-Ni alloy having excellent alkali resistance and a secondary battery using the alloy as a negative electrode. According to the rare earth-Mg-Ni alloy of Patent Document 1, the alkali resistance of the alloy is improved by limiting the contents of La and Ce among the rare earth components, and the cycle life of the secondary battery is improved.

Further, Patent Document 2 discloses a secondary battery using a rare earth -Mg-Ni based alloy and AB ₅ type alloys, the rare earth -Mg-Ni based alloy, it is limited the content of Ce of the rare earth component As a result, alkali resistance is improved.
Furthermore, Patent Document 3 discloses a rare earth-Mg-Ni alloy that does not contain La and Ce, and this alloy also has excellent alkali resistance.

As can be seen from these Patent Documents 1 to 3, the flow of research and development of rare earth-Mg-Ni alloys excellent in alkali resistance is in the direction of further limiting the contents of La and Ce.
JP 2005-290473 A JP 2006-040847 JP JP 2004-263213 A

However, the rare earth-Mg-Ni alloys disclosed in Patent Documents 1 to 3 have a problem in cost.
That is, when producing a conventional AB type ₅ alloy, Mm (Misch metal) was used as the main raw material of the rare earth component. Since Mm is a mixture of La, Ce, Pr, and Nd, it is inexpensive and suitable as a battery raw material.

  On the other hand, when producing the rare earth-Mg-Ni alloys disclosed in Patent Documents 1 to 3, it is necessary to limit the contents of La and Ce. Metal must be used. Since rare earth elemental metals are more expensive than misch metals, their use leads to an increase in the price of rare earth-Mg-Ni alloys, and hydrogen storage alloy electrodes and batteries using such alloys. For this reason, the rare earth-Mg-Ni-based alloy in which the contents of La and Ce are limited has been difficult to use for industrial use.

  The present invention has been made based on the above-described circumstances, and the object thereof is to include a rare earth-Mg—Ni-based hydrogen storage alloy that includes inexpensive La as a main component and is difficult to be pulverized by charge and discharge, and the alloy. It is an object of the present invention to provide a nickel-metal hydride secondary battery having a high capacity and excellent cycle characteristics using a rare earth-Mg—Ni-based hydrogen storage alloy.

In order to achieve the above object, the present inventors have countered the flow of research and development to limit the content of La, while using inexpensive La as a main component, while using rare-earth-Mg-Ni-based hydrogen storage alloys. The means for ensuring the alkali resistance was intensively studied.
In the examination process, the present inventors have found that rare earth element minerals produced in nature contain more Nd than Pr. Therefore, in the conventional rare earth-Mg-Ni alloys, the Pr content is Nd. Focusing on the fact that it was more than the amount, a new rare earth-Mg-Ni alloy containing more Pr than Nd was developed. Among the new rare earth-Mg-Ni alloys having a higher Pr content than the Nd content, a battery using the alloy is used as long as it contains La as a main component and substantially does not contain Ce. Thus, the inventors have found that the cycle characteristics do not deteriorate and have arrived at the present invention.

That is, according to the present invention, the general formula: (La _a Pr _b Nd _c A _d ) _1-x Mg _x Ni _y T _z (where A is Sm, Eu, Gd, Tb, Dy, Ho , Er, Tm, Yb, Lu, Sr, Sc, Y, Zr, Hf, Ca and Ti represent at least one element selected from the group consisting of V, Nb, Ta, Cr, Mo, Mn , Fe, Co, Al, Ga, Zn, Sn, In, Cu, Si, P and at least one element selected from the group consisting of B, and the subscripts a, b, c, and d are a ≧ 0.4, respectively. , B> 0, c ≧ 0, d ≧ 0, a ≧ b> c, a + b + c + d = 1, and the subscripts x, y, z are 0.10 ≦ x ≦ 0.25, 0.05 ≦ z ≦ 0.35, 3.0, respectively. A hydrogen storage alloy having a composition represented by ≦ y + z ≦ 4.0 is provided.

Preferably, the subscript d is 0.1 or less (claim 2).
Moreover, according to this invention, the hydrogen storage alloy electrode provided with the particle | grains which consist of the hydrogen storage alloy of Claim 1 or Claim 2, and the core which has the electroconductivity filled with the said particle | grain is provided. Item 3).
Furthermore, according to the present invention, there is provided a nickel metal hydride secondary battery comprising the hydrogen storage alloy electrode according to claim 3 as a negative electrode (claim 4).

In the hydrogen storage alloy according to claim 1 of the present invention, the subscript b not containing Ce and related to the Pr content is larger than the subscript c related to the Nd content, and the Pr content is higher than the Nd content. Therefore, when applied to an alkaline storage battery or the like, the hydrogen storage alloy is prevented from being pulverized as the charge / discharge cycle progresses.
On the other hand, in this hydrogen storage alloy, the subscript “a” related to the La content is 0.4 or more, and the La content is large.

The hydrogen storage alloy according to claim 2 has a subscript d of 0.1 or less, so that it is more difficult to pulverize when applied to an alkaline storage battery or the like.
Since the hydrogen storage alloy electrode of claim 3 of the present invention includes the hydrogen storage alloy of claim 1 or claim 2, when applied to an alkaline storage battery or the like, the hydrogen storage alloy is prevented from being pulverized and has excellent durability. And inexpensive.

  Since the nickel hydride secondary battery of claim 4 of the present invention includes the hydrogen storage alloy electrode of claim 3 as a negative electrode, it has high capacity, is excellent in cycle characteristics, and is inexpensive.

Hereinafter, a nickel metal hydride secondary battery according to an embodiment of the present invention will be described in detail.
This battery is, for example, an AA size cylindrical battery, and includes an outer can 10 having a bottomed cylindrical shape with an open upper end 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, Also, the concentration of the alkaline electrolyte is not particularly limited, and, for example, 8N 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 alloy, and the main crystal structure is not a CaCu ₅ type, but a superlattice combining an AB ₅ type structure and an AB ₂ type structure. Structure, the composition of which is the general formula:
(La _a Pr _b Nd _c A _d ) _1-x Mg _x Ni _y T _z (1)
Indicated by

  However, in Formula (1), A is at least 1 chosen from the group which consists of Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Sr, Sc, Zr, Hf, Ca, and Ti. T represents at least one element selected from the group consisting of V, Nb, Ta, Cr, Mo, Mn, Fe, Co, Al, Ga, Zn, Sn, In, Cu, Si, P, and B Represents a kind of element, the subscripts a, b, c, d satisfy the relationship indicated by a ≧ 0.4, b> 0, c ≧ 0, d ≧ 0, a ≧ b> c, a + b + c + d = 1, respectively. x, y, and z are in the ranges indicated by 0.10 ≦ x ≦ 0.25, 0.05 ≦ z ≦ 0.35, and 3.0 ≦ y + z ≦ 4.0, respectively.

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 heat-treated 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 an AB ₅ type structure and an AB ₂ type structure. Make the 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-hydrogen secondary battery described above has a high capacity because the hydrogen storage alloy particles 36 are mainly composed of a rare earth-Mg-Ni alloy.
In this nickel metal hydride secondary battery, the rare earth-Mg-Ni alloy constituting the hydrogen storage alloy particles 36 is (1) the subscript a related to the La content is 0.4 or more and contains La as a main component. , (2) substantially free of Ce and (3) the subscript b related to the Pr content is larger than the subscript c related to the Nd content, and the Pr content in terms of molar ratio is Nd Since the amount is larger than the amount, pulverization of the hydrogen storage alloy particles 36 accompanying the progress of the charge / discharge cycle is prevented.

Therefore, this nickel metal hydride secondary battery has excellent cycle characteristics.
Furthermore, in this nickel metal hydride secondary battery, the rare earth-Mg-Ni alloy of the hydrogen storage alloy particles 36 has a subscript a related to the La content of 0.4 or more and contains a large amount of La as a main component. It is produced industrially at a low cost.
In the formula (1), the reasons for limiting the numerical ranges of the subscripts x, y, and z are as follows.

The reason why the subscript x representing the ratio of the number of Mg atoms at the A site is set in a range represented by 0.10 ≦ x ≦ 0.25 is that when x is less than 0.10, the alloy capacity is significantly reduced. Moreover, when x exceeds 0.25, the corrosion resistance of the alloy is lowered, and the life characteristics of the battery are lowered.
The subscript z representing the ratio of the number of T atoms at the B site is set in a range represented by 0.05 ≦ z ≦ 0.35 because the effect of the present invention becomes remarkable when the value of z is in this range. is there.

  The sum of the subscripts y and z representing the ratio of the B site to the A site is set to a range represented by 3.0 ≦ y + z ≦ 4.0 because if y + z becomes too small, the hydrogen in the hydrogen storage alloy As the storage stability of the hydrogen increases, the hydrogen releasing ability deteriorates, and if y + z becomes too large, the hydrogen storage sites in the hydrogen storage alloy decrease and the deterioration of the hydrogen storage capacity begins to occur. It is.

1. Battery assembly Example 1
(1) Fabrication of negative electrode Rare earth component raw materials are prepared so that the breakdown of rare earth components is 45% La, 40% Pr and 15% Zr in terms of atomic ratio, A mass of a hydrogen storage alloy containing Mg, Ni, and Al in an atomic ratio of 0.85: 0.15: 3.30: 0.07 was prepared using an induction melting furnace. This alloy was heat-treated in an argon atmosphere at 1000 ° C. for 10 hours, and a superlattice rare earth-Mg-Ni alloy ingot represented by the composition (La _0.45 Pr _0.40 Zr _0.15 ) _0.85 Mg _0.15 Ni _3.30 Al _0.07 Got.

The ingot of the rare earth-Mg-Ni alloy 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 device, the average particle size corresponding to 50% by weight was 30 μm, and the maximum particle size was 45 μm.
With respect to 100 parts by mass of the alloy particles, 0.4 parts by mass of sodium polyacrylate, 0.1 parts by mass of carboxymethylcellulose, 2.5 parts by mass of polytetrafluoroethylene dispersion (dispersion medium: water, solid content 60 parts by mass) and metal Sn ( After adding 1 part by mass of tin), the mixture was kneaded to obtain a slurry of a 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 In the outer can, and a lithium hydroxide sodium-containing 30% by weight potassium hydroxide aqueous solution containing lithium and sodium is injected into the outer can, so that the battery having the configuration shown in FIG. AA size NiMH secondary battery of 300Wh / l 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 (La _0.45 Pr _0.36 Nd _0.04 Zr _0.15 ) _0.85 Mg _0.15 Ni _3.30 Al _0.07 .
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 (La _0.45 Pr _0.32 Nd _0.08 Zr _0.15 ) _0.85 Mg _0.15 Ni _3.30 Al _0.07 .

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 (La _0.45 Pr _0.28 Nd _0.12 Zr _0.15 ) _0.85 Mg _0.15 Ni _3.30 Al _0.07 .
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 (La _0.45 Pr _0.24 Nd _0.16 Zr _0.15 ) _0.85 Mg _0.15 Ni _3.30 Al _0.07 .

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 (La _0.45 Pr _0.45 Zr _0.10 ) _0.85 Mg _0.15 Ni _3.30 Al _0.07 .
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 (La _0.45 Pr _0.20 Nd _0.20 Zr _0.15 ) _0.85 Mg _0.15 Ni _3.30 Al _0.07 .

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 (La _0.45 Pr _0.16 Nd _0.24 Zr _0.15 ) _0.85 Mg _0.15 Ni _3.30 Al _0.07 .
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 (La _0.45 Pr _0.12 Nd _0.28 Zr _0.15 ) _0.85 Mg _0.15 Ni _3.30 Al _0.07 .

Comparative Example 4
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 (La _0.45 Pr _0.08 Nd _0.32 Zr _0.15 ) _0.85 Mg _0.15 Ni _3.30 Al _0.07 .
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 (La _0.45 Pr _0.04 Nd _0.36 Zr _0.15 ) _0.85 Mg _0.15 Ni _3.30 Al _0.07 .

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 (La _0.45 Nd _0.40 Zr _0.15 ) _0.85 Mg _0.15 Ni _3.30 Al _0.07 .
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 (La _0.10 Pr _0.20 Nd _0.55 Zr _0.15 ) _0.85 Mg _0.15 Ni _3.30 Al _0.07 .

In Examples 1 to 6, when producing a hydrogen storage alloy, Pr and Nd raw materials may be based on didymium (a mixed metal of Pr and Nd), and a Pr single metal may be added as a deficiency. . 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) Cycle life For each battery of Examples 1 to 6 and Comparative Examples 1 to 7, the battery capacity was measured by charging to 1.0V current to 1.0V after charging for 1 hour at 1.0C current. Repeatedly, the number of cycles (cycle life) until the battery could not be discharged was counted. These results are shown in Table 1 and FIG. 2 (except for Comparative Example 7), with the result of Comparative Example 7 being 100.

(2) Average particle size For each of the batteries of Examples 1 to 6 and Comparative Examples 1 to 7, after repeating charge and discharge 50 times under the same charge and discharge conditions as in the above cycle life test, the battery was disassembled to store hydrogen. Alloy particles were collected and their average particle size was examined. These results are converted into a ratio to the initial average particle diameter, and are shown in Table 1 as the average particle diameter after the cycle.

The following is clear from Table 1 and FIG.
(1) It can be seen that in Examples 1 to 4 and Comparative Examples 1 to 6, the value of Pr / (Pr + Nd), that is, the value of b / (b + c) is greatly different at the boundary of 0.5. When Pr / (Pr + Nd) is 0.5 or less, the cycle characteristics are slightly improved in the range of 0.2 to 0.3, but the cycle characteristics are generally low. In contrast, when the value of Pr / (Pr + Nd) exceeds 0.5, that is, when the Pr content exceeds the Nd content, it can be seen that the cycle characteristics are greatly improved.

(2) In Examples 1 to 4 and Comparative Examples 1 to 7, it can be seen that the cycle characteristics are substantially proportional to the post-cycle average particle size. From this, the pulverization of the rare earth-Mg-Ni alloy accompanying the storage and release of hydrogen is suppressed, so that the cycle characteristics are improved in Examples 1 to 4 in which the Pr content is higher than the Nd content. it is conceivable that.
(3) In Comparative Example 7 with a low La content, even when Pr / (Pr + Nd) is 0.5 or less, it is understood that pulverization does not proceed and cycle characteristics do not deteriorate.
(4) From the comparison between Example 1 and Example 6, the cycle characteristics are improved by reducing the Zr content, that is, the subscript d in the formula (1) from 0.15 to 0.10, and the subscript d is 0.10 or less. Is preferable.

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.
In the above-described embodiment, a preferable range of the subscript a is a ≧ 0.45, and a more preferable range is a ≧ 0.50. A preferred range for the subscript b is b ≧ 0.15, and a more preferred range is b ≧ 0.20. A preferred range for the subscript c is c ≦ 0.20, and a more preferred range is c ≦ 0.12.

In the above-described embodiment, in formula (1), the subscript x is in the range represented by 0.10 ≦ x ≦ 0.25, but the preferred range is 0.10 ≦ x ≦ 0.20, and the more preferred range is 0.10 ≦ x. x ≦ 0.15.
In the above-described embodiment, in the formula (1), the subscript z is in a range represented by 0.05 ≦ z ≦ 0.35, but a preferred range is 0.10 ≦ z ≦ 0.30, and a more preferred range is 0.15 ≦ z. z ≦ 0.25.

In the above-described embodiment, in the formula (1), the sum of the subscripts y and z falls within the range represented by 3.0 ≦ y + z ≦ 4.0, but the preferred range is 3.0 ≦ y + z ≦ 3.8. A more preferable range is 3.2 ≦ y + z ≦ 3.6.
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, and schematically shows an enlarged part of a negative electrode in a circle. It is a graph which shows the relationship between Pr / (Pr + Nd) and a cycle characteristic in the nickel hydride secondary battery of an Example and a comparative example.

Explanation of symbols

26 Negative electrode
36 Hydrogen storage alloy particles

Claims (4)

General formula:
(La _a Pr _b Nd _c A _d ) _1-x Mg _x Ni _y T _z
(Wherein, A is at least one selected from the group consisting of Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Sr, Sc, Y, Zr, Hf, Ca and Ti. T represents at least one element selected from the group consisting of V, Nb, Ta, Cr, Mo, Mn, Fe, Co, Al, Ga, Zn, Sn, In, Cu, Si, P, and B Represents a kind of element, the subscripts a, b, c, d satisfy the relationship indicated by a ≧ 0.4, b> 0, c ≧ 0, d ≧ 0, a ≧ b> c, a + b + c + d = 1, respectively. x, y, and z are in the ranges indicated by 0.10 ≦ x ≦ 0.25, 0.05 ≦ z ≦ 0.35, and 3.0 ≦ y + z ≦ 4.0, respectively.
The hydrogen storage alloy which has a composition represented by these.   The hydrogen storage alloy according to claim 1, wherein the subscript d is 0.1 or less.   A hydrogen storage alloy electrode comprising particles comprising the hydrogen storage alloy according to claim 1 and a conductive core filled with the particles.   A nickel metal hydride secondary battery comprising the hydrogen storage alloy electrode according to claim 3 as a negative electrode.

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