JP2008084668A - Hydrogen storage alloy and sealed alkaline storage battery using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rare earth-Mg-Ni system hydrogen storage alloy having high alkali resistance and a low price; and to provide a sealed alkaline storage battery having high capacity and high cycle characteristics, of a low price. <P>SOLUTION: The sealed alkaline storage battery contains hydrogen storage alloy particles 36 in a negative electrode plate 26, and the hydrogen storage alloy has a composition represented by general formula: (Ce<SB>a</SB>Pr<SB>b</SB>Nd<SB>c</SB>Y<SB>d</SB>A<SB>e</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 represents at least one element selected from the group comprising Pm, Sm or the like, T represents at leans one element selected from the group comprising V, Nb or the like, a, b, c, d, e each satisfies the relation of a>0, b≥0, c≥0, d≥0, e≥0, a+b+c+d+e=1, and w, x, y, z each is in a range specified by 0.08≤w≤0.13, 3.2≤x+y+z≤4.2, 0.15≤y≤0.25, 0≤z≤0.1. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a hydrogen storage alloy and a sealed alkaline storage battery using a negative electrode including the hydrogen storage alloy.

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 the hydrogen storage alloy for the negative electrode of the nickel-hydrogen secondary battery, conventionally, AB ₅ type alloy such as LaNi ₅ has been used, because of the high capacity of the battery, a portion of the rare earth elements in AB ₅ type alloys Rare earth-Mg-Ni alloys have been developed in which is substituted with Mg element.

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

When producing a conventional AB type ₅ alloy, Mm (Misch metal) has been 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 a rare earth-Mg-Ni alloy according to the above-described research and development flow, it is necessary to further limit the contents of La and Ce. Metal must be used. Since rare earth elemental metals, especially La, Pr, and Nd elemental metals are more expensive than mischmetals, their use leads to an increase in the price of rare earth-Mg-Ni alloys, and hence batteries using these alloys. End up.

The present invention has been made based on the above-described circumstances, and an object of the present invention is to provide an inexpensive rare earth-Mg-Ni-based hydrogen storage alloy excellent in alkali resistance.
Another object of the present invention is to provide a sealed alkaline storage battery having a high capacity and excellent cycle characteristics at a low cost.

  In order to achieve the above-mentioned object, the present inventors are opposed to the flow of limiting the content of Ce, and include a single metal of Ce, which is cheaper than single metals such as La, Pr and Nd, Means for ensuring the alkali resistance of rare earth-Mg-Ni alloys have been intensively studied. As a result, even if it is a rare earth-Mg-Ni alloy containing Ce substantially without containing La as a rare earth component, it mainly contains Ce, Pr, Nd and Y, and contains Mg content and Al content. The inventors have found that alkali resistance is improved by setting the amounts and stoichiometric ratios in appropriate ranges, and have arrived at the present invention.

That is, according to the present invention, the general formula:
_{(Ce a Pr b Nd c Y} d A e) 1-w Mg w Ni x Al y T z
(Wherein, A is at least one selected from the group consisting of Pm, 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, Ga, Zn, Sn, In, Cu, Si, P, and B A, b, c, d, and e satisfy the relationship represented by a> 0, b ≧ 0, c ≧ 0, d ≧ 0, e ≧ 0, a + b + c + d + e = 1, and w, x, y , Z are in the ranges represented by 0.08 ≦ w ≦ 0.13, 3.2 ≦ x + y + z ≦ 4.2, 0.15 ≦ y ≦ 0.25, and 0 ≦ z ≦ 0.1), respectively. (Claim 1).

Preferably, e in the general formula is 0.1 or less (claim 2).
Preferably, the sum (a + c) of a and c in the general formula is 0.8 or more (Claim 3).
Preferably, b in the general formula is 0.2 or less, and a quotient obtained by dividing c by b is 3.0 or more (Claim 4).
In order to achieve the above object, according to the present invention, there is provided a sealed alkaline storage battery comprising a negative electrode containing the hydrogen storage alloy according to any one of claims 1 to 4. (Claim 5).

  The hydrogen storage alloy according to claim 1 of the present invention is a rare earth-Mg-Ni alloy that does not substantially contain La. This hydrogen storage alloy contains Ce as an essential rare earth component, Pr, Nd and Y as additional rare earth components, and Mg content, Al content and stoichiometric ratio are set in appropriate ranges. ing. As a result, this hydrogen storage alloy has excellent alkali resistance. This is presumably because the atomic radii of Ce, Pr, Nd, and Y are almost the same (1.83 to 1.82 mm), and the lattice length of the alloy crystal is the same throughout the alloy. On the other hand, when the rare earth component contains La, the atomic radius of La (1.88 や) is slightly larger than the atomic radius of Ce, Pr, Nd and Y, so the lattice length of the crystal changes only in the portion containing La, It is estimated that a non-uniform part with low alkali resistance is generated.

And since this hydrogen storage alloy contains Ce with a low price of a single metal, it is less expensive than a hydrogen storage alloy not containing Ce.
The hydrogen storage alloy according to claim 2 has a further excellent alkali resistance when e is 0.1 or less.
Since the sum of a and c (a + c) is 0.8 or more, the hydrogen storage alloy according to claim 3 has further excellent alkali resistance.

Since the hydrogen storage alloy of claim 4 has b of 0.2 or less and the quotient obtained by dividing c by b is 3.0 or more, didymium can be used as a raw material. Didymium is a mixture of Pr and Nd and is cheaper than the simple metals Pr and Nd. For this reason, this hydrogen absorbing alloy is further inexpensive.
The sealed alkaline storage battery according to claim 5 is excellent in cycle characteristics and inexpensive because the negative electrode includes a hydrogen storage alloy having excellent alkali resistance and low cost.

Hereinafter, a nickel metal hydride secondary battery will be described in detail as a sealed alkaline storage battery according to an embodiment of the present invention.
This battery is 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 strip-like positive electrode plate 24, a negative electrode plate 26, and a separator 28, and the separator is sandwiched between the positive electrode plate 24 and the negative electrode plate 26 wound in a spiral shape. That is, the positive electrode plate 24 and the negative electrode plate 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 plate 26 (outermost peripheral portion), and the outermost peripheral portion of the negative electrode plate 26 is in contact with the inner peripheral wall of the outer can 10. Are electrically connected to each other. The positive electrode plate 24, the negative electrode plate 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 lid plate 14, and both ends of the positive electrode lead 30 are connected to the positive electrode plate 24 and the lid plate 14, respectively. Therefore, the positive electrode terminal 20 and the positive electrode plate 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.

  Further, a predetermined amount of an alkaline electrolyte (not shown) is injected into the outer can 10, and charging / discharging is performed between the positive electrode plate 24 and the negative electrode plate 26 through the alkaline electrolyte contained in the separator 28. The reaction proceeds. 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 plate 24 is composed of 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, a positive electrode It consists of various additive particles for improving the characteristics of the plate 24, 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 plate 26 has a conductive negative electrode substrate 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 the negative electrode active material and, if necessary, a conductive auxiliary agent such as carbon (see FIG. 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 hydrogen storage alloy in the hydrogen storage alloy particles 36 of this battery is a rare earth-Mg-Ni alloy, and has a superlattice structure combining an AB ₅ type structure and an AB ₂ type structure, and the composition is of the general formula :
_{(Ce a Pr b Nd c Y} d A e) 1-w Mg w Ni x Al y T z ... (1)
Indicated by
However, in formula (1), A is selected from the group consisting of Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Sr, Sc, Zr, Hf, Ca and Ti. 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 A, b, c, d, e satisfy the relationship shown by a> 0, b ≧ 0, c ≧ 0, d ≧ 0, e ≧ 0, a + b + c + d + e = 1, and w, x , Y, and z are in the ranges represented by 0.08 ≦ w ≦ 0.13, 3.2 ≦ x + y + z ≦ 4.2, 0.15 ≦ y ≦ 0.25, and 0 ≦ z ≦ 0.1, respectively.

The hydrogen storage alloy particles 36 can be obtained 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 hydrogen storage alloy having the composition represented by the formula (1) is a rare earth-Mg-Ni alloy that does not substantially contain La. This hydrogen storage alloy contains Ce as an essential rare earth component, contains elements represented by Pr, Nd, Y and A as additional rare earth components, and has an Mg content, an Al content and a stoichiometric ratio. It is set to an appropriate range. As a result, this hydrogen storage alloy has excellent alkali resistance. This is presumably because Ce, Pr, Nd, and Y have the same atomic radius (1.83 to 1.82 mm), and the lattice length of the alloy crystal is the same throughout the alloy. On the other hand, when the rare earth component contains La, the atomic radius of La (1.88 や) is slightly larger than the atomic radius of Ce, Pr, Nd and Y, so the lattice length of the crystal changes only in the portion containing La, It is estimated that a non-uniform part with low alkali resistance is generated.

And since this hydrogen storage alloy contains Ce with a low price of a single metal, it is less expensive than a hydrogen storage alloy not containing Ce.
Thus, the nickel metal hydride secondary battery of the present embodiment is excellent in cycle characteristics and inexpensive because the negative electrode plate 26 includes a hydrogen storage alloy having excellent alkali resistance and low cost.
In the formula (1), the reasons for limiting the numerical ranges of w, x, y, and z representing the atomic ratio are as follows.

The reason why w representing the atomic ratio of Mg at the A site is set in the range represented by 0.08 ≦ w ≦ 0.13 is that when w is less than 0.08, the alloy capacity is significantly reduced. In addition, if w exceeds 0.13, the corrosion resistance of the alloy is lowered, and the life characteristics of the battery are lowered.
The reason why y representing the atomic ratio of Al at the B site is set in a range represented by 0.15 ≦ y ≦ 0.25 is that the corrosion resistance of the alloy is insufficient when the value of y is less than 0.15. Further, if w exceeds 0.25, the amount of Ni that plays a role of improving the discharge performance is insufficient.

The reason why z representing the atomic ratio of T at the B site is set to a range represented by 0 ≦ z ≦ 0.1 is that the effect of the present invention becomes remarkable when the value of z is within the range.
X + y + z, which represents the ratio of B site to A site, is set in the range shown by 3.2 ≦ x + y + z ≦ 4.2. If x + y + z becomes too small, As hydrogen storage stability increases in hydrogen, the hydrogen release ability deteriorates, and if x + y + z becomes too large, the hydrogen storage sites in the hydrogen storage alloy decrease, and the hydrogen storage capacity deteriorates. Because it begins to happen.

The present invention is not limited to the above-described embodiment, and various modifications can be made.
For example, in the above-described embodiment, in the rare earth-Mg-Ni alloy of the hydrogen storage alloy particles 36, it is preferable that a in the formula (1) is 0.2 or less. This is because the alkali resistance of the alloy decreases when a exceeds 0.2.
In the above-described embodiment, it is preferable that e in the formula (1) is 0.1 or less. This is because, when e is 0.1 or less, the rare earth-Mg-Ni alloy has further excellent alkali resistance.

In the above-described embodiment, the sum (a + c) of a and c in formula (1) is preferably 0.8 or more. This is because when the sum of a and c (a + c) is 0.8 or more, the rare earth-Mg-Ni alloy has further excellent alkali resistance.
In the above-described embodiment, b in the formula (1) is preferably 0.2 or less, and a quotient obtained by dividing c by b is preferably 3.0 or more. When b is 0.2 or less and the quotient obtained by dividing c by b is 3.0 or more, didymium can be used as a raw material for the rare earth-Mg-Ni-based alloy. Didymium is a mixture of Pr and Nd, and usually the Nd content is higher than the Pr content. Didymium is less expensive than Pr and Nd single metals, and using didymium makes hydrogen absorbing alloys even cheaper.

In the above-described embodiment, in Formula (1), w is in the range represented by 0.08 ≦ w ≦ 0.13, but a preferred range is 0.08 ≦ w ≦ 0.11, and a more preferred range is 0.09 ≦ w. ≦ 0.11.
In the above-described embodiment, in Formula (1), a preferable range of x is 3.0 ≦ x ≦ 3.4, and a more preferable range is 3.05 ≦ x ≦ 3.35.

In the above-described embodiment, in the formula (1), x + y + z is in a range represented by 3.2 ≦ x + y + z ≦ 4.2, but a preferable range is 3.2 ≦ x + y + z ≦ 3.8, and a more preferable range is 3.3 ≦ x. x + y + z ≦ 3.5.
In the above-described embodiment, in the formula (1), y is in the range represented by 0.15 ≦ y ≦ 0.25, but the preferred range is 0.15 ≦ y ≦ 0.20, and the more preferred range is 0.17 ≦ y. ≦ 0.20.

  In the above-described embodiment, in the formula (1), z is in the range represented by 0 ≦ z ≦ 0.1, but the preferred range is 0 ≦ z ≦ 0.08, and the more preferred range is 0.02 ≦ z ≦ 0.05.

1. Battery assembly Example 1
1) Preparation of negative electrode plate Prepare the raw materials of the rare earth component so that the breakdown of the rare earth component is 10% Ce, 30% Pr, 30% Nd and 5% Y by atomic ratio, A mass of a hydrogen storage alloy containing rare earth components, Mg, Ni, and Al in an atomic ratio of 0.90: 0.10: 3.5: 0.20 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 (Ce _0.10 Pr _0.30 Nd _0.30 Y _0.30 ) _0.90 Mg _0.10 Ni _3.5 Al _0.2 with a superlattice rare earth-Mg-Ni alloy Got the ingot.

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 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 is applied evenly on both sides of the 60 μm thick Fe punching metal with Ni plating, that is, the thickness is constant, and after drying the slurry, the punching metal is pressed. Then, a negative electrode plate for an AA-size nickel metal hydride secondary battery was produced.
2) Preparation of positive electrode plate A mixed aqueous solution of nickel sulfate, zinc sulfate and cobalt sulfate was prepared so that the ratio of Zn to 3% by mass and Co to 1% by mass with respect to metal Ni 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 plate for an AA size nickel metal hydride secondary battery.
3) Assembling of the nickel hydride secondary battery The negative electrode plate and the positive electrode plate obtained as described above are spirally wound through a separator made of polypropylene or nylon nonwoven fabric to form an electrode group. After housing the group in an outer can, a lithium hydroxide sodium-containing 30% by weight potassium hydroxide aqueous solution containing lithium and sodium is injected into the outer can, and the battery having the configuration shown in FIG. AA size nickel metal hydride secondary battery with 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 (Ce _0.20 Pr _0.20 Nd _0.60 ) _0.90 Mg _0.10 Ni _3.50 Al _0.20 .
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 (Ce _0.20 Pr _0.10 Nd _0.70 ) _0.90 Mg _0.10 Ni _3.50 Al _0.20 .

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 (Ce _0.30 Pr _0.10 Nd _0.60 ) _0.90 Mg _0.10 Ni _3.50 Al _0.20 .
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 _0.60 Pr _0.20 Nd _0.20 ) _0.90 Mg _0.10 Ni _3.50 Al _0.20 .

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 _0.50 Ce _0.10 Pr _0.20 Nd _0.20 ) _0.90 Mg _0.10 Ni _3.50 Al _0.20 .
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 _0.20 Ce _0.10 Pr _0.30 Nd _0.30 Y _0.10 ) _0.90 Mg _0.10 Ni _3.50 Al _0.20 .

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 (Pr _0.40 Nd _0.40 Y _0.20 ) _0.90 Mg _0.10 Ni _3.50 Al _0.20 .
In addition, when producing the hydrogen storage alloys of Examples 1 to 3 and Comparative Examples 1 to 4, single metals of each element were used as raw materials for the rare earth component, but Pr and Nd were used as raw materials for didymium (Pr and Nd (Mixed metal) may be used and the remaining remaining constituent elements may be supplemented with a single metal.
2. Battery cycle life evaluation test For each of the batteries of Examples 1 to 3 and Comparative Examples 1 to 4, the battery capacity measurement was repeated by charging at 1.0 C current for 1 hour and then discharging to 1.0 V at a final voltage of 0.8 V. The number of cycles (cycle life) until the battery could not be discharged was counted. These results are shown in Table 1 with the result of Comparative Example 1 being 100.

From Table 1, the following is clear.
(1) Compared with Comparative Example 1 in which the rare earth component does not contain Ce, Comparative Examples 2 and 3 containing 0.1 Ce in terms of the number of atoms have significantly reduced the cycle life of the battery. From this, it can be seen that in rare earth-Mg-Ni alloys, the inclusion of Ce adversely affects the alkali resistance of the alloy.
(2) Compared with Comparative Examples 1 to 3, in Example 1 where the rare earth component does not contain La, the cycle life is greatly improved, and the rare earth-Mg-Ni alloy containing no La contains Ce. However, it can be seen that the alkali resistance of the alloy does not decrease.

(3) In Comparative Example 4 that does not include both La and Ce, the cycle life of the battery is improved as compared with Comparative Examples 1 to 3, but the degree of improvement does not reach that of Example 1. Thus, when Ce is contained without containing La, the alkali resistance is improved as compared with the case where both La and Ce are not contained, which is a unique effect of the rare earth-Mg—Ni-based hydrogen storage alloy.
(4) In Example 2 configured such that the total amount of Ce and Nd occupies 80% or more of the rare earth component by atomic ratio, the cycle life is further improved as compared with Example 1. It can also be seen that the cycle life does not change even with a composition having a low Pr content as in Example 3. In the composition having a low Pr content, inexpensive didymium (a mixed alloy of Pr and Nd, which usually has a higher Nd content than Pr) can be used as an alloy raw material, which is industrially advantageous.
(5) In Example 4 in which a representing Ce amount exceeded 0.2, the cycle life was reduced as compared with Examples 1 to 3 in which a was 0.2 or less. From this, it is understood that a is preferably 0.2 or less in the rare earth-Mg-Ni hydrogen storage alloy not containing La but containing Ce.

It is a partial notch perspective view which shows the nickel hydride secondary battery as a sealed alkaline storage battery of one Embodiment of this invention, and expanded and showed a part of negative electrode plate in the circle.

Explanation of symbols

26 Negative electrode plate
36 Hydrogen storage alloy particles

Claims (5)

General formula:
_{(Ce a Pr b Nd c Y} d A e) 1-w Mg w Ni x Al y T z
(Wherein, A is at least one selected from the group consisting of Pm, 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, Ga, Zn, Sn, In, Cu, Si, P, and B A, b, c, d, and e satisfy the relationship represented by a> 0, b ≧ 0, c ≧ 0, d ≧ 0, e ≧ 0, a + b + c + d + e = 1, and w, x, y , Z are in the ranges indicated by 0.08 ≦ w ≦ 0.13, 3.2 ≦ x + y + z ≦ 4.2, 0.15 ≦ y ≦ 0.25, and 0 ≦ z ≦ 0.1, respectively.
The hydrogen storage alloy which has a composition represented by these.   The hydrogen storage alloy according to claim 1, wherein e in the general formula is 0.1 or less.   3. The hydrogen storage alloy according to claim 1, wherein the sum (a + c) of a and c in the general formula is 0.8 or more.   4. The hydrogen storage alloy according to claim 1, wherein b in the general formula is 0.2 or less, and a quotient obtained by dividing c by b is 3.0 or more.   A sealed alkaline storage battery comprising a negative electrode containing the hydrogen storage alloy according to any one of claims 1 to 4.

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