JP2022052729A - Hydrogen storage alloy for alkaline storage battery - Google Patents

Abstract

To provide a hydrogen storage alloy suitable for use as a negative electrode of an alkaline storage battery.SOLUTION: There is provided a hydrogen storage alloy having an A2B7-type crystal structure as a main phase. A volume average particle size MV after repeated hydrogen storage/release with respect to the hydrogen storage alloy that is adjusted in particle size in a range of 150 μm or more and 2 mm or less is 75 μm or more, and a hydrogen storage amount (H/M: H represents the number of hydrogen atoms, and M represents the number of metal atoms) when hydrogen is pressurized to 1 MPa at 80°C is 0.9 or more. Herein, a volume average particle size MV is measured after hydrogen storage, where hydrogen pressure is pressurized to 3 MPa at 80°C and kept for one hour, and hydrogen release, where, after vacuum evacuation, hydrogen pressure is reduced to 0.01 MPa at 80°C and kept for one hour, have been repeated 5 times.SELECTED DRAWING: Figure 1

Description

The present invention relates to a hydrogen storage alloy used in an alkaline storage battery.

Nickel-metal hydride secondary batteries, which are a typical example of alkaline storage batteries, are characterized by having a higher capacity than nickel-cadmium batteries and containing no harmful substances in terms of the environment. Therefore, in recent years, for example, it has been widely used for mobile phones, personal computers, electric tools, consumer applications as a substitute for alkaline primary batteries, and storage batteries for hybrid electric vehicles (HEVs).

Initially, a hydrogen storage alloy having an _AB5 type crystal structure was used for the negative electrode of the alkaline storage battery. Among them, for the purpose of completely suppressing the variation in the storage characteristics and the life characteristics of the battery, the average particle size after hydrogen storage and release into the _AB5 series alloy has been studied conventionally. For example, Patent Document 1 describes the average particle size, specific surface area, and alkaline aqueous solution after repeating activation of storing and releasing hydrogen at 45 ° C. for 10 cycles in an alloy powder sieved in the range of 20 to 60 μm. A hydrogen storage alloy electrode having excellent storage characteristics and cycle life characteristics is shown by specifying the Al elution amount and the magnetic susceptibility after elution.

However, with this alloy, there is a limit to reducing the size and weight of the battery, and it has been desired to develop a new hydrogen storage alloy that can realize a small size and a high capacity. Therefore, as a solution thereof, for example, Patent Document 2 and Patent Document 3 propose a rare earth-Mg transition metal-based hydrogen storage alloy containing Mg.

In addition, as a method of miniaturization and weight reduction, for example, it is conceivable to reduce the amount of hydrogen storage alloy used for the negative electrode, but if the amount of hydrogen storage alloy is reduced, the output will decrease due to the decrease of nickel active sites. Problems arise. In order to improve this, Patent Document 4 proposes a method of increasing the operating voltage by using a hydrogen storage alloy having a high hydrogen equilibrium pressure.

Further, as a hydrogen storage alloy, some rare earth-Mg-Ni based alloys have been proposed. For example, Patent Document 5 discloses a general formula: (La _a Ce _b Pr _c Nd _d A _e ) _1-x Mg _x , for the purpose of providing a long-life secondary battery suitable for improving the volumetric energy density. (Ni _1-y T _y ) _z (In the formula, A represents at least one element selected from the group consisting of Pm and the like, and T represents at least one element selected from the group consisting of V and the like. , A, b, c, d, e are in the range indicated by 0 ≦ a ≦ 0.25, 0 ≦ b ≦ 0.2, 0 ≦ c, 0 ≦ d, 0 ≦ e, and at a + b + c + d + e = 1. It satisfies the relationship shown and has a composition represented by 0 <x <1, 0 ≦ y ≦ 0.5, 2.5 ≦ z ≦ 4.5, respectively). Hydrogen storage alloys are disclosed.

In Patent Document 6, as a hydrogen storage alloy that suppresses an increase in the internal pressure of a battery during charging after over-discharge and contributes to an improvement in the cycle life of the battery, a general formula: (La _a Pr _b Nd _c Z _d ) _1-w . Mg _w Ni _z-x-y Al _x T _y (In the formula, the symbol Z represents an element selected from the group consisting of Ce and the like, and the symbol T represents an element selected from the group consisting of V and the like, and is subscripted. The subscripts a, b, c, and d are in the range indicated by 0 ≦ a ≦ a ≦ 0.25, 0 <b, 0 <c, 0 ≦ d ≦ 0.20, and a + b + c + d = 1, 0.20 ≦ b /. The relationship shown by c≤0.35 is satisfied, and the subscripts x, y, z, and w are 0.15≤x≤0.30, 0≤y≤0.5, 3.3≤z≤3, respectively. 8. A hydrogen storage alloy having a composition represented by (8, 0.05 ≦ w ≦ 0.15) is disclosed.

In Patent Document 7, as an inexpensive rare earth-Mg-Ni hydrogen storage alloy having excellent alkali resistance, the general formula: ( _{Cea Pr b Nd c} Y _d A _e ) _1-w Mg _w Ni _x Al _y T. _z (In the formula, A represents at least one element selected from the group consisting of Pm, Sm, etc., T represents at least one element selected from the group consisting of V, Nb, etc., 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 0.08, respectively. Hydrogen storage having a composition represented by (within the range indicated by ≦ w ≦ 0.13, 3.2 ≦ x + y + z ≦ 4.2, 0.15 ≦ y ≦ 0.25, 0 ≦ z ≦ 0.1) Alloys are disclosed.

Further, in Patent Document 8, the general formula: Ln _{1-x Mg x} Ny _Az (in the formula, Ln is at least one element selected from rare earth elements including Y and Ca, Zr and Ti. , A is at least one element selected from Co, Mn, V, Cr, Nb, Al, Ga, Zn, Sn, Cu, Si, P and B, and the subscripts x, y and z are 0. In the hydrogen storage alloy represented by (the condition of 0.05 ≦ x0.25, 0 <z ≦ 1.5, 2.8 ≦ y + z ≦ 4.0), 20 mol% or more of Sm is contained in the above Ln. The hydrogen storage alloys that have been made to be used are disclosed.

Further, in Patent Document 9, as a hydrogen storage alloy having excellent alkali resistance, a general formula: (La _{a Smb} A _c ) _1-w Mg _w Ni _{x Aly} T _z (in the formula, A and T are Pr. , Nd and the like and at least one element selected from the group consisting of V, Nb and the like, respectively, and the subscripts a, b and c represent a> 0, b> 0 and 0.1> c ≧ 0, respectively. , A + b + c = l, and the subscripts w, x, y, and z are 0.1 <w≤1, 0.05≤y≤0.35, 0≤z≤0.5, 3.2, respectively. A hydrogen storage alloy having the composition shown by (within the range shown by ≦ x + y + z ≦ 3.8) is disclosed.

On the other hand, in Patent Document 10, the main crystalline phase of the alloy represented by the formula (I) having no CaCu type ₅ structure is immersed in an 8N potassium hydroxide aqueous solution at 60 ° C. for 24 hours, and then the surface ferromagnetic component. ^A hydrogen storage alloy powder having an increase in saturation magnetization due to the ferromagnetic component on the surface after being immersed in the same potassium hydroxide aqueous solution at 60 ° C. for 96 hours was used. Alkaline secondary batteries have been reported.
Ln _1-x Mg _x (Ni _1-y T _y ) _z ... (I)
However, Ln in the formula is at least one element selected from lanthanoid elements, Ca, Sr, Sc, Y, Ti, Zr and Hf, and T is Li, V, Nb, Ta, Cr, Mo, Mn, Fe and Co. , Al, Ga, Zn, Sn, In, Cu, Si, P and B, at least one element, x, y, z is 0 <x <1, 0 ≦ y ≦ 0.5, 2.5, respectively. ≤z ≤ 4.5 is shown.
This technology pays attention to the magnitude of the concentration unevenness, and when the homogeneity is high, it has the property that it is difficult for pulverization due to occlusion / release of hydrogen to occur and it is difficult for it to be corroded by the electrolytic solution. , It is said that the charge / discharge cycle life will be improved.

On the other hand, Non-Patent Document 1 reports a hydrogen storage alloy in which La is substituted with Ce, La _0.8-x Ce _x Mg _0.2 Ni _3.5 (x = 0 to 0.20). The evaluation results of this alloy conclude that x = 0.1 is the optimum composition by comprehensively looking at the electrochemical properties.

Further, according to Non-Patent Document 2, a chapter on the influence of Ce on the RE-Mg—Ni hydrogen storage alloy (RE: rare earth element) is set. In this chapter
(La _0.5 Nd _0.5 ) _0.85 Mg _0.15 Ni _3.3 Al _0.2
(La _0.45 Nd _0.45 Ce _0.1 ) _0.85 Mg _0.15 Ni _3.3 Al _0.2
(La _0.4 Nd _0.4 Ce _0.2 ) _0.85 Mg _0.15 Ni _3.3 Al _0.2
(La _0.3 Nd _0.3 Ce _0.4 ) _0.85 Mg _0.15 Ni _3.3 Al _0.2
Alloys have been disclosed and the results of their evaluation have been reported.

Further, according to Non-Patent Document 3, the characteristics of the La—Sm—Mg—Ni hydrogen storage alloy are reported. Specifically, the phase composition and electrochemical characteristics of the La _0.6 Sm _0.15 Mg _0.25 Ni _3.4 alloy are shown.

Japanese Unexamined Patent Publication No. 2001-266861 Japanese Unexamined Patent Publication No. 11-323469 International Publication No. 01/48841 Japanese Unexamined Patent Publication No. 2005-32573 Japanese Unexamined Patent Publication No. 2005-290473 Japanese Unexamined Patent Publication No. 2007-169724 Japanese Unexamined Patent Publication No. 2008-84668 Japanese Unexamined Patent Publication No. 2009-74164 Japanese Unexamined Patent Publication No. 2009-108379 Japanese Unexamined Patent Publication No. 2000-188105

S. Xiangqian et al. , Intern. J. Hydrogen Energy, 34, 395 (2009) Shigekazu Yasuoka, Doctoral Dissertation: Practical application of rare earth-Mg-Ni (super lattice) hydrogen storage alloy and development of high-performance commercial nickel-metal hydride battery using this (2017, Kyoto University) L. Zhang et al. , Intern. J. Hydrogen Energy 41 1791 (2016)

Since the technique disclosed in Patent Document 1 evaluates further cracking by storing and releasing hydrogen from an alloy finely pulverized to 20 to 60 μm in advance, it is originally difficult to crack and is not a strict condition for evaluation of crackability. In particular, the target alloy is _AB5 alloy, and there is an essential problem in further improving the durability.

Further, the techniques disclosed in Patent Documents 2 and 3 have not been put into practical use in various applications without optimizing the alloy.

In the technique disclosed in Patent Document 4, a new problem has arisen in which the charge / discharge cycle life is shortened when a hydrogen storage alloy having a high hydrogen equilibrium pressure is used.

In the technique disclosed in Patent Document 5, the La content, which is a relatively inexpensive material, is suppressed to a low level, and as a result, hydrogen containing a large amount of expensive Pr, Nd, and Ti, is inexpensive and has excellent durability. Storage alloys cannot be provided.

Similar to Patent Document 5, the technique disclosed in Patent Document 6 is an alloy in which Pr and Nd are indispensable, and the content of La is low, so that an inexpensive and highly durable hydrogen storage alloy cannot be provided.

Further, in the technique disclosed in Patent Document 7, La is not contained, Ce is contained, but Pr and Nd are contained in a relatively large amount, and the hydrogen storage alloy is inexpensive and has excellent durability. I can't.

Further, the technique disclosed in Patent Document 8 is an alloy containing a relatively large amount of Sm, and although it uses an element cheaper than Pr and Nd, it is an inexpensive and highly durable hydrogen storage alloy. Cannot be offered.

The technology disclosed in Patent Document 9 is an alloy containing a relatively large amount of La and Sm, and although it mainly uses elements that are cheaper than Pr and Nd, it is inexpensive and has excellent durability. Cannot provide storage alloy. In particular, Zr is essential in the examples, and the B / A ratio of 3.6 is only disclosed. Further, it is said that the hydrogen equilibrium pressure lowered by the increase in La content is raised to a level that can be used in a battery, but it is often insufficient to set an inexpensive La-rich composition.

The technique disclosed in Patent Document 10 is made to find a balance between the initial discharge capacity and the cycle life by paying attention to the magnitude of the concentration unevenness of the alloy. Specifically, a sieve with a composition of La _0.7 Mg _0.3 (Ni _0.8 Co _0.16 Cr _0.01 Mn _0.02 Al _0.01 ) _3.1 so as to be 75 μm or less. Through it, it is immersed in an alkaline aqueous solution, and the amount of increase in saturation magnetization per surface area is changed by 0.5 to 5.0 (emu / m ² ) to improve the cycle characteristics. However, since such an alloy is difficult to be micronized and its specific surface area is small, the initial discharge capacity is small. On the other hand, hydrogen storage alloys with a large concentration unevenness tend to be micronized due to the storage and release of hydrogen, and are corroded by contact with the electrolytic solution. As a result, although the secondary battery equipped with such an alloy can obtain a high discharge capacity at the initial stage of the charge / discharge cycle, there is a new problem that the charge / discharge cycle life is shortened. As described above, the alloy described in Patent Document 10 has insufficient discharge capacity and cycle life characteristics, and further improvement of the characteristics is required for practical use.

On the other hand, Non-Patent Document 1 shows a rare-Mg-Ni alloy in which a part of La is replaced with Ce. In the trial evaluation of this alloy, the amount of replacement of Ce is comprehensively considered. It is concluded that the alloy with x = 0.1 has the optimum composition, but it has not been put into practical use yet.

Further, in Non-Patent Document 2, it is concluded that the rare earth-Mg-Ni alloy containing Ce has a small amount of hydrogen storage and release, and is easily pulverized when hydrogen storage and release are repeated, so that the deterioration in the battery is large. Is said to have become clear.

Furthermore, Non-Patent Document 3 reports, in conclusion, the electrochemical characteristics of the La _0.60 Sm _0.15 Mg _0.25 Ni _3.4 alloy, but the cycle characteristics are not sufficient and it is filled 140 times. It has dropped to 80% of the initial capacity in the discharge cycle.

That is, in a rare earth-Mg-Ni hydrogen storage alloy, repeated hydrogen storage and discharge causes cracks in the alloy, which promotes pulverization and a new surface, so if the corrosion resistance is low, the alloy surface reacts and the rare earth Hydrogen oxide is generated and the electrolytic solution is consumed, and as a result, the internal resistance of the battery increases and the discharge capacity decreases, so that the battery life is reached.

The present invention has been made in view of these problems of the prior art, and is an inexpensive hydrogen storage alloy for an alkaline storage battery having the characteristics necessary for achieving the required high durability. The purpose is to provide. Further, the present invention provides a rare earth-Mg-Ni alloy composition that specifically puts it into practical use.

As a result of diligent research to achieve the above object, an alloy having the following conditions was found as a hydrogen storage alloy for the negative electrode of an alkaline storage battery.
That is, the hydrogen storage alloy for an alkaline storage battery according to the present invention is a hydrogen storage alloy having an _A2B7 type crystal structure as a main phase, and has a particle size adjusted to a range of 150 μm or more and ₂ mm or less. Hydrogen storage amount (H / M; H is the number of hydrogen atoms, M is the metal atom) when the volume average particle size MV after repeated hydrogen storage and release is 75 μm or more and the hydrogen pressure is pressurized to 1 MPa at 80 ° C. The number) is 0.9 or more. Here, the hydrogen storage pressurizes the hydrogen pressure to 3 MPa at 80 ° C. and holds it for 1 hour, and the hydrogen release is vacuum exhausted and reduced to 0.01 MPa at 80 ° C. It is characterized in that it is held for 1 hour, and this is repeated 5 times, and then the volume average particle size MV is measured.

Further, the hydrogen storage alloy for an alkaline storage battery according to the present invention preferably has a plateau inclination at the time of release after hydrogen storage in a range satisfying the following formula (A) in terms of hydrogen storage and release characteristics.
0.8 ≤ log [(P0.7 / P0.3) /0.4]≤3.0 ... (A)
Here, P0.7 is the hydrogen pressure [MPa] when the hydrogen storage amount (H / M) = 0.7.
P0.3 is the hydrogen pressure [MPa] when the hydrogen storage amount (H / M) = 0.3.
Represents.

Further, the hydrogen storage alloy for an alkaline storage battery according to the present invention has a saturation magnetization of 60 emu measured by immersing it in a 7.15 mol / L potassium hydroxide aqueous solution at 80 ° C. for 8 hours and then applying a magnetic field of 10 kOe at 25 ° C. It is preferably / m ² or less.

Further, the hydrogen storage alloy for an alkaline storage battery according to the present invention is preferably represented by the following general formula (1).
(La _1-a-b Ce _a Sm _b ) _1-c Mg _{c Nid Me T f} ... (1)
Here, M, T and the subscripts a, b, c, d, e and f in the above equation (1) are
M: At least one selected from Al, Zn, Sn, Si,
T: At least one selected from Cr, Mo, V,
0 <a≤0.10,
0 ≦ b ≦ 0.20,
0 <a + b ≦ 0.22
0.18 ≤ c ≤ 0.32,
0.03 ≤ e ≤ 0.16,
0 ≦ f ≦ 0.03,
3.2 ≦ d + e + f <3.50
Satisfy the conditions of.

Further, the hydrogen storage alloy for an alkaline storage battery according to the present invention contains Al, and the amount of Al eluted after being immersed in a 7.15 mol / L potassium hydroxide aqueous solution at 80 ° C. for 8 hours is the amount of Al eluted into the potassium hydroxide aqueous solution. The amount of Al in the alloy before the dipping treatment is preferably 3.3 mass% or less.

The hydrogen storage alloy for an alkaline storage battery of the present invention is excellent in durability and discharge capacity, and the nickel hydrogen secondary battery using the hydrogen storage alloy has a high output density and an excellent charge / discharge cycle life. Therefore, it can be used for various purposes such as consumer use, industrial use, and in-vehicle use.

It is a partial cut-out perspective view which illustrates the alkaline storage battery using the hydrogen storage alloy of this invention. It is an example of a hydrogen storage release characteristic (PCT characteristic), and is a graph which shows the hydrogen pressure at the time of the hydrogen storage amount H / M = 0.3 and H / M = 0.7.

The alkaline storage battery using the hydrogen storage alloy of the present invention will be described with reference to FIG. 1, which is a partially cutaway perspective view showing an example of the battery. The alkaline storage battery 10 includes a nickel positive electrode 1 using nickel hydroxide (Ni (OH) ₂ ) as the main positive electrode active material, a hydrogen storage alloy negative electrode 2 using the hydrogen storage alloy (MH) according to the present invention as the negative electrode active material, and the negative electrode 2. A storage battery in which an electrode group composed of a separator 3 is provided in a housing 4 together with an electrolyte layer (not shown) filled with an alkaline electrolytic solution.

The battery 10 corresponds to a so-called nickel-metal hydride battery (Ni-MH battery), and the following reaction occurs.

Positive electrode: NiOOH + H ₂ O + e-= Ni ⁽ OH ⁾ ₂ + OH-
Negative electrode ^: MH + OH-= M + H ₂ O + ^e-

[Hydrogen storage alloy]
Hereinafter, the hydrogen storage alloy used for the negative electrode of the alkaline storage battery according to the present invention will be described.

In improving the characteristics of nickel-metal hydride batteries, the discharge capacity is largely determined by the alloy composition. On the other hand, the durability depends on the degree of micronization of the alloy due to hydrogen storage and release, or the elution of alloy components into an alkaline aqueous solution. This depends on the alloy composition, the proportion of the alloy phase produced based on the heat treatment, and the properties of the alloy phase. As a result of diligent research in advancing the development of hydrogen storage alloys that satisfy the requirements for high durability, when evaluating the crackability of the alloy due to repeated hydrogen storage and release, we screened it to 150 μm or more and 2 mm or less. Using this alloy, hydrogen is pressurized to 3 MPa at 80 ° C., hydrogen is stored, and then hydrogen is released by vacuum exhaust. The particle size distribution after repeating this 5 times is evaluated, and the volume average particle size (MV) is used as a representative value. By expressing it, we came to find a hydrogen storage alloy with particularly excellent durability. The detailed conditions are as follows.

Fill the measurement holder of the PCT (Pressure-Composition-Temperature) evaluation device with 7 g of hydrogen storage alloy, perform vacuum exhaust (0.01 MPa or less) at 80 ° C for 1 hour, and then keep the temperature to keep the hydrogen pressure from 0.01. Hydrogen storage / release measurement (PCT characteristic evaluation) is performed in the range of 3 MPa. After that, vacuum exhaust (0.01 MPa) is performed for 1 hour, hydrogen gas is introduced up to 3 MPa and held for 1 hour, the alloy is occluded almost completely with hydrogen, and vacuum exhaust (0.01 MPa) is performed for 1 hour. Release hydrogen. This is repeated 3 times. Finally, hydrogen storage / release measurement (PCT characteristic evaluation) is performed in the range of hydrogen pressure of 0.01 to 3 MPa in the same manner as in the first cycle. The difference between the 1st and 5th hydrogen storage / release and the 2nd to 4th hydrogen storage / release is the processing time, and the 2nd to 4th hydrogen storage / release applies hydrogen pressure up to 3 MPa at once, so the required time is short. After performing the hydrogen storage / release cycle a total of 5 times in this way, the hydrogen storage alloy powder is taken out and the particle size distribution is measured. The range of the volume average particle size MV after repeated storage and release of hydrogen is 75 μm or more, preferably 80 μm. Within this range, it can be seen that the hydrogen storage alloy has not been micronized due to charging and discharging when it is actually incorporated into a battery, and is excellent in durability in combination with good corrosion resistance in an alkaline solution. ..
The volume average particle size MV may be measured by a laser diffraction particle size distribution measuring device, and as the measuring device, for example, MT3300EXII type manufactured by Microtrac Bell can be used.

It is considered that the cracking of the hydrogen storage alloy is caused by the strain due to the expansion and contraction of the crystal lattice due to the hydrogen storage and release. Therefore, when the hydrogen storage amount is small, the expansion / contraction of the lattice is small, and as a result, it is difficult to atomize. However, on the other hand, if the hydrogen storage amount is small, the discharge capacity as a battery material becomes small, and it is not preferable to obtain a constant battery capacity because it leads to an increase in size and cost of the battery. Therefore, as a condition necessary to realize the volume average particle size MV after repeated hydrogen storage and release, the index H / M (hydrogen H and metal) of the hydrogen storage amount at 1 MPa obtained from the PCT measurement at 80 ° C. The value of (atomic ratio of M) is 0.90 or more. It is preferably 0.91 or more. Within this range, it can be said that a hydrogen storage alloy having sufficient discharge capacity and high durability is obtained.

Further, the hydrogen storage amount (H / M; H is the number of hydrogen atoms and M is the number of metal atoms) at 80 ° C. and 1 MPa hydrogen pressurization is set to 0.9 or more, and the plateau inclination at the time of release after hydrogen storage is set to hydrogen. It was calculated based on the hydrogen pressure P0.3 (MPa) when the storage amount H / M = 0.3 and the hydrogen pressure P0.7 (MPa) when H / M = 0.7. That is, it is preferable that the value calculated by log [(P0.7 / P0.3) /0.4] is 0.8 or more and 3.0 or less. If the slope of the plateau is smaller than 0.8, the lattice tends to expand in one direction during hydrogen storage, in other words, it tends to expand and contract anisotropically, and the generated strain may promote cracking. On the other hand, if the plateau tilt exceeds 3.0, it becomes difficult to increase the hydrogen storage amount even if hydrogen pressure is applied, and there is a possibility that the hydrogen storage amount will decrease. Further, it is preferably 0.90 or more and 2.95 or less.

On the other hand, the degree of elution of the alloy component when the hydrogen storage alloy is immersed in the alkaline aqueous solution affects the corrosion resistance, and as a result, an alloy having good durability is realized. Therefore, as a result of repeated evaluations under various conditions, the magnetization of the alloy powder having a volume average particle size MV of about 35 μm after being immersed in the alkaline aqueous solution was measured and linked to the corrosion resistance. Specifically, the sample obtained after being immersed in a 7.15 mol / L potassium hydroxide aqueous solution at 80 ° C. for 8 hours, washed and dried, was subjected to a sample vibration type magnetometer (VSM) at a temperature of 25 ° C. and a magnetic field. Saturation magnetization was measured at 10 kOe, and it was found that an alloy having excellent durability can be obtained when the saturation magnetization is 60 emu / m ² or less. It is preferably 55 emu / m ² or less.

The specific surface area (m ² / ml) calculated based on the measurement of the particle size distribution of the sample measured by VSM and the specific surface area (8.31 g / ml) of the hydrogen storage alloy. m ² / g) is calculated, and the saturation magnetization per surface area (emu / m ² ) is used as the evaluation standard. This is because the value of saturation magnetization is less affected by the particle size distribution.

In addition, as a result of repeated evaluations under various conditions, it was found that in the hydrogen storage alloy containing Al, the elution amount of Al and the corrosion resistance are closely related. Specifically, an alloy powder having a volume average particle size of about 35 μm is immersed in a 7.15 mol / L potassium hydroxide aqueous solution at 80 ° C. for 8 hours in the same manner as in the above magnetization measurement, and then in an alkaline aqueous solution. It was found that a hydrogen storage alloy having excellent durability can be obtained when the amount of Al eluted in is 3.3 mass% or less with respect to the amount of Al in the alloy component before the immersion treatment in the potassium hydroxide aqueous solution. .. It is preferably 3.2 mass% or less. This is because the amount of Al eluted into the alkaline aqueous solution is related to the amount of corrosion of the alloy, and it is necessary to control the alloy structure and design the alloy to suppress this. For rare earth elements, a composition with a large amount of La is preferable.

As the hydrogen storage alloy according to the present invention described above, it is preferable that the main phase is an alloy having an A ₂ B ₇ type crystal structure, and specifically, a hexagonal (2H) Ce ₂ Ni ₇ phase is present. On the other hand, there is no problem even if the Gd ₂ Co ₇ phase of rhombohedral crystal (3R) coexists, and it is preferable that the total is at least 40 mass% or more. In addition, AB ₃ type crystal structure (CeNi ₃ phase which is hexagonal system or PuNi ₃ phase which is rhombic crystal system), A5 B ₁₉ type crystal structure _{(Gd 5 Co 19} phase or rhombic crystal system which is hexagonal system). The system Pr ₅ Co ₁₉ phase) may be included as a subphase. Furthermore, it is preferable that the AB ₂ type crystal structure (MgZn ₂ phase) and the AB ₅ type crystal structure (CaCu ₅ phase) are not included in the alkaline storage battery from the viewpoint of discharge capacity and cycle life characteristics. It may be contained to such an extent that it does not decrease, for example, about 5 mass% or less.

The hydrogen storage alloy according to the present invention preferably satisfies the following general formula (1).
(La _1-a-b Ce _a Sm _b ) _1-c Mg _{c Nid Me T f} ... (1)
Here, M, T and the subscripts a, b, c, d, e and f in the above equation (1) are
M: At least one selected from Al, Zn, Sn, Si,
T: At least one selected from Cr, Mo, V,
0 <a≤0.10,
0 ≦ b ≦ 0.20,
0 <a + b ≦ 0.22
0.18 ≤ c ≤ 0.32,
0.03 ≤ e ≤ 0.16,
0 ≦ f ≦ 0.03,
3.2 ≦ d + e + f <3.50
Satisfy the conditions of.

The alloy represented by the general formula (1) suppresses cracking due to repeated hydrogen storage and discharge, and suppresses elution of constituent elements in an alkaline aqueous solution. As a result, it has good corrosion resistance and is a negative electrode of an alkaline storage battery. When used as an alloy, it imparts high discharge capacity and cycle life characteristics to the battery, which contributes to the miniaturization and weight reduction of alkaline storage batteries and the achievement of high durability.

Hereinafter, the reason for limiting the component composition of the hydrogen storage alloy of the present invention will be described.
Rare earth elements: La _1-ab Ce _{a Smb}
(However, 0 <a≤0.10, 0≤b≤0.20, 0 <a+b≤0.22)
The hydrogen storage alloy of the present invention is a rare earth element as an element of the A component of the main phase A ₂ B ₇ type structure, the sub phase A ₅ B ₁₉ type structure, the AB ₃ type structure, the AB ₂ type structure, and the AB ₅ type structure. Contains elements. As a rare earth element, two elements, La and Ce, are indispensable in principle as basic components that bring about hydrogen storage capacity. Further, since La and Ce have different atomic radii, the hydrogen equilibrium pressure can be controlled by this component ratio, and the hydrogen equilibrium pressure required for the battery can be arbitrarily set. It is necessary that the atomic ratio a value of Ce in the rare earth element is in the range of more than 0 and 0.10 or less. When the a value exceeds 0.10, cracking due to hydrogen storage and release is promoted, and the volume average particle size MV after repeated hydrogen storage and release is out of the range. On the other hand, when the a value is 0, that is, when Ce is not included, it becomes difficult to sufficiently control the hydrogen equilibrium pressure, which adversely affects the battery characteristics, for example, the discharge characteristics at a low temperature. Within this range, it is easy to set the hydrogen equilibrium pressure suitable for the battery. Preferably, the atomic ratio a value of Ce is in the range of 0.005 or more and 0.09 or less.

Sm can be arbitrarily contained as a rare earth element other than La and Ce. Similar to La and Ce, Sm is a rare earth element as an element of A component of A ₂ B ₇ type structure of the main phase, A ₅ B ₁₉ type structure of the sub phase, AB ₃ type structure, AB ₂ type structure, and AB ₅ type structure. It is an element that occupies the site, and like these elements, it is a component that brings about hydrogen storage capacity. Although Sm has a lower effect of increasing the equilibrium pressure than Ce, the durability is improved by substituting La together with Ce. The upper limit of the b value representing the atomic ratio of Sm in the rare earth element is 0.20, and if it exceeds that, the cycle life characteristic deteriorates in balance with the amount of Ce. Preferably, b ≦ 0.18.

The sum of Ce and Sm that replace La is in the range of 0 <a + b ≦ 0.22. If a + b exceeds 0.22, the suppression of cracking becomes insufficient. It is preferably 0.005 ≦ a + b ≦ 0.20.

A composition having a large amount of La increases the discharge capacity, and when combined with other elements, the discharge capacity characteristics are further improved. Further, although Pr and Nd as rare earth elements are not positively utilized, they may be contained at the level of unavoidable impurities.

Mg: Mg _c (however, 0.18 ≤ c ≤ 0.32)
Mg is an essential element in the present invention as an element of the A component of the main phase A ₂ B ₇ type structure, the sub phase A ₅ B ₁₉ type structure, the AB ₃ type structure, the AB ₂ type structure, and the AB ₅ type structure. This contributes to the improvement of discharge capacity and cycle life characteristics. The c value representing the atomic ratio of Mg in the A component shall be in the range of 0.18 or more and 0.32 or less. If the c value is less than 0.18, the hydrogen release capacity is lowered, so that the discharge capacity is lowered. On the other hand, if it exceeds 0.32, cracking due to hydrogen storage and release is particularly promoted, and the cycle life characteristic, that is, durability is deteriorated. Preferably, the c value is in the range of 0.19 or more and 0.30 or less.

Ni: Ni _d
Ni is the main element of the B component of the A ₂ B ₇ type structure of the main phase, the A ₅ B ₁₉ type structure of the sub phase, the AB ₃ type structure, the AB ₂ type structure, and the AB ₅ type structure. The atomic ratio d value will be described later.

M: Me (however, 0.03 ≤ _e ≤ 0.16)
M is at least one selected from Al, Sn, Zn, and Si, and has an _A2B7 type structure of the main phase, an _A5B19 type structure of the _{subphase ,} an _AB3 type structure, an _AB2 type structure, and an _AB5 . It is an element contained as an element of the B component of the mold structure. It is effective in adjusting the hydrogen equilibrium pressure related to the battery voltage, can improve the corrosion resistance, and is effective in improving the durability of the fine hydrogen storage alloy, that is, the cycle life characteristic. In order to surely exhibit the above effect, the e value representing the atomic ratio of M to the component A shall be in the range of 0.03 or more and 0.16 or less. If the e value is less than 0.03, the corrosion resistance becomes insufficient, resulting in an increase in saturation magnetization, and the cycle life becomes insufficient. On the other hand, if the e value exceeds 0.16, the discharge capacity will decrease. The preferred e value is in the range of 0.035 or more and 0.15 or less. Further, it is preferable that Al is present in the M element, and the atomic ratio of Al is preferably 0.03 or more in the range of e.

T: T _f (however, 0 ≦ f ≦ 0.03)
T is at least one selected from Cr, Mo, and V, and like M, it has an _A2B7 type structure of the main phase, an _A5B19 type structure of the _{subphase ,} an _AB3 type structure, and an _AB2 type structure. It is an element contained as an element of the B component of the _AB5 type structure. It is effective in adjusting the hydrogen equilibrium pressure related to the battery voltage, and the synergistic effect with the M element enhances the corrosion resistance and the durability. In particular, it is effective in improving the durability of fine hydrogen storage alloys, that is, in cycle life characteristics. In order to surely exhibit the above effect, the f value representing the atomic ratio of T to the component A is 0.03 or less. When the f value exceeds 0.03, the excess T induces cracking due to the occlusion and release of hydrogen, and as a result, the durability is lowered and the cycle life is not sufficient. The preferable f value is in the range of 0.025 or less, and it is particularly preferable that the T element, particularly Cr, is present in the range of the invention in which the amount of the M element is small. Further, a combination of Cr and Mo or V is preferable.

Ratio of A component and B component: 3.2 ≤ d + e + f <3.50
Mol of B component (Ni, M and T) with respect to A component consisting of A ₂ B ₇ type structure of main phase, A ₅ B ₁₉ type structure of sub phase, AB ₃ type structure, AB ₂ type structure, AB ₅ type structure The chemical quantitative ratio, that is, the value of d + e + f represented by the general formula, is preferably in the range of 3.2 or more and less than 3.50. If it is less than 3.2, the number of _AB2 phases as subphases will gradually increase, and in particular, the discharge capacity will decrease and the cycle life will also decrease. On the other hand, when it is 3.50 or more, the number of _AB5 phases increases, cracking due to hydrogen storage and release is promoted, and as a result, durability, that is, cycle life is lowered. It is preferably in the range of 3.25 or more and 3.48 or less.

[Manufacturing method of hydrogen storage alloy]
Next, a method for producing the hydrogen storage alloy of the present invention will be described.
The hydrogen storage alloy of the present invention contains a predetermined molar ratio of substitution elements for Ni such as rare earth elements (Ce, Sm, La, etc.), magnesium (Mg), nickel (Ni), and other aluminum (Al), chromium (Cr). After weighing, these raw materials are put into an alumina pot installed in a high-frequency induction furnace, melted in an inert gas atmosphere such as argon gas, and then cast into a mold to form a hydrogen storage alloy ingot. To make. Alternatively, a flake-shaped sample having a thickness of about 200 to 500 μm may be directly prepared by using a strip casting method.

Since the hydrogen storage alloy of the present invention contains Mg having a low melting point and a high vapor pressure as a component, if the raw materials of all the alloy components are melted at once, the Mg evaporates and the target chemical composition is obtained. It may be difficult to obtain the alloy of. Therefore, in producing the hydrogen storage alloy of the present invention by the melting method, first, after melting the other alloy components excluding Mg, it is necessary to put the Mg raw materials such as metallic Mg and Mg alloy into the molten metal. preferable. Further, this melting step is preferably performed in an atmosphere of an inert gas such as argon or helium. Specifically, the inert gas containing 80 vol% or more of argon gas was adjusted to 0.05 to 0.2 MPa. It is preferably performed under a reduced pressure / pressurized atmosphere.

It is preferable that the alloy melted under the above conditions is then cast in a water-cooled mold and solidified to form an ingot of a hydrogen storage alloy. Next, the melting point ( _Tm ) of each of the obtained ingots of the hydrogen storage alloy is measured using a DSC (Differential Scanning Calorimeter). This is because the hydrogen storage alloy of the present invention makes the cast ingot the melting point of the alloy at 700 ° C. or higher under either an inert gas such as argon or helium or a nitrogen gas, or a mixed gas atmosphere thereof. This is because it is preferable to perform a heat treatment for holding the temperature at a temperature of T _m ) or less for 3 to 50 hours. By this heat treatment, the ratio of the main phase including the A ₂ B ₇ type crystal structure in the hydrogen storage alloy can be set to 40 mass% or more, and the AB ₂ phase and the AB ₅ phase can be reduced or eliminated. The crystal structure of the main phase of the obtained hydrogen storage alloy can be confirmed by X _- ray diffraction measurement using Cu _— Kα rays, SEM observation, and the like. Specifically, it is preferable that the hexagonal Ce ₂ Ni ₇ type structure is mainly used, but there is no problem even if the rhombohedral Gd ₂ Co ₇ type structure coexists.

If the heat treatment temperature is less than 700 ° C., the diffusion of the elements is insufficient, so that the secondary phase remains, which may lead to a decrease in the discharge capacity of the battery and a deterioration in the cycle life characteristics. On the other hand, when the heat treatment temperature becomes -20 ° C or higher ( _Tm -20 ° C or higher) from the melting point _Tm of the alloy, the crystal grains of the main phase become coarse and the Mg component evaporates, resulting in pulverization and chemical composition. There is a possibility that the hydrogen storage amount will decrease due to the change. Therefore, the heat treatment temperature is preferably in the range of 750 ° C to ( _Tm -30 ° C). More preferably, it is in the range of 770 ° C to ( _Tm -50 ° C).

Further, if the heat treatment holding time is 3 hours or less, the ratio of the main phase may not be stably set to 40 mass% or more. In addition, since the homogenization of the chemical components of the main phase is insufficient, the expansion and contraction during hydrogen storage and release become non-uniform, and the strain and defect amount generated may increase, which may adversely affect the cycle life characteristics. There is. The holding time of the heat treatment is preferably 4 hours or more, and more preferably 5 hours or more from the viewpoint of homogenization of the main phase and improvement of crystallinity. However, if the holding time exceeds 50 hours, the amount of evaporation of Mg increases and the chemical composition changes, and as a result, AB5 type _subphase may be generated. Further, it is not preferable because it may increase the manufacturing cost and cause a dust explosion due to the evaporated Mg fine powder.

The heat-treated alloy is micronized by a dry method or a wet method. When pulverized by a dry method, a powder having an average particle size D50 of 20 to 100 μm can be obtained by pulverizing using, for example, a hammer mill or an ACM palverizer. On the other hand, when micronized by the wet method, it is pulverized using a bead mill or an attritor. In particular, when fine powder having an average particle size D50 of 20 μm or less is obtained, wet pulverization is preferable because it can be produced safely. The particle size may be set in an appropriate range depending on the application, for example, D50 = 8 to 100 μm.
Here, the average particle size D50 of the alloy particles described above is measured by using the value measured by the laser diffraction / scattering type particle size distribution measuring device in the same manner as the measurement of the volume average particle size MV after repeated hydrogen storage / release. As the apparatus, for example, MT3300EXII type manufactured by Microtrac Bell can be used.

The finely divided alloy particles may then be subjected to surface treatment such as alkali treatment using an alkaline aqueous solution such as KOH or NaOH, or acid treatment using an aqueous solution of nitric acid, sulfuric acid or hydrochloric acid. By applying these surface treatments, a layer made of Ni (alkali-treated layer or acid-treated layer) can be formed on at least a part of the surface of the alloy particles, the progress of alloy corrosion can be suppressed, and the durability is enhanced. Therefore, it is possible to improve the cycle life characteristics of the battery and the discharge characteristics in a wide temperature range. In particular, in the case of acid treatment, it is possible to precipitate Ni with less damage to the alloy surface, so it is preferable to use hydrochloric acid. Further, when the alloy is pulverized by a wet method, surface treatment can be performed at the same time.

Hereinafter, the present invention will be described based on examples.
No. 1 having the component composition shown in Tables 1-1 to 1-3 below. The hydrogen storage alloys 1 to 58 and the evaluation cells using the hydrogen storage alloy as the negative electrode active material were prepared as described below, and an experiment was conducted to evaluate their characteristics. No. 1 shown in Tables 1-1 to 1-3. The alloys 1 to 26 and 36 to 58 are alloy examples (invention examples) conforming to the conditions of the present invention, No. 27 to 35 are alloy examples (comparative examples) that do not satisfy the conditions of the present invention. In addition, No. of Comparative Example. The 27 alloys were used as reference alloys for evaluating various characteristics of the alloy and the characteristics of the cell.

(Preparation of negative electrode active material)
No. 1 shown in Tables 1-1 to 1-3. Raw materials for alloys 1 to 58 (Sm, La, Ce, Mg, Ni, Al, Cr, Zn, Sn, Si, V and Mo each have a purity of 99% or more) are used in an argon atmosphere using a high frequency induction heating furnace. It was melted at (Ar: 100 vol%, 0.1 MPa) and cast into an ingot. Next, these alloy ingots are subjected to a heat treatment in which they are held in an argon atmosphere (Ar: 90 vol%, 0.1 MPa) at a temperature (900 to 1130 ° C.) of the melting point _Tm -50 ° C. of each alloy for 10 hours. , Coarsely crushed. No. of the invention example of the present invention. After the heat treatment, the crushed powders of the alloys 1 to 26 and 36 to 58 were subjected to X _- ray diffraction measurement, and it was confirmed that the main phase of each of them had an _A2B7 type crystal structure. In addition, No. of Comparative Example. 27 is CaCu ₅ -phase single-phase, No. It has been confirmed that the main phases of 28 to ₃₅ each have a crystal structure selected from either _A2B7 phase or _AB3 type.

<Evaluation of crackability due to repeated storage and release of hydrogen>
The crackability evaluation due to repeated hydrogen storage and release is as follows.
The hydrogen storage alloy ingot was pulverized and the particle size was adjusted so that it remained on a sieve of 150 μm and had a particle size of 2 mm or less. Fill the measurement holder of the PCT (Pressure-Composition-Temperature) evaluation device with 7 g of hydrogen storage alloy, perform vacuum exhaust (0.01 MPa or less) at 80 ° C for 1 hour, and then keep the temperature to keep the hydrogen pressure from 0.01. Hydrogen storage / release measurement (PCT characteristic evaluation) is performed in the range of 3 MPa. After that, vacuum exhaust (0.01 MPa or less) is performed for 1 hour, hydrogen gas is introduced up to 3 MPa and held for 1 hour to allow the alloy to occlude hydrogen almost completely, and vacuum exhaust (0.01 MPa or less) for 1 hour. And release hydrogen. This is repeated 3 times. Finally, hydrogen storage / release measurement (PCT characteristic evaluation) is performed in the range of hydrogen pressure of 0.01 to 3 MPa in the same manner as in the first cycle. After performing this hydrogen storage / release cycle 5 times, the hydrogen storage alloy powder was taken out and the particle size distribution was measured. The values of the volume average particle size MV after the repeated storage and release of hydrogen are shown in Tables 1-1 to 1-3.

<Saturation magnetization>
Saturation magnetization measurement after immersion in an alkaline aqueous solution is performed according to the following procedure.
First, 50 g of a 7.15 mol / L potassium hydroxide aqueous solution at 80 ° C. and 20 g of a hydrogen storage alloy adjusted to a volume average diameter (MV) of 35 μm are placed in a glass beaker. Next, the liquid temperature is maintained at 80 ° C. and the mixture is immersed for 8 hours while stirring with a magnetic stirrer. After a lapse of time, wash with water, repeat until the pH of the washing water becomes 12 or less, and vacuum dry at 70 ° C. for 6 hours. Approximately 200 mg is weighed from the obtained sample, fixed in a measuring container, and a magnetic field of 10 kOe is applied at 25 ° C. using a sample vibration type magnetometer (VSM) to measure saturation magnetization (emu / g). On the other hand, the specific surface area CS value (m ² / ml) and the density of the hydrogen storage alloy (8.31 g / ml) calculated based on the measurement of the particle size distribution of the sample immersed in the alkaline aqueous solution are used. (M ² / g) is calculated, and the saturation magnetization per surface area (emu / m ² ) is used as an evaluation standard, and Tables 1-1 to 1-3 show the amount of magnetization. This process does not make the saturation magnetization dependent on the particle size distribution.

<Amount of eluted Al>
The Al elution amount by immersion in an alkaline aqueous solution is measured by the following procedure.
After immersing the hydrogen storage alloy in the potassium hydroxide aqueous solution performed in the above magnetization measurement for 8 hours, the filtered potassium hydroxide aqueous solution is taken out, and the amount of Al contained in the solution is measured by ICP. The mass of the eluted Al amount is calculated from the Al concentration and the amount of the alkaline aqueous solution, the Al concentration before the treatment is compared with the mass of the Al amount in the alloy obtained from the sample amount, and the eluted Al amount is evaluated by the mass percentage. , It is shown as the amount of Al in Tables 1-1 to 1-3.

<PCT characterization>
The PCT characteristic evaluation is carried out by the following procedure.
The hydrogen storage alloy ingot is crushed, the particle size is adjusted by sieving to 150 μm or more and 2 mm or less in the same manner as above, the mixture is filled in a PCT measuring device, and vacuum exhaust (0.01 MPa or less) is performed at 80 ° C. for 1 hour. Next, the temperature is maintained, hydrogen gas of 3 MPa is pressurized and held for 3.5 hours, hydrogen is occluded in the hydrogen storage alloy, and then vacuum exhausted for 1 hour to release hydrogen for activation treatment. Then, hydrogen storage / release measurement (PCT characteristic evaluation) is performed in the range of hydrogen pressure of 0.01 to 1 MPa. In Tables 1-1 to 1-3, the calculated value of log [(P0.7 / P0.3) /0.4] is used as the hydrogen storage amount at 1 MPa pressurization as H / M and as the plateau slope. show.

As a negative electrode active material for a battery, the prepared hydrogen storage alloy was finely pulverized with a hammer mill to a mass-based D50 of 35 μm to obtain a sample for cell evaluation (negative electrode active material).

(Preparation of evaluation cell)
<Negative electrode>
The negative electrode active material adjusted above, the Ni powder of the conductive auxiliary agent, and the two types of binders (styrene-butadiene rubber (SBR) and carboxymethyl cellulose (CMC)) are mixed in a weight ratio of the negative electrode active material: Ni powder: SBR: CMC = 95.5: 3.0: 1.0: 0.5 was mixed and kneaded to obtain a paste-like composition. This paste-like composition was applied to a punching metal, dried at 80 ° C., and then roll-pressed with a load of 15 kN to obtain a negative electrode.

<Positive electrode>
Nickel hydroxide (Ni (OH) ₂ ), metallic cobalt (Co) as a conductive aid, and two types of binders (styrene-butadiene rubber (SBR) and carboxymethyl cellulose (CMC)) are mixed in a mass ratio of Ni. (OH) ₂ : Co: SBR: CMC = 95.5: 2.0: 2.0: 0.5 was mixed and kneaded to obtain a paste-like composition. This paste-like composition was applied to porous nickel, dried at 80 ° C., and then roll-pressed with a load of 15 kN to obtain a positive electrode.

<Electrolytic solution>
As the electrolytic solution, an alkaline aqueous solution in which potassium hydroxide (KOH) was mixed with pure water so as to have a concentration of 6 mol / L was used.

<Evaluation cell>
After arranging the positive electrode as the counter electrode and the negative electrode as the working electrode in the acrylic housing, the electrolytic solution is injected to prepare a cell using the Hg / HgO electrode as the reference electrode for evaluation test. Served. At this time, the volume ratio of the working electrode and the counter electrode was adjusted so that the working electrode: the counter electrode = 1: 3. A polyethylene non-woven fabric is installed between the positive electrode and the negative electrode to serve as a separator.

(Cell characteristic evaluation)
Alloy No. obtained as described above. The evaluation test of the evaluation cells from 1 to 58 was performed as follows.

(1) Electrode discharge capacity The discharge capacity of the electrode of the working electrode was confirmed by the following procedure. After constant current charging at a current value of 80 mA / g per active material of the working electrode for 10 hours, constant current discharge was performed at a current value of 40 mA / g per active material of the working electrode. The end condition of the discharge was set to the working potential of −0.5 V. The above charging and discharging were repeated 10 times, and the maximum value of the discharging capacity was taken as the discharging capacity of the electrode of the working electrode. It has been confirmed that the discharge capacity of the working electrode is saturated and stable by charging and discharging 10 times. The evaluation temperature is 25 ° C.
The measured discharge capacity is the alloy No. shown in Table 1-2. Using the discharge capacity of 27 as the reference capacity, the ratio to it is calculated by the following equation (2), and the alloy No. 1 having this ratio larger than 1.15 is used. The discharge capacity was larger than that of 27, and it was evaluated to be excellent.
Discharge capacity = (Discharge capacity of evaluation alloy) / (Discharge capacity of alloy No. 27) ... (2)

(2) Cycle life characteristics Using the cell in which the discharge capacity of the electrode of the working electrode was confirmed by the discharge capacity of the above (1) electrode, the cycle life characteristics of the working electrode were determined by the following procedure. This evaluation temperature is 45 ° C.
When the discharge capacity of the electrode of the working electrode confirmed by the discharge capacity of the above (1) electrode is 1C and the current value required to complete charging or discharging in 1 hour is 1C, the charging rate of the working electrode is 30-. In the range of 70%, constant current charging and constant current discharging with a current value of C / 2 are regarded as one cycle, and this is repeated for 300 cycles, and the discharge capacity after 300 cycles is measured. The capacity retention rate was calculated by the formula.
Capacity retention rate = (Discharge capacity in the 300th cycle) / (Discharge capacity in the 1st cycle) ... (3)
The evaluation of the cycle life characteristics is based on the alloy No. 1 shown in Table 1-2. The capacity retention rate after 300 cycles of 27 is used as the reference capacity retention rate, and the ratio to the standard capacity retention rate is calculated by the following equation (4). It was evaluated as having a larger cycle life characteristic than 27 and being excellent.
Cycle life characteristics = (Capacity retention rate after 300 cycles of measured alloy) / (Capacity retention rate of alloy No. 27 after 300 cycles) ... (4)

As is clear from Tables 1-1 to 1-3, No. 1 of the invention examples. The alloys selected from 1 to 26 and 36 to 58 are No. 1 and No. It is clear that the characteristics of various parameters are good with respect to 27, and as a result, the good discharge capacity and cycle life characteristics are improved in a well-balanced manner in the battery evaluation. Specifically, the discharge capacity is 1.15 times or more that of the reference alloy, and the cycle life characteristic is 1.15 times or more. On the other hand, No. of the comparative example. It can be seen that the alloys selected in 27 to 4 do not satisfy the above conditions in either or both of these evaluation values. Further, it is clear that all of the alloys of the present invention have a La-rich composition with reduced Sm, are expensive and do not contain Co with a fluctuation risk, and are low-cost alloys.

Since the hydrogen storage alloy of the present invention is superior in both discharge capacity and cycle life characteristics to the _AB5 type hydrogen storage alloy that has been conventionally used, it can be used for various industrial applications and in-vehicle applications as a substitute for alkaline primary batteries. Suitable as an alloy for the negative electrode of a wide range of alkaline storage batteries.

1: Positive electrode 2: Negative electrode 3: Separator 4: Housing (battery case)
10: Alkaline storage battery

Claims (5)

The main phase is a hydrogen storage alloy having an _{A2B7 type} crystal structure.
Hydrogen when the volume average particle size MV after repeated hydrogen storage and release is 75 μm or more and the hydrogen pressure is pressurized to 1 MPa at 80 ° C. for the hydrogen storage alloy whose particle size is adjusted to the range of 150 μm or more and 2 mm or less. The storage capacity (H / M; H is the number of hydrogen atoms and M is the number of metal atoms) is 0.9 or more.
Here, the hydrogen storage is performed by pressurizing the hydrogen pressure to 3 MPa at 80 ° C. and holding it for 1 hour, and the hydrogen release is vacuum exhausted and reduced to 0.01 MPa or less at 80 ° C. and held for 1 hour. After repeating this time, measure the volume average particle size MV,
A hydrogen storage alloy for alkaline storage batteries. The hydrogen storage alloy for an alkaline storage battery according to claim 1, wherein the plateau inclination at the time of release after hydrogen storage is in a range satisfying the following formula (A) in terms of hydrogen storage and release characteristics.
0.8 ≤ log [(P0.7 / P0.3) /0.4]≤3.0 ... (A)
Here, P0.7 is the hydrogen pressure [MPa] when the hydrogen storage amount (H / M) = 0.7.
P0.3 is the hydrogen pressure [MPa] when the hydrogen storage amount (H / M) = 0.3.
Represents. The hydrogen storage alloy was immersed in a 7.15 mol / L potassium hydroxide aqueous solution at 80 ° C. for 8 hours, and then a magnetic field of 10 kOe was applied at 25 ° C. to measure the saturation magnetization of 60 emu / m ² or less. The hydrogen storage alloy for an alkaline storage battery according to claim 1 or 2, wherein the hydrogen storage alloy is characterized. The hydrogen storage alloy for an alkaline storage battery according to any one of claims 1 to 3, wherein the hydrogen storage alloy is represented by the following general formula (1).
(La _1-a-b Ce _a Sm _b ) _1-c Mg _{c Nid Me T f} ... (1)
Here, M, T and the subscripts a, b, c, d, e and f in the above equation (1) are
M: At least one selected from Al, Zn, Sn, Si,
T: At least one selected from Cr, Mo, V,
0 <a≤0.10,
0 ≦ b ≦ 0.20,
0 <a + b ≦ 0.22
0.18 ≤ c ≤ 0.32,
0.03 ≤ e ≤ 0.16,
0 ≦ f ≦ 0.03,
3.2 ≦ d + e + f <3.50
Satisfy the conditions of. The hydrogen storage alloy contains Al, and the amount of Al eluted after being immersed in a 7.15 mol / L potassium hydroxide aqueous solution at 80 ° C. for 8 hours is the Al in the alloy before the immersion treatment in the potassium hydroxide aqueous solution. The hydrogen storage alloy for an alkaline storage battery according to any one of claims 1 to 4, wherein the amount is 3.3 mass% or less.

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