JP5342499B2 - Hydrogen storage alloy - Google Patents

Description

The present invention relates to an AB ₅ type hydrogen storage alloy having a CaCu ₅ type crystal structure. Specifically, the present invention relates to a hydrogen storage alloy suitable as a negative electrode active material used for a Ni-MH battery mounted in an electric vehicle and a hybrid vehicle.

  A hydrogen storage alloy is an alloy that reacts with hydrogen to form a metal hydride and can reversibly store and release a large amount of hydrogen near room temperature. Therefore, an electric vehicle (EV: Electric Vehicle) and a hybrid vehicle (HEV: Hybrid Electric Vehicle; an automobile that uses two power sources, an electric motor and an internal combustion engine), a nickel-hydrogen battery (referred to as a “Ni-MH battery”), a fuel cell, etc. mounted on a digital still camera Practical use is in progress.

As the hydrogen storage alloy, various alloys such as AB ₅ type alloy represented by LaNi ₅ , AB ₂ type alloy represented by ZrV _0.4 Ni _1.5 , and other AB type alloy and A ₂ B type alloy are known. It has been. Many of them have a high affinity with hydrogen and have an element group (Ca, Mg, rare earth elements, Ti, Zr, V, Nb, Pt, Pd, etc.) that plays a role in increasing the hydrogen storage capacity, and the affinity with hydrogen. Although it is relatively low and has a small amount of occlusion, it is composed of a combination with element groups (Ni, Mn, Cr, Fe, etc.) that promote the hydrogenation reaction and lower the reaction temperature.

Among these, AB ₅ type hydrogen storage alloy having a CaCu ₅ type crystal structure, such as Mm (Misch metal), which is a rare earth mixture, is used at the A site, and Ni, Al, Mn, Co, etc. are used at the B site. An alloy using an element (hereinafter, this type of alloy is referred to as an “Mm—Ni—Mn—Al—Co alloy”) can form a negative electrode with a relatively inexpensive material compared to other alloy compositions, In addition, it has a feature that it can constitute a sealed nickel-metal hydride storage battery having a long cycle life and little increase in internal pressure due to gas generated during overcharge.

  In the future, it is necessary to further improve the life characteristics and output characteristics in order to spread the use of hydrogen storage alloys to electric cars and hybrid cars. In particular, in Ni-MH batteries using a hydrogen storage alloy as the negative electrode active material, the corrosion of the hydrogen storage alloy gradually progresses due to the strong alkaline electrolyte, so it is necessary to increase the corrosion resistance of the alloy in order to extend the life of the battery. is there.

As the hydrogen storage alloy to solve such a problem, for example, Patent Document 1, the general formula _{MmNi a Mn b Al c Co d} X e ( wherein, Mm is the mischmetal, X is Fe and / or Cu, 3. 7 ≦ a ≦ 4.2, 0 ≦ b ≦ 0.3, 0 ≦ c ≦ 0.4, 0.2 ≦ d ≦ 0.4, 0 ≦ e ≦ 0.4, 5.00 ≦ a + b + c + d + e ≦ 5. 20, except in the case of b = c = 0, and if the 0 <b ≦ 0.3 and 0 <c ≦ 0.4, is, b + c <CaCu ₅ type represented by a is) 0.5 A hydrogen storage alloy having a crystalline structure is disclosed.

Patent Document 2 discloses _a general formula MmNi _a Mn _b Al _c Co _d (where Mm is a misch metal, 4.0 <a ≦ 4.3, 0.25 ≦ b ≦ 0.4, 0.25 ≦ c). ≦ 0.4, 0.3 ≦ d ≦ 0.5, 5.05 ≦ a + b + c + d ≦ 5.25) or the general formula MmNi _a Mn _b Al _c Co _d X _e (where Mm is Misch metal, X is Cu And / or Fe, 4.0 <a ≦ 4.3, 0.25 ≦ b ≦ 0.4, 0.25 ≦ c ≦ 0.4, 0.3 ≦ d ≦ 0.5, 0 <e ≦ 0 .1, 5.05 ≦ a + b + c + d + e ≦ 5.25), which is an AB5 type hydrogen storage alloy having a CaCu ₅ type crystal structure, characterized by having a c-axis lattice length of 404.9 pm or more. A hydrogen storage alloy is disclosed.

  In addition, as a hydrogen storage alloy capable of improving corrosion resistance, Patent Document 3 includes at least a rare earth element, Mg, Ni, and Al, and in an X-ray diffraction measurement using Cu—Kα rays as an X-ray source, 2θ = 30 °. The intensity ratio (IA / IB) between the intensity (IA) of the strongest peak appearing in the range of ˜34 ° and the intensity (IB) of the strongest peak appearing in the range of 2θ = 40 ° to 44 ° is 0.6 or more. A hydrogen storage alloy is disclosed that is substantially free of La as a rare earth element.

Similarly, as a hydrogen storage alloy capable of improving corrosion resistance, Patent Document 4 discloses a general formula Ln _1-x Mg _x Ni _yab Al _a M _b (wherein Ln is at least one element selected from rare earth elements including Y). , M is at least one element selected from V, Nb, Ta, Cr, Mo, Mn, Fe, Co, Ga, Zn, Sn, In, Cu, Si, P, B, Zr and Ti, 0.05 ≦ x ≦ 0.35, 2.8 ≦ y ≦ 3.9, 0.05 ≦ a ≦ 0.30, and 0 ≦ b ≦ 0.5.), Cu—Kα In an X-ray diffraction measurement using a line as an X-ray source, the half-value width Δθ _{1 of the} strongest peak appearing in the range of 2θ = 44 to 46 ° is half of the strongest peak appearing in the range of 2θ = 34.5 to 36.5 ° A hydrogen storage alloy for alkaline batteries is disclosed which is smaller than the value range Δθ ₂ .

  In Patent Document 5, in order to obtain a hydrogen storage alloy having particularly excellent life characteristics, that is, a hydrogen storage alloy having a homogeneous structure and characteristics, a nickel-based hydrogen storage alloy raw material is melted, and the obtained molten metal is poured into a mold. Disclosed is a manufacturing method in which the obtained alloy is pulverized by rapid cooling, the alloy powder is classified, the alloy powder is classified, and the classified alloy powder is heat-treated at a temperature of 1000 to 1200 ° C. in an inert gas atmosphere (high temperature holding treatment). Has been.

JP 2001-40442 A Japanese Patent No. 3493516 JP 2004-263213 A JP 2007-250439 A JP 2002-212601 A

  The present invention intends to provide a new hydrogen storage alloy excellent in corrosion resistance by a completely different approach.

In order to solve this problem, the present invention is an Al-containing hydrogen storage alloy having a CaCu ₅ type crystal structure having a space group of International Table No. 191 (P6 / mmm), and a crystal structure analysis of the hydrogen storage alloy In which the Beq ratio (2c / 3g) as a ratio of the thermal vibration parameter Beq (2c) of the 2c site to the thermal vibration parameter Beq (3g) of the 3g site is 1.4 to 10.0 Propose a storage alloy.

In a hydrogen storage alloy having a CaCu ₅ type crystal structure having a space group of International Table No. 191 (P6 / mmm), the proportion of 3g sites and 2c sites in each constituent element, particularly Al, is adjusted, that is, the Beq ratio (2c It was found that by preparing the hydrogen storage alloy so that / 3 g) is within a predetermined range, the crystal structure can be stabilized and the corrosion resistance can be improved without impairing the output characteristics.

The vertical axis is an index of the rate of increase in magnetization (: VSM increase rate) (vs comparative example 3), and the horizontal axis is in coordinates consisting of the Bec ratio (2c / 3g) of the thermal vibration parameter of the 2c site to the thermal vibration parameter of the 3g site It is the graph which plotted the value of the Example and the comparative example, and showed these tendencies.

  Embodiments of the present invention will be described in detail below, but the scope of the present invention is not limited to the embodiments described below.

(composition)
The hydrogen storage alloy of the present embodiment (hereinafter referred to as “the present hydrogen storage alloy”) is a hydrogen storage alloy having a CaCu ₅ type crystal structure having a space group of International Table No. 191 (P6 / mmm) and containing Al. . For example, the general formula _{MmNi a Mn b Al c Co d} ( wherein, Mm is the mischmetal, a + b + c + d > 5), or, in the general formula _{MmNi a Mn b Al c Co d} M e ( wherein, Mm is misch metal, M is one or more of Fe, Cu, V, Zn, and Zr, and AB ₅ type hydrogen storage alloy that can be represented by a + b + c + d + e> 5) Can be mentioned.

In the present hydrogen storage alloy, the ratio of the total number of moles of elements constituting the B site to the total number of moles of elements constituting the A site in the ABx composition “a + b + c + d” or “a + b + c + d + e” (this ratio is also referred to as “ABx”) Is not particularly limited, from the viewpoint of use as a negative electrode active material for Ni-MH batteries mounted on electric vehicles (referred to as “EV”) and hybrid vehicles (referred to as “HEV”). It is important that it is greater than 0, and it is particularly preferable that 5.0 <ABx ≦ 5.5.
When ABx is greater than 5.0, that is, a B-site rich non-stoichiometric composition, it is possible to suppress a decrease in low-temperature capacity and life characteristics (capacity maintenance ratio). Therefore, from such a viewpoint, ABx is more preferably 5.1 or more, more preferably 5.2 or more, particularly preferably 5.3 or more, and further preferably 5.4 or less. .

  The composition ratio of Mm, Ni, Mn, Al, Co, and M is not particularly limited, but is considered as follows from the viewpoint of use as a negative electrode active material of a Ni-MH battery mounted on EV and HEV. be able to.

  The ratio (d) of Co can be provided at low cost if the amount is reduced, but it is difficult to maintain the life characteristics, so it is preferably 0.10 to 0.80, particularly 0.10 or more, Alternatively, it is preferably 0.50 or less, particularly 0.20 or more, or 0.40 or less, and particularly preferably 0.30 or less.

The ratio (a) of Ni is 3.70 to 4.70, preferably 4.00 or more, or 4.50 or less, more preferably 4.10 or more, or 4.40 or less, especially 4.15 or more, or It is good to adjust within the range of 4.35 or less. If it is in the range of 3.70 ≦ a ≦ 4.70, it is easy to maintain the output characteristics, and the pulverization characteristics and the life characteristics are not particularly deteriorated.
The ratio (b) of Mn is 0 to 0.70, preferably 0.10 or more, or 0.50 or less, particularly preferably 0.20 or more, or 0.45 or less, more preferably 0.30 or more, or It is preferable to adjust within the range of 0.41 or less. If the ratio of Mn is within such a range, the pulverization residual rate can be easily maintained.
The proportion (c) of Al is adjusted within the range of 0.10 to 0.50, preferably 0.20 or more, or 0.50 or less, particularly preferably 0.35 or more, or 0.45 or less. Good. If the ratio of Al is within such a range, it can be suppressed that the plateau pressure becomes higher than necessary and the energy efficiency of charge / discharge is deteriorated, and further, the decrease of the hydrogen storage amount can be suppressed.

Element M, may be mentioned such an essential element bur, for example Fe, Cu, V, Zn, Zr and the like. Among these, from the viewpoint of life characteristics, one or two of Fe and Cu, and among them, Fe can be preferably exemplified. For example, the addition of an appropriate amount of Fe can suppress the pulverization, that is, improve the life characteristics.
The ratio (e) of the M element is preferably 0 ≦ e ≦ 0.20, more preferably 0.15 or less, and particularly preferably 0.13 or less.

  Mm may be a rare earth-based mixture (Misch metal) containing at least La and Ce. Normal Mm contains rare earths such as Pr, Nd, and Sm in addition to La and Ce. For example, a rare earth mixture having Ce (40 to 50%), La (20 to 40%), Pr, and Nd as main constituent elements can be mentioned. In this hydrogen storage alloy, the La content is a hydrogen storage alloy. 13-30 wt%, especially 18-27 wt%, especially 20-25 wt%, Ce content is 3-10 wt%, especially 4-9 wt%, especially 4.5-8.5 wt% in the hydrogen storage alloy Is preferred.

  Note that any impurity of Ti, Mo, W, Si, Ca, Pb, Cd, and Mg may be included as long as it is about 0.05 mass% or less.

(Thermal vibration parameters)
The hydrogen storage alloy has a Beq ratio (2c / 3g) of 1.4 or more as a ratio of the thermal vibration parameter Beq (2c) at the 2c site to the thermal vibration parameter Beq (3g) at the 3g site in the crystal structure analysis. This is very important.
General formula MmNi _a Mn _b Al _c Co _d (where Mm is misch metal, a + b + c + d> 5), or general formula MmNi _a Mn _b Al _c Co _d M _e (where Mm is Mish metal, M is one or more of Fe, Cu, V, Zn, Zr , a conventional AB type ₅ hydrogen storage alloy that can be represented by a + b + c + d + e> 5) As far as we investigated, the Beq ratio (2c / 3g) is usually less than 1.4, but by making this Beq ratio (2c / 3g) 1.4 or more, the corrosion resistance becomes remarkably excellent. Further, it was found that if this Beq ratio (2c / 3g) is further increased, the corrosion resistance is further improved.
However, if the Beq ratio (2c / 3g) is too high, the effect of segregation increases, so that it is realistic that it is 10.0 or less, preferably 8.0 or less, particularly 6.1 or less. It is considered that it is more preferable.

In the AB type ₅ hydrogen storage alloy, a site containing B element, for example, an alloy represented by an Mm-Ni-Mn-Al-Co alloy, a site containing Ni, Mn, Al and Co is a 3g site or a 2c site. is there. It is known that the 2c site exists in a relatively narrow space and has a low electron density, while the 3g site exists in a relatively wide space and has a high electron density. Among these, the occupation ratio of Al at the 2c site and the 3g site greatly affects the Beq (2c / 3g) of the alloy. Al has been reported to selectively occupy 3g sites, but by increasing the occupancy of Al at 2c sites, that is, by increasing Beq (2c / 3g), the crystal structure becomes more stable and corrosion resistance is improved. Can be increased.

  The thermal vibration parameter is for correcting the difference between the electron density at each site and the actually measured electron density when it is assumed that the B element of the ABx alloy composition is present in the 2c site and the 3g site at the same ratio. Since the parameter is a parameter, a small thermal vibration parameter means that the actually measured electron density is large, and conversely, a large thermal vibration parameter means that the actually measured electron density is small.

(Method for producing hydrogen storage alloy)
The present hydrogen storage alloy is, for example, weighed and mixed each hydrogen storage alloy raw material so as to have a predetermined alloy composition, and melted the hydrogen storage alloy raw material using a high frequency heating melting furnace by induction heating, for example. Then, this is poured into a mold, for example, a water-cooled mold, cast at a casting temperature of, for example, 1350 to 1550 ° C., cooled at a predetermined cooling rate (a predetermined amount of cooling water), and then, for example, in an inert gas atmosphere, Immediately before the high temperature holding process for holding the target temperature (referred to as “holding temperature”), the temperature is raised to a temperature higher than the holding temperature, and then the preliminary heat treatment (“overshoot”) is performed to lower the temperature to the holding temperature. Can be obtained.
However, the manufacturing method of this hydrogen storage alloy is not limited to such a manufacturing method.

After overshooting under certain conditions, performing a high-temperature holding process that maintains the target temperature (“holding temperature”) means that the holding temperature immediately before the high-temperature holding process for homogenizing the crystal. Since heat energy at a higher temperature is primarily given to the hydrogen-absorbing alloy, rearrangement of the B element can be promoted to achieve a more stable state, and then homogenization within the crystal can be achieved.
In the AB type ₅ hydrogen storage alloy, in the case of an alloy represented by an element B, for example, an Mm—Ni—Mn—Al—Co alloy, the sites where Ni, Mn, Al, and Co enter are 3 g sites or 2 c sites. In the heat treatment step, the thermal energy higher than the holding temperature is temporarily given to the hydrogen storage alloy immediately before the high temperature holding treatment, so that the ion density is relatively large, such as Ni, Co and Mn, and the electron density. Element can be released from the 2c site and elements such as Al having a relatively small ionic radius and a low electron density can be left at the 2c site, so that each B element is fixed to a more stable site. Thus, the corrosion resistance can be improved.

  As a specific method of such a planned overshoot, for example, in the case of performing a high temperature holding treatment for holding for about 3 to 6 hours at a holding temperature of 1040 to 1080 ° C., 5 to 40 ° C. above the holding temperature. The temperature may be raised to a high temperature, the temperature may be maintained for more than 0 minutes for 60 minutes, and then the temperature may be lowered to the holding temperature.

The above production method is an example of the production method of the present hydrogen storage alloy, and is not limited thereto.
For example, it is preferable to appropriately select and control the production conditions such as casting conditions (casting method, casting temperature, cooling rate, etc.) and heat treatment conditions according to the alloy composition.
As for the casting method, the mold casting method is one of the preferable casting methods. For example, the twin roll method (specifically, refer to paragraphs [0013] to [0016] of Japanese Patent Application No. 2002-299136), and other casting methods may be used. It can be manufactured.

The obtained hydrogen storage alloy (ingot) is made into a hydrogen alloy powder having a required particle size by coarse pulverization and fine pulverization, if necessary. For example, it can be pulverized to a particle size (−500 μm) passing through a 500 μm sieve to obtain a hydrogen storage alloy powder.
In addition, if necessary, the surface of the alloy may be coated with a metal material or polymer resin, or the surface may be treated with an acid or alkali, and used as a negative electrode active material for various batteries. it can.

(Use of hydrogen storage alloy)
The present hydrogen storage alloy (including ingot and powder) can prepare a negative electrode for a battery by a known method. That is, a hydrogen storage alloy negative electrode can be formed by mixing and forming a binder, a conductive additive and the like by a known method.

The hydrogen storage alloy negative electrode thus obtained can be used not only for secondary batteries but also for primary batteries (including fuel cells). For example, a Ni-MH battery can be composed of a positive electrode using nickel hydroxide as an active material, an electrolytic solution made of an alkaline aqueous solution, and a separator.
In particular, the present hydrogen storage alloy is excellent in corrosion resistance, and can improve the life characteristics without lowering the output. Therefore, the hydrogen storage alloy is particularly preferably used as a Ni-MH battery mounted on an EV, HEV or the like that requires these characteristics. be able to.

(Explanation of words)
In the present specification, when expressed as “X to Y” (X and Y are arbitrary numbers), “X is preferably greater than X” or “preferably more than Y” with the meaning of “X to Y” unless otherwise specified. The meaning of “small” is also included.
In addition, when expressed as “more than X” or “X ≦” (X is an arbitrary number) or “Y or less” or “≦ Y” (Y is an arbitrary number), “preferably greater than X” or “ The intention of “preferably less than Y” is also included.

  Next, the present invention will be further described based on examples, but the present invention is not limited to the following examples.

<Measuring method of thermal vibration parameter (Beq)>
The hydrogen storage alloys obtained in the examples and comparative examples are roughly crushed using a jaw crusher (manufactured by Fuji Paudal: model 1021-B), and further passed through a 500 μm sieve using a horizontal brown pulverizer (manufactured by Yoshida Seisakusho). Grinding was performed to a particle size (−500 μm).
20 g of the obtained hydrogen-absorbing alloy powder of −500 μm (particles passing through a 500 μm sieve mesh) was pulverized for 1 minute with a cyclomill ((type 1033-200) manufactured by Yoshida Seisakusho) and classified with a sieve with an opening of 20 μm. A hydrogen storage alloy powder (sample) of 20 μm (particles passing through a 20 μm sieve) was obtained.
The obtained sample was filled in a sample holder, and measurement was performed using an X-ray diffractometer (D8ADVANCE manufactured by Bruker AXS Co., Ltd.).

The specifications and conditions of the X-ray diffraction apparatus used are as follows.
Tube: CuKα ray Spacegroup: P6 / mmm
* Sample disp (mm): Refine
Detector: PSD
Detector Type: VANTEC-1
High Voltage: 5616V
Discr. Lower Level: 0.45V
Discr. Window Width: 0.15V
Grid Lower Level: 0.075V
Grid Window Width: 0.524V
Flood Field Correction: Disabled
Primary radius: 250mm
Secondary radius: 250mm
Receiving slit width: 0.1436626mm
Divergence angle: 0.3 °
Filament Length: 12mm
Sample Length: 25mm
Receiving Slit Length: 12mm
Primary Sollers: 2.623 °
Secondary Sollers: 2.623 °
Lorentzian, 1 / Cos: 0.01630098Th
Det. 1 voltage: 760.00V
Det. 1 gain: 80.000000
Det. 1 discr. 1 LL: 0.6900000
Det. 1 discr. 1 WW: 1.078000
Scan Mode: Continuous Scan
Scan Type: Locked Coupled
Spinner Speed: 15rpm
Divergence Slit: 0.300 °
Start: 15.000000
Time per step: 1.00s
Increment: 0.01456
#Steps: 7152
Generator voltage: 35kV
Generator current: 40 mA

Using the X-ray diffraction pattern (diffraction angle 2θ = 15 to 120 °) obtained by the measurement, analysis was performed with analysis software (software name: Topas Version 3).
In the analysis, firstly, a numerical value that is mol% so that only the compositional component of Mm of the measured alloy is 100%, and so that it is 100% only by the compositional component of Ni, Al, Mn, Co, and additive metal M. The numerical value to be mol% is obtained, 1a is set to the composition component of Mm and the obtained numerical value is set to Occ (occupancy), and 2c and 3g are obtained to be the compositional components of Ni, Al, Mn, Co and added metal M The numerical value was set to Occ (occupancy), the Fundamental Parameter method was adopted, and the lattice constant was refined by the Rietveld method with the crystallite size (Lorentzian method) as a variable.
Next, the obtained lattice constant was fixed, and the thermal vibration parameters of 1a, 2c, and 3g were all fixed to 0.5 at first, and then the calculation was repeated by using individual variables to obtain each thermal vibration parameter.

The peaks of the X-ray diffraction pattern used for the analysis are as follows.
・ Peak indexed by Miller index (010) near 20.5 ° ・ Peak indexed by Miller index (001) near 21.9 ° ・ Miller index (011) near 30.1 ° ) Peak indexed by Miller index (110) near 35.8 ° Peak indexed by Miller index (020) near 41.6 ° 42.4 ° Peak indexed by Miller index (111) near • Peak indexed by Miller index (002) near 44.6 ° • Indexed by Miller index (021) near 47.5 °・ Peak indexed by Miller index (012) near 49.5 ° ・ Peak indexed by Miller index (210) near 56.1 ° ・ Mira near 58.5 ° Peak indexed by index (112)-Peak indexed by Miller index (211) near 60.9 °-Peak indexed by Miller index (022) near 62.6 °-64 • Peak indexed with Miller index (030) near 4 ° • Peak indexed with Miller index (031) near 68.9 ° • Miller index (003) near 69.4 ° Indexed peak • Peak indexed with Miller index (013) near 73.2 ° • Peak indexed with Miller index (212) near 74.3 ° • Near 76.0 ° Peak indexed by a certain Miller index (220) • Peak indexed by a Miller index (310) near 79.7 ° • Indexed by a Miller index (221) near 80.2 °・ Peak indexed by Miller index (113) near 80.7 ° ・ Peak indexed by Miller index (032) near 81.8 ° ・ Miller index near 83.9 ° The peak indexed by (311)-The peak indexed by the Miller index (023) near 84.3 °-The peak indexed by the Miller index (040) near 90.6 °-92. Peak indexed with Miller index (222) near 7 ° • Peak indexed with Miller index (041) near 94.7 ° • Index with Miller index (213) near 95.2 ° • Peaks indexed by Miller index (312) near 96.3 ° • Peaks indexed by Miller index (004) near 98.8 ° • With 101.5 ° Peak indexed with Miller index (320) at • Index peaked with Miller index (014) near 102.5 ° • Indexed with Miller index (033) near 102.6 ° Peak ・ Peak indexed by Miller index (321) near 105.8 ° ・ Peak indexed by Miller index (042) near 107.4 degrees ・ Miller index near 109.0 degrees ( Peak indexed at 410) • peak indexed at Miller index (114) near 110.0 ° • peak indexed at Miller index (411) near 113.4 ° • 113.9 • Peak indexed with Miller index (024) near ° • Peak indexed with Miller index (223) near 114.0 ° • Near 118.0 ° Peak indexed by the Miller index (322) in the peak 119.2 vicinity ° which is indexed by the Miller index (313)

<Evaluation of corrosion resistance: VSM increase rate index>
When hydrogen storage alloy powder is immersed in a high-temperature alkaline solution, Mn, Al, and Mm (La, Ce, Nd, Pr), among alloy components, are eluted from the alloy surface into the alkaline solution, and are the remaining alloy components. Components mainly composed of Ni, Co, and Fe form a hydrogen storage alloy surface layer. Therefore, when immersed in a high-temperature alkaline solution, Ni, Co, and Fe that are ferromagnetic materials exist on the surface of the hydrogen storage alloy. Therefore, by measuring the magnetization when the hydrogen storage alloy powder is immersed in an alkaline solution, it is possible to indicate how much Ni, Co, and Fe are present on the alloy surface, that is, the degree of corrosion.
Here, the magnetization before and after charging / discharging is measured, the change rate (%) of the magnetization after charging / discharging with respect to the magnetization before charging / discharging is calculated as the VSM increasing rate, and the VSM increasing rate of Comparative Example 3 is set to 100 The value of the VSM increase rate of each sample was shown as a VSM increase rate index.

(Sample preparation)
The hydrogen storage alloys obtained in Examples and Comparative Examples are roughly crushed using a jaw crusher (manufactured by Fuji Paudal: model 1021-B), and further passed through a 500 μm sieve using a horizontal brown grinder (manufactured by Yoshida Seisakusho). Grinding was performed to a particle size (−500 μm).
Further, 20 g of the obtained −500 μm alloy powder was pulverized for 1 minute with a cyclomill (model 1033-200, Yoshida Seisakusho). Next, a sieve having a mesh size of 22 μm and 53 μm was set in an automatic classifier (“GILSONIC AUTO SIEVER” manufactured by GILSON), and the obtained alloy powder was classified using the automatic classifier for 5 minutes. The powder obtained with a 53 μm sieve was used as a sample.

(Device used)
・ Constant bath / heater: THERMO MINDER SH-12 (Tytec Corporation)
-Shaker: WATER BATH SHAKER PERSONAL H-10 (Tytec Corporation)
・ Heat medium: Heater lube oil K-1 (King Manufacturing Co., Ltd.)
・ Vibrating sample type magnetometer (vibrating sample type magnetometer: TM-VSM1014-MRO-M type, electromagnet: TM-WTF51.406-101.5FA type) (Tamagawa Manufacturing Co., Ltd.)

(Measurement procedure)
(1) 30 mL of 31 wt% KOH aqueous solution was put into a 100 mL Erlenmeyer flask (made of fluororesin), capped and set on a shaker.
(2) The temperature was adjusted with THERMO MINDER SH-12 (Tytec Corp.), and the 31 wt% KOH aqueous solution in the Erlenmeyer flask was adjusted to 120 ° C.
(3) 3 g of 20-53 μm alloy powder (sample) prepared as described above was added, and the shaking speed of WATER BATH SHAKEPERPERSONAL H-10 (Tytec Co., Ltd.) was adjusted to 160 min−1 at 120 ° C. Shake for a predetermined time (1 hour).
(4) The 31 wt% KOH aqueous solution in the Erlenmeyer flask was decanted.
(5) 75 mL of 80 ° C. hot water was placed in an Erlenmeyer flask, and stirring and decantation were repeated three times.
(6) The alloy powder washed with hot water was suction-filtered and dried for 15 minutes with a circulating dryer at 80 ° C.
(7) To 1 g of the obtained sample, 3 g of Cu powder as a conductive agent and 0.12 g of polyethylene powder as a binder were added and mixed to obtain a mixed powder (mixed powder before charge / discharge). This mixed powder (mixed powder before charging / discharging) was converted into a vibrating sample magnetometer (vibrating sample magnetometer: TM-VSM1014-MRO-M type, electromagnet: TM-WTF 51.406-101.5FA type) (Tamagawa Corporation). The sweep pattern 3 (hysteresis loop) was measured.

(Measurement conditions of vibrating sample magnetometer)
Max magnetic field ... 10 (kOe)
-Time constant lock-in amp ... 100 (msec)
Measuring method... Sweep {speed 1: 5 sec / 1 kOe speed 2: 10 sec / 1 kOe (1 to −1 [kOe])}
・ Angle ・ ・ ・ fix 0 [°]
・ Gap of pole chips ・ ・ ・ 14mm
・ Measuring loop ・ ・ ・ half

Magnetization was determined from the obtained hysteresis loop as follows: Magnetization (emu / g) = M (10) −2 {M (10) −M (5)}
Here, M (10) is the magnetization when the X axis is 10 [kOe], and M (5) is the magnetization when the X axis is 5 [kOe].
In this magnetization, since the conductive material and the binder are contained as masses, the magnetization of only the alloy powder was calculated by the following equation.
(Magnetization before charge / discharge)
Magnetization of alloy powder only = (magnetization obtained / 0.2427)

Also, 1.24 g of the mixed powder (mixed powder before charging / discharging) obtained above was pressure-molded on foamed Ni to form a pellet type having a diameter of 18 mm and a thickness of 1.8 mm, and vacuum firing at 150 ° C. for 1 hour. The pellet electrode was produced by sintering.
This pellet electrode is used as a negative electrode, sandwiched by a positive electrode (sintered nickel hydroxide) with a sufficient capacity via a separator (manufactured by Japan Vilene), and immersed in a 31 wt% aqueous KOH solution (see FIG. 1). ) And a charge / discharge test is performed using the equipment (TOSCAT3000 (manufactured by Toyo System Co., Ltd.)) based on the test cycle pattern ("activation"->"constant charge cycle"->"capacitycheck") under the following conditions It was.

[Charging / discharging conditions]
(Activation and capacity check cycle)
・ Charging 0.2C-120%; discharging 0.2C-0.9V cut ・ Cycle: 1-10 cycles, 59-60 cycles ・ Temperature: 20 ° C.

(Constant charge cycle)
・ Charging 0.2C-80%; Discharging 1.0C-0.9V cut ・ Cycle: 11-58 cycles ・ Temperature: 20 ° C.
After the charge / discharge, the same apparatus was used and discharged under the following conditions.

(Discharge before dismantling)
・ 0.2C-0.9V cut ・ Temperature: 20 ℃
The open test cell after discharge was disassembled, the pellet electrode was collected, the collected pellet electrode was washed in flowing water for 90 minutes to 180 minutes, and dried under the following conditions in a vacuum dryer.

(Drying conditions)
Degree of vacuum: -0.1 MPa
Drying temperature: 30 ° C
Drying time: 12 hours

The foamed Ni portion was peeled off from the dried pellet electrode, and only the electrode portion was collected. The collected electrode portion was pulverized in an alumina mortar to obtain a mixed powder after charge and discharge.
The obtained mixed powder after charging / discharging was measured and calculated in the same manner as the magnetization of the mixed powder before charging / discharging, and the magnetization of the mixed powder after charging / discharging was calculated.
Then, the VSM increase rate is calculated from the magnetizations before and after charging / discharging obtained in this way using the following formula, and the VSM increase rate of each sample when the VSM increase rate of Comparative Example 3 is set to 100 is increased by VSM. It is shown in the table as a rate index.
VSM increase rate = (magnetization after charge / discharge / magnetization before charge / discharge) × 100

Example 1
By mass ratio of each element, Mm: 31.79%, Ni: 57.98%, Mn: 5.09%, Al: 2.15%, Co: 2.69%, Fe: 0.30% Thus, raw materials (pure metals were used as raw materials for Ni, Mn, Al, Co, and Fe) were weighed and mixed.
Mm is a misch metal that is a rare earth mixture of La and Ce, and the content ratio of each component in Mm is La: 78.7%, Ce: 15.0%, Nd: What was adjusted so that it might become 4.8% and Pr: 1.5% was used as a raw material.

The obtained mixture was put in a crucible and fixed in a high-frequency melting furnace, and the pressure was reduced to 10 ⁻⁴ to 10 ⁻⁵ Torr. Then, argon gas was introduced, heated to 1450 ° C. in an argon gas atmosphere, and then a total mass of 200 kg. Then, 10 kg of molten metal was poured into the water-cooled copper mold at 4 kg / second to obtain a hydrogen storage alloy. Furthermore, the obtained hydrogen storage alloy was put in a stainless steel container and set in a vacuum heat treatment apparatus, and a high temperature holding treatment was performed after overshooting in an argon gas atmosphere to obtain a hydrogen storage alloy (sample).

At this time, in the overshoot and high temperature holding treatment, the temperature is increased from 1080 ° C. to 2090 ° C. in 20 minutes, and the temperature decrease starts immediately after reaching 1090 ° C. After the temperature was lowered to 20 minutes until overshooting was performed, a high temperature holding treatment was performed so that the temperature was maintained at 1080 ° C. for 4 hours and 5 minutes.
The holding temperature of the high temperature holding treatment is a temperature measured by thermocouples installed at the upper and lower parts in the vacuum heat treatment apparatus, and is considered to be substantially the same temperature as the product temperature (the following examples and comparative examples) The same applies to the above).
The table shows the difference (10 ° C.) between the maximum attained temperature (1090 ° C.) and the holding temperature (1080 ° C.) as the temperature in overshoot (the same applies to other examples and comparative examples).

The obtained hydrogen storage alloy (sample) was confirmed to be MmNi _4.35 Al _0.35 Mn _0.41 Co _0.20 Fe _0.02 (ABx = 5.33) by ICP analysis.

(Example 2)
By mass ratio of each element, Mm: 31.76%, Ni: 57.93%, Mn: 3.84%, Al: 2.14%, Co: 4.03%, Fe: 0.30% Thus, raw materials (pure metals were used as raw materials for Ni, Mn, Al, Co, and Fe) were weighed and mixed.
Mm is a misch metal which is a rare earth mixture of La and Ce, and the content ratio of each component in Mm is La: 78.9%, Ce: 14.9%, Nd: What adjusted 4.7% and Pr: 1.5% was used as a raw material.

The obtained mixture was put in a crucible and fixed in a high-frequency melting furnace, and the pressure was reduced to 10 ⁻⁴ to 10 ⁻⁵ Torr. Then, argon gas was introduced, heated to 1450 ° C. in an argon gas atmosphere, and then a total mass of 200 kg. Then, 10 kg of molten metal was poured into the water-cooled copper mold at 4 kg / second to obtain a hydrogen storage alloy. Furthermore, the obtained hydrogen storage alloy was put in a stainless steel container and set in a vacuum heat treatment apparatus, and a high temperature holding treatment was performed after overshooting in an argon gas atmosphere to obtain a hydrogen storage alloy (sample).

  At this time, in the overshoot and high temperature holding treatment, the temperature is increased from 1080 ° C. to 2090 ° C. in 20 minutes, and the temperature decrease starts immediately after reaching 1090 ° C. After the temperature was lowered to 20 minutes until overshooting was performed, a high temperature holding treatment was performed so that the temperature was maintained at 1080 ° C. for 4 hours and 5 minutes.

The obtained hydrogen storage alloy (sample) was confirmed to be MmNi _4.35 Al _0.35 Mn _0.31 Co _0.30 Fe _0.02 (ABx = 5.33) by ICP analysis.

(Example 3)
The mass ratio of each element is Mm: 31.80%, Ni: 55.35%, Mn: 5.10%, Al: 2.15%, Co: 4.03%, Fe: 1.57% Thus, raw materials (pure metals were used as raw materials for Ni, Mn, Al, Co, and Fe) were weighed and mixed.
Mm is a misch metal which is a rare earth mixture of La and Ce, and the content ratio of each component in Mm is La: 62.9%, Ce: 26.1%, Nd: Materials adjusted to be 8.3% and Pr: 2.7% were used as raw materials.

The obtained mixture was put in a crucible and fixed in a high-frequency melting furnace, and the pressure was reduced to 10 ⁻⁴ to 10 ⁻⁵ Torr. Then, argon gas was introduced, heated to 1450 ° C. in an argon gas atmosphere, and then a total mass of 200 kg. Then, 10 kg of molten metal was poured into the water-cooled copper mold at 4 kg / second to obtain a hydrogen storage alloy. Furthermore, the obtained hydrogen storage alloy was put in a stainless steel container and set in a vacuum heat treatment apparatus, and a high temperature holding treatment was performed after overshooting in an argon gas atmosphere to obtain a hydrogen storage alloy (sample).

  At this time, in the overshoot and high temperature holding treatment, the temperature was raised from 1,070 ° C. to 1080 ° C. in 20 minutes, and the temperature reduction was started immediately after reaching 1080 ° C. After overshooting so that the temperature was lowered in 20 minutes, a high temperature holding treatment was performed so as to maintain the temperature at 1070 ° C. for 4 hours and 5 minutes.

The obtained hydrogen storage alloy (sample) was confirmed to be MmNi _4.15 Al _0.35 Mn _0.41 Co _0.30 Fe _0.12 (ABx = 5.33) by ICP analysis.

Example 4
By mass ratio of each element, Mm: 31.76%, Ni: 57.93%, Mn: 3.84%, Al: 2.14%, Co: 4.03%, Fe: 0.30% Thus, raw materials (pure metals were used as raw materials for Ni, Mn, Al, Co, and Fe) were weighed and mixed.
Mm is a misch metal which is a rare earth mixture of La and Ce, and the content ratio of each component in Mm is La: 78.9%, Ce: 14.9%, Nd: What adjusted 4.7% and Pr: 1.5% was used as a raw material.

The obtained mixture was put in a crucible and fixed in a high-frequency melting furnace, and the pressure was reduced to 10 ⁻⁴ to 10 ⁻⁵ Torr. Then, argon gas was introduced, heated to 1450 ° C. in an argon gas atmosphere, and then a total mass of 200 kg. Then, 10 kg of molten metal was poured into the water-cooled copper mold at 4 kg / second to obtain a hydrogen storage alloy. Furthermore, the obtained hydrogen storage alloy was put in a stainless steel container and set in a vacuum heat treatment apparatus, and a high temperature holding treatment was performed after overshooting in an argon gas atmosphere to obtain a hydrogen storage alloy (sample).

  At this time, in the overshoot and high temperature holding treatment, the temperature is raised from 1100 ° C. to 1110 ° C. in 20 minutes after the temperature is raised to 1100 ° C., and the temperature lowering starts immediately after reaching 1110 ° C. After overshooting so that the temperature was lowered in 20 minutes, 1100 ° C. was maintained at a high temperature for 4 hours and 5 minutes.

The obtained hydrogen storage alloy (sample) was confirmed to be MmNi _4.35 Al _0.35 Mn _0.31 Co _0.30 Fe _0.02 (ABx = 5.33) by ICP analysis.

(Example 5)
Raw materials (Ni, Mn) so that the mass ratio of each element is Mm: 31.75%, Ni: 58.24%, Mn: 3.84%, Al: 2.14%, Co: 4.03% Pure metal was used as a raw material for Al and Co.) and weighed and mixed.
Mm is a misch metal that is a rare earth mixture of La and Ce, and the content ratio of each component in Mm is La: 78.8%, Ce: 15.1%, Nd: What adjusted 4.6% and Pr: 1.5% was used as a raw material.

The obtained mixture was put in a crucible and fixed in a high-frequency melting furnace, and the pressure was reduced to 10 ⁻⁴ to 10 ⁻⁵ Torr. Then, argon gas was introduced, heated to 1450 ° C. in an argon gas atmosphere, and then a total mass of 200 kg. Then, 10 kg of molten metal was poured into the water-cooled copper mold at 4 kg / second to obtain a hydrogen storage alloy. Furthermore, the obtained hydrogen storage alloy was put in a stainless steel container and set in a vacuum heat treatment apparatus, and a high temperature holding treatment was performed after overshooting in an argon gas atmosphere to obtain a hydrogen storage alloy (sample).

  At this time, in the overshoot and high temperature holding treatment, the temperature is raised from 1100 ° C. to 1110 ° C. in 20 minutes after the temperature is raised to 1100 ° C., and the temperature lowering starts immediately after reaching 1110 ° C. After overshooting so that the temperature was lowered in 20 minutes, 1100 ° C. was maintained at a high temperature for 4 hours and 5 minutes.

It was confirmed by ICP analysis that the obtained hydrogen storage alloy (sample) was MmNi _4.37 Al _0.35 Mn _0.31 Co _0.30 (ABx = 5.33).

(Example 6)
Raw materials (Ni, Mn) so that the mass ratio of each element is Mm: 31.98%, Ni: 57.31%, Mn: 3.87%, Al: 2.78%, Co: 4.06% Pure metal was used as a raw material for Al and Co.) and weighed and mixed.
Mm is a misch metal which is a rare earth mixture of La and Ce, and the content ratio of each component in Mm is La: 78.2%, Ce: 15.4%, Nd: The material adjusted to be 4.8% and Pr: 1.6% was used as a raw material.

The obtained mixture was put in a crucible and fixed in a high-frequency melting furnace, and the pressure was reduced to 10 ⁻⁴ to 10 ⁻⁵ Torr. Then, argon gas was introduced, heated to 1450 ° C. in an argon gas atmosphere, and then a total mass of 200 kg. Then, 10 kg of molten metal was poured into the water-cooled copper mold at 4 kg / second to obtain a hydrogen storage alloy. Furthermore, the obtained hydrogen storage alloy was put in a stainless steel container and set in a vacuum heat treatment apparatus, and a high temperature holding treatment was performed after overshooting in an argon gas atmosphere to obtain a hydrogen storage alloy (sample).

  At this time, in the overshoot and high temperature holding treatment, the temperature is increased from 1068 ° C. to 1078 ° C. in 20 minutes, and the temperature decrease starts immediately after reaching 1078 ° C. After overshooting so as to lower the temperature in 20 minutes, a high temperature holding treatment was performed so that the temperature was maintained at 1,068 ° C. for 4 hours and 5 minutes.

It was confirmed by ICP analysis that the obtained hydrogen storage alloy (sample) was MmNi _4.27 Al _0.45 Mn _0.31 Co _0.30 (ABx = 5.33).

(Example 7)
Raw materials (Ni, Mn) so that the mass ratio of each element is Mm: 31.95%, Ni: 56.79%, Mn: 5.08%, Al: 2.14%, Co: 4.04% Pure metal was used as a raw material for Al and Co.) and weighed and mixed.
Mm is a misch metal which is a rare earth mixture of La and Ce, and the content ratio of each component in Mm is La: 78.3%, Ce: 15.4%, Nd: What adjusted so that it might become 4.7% and Pr: 1.6% was used as a raw material.

The obtained mixture was put in a crucible and fixed in a high-frequency melting furnace, and the pressure was reduced to 10 ⁻⁴ to 10 ⁻⁵ Torr. Then, argon gas was introduced, heated to 1450 ° C. in an argon gas atmosphere, and then a total mass of 200 kg. Then, 10 kg of molten metal was poured into the water-cooled copper mold at 4 kg / second to obtain a hydrogen storage alloy. Furthermore, the obtained hydrogen storage alloy was put in a stainless steel container and set in a vacuum heat treatment apparatus, and a high temperature holding treatment was performed after overshooting in an argon gas atmosphere to obtain a hydrogen storage alloy (sample).

  At this time, in the overshoot and high temperature holding treatment, the temperature is raised from 1088 ° C. to 1098 ° C. in 20 minutes, and the temperature is lowered immediately after reaching 1098 ° C. After overshooting by lowering the temperature to 20 minutes until 1088 ° C., a high temperature holding treatment was performed by maintaining the temperature at 1088 ° C. for 4 hours and 5 minutes.

It was confirmed by ICP analysis that the obtained hydrogen storage alloy (sample) was MmNi _4.24 Al _0.35 Mn _0.40 Co _0.30 (ABx = 5.29).

(Example 8)
Raw materials (Ni, Mn) so that the mass ratio of each element is Mm: 31.78%, Ni: 56.95%, Mn: 5.09%, Al: 2.15%, Co: 4.03% Pure metal was used as a raw material for Al and Co.) and weighed and mixed.
Mm is a misch metal that is a rare earth mixture of La and Ce, and the content ratio of each component in Mm is La: 78.8%, Ce: 15.1%, Nd: What adjusted 4.6% and Pr: 1.5% was used as a raw material.

The obtained mixture was put in a crucible and fixed in a high-frequency melting furnace, and the pressure was reduced to 10 ⁻⁴ to 10 ⁻⁵ Torr. Then, argon gas was introduced, heated to 1450 ° C. in an argon gas atmosphere, and then a total mass of 200 kg. Then, 10 kg of molten metal was poured into the water-cooled copper mold at 4 kg / second to obtain a hydrogen storage alloy. Furthermore, the obtained hydrogen storage alloy was put in a stainless steel container and set in a vacuum heat treatment apparatus, and a high temperature holding treatment was performed after overshooting in an argon gas atmosphere to obtain a hydrogen storage alloy (sample).

  At this time, in the overshoot and high temperature holding treatment, the temperature was raised from 1074 ° C. to 1084 ° C. in 20 minutes after the temperature was raised to 1074 ° C., and the temperature reduction was started immediately after reaching 1084 ° C. After overshooting so that the temperature was lowered in 20 minutes, a high temperature holding treatment was performed so as to maintain the temperature at 1074 ° C. for 4 hours and 5 minutes.

It was confirmed by ICP analysis that the obtained hydrogen storage alloy (sample) was MmNi _4.27 Al _0.35 Mn _0.41 Co _0.30 (ABx = 5.33).

Example 9
Raw materials (Ni, Mn) so that the mass ratio of each element is Mm: 31.78%, Ni: 58.29%, Mn: 5.09%, Al: 2.15%, Co: 2.69% Pure metal was used as a raw material for Al and Co.) and weighed and mixed.
Mm is a misch metal that is a rare earth mixture of La and Ce, and the content ratio of each component in Mm is La: 78.7%, Ce: 15.0%, Nd: What was adjusted so that it might become 4.8% and Pr: 1.5% was used as a raw material.

The obtained mixture was put in a crucible and fixed in a high-frequency melting furnace, and the pressure was reduced to 10 ⁻⁴ to 10 ⁻⁵ Torr. Then, argon gas was introduced, heated to 1450 ° C. in an argon gas atmosphere, and then a total mass of 200 kg. Then, 10 kg of molten metal was poured into the water-cooled copper mold at 4 kg / second to obtain a hydrogen storage alloy. Furthermore, the obtained hydrogen storage alloy was put in a stainless steel container and set in a vacuum heat treatment apparatus, and a high temperature holding treatment was performed after overshooting in an argon gas atmosphere to obtain a hydrogen storage alloy (sample).

  At this time, in the overshoot and the high temperature holding treatment, the temperature is raised from 1071 ° C. to 2081 ° C. in 20 minutes, and the temperature lowering starts immediately after reaching 1081 ° C., and from 1081 ° C. to 1071 ° C. After overshooting so that the temperature was lowered in 20 minutes, 1071 ° C. was maintained at a high temperature for 4 hours and 5 minutes.

It was confirmed by ICP analysis that the obtained hydrogen storage alloy (sample) was MmNi _4.37 Al _0.35 Mn _0.41 Co _0.20 (ABx = 5.33).

(Comparative Example 1)
By mass ratio of each element, Mm: 31.79%, Ni: 57.98%, Mn: 5.09%, Al: 2.15%, Co: 2.69%, Fe: 0.30% Thus, raw materials (pure metals were used as raw materials for Ni, Mn, Al, Co, and Fe) were weighed and mixed.
Mm is a misch metal that is a rare earth mixture of La and Ce, and the content ratio of each component in Mm is La: 78.7%, Ce: 15.0%, Nd: What was adjusted so that it might become 4.8% and Pr: 1.5% was used as a raw material.

The obtained mixture was put in a crucible and fixed in a high-frequency melting furnace, and the pressure was reduced to 10 ⁻⁴ to 10 ⁻⁵ Torr. Then, argon gas was introduced, heated to 1450 ° C. in an argon gas atmosphere, and then a total mass of 200 kg. Then, 10 kg of molten metal was poured into the water-cooled copper mold at 4 kg / second to obtain a hydrogen storage alloy. Further, the obtained hydrogen storage alloy is put in a stainless steel container and set in a vacuum heat treatment apparatus. After the temperature is raised to 1080 ° C. in an argon gas atmosphere, the temperature is kept high at 1080 ° C. for 4 hours and 45 minutes. Holding treatment was performed to obtain a hydrogen storage alloy (sample).

The obtained hydrogen storage alloy (sample) was confirmed to be MmNi _4.35 Al _0.35 Mn _0.41 Co _0.20 Fe _0.02 (ABx = 5.33) by ICP analysis.

(Comparative Example 2)
By mass ratio of each element, Mm: 32.02%, Ni: 57.06%, Mn: 5.13%, Al: 2.78%, Co: 2.71%, Fe: 0.30% Thus, raw materials (pure metals were used as raw materials for Ni, Mn, Al, Co, and Fe) were weighed and mixed.
Mm is a misch metal which is a rare earth mixture of La and Ce, and the content ratio of each component in Mm is La: 62.5%, Ce: 26.4%, Nd: Materials adjusted to be 8.4% and Pr: 2.7% were used as raw materials.

The obtained mixture was put in a crucible and fixed in a high-frequency melting furnace, and the pressure was reduced to 10 ⁻⁴ to 10 ⁻⁵ Torr. Then, argon gas was introduced, heated to 1450 ° C. in an argon gas atmosphere, and then a total mass of 200 kg. Then, 10 kg of molten metal was poured into the water-cooled copper mold at 4 kg / second to obtain a hydrogen storage alloy. Further, the obtained hydrogen storage alloy is put in a stainless steel container, set in a vacuum heat treatment apparatus, heated to 1070 ° C. in an argon gas atmosphere, and then heated to 1070 ° C. for 4 hours and 45 minutes. Holding treatment was performed to obtain a hydrogen storage alloy (sample).

The obtained hydrogen storage alloy (sample) was confirmed to be MmNi _4.25 Al _0.45 Mn _0.41 Co _0.20 Fe _0.02 (ABx = 5.33) by ICP analysis.

(Comparative Example 3)
By mass ratio of each element, Mm: 32.02%, Ni: 57.06%, Mn: 5.13%, Al: 2.78%, Co: 2.71%, Fe: 0.30% Thus, raw materials (pure metals were used as raw materials for Ni, Mn, Al, Co, and Fe) were weighed and mixed.
Mm is a misch metal which is a rare earth mixture of La and Ce, and the content ratio of each component in Mm is La: 62.5%, Ce: 26.4%, Nd: Materials adjusted to be 8.4% and Pr: 2.7% were used as raw materials.

The obtained mixture was put in a crucible and fixed in a high-frequency melting furnace, and the pressure was reduced to 10 ⁻⁴ to 10 ⁻⁵ Torr. Then, argon gas was introduced, heated to 1450 ° C. in an argon gas atmosphere, and then a total mass of 200 kg. Then, 10 kg of molten metal was poured into the water-cooled copper mold at 4 kg / second to obtain a hydrogen storage alloy. Further, the obtained hydrogen storage alloy is put in a stainless steel container and set in a vacuum heat treatment apparatus. After the temperature is raised to 1090 ° C. in an argon gas atmosphere, the temperature is kept high at 1090 ° C. for 4 hours and 45 minutes. Holding treatment was performed to obtain a hydrogen storage alloy (sample).

The obtained hydrogen storage alloy (sample) was confirmed to be MmNi _4.25 Al _0.45 Mn _0.41 Co _0.20 Fe _0.02 (ABx = 5.33) by ICP analysis.

(Comparative Example 4)
By mass ratio of each element, Mm: 32.01%, Ni: 57.05%, Mn: 3.87%, Al: 2.78%, Co: 2.71%, Fe: 1.58% Thus, raw materials (pure metals were used as raw materials for Ni, Mn, Al, Co, and Fe) were weighed and mixed.
Mm is a misch metal which is a rare earth mixture of La and Ce, and the content ratio of each component in Mm is La: 78.1%, Ce: 15.4%, Nd: What was adjusted so that it might become 4.9% and Pr: 1.6% was used as a raw material.

The obtained mixture was put in a crucible and fixed in a high-frequency melting furnace, and the pressure was reduced to 10 ⁻⁴ to 10 ⁻⁵ Torr. Then, argon gas was introduced, heated to 1450 ° C. in an argon gas atmosphere, and then a total mass of 200 kg. Then, 10 kg of molten metal was poured into the water-cooled copper mold at 4 kg / second to obtain a hydrogen storage alloy. Further, the obtained hydrogen storage alloy is put in a stainless steel container and set in a vacuum heat treatment apparatus. After the temperature is raised to 1090 ° C. in an argon gas atmosphere, the temperature is kept high at 1090 ° C. for 4 hours and 45 minutes. Holding treatment was performed to obtain a hydrogen storage alloy (sample).

It was confirmed by ICP analysis that the obtained hydrogen storage alloy (sample) was MmNi _4.25 Al _0.45 Mn _0.31 Co _0.20 Fe _0.12 (ABx = 5.33).

As far as we have confirmed, a hydrogen storage alloy containing CaCu ₅ type crystal structure having a space group of International Table No. 191 (P6 / mmm), when heat-treated as usual, has a Beq ratio ( 2c / 3g) was less than 1.4, but as shown in FIG. 1, when Beq (2c / 3g) was adjusted to 1.4 to 10.0, the rate of increase in VSM compared to a normal hydrogen storage alloy As a result, it was found that the resistance was significantly reduced and the corrosion resistance was excellent.

Further, since the value of Beq is determined by the crystal structure, if the crystal structure is the same and the transition metal element is the same, the atomic radius is close, and particularly the influence of Al is large. since conceivable, for example, (wherein, Mm is the mischmetal, a + b + c + d > 5) general formula MmNi _a Mn _b Al _c Co _d or formula _{MmNi a Mn b Al c Co d} M e ( wherein , Mm is misch metal, M is one or more of Fe, Cu, V, Zn, Zr , a + b + c + d + e> 5), international table number 191 A hydrogen storage alloy having a CaCu ₅ type crystal structure having a space group of (P6 / mmm) can be assumed to show the same tendency.

Claims (2)

An Al-containing hydrogen storage alloy having a CaCu5 type crystal structure having a space group of International Table No. 191 (P6 / mmm). In the crystal structure analysis of the hydrogen storage alloy, the thermal vibration parameter Beq (3 g The Beq ratio (2c / 3g) as a ratio of the thermal vibration parameter Beq (2c) of the 2c site to) is 1.4 to 10.0,
It can be represented by the general formula MmNiaMnbAlcCod (where Mm is misch metal, a + b + c + d> 5), or the general formula MmNiaMnbAlcCodMe (where Mm is misch metal, M is Fe, Cu, One or more of V, Zn, Zr , a + b + c + d + e> 5), and
A indicating the molar ratio of Ni is 3.70 to 4.70, c indicating the molar ratio of Al is 0.10 to 0.50, and d indicating the molar ratio of Co is 0.10 to 0.10. Hydrogen storage alloy characterized by being 0.80. A Ni-MH battery comprising the hydrogen storage alloy according to claim 1 as a negative electrode active material.

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