JP3834329B2 - AB5 type hydrogen storage alloy with excellent life characteristics - Google Patents

Description

The present invention relates to an AB ₅ type hydrogen storage alloy having a CaCu ₅ type crystal structure, and more particularly to a hydrogen storage alloy having excellent life characteristics.

  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, so this property can be used, for example, in hybrid vehicles and digital still cameras. Practical use is being promoted in various fields such as nickel-hydrogen batteries to be installed.

As the hydrogen storage alloy, various alloys such as an AB ₅ type alloy typified by LaNi ₅ , an AB ₂ type alloy typified by ZrV _0.4 Ni _1.5 , and other AB type alloys and A ₂ B type alloys are known.
Many of them have a relatively low affinity for hydrogen with element groups (Ca, Mg, rare earth elements, Ti, Zr, V, Nb, Pt, Pd, etc.) that have a high affinity for hydrogen and a large amount of hydrogen storage. Although the amount of occlusion is small, it is composed of a combination with an element group (Ni, Mn, Cr, Fe, etc.) that has a fast hydrogenation reaction and lowers the reaction temperature. Since the characteristics of all types of alloys vary greatly depending on the composition, various alloy compositions have been studied for the purpose of improving the maximum hydrogen storage capacity and effective hydrogen storage capacity (high capacity), extending the service life, and increasing output. ing.

Among hydrogen storage alloys, AB ₅ type hydrogen storage alloy having a CaCu ₅ type crystal structure, for example, A site element is composed of a rare earth-based mixture Mm (Misch metal), and B site element is Ni, Al Mm-Ni-Mn-Al-Co alloy composed of four elements, Mn and Co can be manufactured at a relatively low cost compared to La-based alloys such as LaNi ₅ and has a long cycle life. A feature is that a sealed nickel-metal hydride storage battery with a small increase in internal pressure due to the generated gas can be obtained.

As a method for producing such an AB ₅ type hydrogen storage alloy, conventionally, an alloy lump (ingot) cast by a mold casting method or the like is heat-treated in an inert gas atmosphere such as argon, and the heat-treated alloy has a predetermined particle size. The method of pulverizing was generally used. In this production, the disorder of the structure at the time of casting is homogenized by heat treatment, and the heat treatment with the alloy lump is performed to prevent oxidation at the time of heat treatment as much as possible.

  On the other hand, 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, the present applicant melts a nickel-based hydrogen storage alloy raw material and pours the obtained molten metal into a mold. And the obtained alloy is pulverized into an alloy powder, 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 ( Patent Document 1).

JP 2002-212601 A

  The present invention researches to obtain a hydrogen storage alloy having even better life characteristics, and provides a new hydrogen storage alloy based on the new knowledge obtained as a result.

In the AB ₅ type hydrogen storage alloy having a CaCu ₅ type crystal structure with a discharge capacity of 305 mAh / g or more, the present inventor has a full width at half maximum of (002) plane obtained by X-ray diffraction of around 0.20 °. The tendency of the life characteristics (pulverization residual ratio) changes greatly with the boundary of the above, and it has been found that those with a full width at half maximum of less than about 0.20 ° are significantly superior in life characteristics (pulverization residual ratio), The present invention has been conceived based on such knowledge.

That is, the hydrogen storage alloy proposed by the present invention is an AB ₅ type hydrogen storage alloy having a CaCu ₅ type crystal structure and having a discharge capacity of 305 mAh / g or more determined by the following discharge capacity measurement test, The AB ₅ type hydrogen storage alloy is characterized in that the full width at half maximum of the (002) plane obtained from line diffraction is less than 0.20 °.

-Discharge capacity measurement test-
1) 3 g of nickel powder as a conductive material and 0.12 g of polyethylene powder as a binder are mixed with 1 g of a hydrogen storage alloy, and 0.3 g of the obtained mixed powder is pressure-molded on foamed Ni, and the diameter is 15 mm. Then, a pellet type with a thickness of 1.8 mm is formed by vacuum firing at 150 ° C. for 1 hour to produce a pellet electrode. This pellet electrode is used as a negative electrode, and this is used as a positive electrode (sintered nickel hydroxide) through a separator. An open test cell is produced by sandwiching and immersing in a 30 wt% KOH aqueous solution.
2) Connect the open test cell to the charge / discharge device, charge: 0.2C-130%, discharge: 0.2C-0.7V cut, charge / discharge at a temperature of 20 ° C, discharge capacity of 15th cycle ( mAh / g) is measured.

  The hydrogen storage alloy of the present invention is characterized by high discharge capacity and excellent pulverization residual rate. Generally, there is a trade-off (incompatible) relationship between the discharge capacity and the pulverization residual rate. The higher the discharge capacity, the lower the pulverization residual rate. The lower the discharge capacity, the higher the pulverization residual rate. However, the hydrogen storage alloy of the present invention is characterized in that both are excellent. Since the hydrogen storage alloy of the present invention has such characteristics, it can be particularly suitably used as a negative electrode material for a battery having a high discharge capacity, for example, a high capacity battery for consumer use. In the present invention, the “high capacity battery” differs depending on the size of the battery. For example, it is 6000 mAh or more for a D battery, 3000 mAh or more for an S-C battery, 2000 mAh or more for an AA battery, and an AAA battery. Means 700 mAh or more.

Hereinafter, although demonstrated based on the example of embodiment, this invention is not limited to the following embodiment.
In this specification, “X to Y” (X and Y are arbitrary numbers) means “X or more and Y or less” unless otherwise specified, “preferably larger than X, Y It includes the meaning of “smaller”.

The hydrogen storage alloy of the present embodiment has a CaCu ₅ type crystal structure that can be represented by the general formula MmNi _a Mn _b Al _c Co _d or MmNi _a Mn _b Al _c Co _d F _e (where Mm is a misch metal). a AB ₅ type hydrogen storage alloy having the discharge capacity is at 305mAh / g or more, AB ₅ having the characteristic that and obtained from X-ray diffraction (002) plane full width at half maximum is less than 0.20 ° Type hydrogen storage alloy.

The hydrogen storage alloy of the present invention is not particularly limited to the above composition as long as it is an AB ₅ type hydrogen storage alloy having a CaCu ₅ type crystal structure. However, a nickel-based hydrogen storage alloy containing nickel and misch metal as components is preferable.

  The total value of x in the ABx composition, that is, a + b + c + d or a + b + c + d + e (this ratio is referred to as “ABx”) as a 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. It is preferable that 7 ≦ ABx ≦ 5.5, especially 4.7 ≦ ABx or ABx ≦ 5.4, and more preferably 4.9 ≦ ABx or ABx ≦ 5.4.

  Regarding the composition ratio of the elements Ni, Mn, Al, Fe and Co constituting the B site in the ABx composition, as described above, 4.7 ≦ ABx ≦ 5.5, preferably 4.7 ≦ ABx ≦ 5.4. It may be adjusted as appropriate within the range. For example, if the priority is given to reducing the Co content, the Co composition ratio (molar ratio) is lowered, and instead the Ni composition ratio (molar ratio) is increased. Then, it is preferable to adjust the alloy composition so that the ratio of Mn falls within a predetermined range, and then adjust the manufacturing conditions so that the discharge capacity becomes 305 mAh / g or more. Therefore, in this case, the composition ratio (molar ratio) of Co and Ni is first determined, and then ABx is adjusted by changing the composition ratio of Mn, Al, and Fe so that the composition ratio of Mn falls within a predetermined range. It is preferable to determine the alloy composition.

The ratio (d) of Co is 0 <d ≦ 0.80, preferably 0.10 ≦ d or d ≦ 0.80, and more preferably 0.30 ≦ d. If it is in the range of d <= 0.80, the profit of cost reduction can fully be enjoyed.
The proportion (a) of Ni is 3.45 ≦ a ≦ 4.70, preferably 3.45 ≦ a or a ≦ 4.30. If it is in the range of 3.45 ≦ a ≦ 4.70, excellent output characteristics can be obtained, and further, the pulverization characteristics and life characteristics are not adversely affected.
The ratio (b) of Mn is 0.20 ≦ b ≦ 0.70, preferably 0.20 ≦ b or b ≦ 0.50. In the alloy of the present invention, the proportion of Mn is an important factor. If the ratio of Mn is adjusted to the range of 0.20 ≦ b ≦ 0.70, the life characteristics can be maintained well.
The proportion (c) of Al is 0.10 ≦ c ≦ 0.50, preferably 0.30 ≦ c or c ≦ 0.40. If it is in the range of 0.10 ≦ c ≦ 0.50, the plateau pressure becomes higher than necessary, and the influence of deteriorating the energy efficiency of charge / discharge is small, and the influence of reducing the hydrogen storage amount is small.

  The ratio (e) of Fe is within the range of 0 <e ≦ 0.11, particularly preferably 0.001 ≦ e or e ≦ 0.11, and more preferably 0.002 ≦ e or e ≦ 0.11. It is good to adjust. The addition of Fe can further improve the pulverization characteristics (that is, the life characteristics). Therefore, in applications where Fe content is allowed, the activity can be increased by including within the range of 0 <e ≦ 0.11. The effect of lowering the degree is small, and the pulverization characteristics can be improved.

On the other hand, “Mm” constituting the A site in the ABx composition 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 containing Ce (40 to 50%), La (20 to 40%), Pr, and Nd as main constituent elements can be given. The content of La in Mm is generally 10 to 90% by mass, particularly preferably 10 to 85% by mass, based on the content in Mm.
Note that impurities such as Ti, Mo, W, Si, Ca, Pb, Cd, and Mg may be included as long as they are about 0.05% by weight or less.

In addition, in the AB ₅ type hydrogen storage alloy having a low Co composition of 0 <d ≦ 0.20, preferably 0.10 ≦ d ≦ 0.20, it is particularly preferable to design the AB ₅ type to be high. Specifically, it is preferable to satisfy 5.15 ≦ ABx ≦ 5.40, particularly 5.20 ≦ ABx or ABx ≦ 5.40. In other words, the general formula MmNi _a Mn _b Al _c Co _d or _{MmNi a Mn b Al c Co d} Fe e ( wherein, Mm is the mischmetal, 0 <d ≦ 0.20,5.15 ≦ ABx ≦ 5.40) An AB ₅ type hydrogen storage alloy having a CaCu ₅ type crystal structure that can be represented by
In this case, the Ni ratio (a) is preferably adjusted within the range of 3.45 ≦ a ≦ 4.70, particularly 4.20 ≦ a or a ≦ 4.48, and the Mn ratio (b) Is preferably adjusted within the range of 0.20 ≦ b ≦ 0.70, particularly 0.30 ≦ b or b ≦ 0.60, and the Al ratio (c) is 0.10 ≦ c ≦ 0. 50, especially 0.20 ≦ c or c ≦ 0.40 is preferable, and the ratio (e) of Fe is 0 <e ≦ 0.11, especially 0.001 ≦ e or e ≦ 0. .11, and it is particularly preferable to adjust within the range of 0.025 ≦ e or e ≦ 0.10.

  It is important for the hydrogen storage alloy of this embodiment that the discharge capacity calculated | required by the following discharge capacity measurement test is 305 mAh / g or more. The hydrogen storage alloy having a discharge capacity of 305 mAh / g or more has a unique property that the tendency of the life characteristics (pulverization residual ratio) greatly changes when the full width at half maximum of the (002) plane is around 0.20 °. The inventor has found to show.

-Discharge capacity measurement test-
The discharge capacity defined by the present invention can be determined by the following test method according to JIS H7205.
1) 3 g of nickel powder as a conductive material and 0.12 g of polyethylene powder as a binder are mixed with 1 g of a hydrogen storage alloy, and 0.3 g of the obtained mixed powder is pressure-molded on foamed Ni to obtain a diameter. A pellet electrode of 15 mm and a thickness of 1.8 mm was formed by vacuum baking at 150 ° C. for 1 hour, and this pellet electrode was used as a negative electrode. An open type test cell is prepared by sandwiching with a sintered nickel hydroxide) through a separator and dipping in a 30 wt% KOH aqueous solution.
2) Connect the open test cell to the charge / discharge device, charge: 0.2C-130% (vs. calculated negative electrode capacity), discharge: 0.2C-0.7V cut, charge / discharge at 20 ° C, 15 The discharge capacity (mAh / g) at the cycle is measured.

  In addition, said "countermeasurement negative electrode capacity | capacitance" is the capacity | capacitance which converted H / M obtained by the measuring method of PCT (H / M) into the electrochemical capacity. For example, in the case of H / M = 0.8, it is converted by the formula of “calculated negative electrode capacity” = ((96500 × 0.8) / (3600 × hydrogen storage alloy average atomic weight)) × 1000 (mAh / g). be able to.

  In the hydrogen storage alloy of this embodiment, since there is a linear correlation between the discharge capacity and the PCT (H / M) value, the “discharge capacity of 305 mAh / g or more” obtained in the above test is “ The PCT (H / M) value at 45 ° C. can be replaced with 0.820 or more ”.

As means for adjusting the discharge capacity and the PCT (H / M) value, discharge can be performed by adjusting ABx (total value of a + b + c + d or a + b + c + d + e: in other words, the molar ratio of A site to B site), Mn amount, La amount and the like. A means for adjusting the capacity and the PCT (H / M) value can be mentioned, but is not limited thereto.
More specifically, in order for the hydrogen storage alloy of this embodiment to have a discharge capacity of 305 mAh / g or more, or a PCT (H / M) value at 45 ° C. of 0.820 or more, the inclusion of La contained in Mm It is important to adjust the balance in a balanced manner: increasing the amount, increasing the amount of Mn (ie, “b”), and bringing ABx close to the stoichiometric ratio. However, it is not limited to such means.

In the hydrogen storage alloy of this embodiment, it is also important that the full width at half maximum of the (002) plane obtained from X-ray diffraction is less than 0.20 °.
As described above, in the AB ₅ type hydrogen storage alloy having a discharge capacity of 305 mAh / g or more, the tendency of the life characteristics (pulverization residual ratio) changes greatly when the full width at half maximum of the (002) plane is around 0.20 °. However, even when the discharge capacity is 305 mAh / g or more, if the full width at half maximum of the (002) plane is less than 0.20 °, the crystal homogeneity is improved, and the life characteristics ( The pulverization residual ratio becomes 76% or more, preferably 77% or more, and more preferably 80% or more.
From such a viewpoint, the full width at half maximum of the (002) plane is more preferably 0.19 ° or less, further preferably 0.18 ° or less, and particularly preferably 0.15 ° or less. .
However, in general, if the La content is increased as described above, the Mn content is increased, or ABx (the total value of a + b + c + d or a + b + c + d + e) is limited to a predetermined range in order to increase the discharge capacity, the full width at half maximum is increased. Therefore, it is necessary to appropriately devise the manufacturing method to increase the crystallinity and reduce the full width at half maximum of the (002) plane. An example of the manufacturing method is a manufacturing method described in detail below.

(Method for producing hydrogen storage alloy)
The hydrogen storage alloy of this embodiment can be manufactured as follows. However, the manufacturing method of the hydrogen storage alloy of this invention is not limited to the following manufacturing method. In the following, the general formula MmNi _a Mn _b Al _c Co _d (where Mm is Misch metal, 3.45 ≦ a ≦ 4.70, 0.20 ≦ b ≦ 0.65, 0.10 ≦ c ≦ 0.50, 0 <d ≦ 0.80, 4.7 ≦ a + b + c + d ≦ 5.5) A method for producing a hydrogen storage alloy having a CaCu ₅ type crystal structure, which can be represented by the following formula, will be described. For example, a hydrogen storage alloy having a CaCu ₅ type crystal structure represented by, for example, MmNi _a Mn _b Al _c Co _d Fe _e ) can be produced in the same manner.

In order to produce the hydrogen storage alloy, for example, the general formula MmNi _a Mn _b Al _c Co _d (where Mm is Misch metal, 3.45 ≦ a ≦ 4.70, 0.20 ≦ b ≦ 0.65). 0.10 ≦ c ≦ 0.50, 0 <d ≦ 0.80, 4.7 ≦ a + b + c + d ≦ 5.5), each hydrogen storage alloy raw material is weighed and mixed, and this mixture The alloy obtained by casting is pulverized by a predetermined method to obtain an alloy powder, the alloy powder is classified, and the alloy powder obtained by classification is inert gas by a predetermined method. The heat treatment may be performed in an atmosphere, and then pulverized and classified so as to obtain a predetermined particle size distribution.

As a casting method, for example, the pressure is reduced to 10 ⁻⁴ to 10 ⁻⁵ Torr using a high-frequency heating melting furnace by induction heating, and then heated and melted in an argon gas atmosphere to form a molten metal with a casting temperature of 1350 to 1550 ° C. ( The hydrogen storage alloy may be obtained by casting by casting into a water-cooled mold at a casting temperature of 1200 to 1450 ° C.). The casting temperature is the temperature of the molten metal in the crucible at the start of casting, and the casting temperature is the mold pouring port temperature (temperature before casting).

Next, the obtained hydrogen storage alloy is pulverized to obtain an alloy powder, which is classified, and the obtained alloy powder may be heat-treated in a vacuum or in an inert gas atmosphere, for example, argon gas.
The degree of pulverization and classification is preferably such that the content of 150 μm or less is 30% or more, particularly 40% or more, and especially 65% or more in the particle size distribution measured by a vibration classifier.
When the content of 150 μm or less is 30% or more, as described above, the crystallinity of the obtained alloy is further increased, the full width at half maximum of the (002) plane can be further reduced, and the life characteristics (fine powder) The residual ratio) can be further increased.

The heat treatment after the classification is performed at a higher temperature than the conventional heat treatment at 1000 ° C. or lower to further promote the atomic diffusion, thereby making it possible to achieve uniform characteristics due to the disappearance of the segregation phase, which could not be achieved by the prior art. It is preferable to carry out. Therefore, the heat treatment at this time is preferably performed at 1040 to 1100 ° C. for 1 to 6 hours.
The obtained alloy is preferably crushed as necessary and further pulverized.

Note that casting and pulverization may be simultaneously performed by a twin roll method (for details, refer to paragraphs [0013] to [0016] of Japanese Patent Application No. 2002-299136). That is, for example, using an induction heating high-frequency melting furnace, the pressure is reduced to 10 ⁻⁴ to 10 ⁻⁵ Torr, and then heated and melted in an argon gas atmosphere. The molten metal is discharged onto a rotating roll, The molten metal repeatedly collides between the arranged Cu rolls, so that it can be rapidly cooled and solidified to form a hydrogen storage alloy ribbon (thin plate shape).
The obtained hydrogen storage alloy powder may be classified and heat-treated in the same manner as described above.

Further, instead of the above manufacturing method, for example, each hydrogen storage alloy raw material is weighed and mixed so as to have a predetermined composition, the mixture is cast by a predetermined method, and a predetermined cooling rate (a predetermined amount of cooling water) is obtained. Then, after heat treatment in vacuum or in an inert gas atmosphere, for example, argon gas at 1040 to 1080 ° C. for 3 to 6 hours, rapidly cool at a predetermined temperature drop rate, and then have a predetermined particle size distribution It can also be produced by pulverization and classification.
At this time, the temperature lowering rate after the heat treatment needs to be rapidly cooled from the heat treatment temperature (maintenance temperature) to 15 to 25 ° C./min, particularly 20 to 25 ° C./min to around 500 ° C., and then naturally cooled. Is preferred.

(Using hydrogen storage alloy)
The hydrogen storage alloy powder thus obtained is appropriately subjected to surface treatment such as coating the alloy surface with a metal material or polymer resin, or treating the surface with an acid or alkali, if necessary. It can be used as the negative electrode active material of the battery.
The negative electrode for a battery can be prepared by mixing a negative electrode active material with a binder, a conductive auxiliary agent, and the like by a known method and molding the negative electrode active material.
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 nickel-MH (Metal Hydride) secondary 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. It can be suitably used for power supply applications such as various electric devices and electric tools. The hydrogen storage alloy of the present invention is particularly suitable as a negative electrode active material for next-generation electric vehicles and hybrid vehicle batteries that require low price, high output, and high durability because the cobalt content can be suppressed. is there.
It can also be used for heat pumps, storage of natural energy such as solar and wind power, hydrogen storage, and actuators.

  Hereinafter, the present invention will be specifically described based on examples.

(Comparative Examples 1-4: 1st composition group)
First composition: Mm (La 20%) Al _0.30 Mn _0.50 Co _0.30 Ni _4.20 (ABx = 5.30) (Mm is a mixture of rare earth metals such as La, Ce, Nd, Pr, etc. La content in Mm in alloy) In order to obtain a hydrogen storage alloy having a composition of 62.9%), Mm: 31.8% (La is 20% of the whole alloy), Ni: 56%, Mn: 6. 3%, Al: 1.8%, Co: 4.0% Weigh and mix so that the mixture is put in a crucible and fixed in a high-frequency melting furnace, and the pressure is reduced to 10 ⁻⁴ to 10 ⁻⁵ Torr. Then, the mixture was heated and melted in an argon gas atmosphere to form a molten metal, and cast into a water-cooled copper mold at a casting temperature of 1450 ° C. (the casting temperature was 1350 ° C.) to obtain an alloy.
The obtained alloy was coarsely crushed using a jaw crusher (Fuji Paudal: model1021-B), and further the pulverization time was changed using a horizontal brown grinder (Yoshida Seisakusho) to each particle size shown in the table. Crushed. The particle size distribution is measured by setting a sieve (JIS Z 8801) in the order of 500 μm, 300 μm, 150 μm, 106 μm, 75 μm, and 45 μm on an OCTAGON DIGITAL automatic classifier (manufactured by CSC SCIENTIFIC COMPANY) and classifying for 10 minutes. After that, the mass of the classified powder was measured.
Next, the obtained alloy powder was put in a SUS container, set in a vacuum heat treatment apparatus (manufactured by Nisshin Giken), and heat-treated at 1060 ° C. for 3 hours. In addition, after heat processing, it cooled by the temperature-fall rate: 5 degree-C / min to 500 degreeC, and reached natural temperature after reaching 500 degreeC.

(Comparative Example 5: first composition group)
The casting was performed in the same manner as in Comparative Example 1, and the obtained alloy was roughly crushed using a jaw crusher (Fuji Paudal: model1021-B) and opened on an OCTAGON DIGITAL automatic classifier (CSC SCIENTIFIC COMPANY) with a mesh opening of 5 mm. Sieves were set in the order of 1 mm and classified for 10 minutes to obtain alloy grains having a particle size distribution of 1 mm to 5 mm. The obtained alloy particles were put in a SUS container and set in a vacuum heat treatment apparatus (manufactured by Nisshin Giken), and heat treatment was performed at 1060 ° C. for 3 hours. In addition, after heat processing, it cooled by the temperature-fall rate: 5 degree-C / min to 500 degreeC, and reached natural temperature after reaching 500 degreeC.

(Comparative Example 6: first composition group)
Casting was performed in the same manner as in Comparative Example 1, and the obtained alloy (ingot) was placed in a SUS container and set in a vacuum heat treatment apparatus (manufactured by Nisshin Giken), and heat treatment was performed at 1060 ° C. for 3 hours. In addition, after heat processing, it cooled by the temperature-fall rate: 5 degree-C / min to 500 degreeC, and reached natural temperature after reaching 500 degreeC.

(Comparative Example 7: first composition group)
Casting was performed in the same manner as in Comparative Example 1, and the obtained alloy (ingot) was placed in a SUS container and set in a vacuum heat treatment apparatus (manufactured by Nisshin Giken) and heat treatment was performed at 1060 ° C. for 10 hours. In addition, after heat processing, it cooled by the temperature-fall rate: 5 degree-C / min to 500 degreeC, and reached natural temperature after reaching 500 degreeC.

(Comparative Example 8: first composition group)
Casting and crushing are performed in the same manner as in Comparative Example 1, and a sieve is set in the order of 300 μm and 50 μm openings on an OCTAGON DIGITAL automatic classifier (manufactured by CSC SCIENTIFIC COMPANY), and classification is performed for 10 minutes. I got a powder. The obtained alloy powder was put in a SUS container and set in a vacuum heat treatment apparatus (manufactured by Nisshin Giken), and heat treatment was performed at 1060 ° C. for 3 hours. In addition, after heat processing, it cooled by the temperature-fall rate: 5 degree-C / min to 500 degreeC, and reached natural temperature after reaching 500 degreeC.

(Examples 1-3: 2nd composition group)
Second composition: Mm (La 25%) Al _0.40 Mn _0.20 Co _0.60 Ni _4.00 (ABx = 5.20) (Mm is a mixture of rare earth metals such as La, Ce, Nd, Pr. La content in Mm in alloy) In order to obtain a hydrogen storage alloy having a composition of 77.2%), Mm: 32.4% (La is 25% of the whole alloy), Ni: 54.4%, and Mn: Weigh and mix to 2.5%, Al: 2.5%, Co: 8.2%, and place the mixture in a crucible and fix to a high-frequency melting furnace, up to 10 ⁻⁴ to 10 ⁻⁵ Torr After the pressure was reduced, the mixture was heated and melted in an argon gas atmosphere to form a molten metal, and cast into a water-cooled copper mold at a casting temperature of 1450 ° C. (the casting temperature was 1350 ° C.) to obtain an alloy.
The obtained alloy was roughly crushed using a jaw crusher (Fuji Paudal: model 1021-B), and further pulverized to each particle size shown in the table by changing the pulverization time with a horizontal brown pulverizer (Yoshida Seisakusho). This was set in an OCTAGON DIGITAL automatic classifier (manufactured by CSC SCIENTIFIC COMPANY) with sieves (JIS Z 8801) in the order of openings of 500 μm, 300 μm, 150 μm, 106 μm, 75 μm, 45 μm, classified for 10 minutes, and then classified. The particle size distribution was measured by measuring the mass of the powder.
Next, the obtained alloy powder was put in a SUS container, set in a vacuum heat treatment apparatus (manufactured by Nisshin Giken), and heat-treated at 1060 ° C. for 3 hours. In addition, after heat processing, it cooled by the temperature-fall rate: 5 degree-C / min to 500 degreeC, and reached natural temperature after reaching 500 degreeC.

(Comparative Example 9: second composition group)
The casting was performed in the same manner as in Example 1, and the obtained alloy was roughly crushed using a jaw crusher (manufactured by Fuji Paudal: model1021-B), and the aperture was 5 mm in an OCTAGON DIGITAL automatic classifier (manufactured by CSC SCIENTIFIC COMPANY). Sieves were set in the order of 1 mm and classified for 10 minutes to obtain alloy grains having a particle size distribution of 1 mm to 5 mm. The obtained alloy particles were put in a SUS container and set in a vacuum heat treatment apparatus (manufactured by Nisshin Giken), and heat treatment was performed at 1060 ° C. for 3 hours. In addition, after heat processing, it cooled by the temperature-fall rate: 5 degree-C / min to 500 degreeC, and reached natural temperature after reaching 500 degreeC.

(Comparative Example 10: second composition group)
Casting was performed in the same manner as in Example 1. The obtained alloy (ingot) was placed in a SUS container and set in a vacuum heat treatment apparatus (manufactured by Nisshin Giken), and heat treatment was performed at 1060 ° C. for 3 hours. In addition, after heat processing, it cooled by the temperature-fall rate: 5 degree-C / min to 500 degreeC, and reached natural temperature after reaching 500 degreeC.

(Examples 4, 5: third composition group)
Third composition: Mm (La 16%) Al _0.30 Mn _0.40 Co _0.75 Ni _3.45 (ABx = 4.90) (Mm is a mixture of rare earth metals of La, Ce, Nd, Pr. La content in Mm in alloy) In order to obtain a hydrogen storage alloy having a composition of 47.6%), Mm: 33.6% (La is 16% of the whole alloy), Ni: 48.6%, Mn: 5 .3%, Al: 1.9%, Co: 10.6%, weighed and mixed, put the mixture in a crucible and fixed in a high-frequency melting furnace, reduced pressure to 10 ⁻⁴ to 10 ⁻⁵ Torr Then, the mixture was heated and melted in an argon gas atmosphere to form a molten metal, which was cast into a water-cooled copper mold at a casting temperature of 1450 ° C. (the casting temperature was 1350 ° C.) to obtain an alloy.
The obtained alloy was roughly crushed using a jaw crusher (Fuji Paudal: model 1021-B), and further pulverized to each particle size shown in the table by changing the pulverization time with a horizontal brown pulverizer (Yoshida Seisakusho). This was set in an OCTAGON DIGITAL automatic classifier (manufactured by CSC SCIENTIFIC COMPANY) with sieves (JIS Z 8801) in the order of openings of 500 μm, 300 μm, 150 μm, 106 μm, 75 μm, 45 μm, classified for 10 minutes, and then classified. The mass of the powder was measured and the particle size distribution was measured.
Next, the obtained alloy (ingot) was placed in a SUS container and set in a vacuum heat treatment apparatus (manufactured by Nisshin Giken), and heat treatment was performed at 1060 ° C. for 3 hours. In addition, after heat processing, it cooled by the temperature-fall rate: 5 degree-C / min to 500 degreeC, and reached natural temperature after reaching 500 degreeC.

(Comparative Example 11: third composition group)
The casting was performed in the same manner as in Example 4. The obtained alloy was roughly crushed using a jaw crusher (manufactured by Fuji Paudal: model1021-B), and the aperture was 5 mm in an OCTAGON DIGITAL automatic classifier (manufactured by CSC SCIENTIFIC COMPANY). Sieves were set in the order of 1 mm and classified for 10 minutes to obtain alloy grains having a particle size distribution of 1 mm to 5 mm. The obtained alloy particles were put in a SUS container and set in a vacuum heat treatment apparatus (manufactured by Nisshin Giken), and heat treatment was performed at 1060 ° C. for 3 hours. In addition, after heat processing, it cooled by the temperature-fall rate: 5 degree-C / min to 500 degreeC, and reached natural temperature after reaching 500 degreeC.

(Comparative Example 12: third composition group)
Casting was performed in the same manner as in Example 4, and the obtained alloy (ingot) was placed in a SUS container and set in a vacuum heat treatment apparatus (manufactured by Nisshin Giken), and heat treatment was performed at 1060 ° C. for 5 hours. In addition, after heat processing, it cooled by the temperature-fall rate: 5 degree-C / min to 500 degreeC, and reached natural temperature after reaching 500 degreeC.

(Comparative Example 13: third composition group)
Casting was performed in the same manner as in Example 4. The obtained alloy (ingot) was placed in a SUS container and set in a vacuum heat treatment apparatus (manufactured by Nisshin Giken), and heat treatment was performed at 1060 ° C. for 3 hours. In addition, after heat processing, it cooled by the temperature-fall rate: 5 degree-C / min to 500 degreeC, and reached natural temperature after reaching 500 degreeC.

(Example 6: Third composition group)
Third composition: Mm (La 16%) Al _0.30 Mn _0.40 Co _0.75 Ni _3.45 (ABx = 4.90) (Mm is a mixture of rare earth metals such as La, Ce, Nd, Pr. La content in Mm in alloy) In order to obtain a hydrogen storage alloy having a composition of 47.6%), Mm: 33.6% (La is 16% of the whole alloy), Ni: 48.6%, and Mn: Weigh and mix so that 5.3%, Al: 1.9%, Co: 10.6%, and place the mixture in a crucible and fix in a high-frequency melting furnace until 10 ^-4 to 10 ^-5 Torr. After the pressure was reduced, the mixture was heated and melted in an argon gas atmosphere to form a molten metal, and cast into a water-cooled copper mold at a casting temperature of 1450 ° C. (the casting temperature was 1350 ° C.) to obtain an alloy.
The obtained alloy is put in a crucible, fixed to a twin roll device (manufactured by Nisshin Giken), reduced in pressure to 10 ⁻⁴ to 10 ⁻⁵ Torr, heated and melted in an argon gas atmosphere, and the molten metal at 2000 rpm. The hot water was discharged onto a rotating roll, and the molten ribbon repeatedly collided between Cu rolls arranged at different levels to obtain a rapidly solidified alloy ribbon (thin plate having a thickness of 350 μm or less).
Next, the obtained alloy ribbon was put into a SUS container and set in a vacuum heat treatment apparatus (manufactured by Nisshin Giken), and heat treatment was performed at 1060 ° C. for 3 hours. In addition, after heat processing, it cooled by the temperature-fall rate: 5 degree-C / min to 500 degreeC, and reached natural temperature after reaching 500 degreeC.

(Example 7: Fourth composition group)
Fourth composition: Mm (La 19%) Al _0.20 Mn _0.60 Co _0.10 Ni _4.20 Fe _0.10 (ABx = 5.20) (Mm is a mixture of rare earth metals of La, Ce, Nd, Pr. La in Mm in the alloy) In order to obtain a hydrogen storage alloy having a composition of 59.2%), Mm: 32.1% (La is 19% of the whole alloy), Ni: 56.5%, Mn : 7.6%, Al: 1.2%, Co: 1.4%, Fe: 1.3% Weighed and mixed so that the mixture was put in a crucible and fixed in a high-frequency melting furnace, 10 After reducing the pressure to ^-4 to 10 ^-5 Torr, the mixture is heated and melted in an argon gas atmosphere to form a molten metal, cast into a water-cooled copper mold at a casting temperature of 1450 ° C (casting temperature is 1350 ° C), and cast. An alloy was obtained.
The obtained alloy lump is put in a SUS container and set in a vacuum heat treatment apparatus (manufactured by Nisshin Giken), heat treated at 1060 ° C. for 3 hours, and then cooled in a cooling water pipe arranged outside the vacuum heat treatment apparatus. Water was circulated and cooled to 500 ° C. at a temperature decrease rate of 20 ° C./min. Thereafter, the cooling water flow was turned off to naturally cool to room temperature.
The obtained alloy is roughly crushed using a jaw crusher (manufactured by Fuji Paudal: model1021-B), and further pulverized to a particle size (−500 μm) passing through a 500 μm sieve with a horizontal brown grinder (Yoshida Seisakusho). went.

(Comparative Example 14: Fourth composition group)
A hydrogen storage alloy was obtained in the same manner as in Example 7 except that the temperature lowering rate to 500 ° C. after the heat treatment was changed to 5 ° C./min.

(Example 8: Fifth composition group)
Fifth composition: Mm (La 27%) Al _0.30 Mn _0.40 Co _0.10 Ni _4.45 Fe _0.075 (ABx = 5.325) (Mm is a mixture of rare earth metals of La, Ce, Nd and Pr. La in Mm in the alloy. In order to obtain a hydrogen storage alloy having a composition with a content of 85.2%, Mm: 31.7% (La is 27% of the total alloy), Ni: 59.2%, Mn : 5.0%, Al: 1.8%, Co: 1.3%, Fe: 1.0% Weighed and mixed so that the mixture was put in a crucible and fixed in a high frequency melting furnace. After reducing the pressure to ^-4 to 10 ^-5 Torr, the mixture is heated and melted in an argon gas atmosphere to form a molten metal, cast into a water-cooled copper mold at a casting temperature of 1450 ° C (casting temperature is 1350 ° C), and cast. An alloy was obtained.
The obtained alloy lump is put in a SUS container and set in a vacuum heat treatment apparatus (manufactured by Nisshin Giken), heat treated at 1060 ° C. for 3 hours, and then cooled in a cooling water pipe arranged outside the vacuum heat treatment apparatus. Water was circulated and cooled to 500 ° C. at a temperature decrease rate of 20 ° C./min. Thereafter, the cooling water flow was turned off to naturally cool to room temperature.
The obtained alloy is roughly crushed using a jaw crusher (Fuji Paudal: model 1021-B), and further pulverized to a particle size (-500 μm) passing through a 500 μm sieve with a horizontal brown grinder (Yoshida Seisakusho). went.

(Example 9: Sixth composition group)
Sixth composition: Mm (La 27%) Al _0.40 Mn _0.30 Co _0.10 Ni _4.45 Fe _0.025 (ABx = 5.275) (Mm is a mixture of rare earth metals of La, Ce, Nd, and Pr. La in Mm in the alloy) In order to obtain a hydrogen storage alloy having a composition of 84.1% in content, Mm: 32.1% (La is 27% of the total alloy), Ni: 60.0%, Mn : 3.8%, Al: 2.5%, Co: 1.4%, Fe: 0.3% Weighed and mixed so that the mixture was put in a crucible and fixed in a high-frequency melting furnace, 10 After reducing the pressure to ^-4 to 10 ^-5 Torr, the mixture is heated and melted in an argon gas atmosphere to form a molten metal, cast into a water-cooled copper mold at a casting temperature of 1450 ° C (casting temperature is 1350 ° C), and cast. An alloy was obtained.
The obtained alloy lump is put in a SUS container and set in a vacuum heat treatment apparatus (manufactured by Nisshin Giken), heat treated at 1060 ° C. for 3 hours, and then cooled in a cooling water pipe arranged outside the vacuum heat treatment apparatus. Water was circulated and cooled to 500 ° C. at a temperature decrease rate of 20 ° C./min. Thereafter, the cooling water flow was turned off to naturally cool to room temperature.
The obtained alloy is roughly crushed using a jaw crusher (manufactured by Fuji Paudal: model1021-B), and further pulverized to a particle size (−500 μm) passing through a 500 μm sieve with a horizontal brown grinder (Yoshida Seisakusho). went.

(Example 10: seventh composition group)
Seventh composition: Mm (La 25%) Al _0.35 Mn _0.40 Co _0.10 Ni _4.52 Fe _0.025 (ABx = 5.395) (Mm is a mixture of rare earth metals La, Ce, Nd, Pr. La in Mm in the alloy) Mm: 31.5% (La is 25% of the whole alloy), Ni: 59.8%, Mn so that a hydrogen storage alloy having a composition of 79.3% is obtained. : 5.0%, Al: 2.1%, Co: 1.3%, Fe: 0.3%, and weighed and mixed so that the mixture was put in a crucible and fixed in a high-frequency melting furnace. After reducing the pressure to ^-4 to 10 ^-5 Torr, the mixture is heated and melted in an argon gas atmosphere to form a molten metal, cast into a water-cooled copper mold at a casting temperature of 1450 ° C (casting temperature is 1350 ° C), and cast. An alloy was obtained.
The obtained alloy lump is put in a SUS container and set in a vacuum heat treatment apparatus (manufactured by Nisshin Giken), heat treated at 1060 ° C. for 3 hours, and then cooled in a cooling water pipe arranged outside the vacuum heat treatment apparatus. Water was circulated and cooled to 500 ° C. at a temperature decrease rate of 20 ° C./min. Thereafter, the cooling water flow was turned off to naturally cool to room temperature.
The obtained alloy is roughly crushed using a jaw crusher (manufactured by Fuji Paudal: model1021-B), and further pulverized to a particle size (−500 μm) passing through a 500 μm sieve with a horizontal brown grinder (Yoshida Seisakusho). went.

(Example 11: eighth composition group)
Eighth composition: Mm (La 25%) Al _0.35 Mn _0.40 Co _0.15 Ni _4.43 Fe _0.025 (ABx = 5.355) (Mm is a mixture of rare earth metals of La, Ce, Nd, and Pr. La in Mm in the alloy) In order to obtain a hydrogen storage alloy having a composition with a content of 78.9%, Mm: 31.7% (La is 25% of the total alloy), Ni: 58.9%, Mn : 5.0%, Al: 2.1%, Co: 2.0%, Fe: 0.3% Weighed and mixed so that the mixture was put in a crucible and fixed in a high frequency melting furnace. After reducing the pressure to ^-4 to 10 ^-5 Torr, the mixture is heated and melted in an argon gas atmosphere to form a molten metal, cast into a water-cooled copper mold at a casting temperature of 1450 ° C (casting temperature is 1350 ° C), and cast. An alloy was obtained.
The obtained alloy lump is put in a SUS container and set in a vacuum heat treatment apparatus (manufactured by Nisshin Giken), heat treated at 1060 ° C. for 3 hours, and then cooled in a cooling water pipe arranged outside the vacuum heat treatment apparatus. Water was circulated and cooled to 500 ° C. at a temperature decrease rate of 20 ° C./min. Thereafter, the cooling water flow was turned off to naturally cool to room temperature.
The obtained alloy is roughly crushed using a jaw crusher (manufactured by Fuji Paudal: model1021-B), and further pulverized to a particle size (−500 μm) passing through a 500 μm sieve with a horizontal brown grinder (Yoshida Seisakusho). went.

[Characteristics and physical property evaluation]
About the hydrogen storage alloy powder obtained by the said Example and comparative example, various physical-property values and various characteristic values were measured by the method shown below, and the result was shown to the said Tables 1-8.

<Particle size distribution measured by vibration classifier>
About the hydrogen storage alloy powder obtained by the said Example and comparative example, the sieve (JIS Z 8801) is applied to OCTAGON DIGITAL automatic classifier (made by CSC SCIENTIFIC COMPANY) in order of openings of 500 μm, 300 μm, 150 μm, 106 μm, 75 μm, and 45 μm. Each was classified for 10 minutes, and the content ratio (%) of each particle size was determined.

<Micronized residual rate>
The hydrogen storage alloy powders obtained in the above Examples and Comparative Examples were sieved and adjusted to a particle size range of 20 μm to 53 μm to obtain measurement samples. In addition, when the hydrogen storage alloy obtained by the Example and the comparative example was ingot shape or ribbon shape, it pulverized and prepared.
2 g of the obtained measurement sample was put into a PCT holder and connected to a PCT characteristic measurement device (Suzuki Shokan Co., Ltd.). Further, the remaining sample was a sample before 50 cycles.

The following operation was carried out before turning the cycle.
(1) Alloy adhesion moisture treatment: In a mantle heater (250 ° C.), 1.75 MPa of hydrogen was introduced while the PCT holder was heated, and after standing for 10 minutes, a series of operations for evacuation was performed twice.
(2) Alloy activation treatment: The PCT holder was taken out from the mantle heater, 3 MPa hydrogen was introduced, and held for 10 minutes. Thereafter, evacuation was performed for 10 minutes while the PCT holder was heated in a mantle heater (250 ° C.). This series of operations was performed twice.

After removing the PCT holder from the mantle heater and moving the holder to a 45 ° C. thermostatic chamber, evacuation was performed for 30 minutes, and then a hydrogen storage / release cycle was performed under the following condition settings.
(Introduction pressure) 1.1 MPa
(Occlusion time) 300 sec
(Release time) 420 sec
(Number of cycles) 50 cycles

  After completion of 50 cycles, vacuuming was performed for 30 minutes, and then a sample was taken out from the PCT holder to obtain a sample after 50 cycles.

The average particle size (D50) of the powder before and after 50 cycles was measured under the following condition settings using a Microtrac (Nikkiso Co., Ltd., HRA9320-X100), and the pulverization residual rate (%) was obtained by the following formula. It was.
(Formula) .. Micronized residual rate (%) = (D50 after cycle / D50 before cycle) × 100
(Transp): Reflect
(Sphere): No
(Ref Inx): 1.51
(Flow): 60 ml / sec
(Power): 25 watts
(Time): 10 sec

<XRD measurement>
20 g of the hydrogen storage alloy powder obtained in the examples and comparative examples was pulverized with a cyclomill (manufactured by Yoshida Seisakusho Co., Ltd .: model 1033-200) for 1 minute, classified with a sieve having an opening of 20 μm, and −20 μm (with 20 μmφ). A hydrogen storage alloy powder of particles passing through a sieve mesh) was obtained. An X-ray diffraction sample was prepared by mixing 10 parts by weight of Si powder as an internal standard with respect to 100 parts by weight of the hydrogen storage alloy powder thus obtained.

A sample for X-ray diffraction is filled in a glass holder with bioden mesh cement, measured using RINT-2200V (manufactured by Rigaku Corporation) under the following conditions, and subjected to a predetermined refinement to a temperature around 45 °. The full width at half maximum (FWHM) of the (002) plane was determined.
The refinement at this time was performed using the application software (software name: refinement of lattice constant) attached to the RINT-2200V. As a precaution, detailed setting conditions at the time of analysis are shown below.

(Smoothing)
・ Smoothing method: Weighted average ・ Smoothing points: 15
・ Harmonic: 128
(Background removal)
・ Background removal method: Straight line in contact with both ends ・ Average number of low-angle side points: 3
・ High angle side average score: 3
(Kα2 removal)
Strength ratio (Kα2 / Kα1): 0.500

(Tube) CuKα line (Tube voltage) 40 kV
(Tube current) 40 mA
(Diverging slit) 1 deg.
(Scattering slit) 1 deg
(Light receiving slit) 0.3mm
(Goniometer) RINT2000 vertical goniometer (attachment) ASC-43 (vertical)
(Slit) Fully automatic wide angle goniometer slit (Monochromator) Fully automatic monochromator (Counter) Scintillation counter (Start angle) 40 °
(End angle) 46 °
(Step) 0.002 °
(Scanning speed) 0.25 ° / min

The pulverization residual ratio (%) with respect to the full width at half maximum of each example and comparative example is shown in FIG. The straight line shown in FIG. 1 is a straight line approximated by the method of least squares.
Incidentally, while Comparative Examples 1 to 8 belonging to the first composition group had a discharge capacity of less than 305 mAh / g, Examples 1 to 3 and Comparative Examples 9 to 10 belonging to the second composition group, the third composition group Examples 4 to 6 and Comparative Examples 11 to 13 belonging to Example 4, Example 7 and Comparative Example 14 belonging to the fourth composition group, Example 8 belonging to the fifth composition group, Example 9 belonging to the sixth composition group, Seventh Since Example 10 belonging to the composition group and Example 11 belonging to the seventh composition group had a discharge capacity of 305 mAh / g or more, in FIG. 1, the plot was made based on the discharge capacity of 305 mAh / g and Examples / Comparative Examples. Different shapes were used, and approximate lines were shown for each.

<Production of electrode cell>
1 g of the hydrogen storage alloy powder obtained in Examples and Comparative Examples was mixed with 3 g of nickel powder as a conductive material and 0.12 g of polyethylene powder as a binder, and 0.3 g of the obtained mixed powder was added to the foamed Ni. To form a pellet mold having a diameter of 15 mm and a thickness of 1.8 mm, and vacuum sintering was performed at 150 ° C. for 1 hour to produce a pellet electrode.
This pellet electrode is used as a negative electrode, and this is sandwiched by a positive electrode (sintered nickel hydroxide) having a capacity more than twice the calculated negative electrode capacity via a separator (Nihon Vilene) and immersed in a 30 wt% KOH aqueous solution. An open type test cell (see FIG. 2) was prepared.

<15 cycle capacity (15∞ / mAh / g)>
Connect the above open-type test cell to a charge / discharge device (HOKUTO charge / discharge tester), charge: 0.2C-130%, discharge: 0.2C-0.7V cut, charge / discharge at a temperature of 20 ° C. The discharge capacity (mAh / g) at the 15th cycle was set to the 15th cycle capacity.

<PCT (H / M)>
5 g of the hydrogen storage alloy powders obtained in Examples and Comparative Examples were weighed and put into a PCT holder, and connected to a PCT characteristic measuring device (Suzuki Shokan Co., Ltd.).

The following operation was performed before the PCT measurement.
1) Alloy adhesion moisture treatment: In a mantle heater (250 ° C.), 1.75 MPa of hydrogen was introduced while the PCT holder was heated, and after standing for 10 minutes, a series of operations for evacuation was performed twice.
2) Alloy activation treatment: The PCT holder was taken out from the mantle heater, 3 MPa hydrogen was introduced, and held for 10 minutes. Thereafter, evacuation was performed for 10 minutes while the PCT holder was heated in a mantle heater (250 ° C.). This series of operations was performed twice.

  The PCT holder was taken out from the mantle heater, moved to a 45 ° C. constant temperature bath, evacuated for 30 minutes, and then subjected to PCT measurement until the occlusion end pressure was 1.7 MPa. From the obtained pressure-composition isotherm diagram at 45 ° C., the hydrogen storage amount at a pressure of 0.5 MPa was determined as PCT capacity H / M (H / M: hydrogen atom H amount per metal atom M). .

(Discussion)
From FIG. 1, in the hydrogen storage alloy having a discharge capacity of less than 305 mAh / g, the life characteristics (micronized residual ratio) linearly increase as the full width at half maximum of the (002) plane obtained from X-ray diffraction decreases. On the other hand, in the hydrogen storage alloy having a discharge capacity of 305 mAh / g or more, fine powder with a full width at half maximum of (002) plane of 0.20 ° to 0.28 ° (difference; 0.08 °). The change in the residual rate of pulverization is about 5%, but if it is less than 0.20 °, the change in the residual rate of pulverization from 0.12 ° to 0.20 °, which is also 0.08 °, is 10%. In the case of hydrogen storage alloys with a discharge capacity of 305 mAh / g or more, the half-value of the (002) plane is clearly changed. The total width is less than 0.20 °, especially 0.19 ° or less, especially 0.1 ° or less, by adjusting the following 0.15 ° among them, it was found that it is possible to increase significantly the lifetime characteristics (micronized residual rate).
In the original application, it was judged that the tendency of the pulverization residual rate was changing around the full width at half maximum of around 0.19 °, but this time, the number of plots was increased in addition to the examples and comparative examples. As a result of the approximation by the least square method, it was confirmed that the change point of the tendency was near 0.20 ° rather than 0.19 °.

It is the graph which showed the relationship between the full width at half maximum (FWHM) of a (002) surface and the pulverization residual rate for every discharge capacity. It is a sectional side view explaining the structure of the open type test cell produced by the test.

Claims (9)

In an AB ₅ type hydrogen storage alloy having a CaCu ₅ type crystal structure and having a discharge capacity of 305 mAh / g or more obtained in the following test, the full width at half maximum of the (002) plane obtained from X-ray diffraction is 0.20 °. AB ₅ -type hydrogen absorbing alloy and less than.
(Discharge capacity measurement test)
1) 3 g of nickel powder as a conductive material and 0.12 g of polyethylene powder as a binder are mixed with 1 g of a hydrogen storage alloy, and 0.3 g of the obtained mixed powder is pressure-molded on foamed Ni to have a diameter of 15 mm, A pellet type with a thickness of 1.8 mm is vacuum-baked at 150 ° C. for 1 hour to produce a pellet electrode. This pellet electrode is used as a negative electrode, and this is sandwiched by a positive electrode (sintered nickel hydroxide) through a separator. Then, it is immersed in a 30 wt% KOH aqueous solution to produce an open test cell.
2) Connect the open test cell to the charge / discharge device, charge: 0.2C-130%, discharge: 0.2C-0.7V cut, charge / discharge at a temperature of 20 ° C, discharge capacity of 15th cycle ( mAh / g) is measured. (Wherein, Mm is the mischmetal, 4.7 ≦ a + b + c + d or a + b + c + d + e ≦ 5.5) formula MmNi _a Mn _b Al _c Co _d or _{MmNi a Mn b Al c Co d} Fe e CaCu 5 type which can be represented by AB ₅ type hydrogen storage alloy according to claim 1, characterized in that a hydrogen absorbing alloy having a crystal structure. 3. The general formula according to claim 2, wherein 3.45 ≦ a ≦ 4.70, 0.20 ≦ b ≦ 0.70, 0.10 ≦ c ≦ 0.50, 0 <d ≦ 0.80, 0 < The AB ₅ type hydrogen storage alloy according to claim 2, wherein e ≦ 0.11. Formula MmNi _a Mn _b Al _c Co _d or _{MmNi a Mn b Al c Co d} Fe e ( wherein, Mm is the mischmetal, 0 <d ≦ 0.20,5.15 ≦ a + b + c + d or a + b + c + d + e ≦ 5.40) The AB ₅ type hydrogen storage alloy according to claim 1, which is a hydrogen storage alloy having a CaCu ₅ type crystal structure that can be expressed by: 5. The general formula according to claim 4, wherein 3.45 ≦ a ≦ 4.70, 0.20 ≦ b ≦ 0.70, 0.10 ≦ c ≦ 0.50, and 0 <e ≦ 0.11. AB ₅ type hydrogen storage alloy of claim 2, wherein. A hydrogen storage alloy obtained by mixing the hydrogen storage alloy raw material, casting the mixture, pulverizing and classifying the alloy obtained by casting to form an alloy powder, and heat-treating the alloy powder in an inert gas atmosphere. There,
6. The particle size distribution of the alloy powder before heat treatment in an inert gas atmosphere, wherein the content of 150 μm or less is 30% or more in the particle size distribution measured by a vibration classifier. AB ₅ type hydrogen storage alloy crab according. A hydrogen storage alloy obtained by mixing the hydrogen storage alloy raw material, casting the mixture, pulverizing and classifying the alloy obtained by casting to form an alloy powder, and heat-treating the alloy powder in an inert gas atmosphere. There,
6. The particle size distribution of the alloy powder before heat treatment in an inert gas atmosphere is such that the content of 150 μm or less is 40% or more in the particle size distribution measured by a vibration classifier. AB ₅ type hydrogen storage alloy crab according. A hydrogen storage alloy obtained by mixing the hydrogen storage alloy raw material, casting the mixture, pulverizing and classifying the alloy obtained by casting to form an alloy powder, and heat-treating the alloy powder in an inert gas atmosphere. There,
6. The particle size distribution of the alloy powder before heat treatment in an inert gas atmosphere, wherein the content of 150 μm or less is 65% or more in the particle size distribution measured by a vibration classifier. AB ₅ type hydrogen storage alloy crab according. A battery comprising a structure using the hydrogen storage alloy according to any one of claims 1 to 8 as a negative electrode active material.

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