JP2011127185A - Hydrogen storage alloy, method for producing the same, negative electrode for nickel hydrogen secondary battery and nickel hydrogen secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an Mg and Al-containing hydrogen storage alloy maintaining high capacity and also having high cycle properties, and a method for producing the same. <P>SOLUTION: The hydrogen storage alloy has a composition expressed by R<SB>a</SB>Mg<SB>b</SB>Ni<SB>c</SB>Al<SB>d</SB>M<SB>e</SB>(R denotes at least one kind selected from rare earth elements including Y, and Zr, Hf and Ca; M denotes at least one kind selected from the elements other than the R, Mg, Ni and Al, 0.75≤a≤0.85, 0.15≤b≤0.25, 3.30≤c≤3.65, 0.15≤d≤0.25, 0≤e≤0.20, a+b+=1, 0.33≤b+d≤0.45, and 3.45≤c+d+e≤3.80). The total of the ratio occupied by a phase having a high Mg concentration and a phase having a high Al concentration than that of the host phase confirmed by a host phase confirmed by a COMP image of 500 magnifications by the EPMA of the cross-sectional structure in the alloy and the element mapping image of Mg and Al produced by a strip casting process is ≤5.0% in the whole. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a nickel metal hydride secondary battery, a negative electrode used therefor, a hydrogen storage alloy containing rare earth, Mg, Ni and Al as main constituent elements and a method for producing the same.

  A nickel metal hydride secondary battery using a negative electrode containing a hydrogen storage alloy has a higher energy density than a nickel cadmium secondary battery, and does not use harmful Cd. Nickel metal hydride secondary batteries are also used in portable devices such as digital cameras and electric tools, as well as electric vehicles or hybrid electric vehicles, and various battery characteristics are required depending on the application.

As a negative electrode material for a nickel-metal hydride secondary battery, a LaNi ₅ -based hydrogen storage alloy that is a rare earth-Ni-based intermetallic compound having a CaCu ₅ -type crystal as a main phase, or a Laves phase containing Ti, Zr, V, and Ni as constituent elements A hydrogen storage alloy whose main phase is is used.
In recent years, rare earth-Mg-Ni-based hydrogen storage alloys have been put into practical use, and nickel-metal hydride secondary batteries using this alloy are known to have a high capacity.

  In Patent Document 1, in a rare earth-Mg—Ni-based hydrogen storage alloy, the hydrogen storage amount is improved by controlling the average particle size and particle size distribution of the precipitated phase and powder, and reversible hydrogen storage / A hydrogen storage alloy that suppresses a decrease in the release amount is disclosed.

  In Patent Document 2, a rare earth-Mg-Ni hydrogen storage alloy containing Al produced by a liquid quenching method has a homogeneous structure, and a nickel metal hydride secondary battery using this alloy improves cycle life. High capacity is disclosed.

JP 2002-105564 A JP 2008-84818 A

  However, the hydrogen storage alloys of Patent Document 1 and Patent Document 2 are not highly compatible with each of the battery capacity, the hydrogen storage amount related to cycle characteristics, and the corrosion resistance when used in nickel-hydrogen secondary batteries. In a rare earth-Mg—Ni-based hydrogen storage alloy containing Al, generally, increasing the amount of Mg increases the amount of hydrogen storage, and increasing the amount of Al improves corrosion resistance. However, when the amount of Mg and the amount of Al are increased, segregation occurs in the alloy structure and is not homogenized even when heat treatment is performed, and as a result, the corrosion resistance tends to decrease. It has been extremely difficult to manufacture a nickel metal hydride secondary battery that achieves excellent cycle characteristics and high capacity.

An object of the present invention is to provide a nickel metal hydride secondary battery exhibiting excellent cycle characteristics and high capacity, and a negative electrode used therefor.
Another object of the present invention is to efficiently provide a hydrogen storage alloy that has both a high hydrogen storage capacity and corrosion resistance for realizing a nickel hydrogen secondary battery exhibiting excellent cycle characteristics and high capacity, and the alloy, Another object of the present invention is to provide a production method that can be obtained industrially.

According to the present invention, the formula (1) R _a Mg _b Ni _c Al _{d Me} (wherein R is a rare earth element including Y, Zr, Hf and Ca, at least one selected from the group consisting of R, Mg, It represents at least one selected from elements other than Ni and Al, a is 0.75 ≦ a ≦ 0.85, b is 0.15 ≦ b ≦ 0.25, and c is 3.30 ≦ c ≦ 3.65. D is 0.15 ≦ d ≦ 0.25, e is 0 ≦ e ≦ 0.20, a + b = 1, 0.33 ≦ b + d ≦ 0.45, 3.45 ≦ c + d + e ≦ 3.80) Than the parent phase confirmed by the EPMA and the elemental mapping image of Mg and Al of the cross-sectional structure of the alloy manufactured by the strip casting method. , The total proportion of the phase with high Mg concentration and the phase with high Al concentration is Hydrogen storage alloy, wherein the body is 5.0% or less is provided.

Further, according to the present invention, the metal element or mother alloy constituting the composition represented by the above formula (1) is used as a raw material, the raw material is heated and melted to obtain an alloy melt higher than the melting point by 300 ° C., and then the alloy The production of a hydrogen storage alloy according to claim 1, wherein the melt is cooled and solidified by a strip casting method to obtain an alloy, and the obtained alloy is heat-treated at a temperature lower by 10 to 100 ° C than the melting point of the alloy for 30 minutes to 10 hours. A method is provided.
Furthermore, according to this invention, the nickel hydride secondary battery using the negative electrode for nickel hydride secondary batteries containing the said hydrogen storage alloy and the said negative electrode is provided.

  The hydrogen storage alloy of the present invention is excellent in corrosion resistance and hydrogen storage capacity. The negative electrode for a nickel metal hydride secondary battery manufactured using the same, and the nickel metal hydride secondary battery manufactured using the negative electrode have high capacity and life characteristics. It is good.

2 is a copy of a Comp image of a cross-sectional structure of the hydrogen storage alloy of Example 1. 2 is a copy of an Mg mapping image of a cross-sectional structure of the hydrogen storage alloy of Example 1; 2 is a copy of an Al mapping image of a cross-sectional structure of the hydrogen storage alloy of Example 1. 6 is a copy of a Comp image of a cross-sectional structure of the hydrogen storage alloy of Example 4. 6 is a copy of an Mg mapping image of a cross-sectional structure of the hydrogen storage alloy of Example 4; 6 is a copy of an Al mapping image of a cross-sectional structure of the hydrogen storage alloy of Example 4. 10 is a copy of a Comp image of a cross-sectional structure of the hydrogen storage alloy of Comparative Example 8. 10 is a copy of an Mg mapping image of a cross-sectional structure of the hydrogen storage alloy of Comparative Example 8. 10 is a copy of an Al mapping image of a cross-sectional structure of the hydrogen storage alloy of Comparative Example 8. 10 is a copy of a Comp image of a cross-sectional structure of the hydrogen storage alloy of Comparative Example 9. It is a copy of Mg mapping image of the cross-sectional structure of the hydrogen storage alloy of Comparative Example 9. 10 is a copy of an Al mapping image of a cross-sectional structure of the hydrogen storage alloy of Comparative Example 9. 10 is a copy of a Comp image of a cross-sectional structure of the hydrogen storage alloy of Comparative Example 10. It is a copy of Mg mapping image of the cross-sectional structure of the hydrogen storage alloy of Comparative Example 10. It is a copy of Al mapping image of the cross-sectional structure of the hydrogen storage alloy of Comparative Example 10. 10 is a copy of a Comp image of a cross-sectional structure of the hydrogen storage alloy of Comparative Example 11. It is a copy of Mg mapping image of the cross-sectional structure of the hydrogen storage alloy of Comparative Example 11. It is a copy of Al mapping image of the cross-sectional structure of the hydrogen storage alloy of Comparative Example 11.

The hydrogen storage alloy of the present invention has a composition represented by the formula _{(1) R a Mg b Ni} c Al d M e.
R is at least one element selected from rare earth elements including Y, Zr, Hf, and Ca. a represents the content of R. a is 0.75 ≦ a ≦ 0.85. R is preferably La, Nd, Pr, Sm, or Zr. La tends to lower the equilibrium pressure at the time of hydrogen occlusion and release of the alloy, and Nd, Pr, Sm, and Zr tend to increase.

  b represents the Mg content. b is 0.15 ≦ b ≦ 0.25. When the amount of Mg is less than this range, a sufficient hydrogen storage amount cannot be obtained. Conversely, when the amount of Mg is large, sufficient corrosion resistance cannot be obtained. As described above, Mg tends to increase the hydrogen storage amount and increase the equilibrium pressure at the time of hydrogen storage / release of the alloy. Preferably 0.18 ≦ b ≦ 0.20.

  c represents the content of Ni. c is 3.30 ≦ c ≦ 3.65. When the amount of Ni is less than this range, pulverization tends to proceed. Conversely, when the amount of Ni is large, a sufficient hydrogen storage amount cannot be obtained. Preferably, 3.35 ≦ c ≦ 3.55.

  d represents the content of Al. d is 0.15 ≦ d ≦ 0.25. The Al content affects the equilibrium pressure. When the amount of Al is less than this range, sufficient corrosion resistance cannot be obtained. On the contrary, when the amount of Al is large, a sufficient hydrogen storage amount cannot be obtained, and sufficient corrosion resistance cannot be obtained due to segregation of Al. Further, Al tends to lower the equilibrium pressure at the time of hydrogen storage and release of the alloy. Preferably, 0.15 ≦ d ≦ 0.22.

  e represents the content of the M element. e is 0 ≦ e ≦ 0.20. The element M is not always necessary, and is contained when fine adjustment of characteristics is required depending on the use of the battery. M element shows at least 1 sort (s) chosen from elements other than R, Mg, Ni, and Al. Specific examples of the M element include Ti, V, Nb, Ta, Cr, Mo, W, Mn, Fe, Co, Cu, Zn, B, Ga, Sn, and Sb. Preferably, the M element is It is at least one selected from Ti, Nb, Mo, W, Mn, Fe, Co, Cu, B, and Sn. For example, when Fe, Cu, Sn, Ti, Nb, Mo, W, or B is contained, pulverization is suppressed, or elution of Al into the electrolytic solution is suppressed.

  a + b represents the total content of R and Mg. a + b = 1. B + d represents the total content of Mg and Al. b + d is 0.33 ≦ b + d ≦ 0.45. Outside this range, it is difficult to achieve both high hydrogen storage capacity and corrosion resistance. Particularly for nickel-hydrogen secondary batteries with good cycle characteristics, an alloy of 0.33 ≦ b + d ≦ 0.40, and when R and La contain La and Sm, an alloy of 0.33 ≦ b + d ≦ 0.42 Is preferably used. Furthermore, an alloy of 0.40 <b + d ≦ 0.45 is preferably used particularly for a high-capacity nickel-hydrogen secondary battery.

  c + d + e represents the total content of Ni, Al and M elements. c + d + e is 3.45 ≦ c + d + e ≦ 3.80. Outside this range, it is difficult to achieve both high hydrogen storage capacity and corrosion resistance. In addition, the higher the total content of Ni and M elements, the higher the equilibrium pressure during hydrogen storage and release of the alloy. Preferably 3.50 ≦ c + d + e ≦ 3.70. Considering cost, it is desirable to use only La as R, but it is preferable to satisfy 3.60 ≦ c + d + e ≦ 3.80 in order to adjust the decreasing equilibrium pressure.

The hydrogen storage alloy of the present invention occupies a phase having a higher Mg concentration and a phase having a higher Al concentration than the matrix phase confirmed by a 500-fold COMP image and an element mapping image of Mg and Al of the cross-sectional structure of the alloy. The total ratio is 5.0% or less. Preferably it is 3.0% or less, More preferably, it is 1.0% or less. The cross-sectional structure of the hydrogen storage alloy was observed with EPMA by the method described below, and the ratio of the phase having a higher Mg concentration and the phase having a higher Al concentration than the parent phase was determined.
An area corresponding to about 160 μm square is observed by EPMA about the thickness of the cross section substantially parallel to the heat removal direction during casting of the hydrogen storage alloy. First, for a segregation phase of 2 μm or more in a COMP image, it is confirmed from the element mapping image of Mg and Al whether the segregation phase has a higher Mg concentration than the parent phase or a higher Al concentration. The area ratios of the segregation phase having a high Mg concentration and the segregation phase having a high Al concentration are respectively calculated. The area ratio is calculated for five randomly selected visual fields, and the average value is used. When observing the hydrogen storage alloy powder, a plurality of powder cross sections can be observed so as to have an area equivalent to the above.

  The hydrogen storage alloy of the present invention is manufactured by a strip casting method. As the strip casting method, a single roll method, a twin roll method, a disc method or the like can be adopted.

  The hydrogen storage alloy of the present invention has an equilibrium pressure of 0.03 to 0.07 MPa with an H / M of 0.4 in a hydrogen release curve obtained by measurement at 80 ° C. Preferably, it is 0.04 to 0.07 MPa. The measurement of the equilibrium pressure was based on JIS H7201 (1991) “Measurement Method of Pressure-Composition Isotherm (PCT Line) of Hydrogen Storage Alloy”. If the equilibrium pressure is lower than 0.03 MPa, the discharge capacity of the battery may be reduced.

The method for producing a hydrogen storage alloy of the present invention uses a metal element or a mother alloy constituting the composition represented by the formula (1) as a raw material, and heat-melts the raw material to obtain an alloy melt higher by 300 ° C. or higher than the melting point. The alloy melt is cooled and solidified by a strip casting method to obtain an alloy, and the obtained alloy is heat-treated at a temperature range 10 to 100 ° C. lower than the melting point of the alloy for 30 minutes to 10 hours.
First, a raw material is prepared by blending R, Mg, Ni, Al, and optionally a metal containing M and a master alloy so that an alloy having the above composition is obtained. Subsequently, the blended raw materials are heated and melted in an inert gas atmosphere to obtain an alloy melt. The obtained alloy melt is cooled and solidified. However, the alloy having the above composition tends to cause segregation of Mg and Al in the alloy structure. The concentration distribution is such that the Al concentration is low in the portion where the Mg concentration is high and the Mg concentration is low in the portion where the Al concentration is high. In order to form a homogeneous alloy structure, the cooling and solidification process is performed by a single-roll method, a twin-roll method, or a strip casting method using a disk method, which can obtain a large cooling rate.
In addition, the temperature of the alloy melt immediately before cooling solidification (pour temperature) is important because the mixing state of each component differs depending on the temperature even if the temperature is higher than the melting point. In order to eliminate the segregation of Mg and Al, the melting point is important. More than 300 ° C. More preferably, the temperature is increased by 350 ° C. or more. The upper limit of the temperature is not particularly limited, but is usually 500 ° C. higher than the melting point. The alloy melt needs to be sufficiently mixed, and in that respect, it is preferably performed in a high-frequency melting furnace in which the alloy melt is largely convected.

  Next, the cooled and solidified alloy is quickly cooled to 500 ° C. or lower. The alloy immediately after peeling from the cooling roll by the strip casting method is about 800 to 1000 ° C. Diffusion occurs at such a high temperature, and particularly segregation of Al tends to occur. Therefore, it cools rapidly to 500 degrees C or less in which a diffusion rate becomes small enough. Cooling is performed from the time when the alloy is peeled off from the cooling roll until it is put into the recovery container and / or by blowing argon gas or the like in the recovery container, or the alloy is put into a water-cooled cooling drum. It can be carried out. In either case, it is performed in an inert atmosphere as in the case of melting and casting. The time from the pouring to reaching 500 ° C. is preferably within 3 hours, more preferably within 1 hour, and most preferably within 30 minutes.

  In the method for producing a hydrogen storage alloy of the present invention, heat treatment is performed after casting. The heat treatment is performed in an inert atmosphere at a temperature range 10 to 100 ° C. lower than the melting point of the alloy obtained above, preferably 10 to 50 ° C. Since the alloy obtained by the strip casting method has a thickness of about 0.1 to 1 mm, it is easily heat-treated, and the normal heat treatment time is about 30 minutes to 10 hours, preferably about 30 minutes to 6 hours. .

  The negative electrode for a nickel metal hydride secondary battery of the present invention has the hydrogen storage alloy of the present invention. The hydrogen storage alloy of the present invention is preferably contained as pulverized powder. The pulverization can be performed by a known pulverization means, preferably MV (volume average diameter) of 10 to 80 μm, more preferably 25 to 75 μm. The pulverized powder can be subjected to known treatments such as plating, surface coating with a polymer or the like, or surface treatment with a solution of acid, alkali, or the like according to desired characteristics.

In the negative electrode for nickel metal hydride secondary battery of the present invention, the content of the hydrogen storage alloy is 80% by mass or more based on the total amount of materials constituting the negative electrode other than the current collector such as a conductive agent and a binder. Is more preferable, and more preferably 95% by mass or more.
As the conductive agent, known ones can be used, and examples thereof include carbonaceous materials such as graphite and carbon black (acetylene black, furnace black, etc.), copper, nickel, and cobalt.
As the binder, known ones can be used, such as carboxymethyl cellulose, polyvinyl alcohol, polyvinyl butyral, polyvinyl pyrrolidone, polyethylene oxide, polytetrafluoroethylene (PTFE), 4-fluoroethylene-6-fluoropropylene copolymer. (FEP) and the like.

  As the current collector, for example, punching metal, foam metal, or the like can be used. Usually, since the negative electrode for nickel metal hydride secondary batteries is produced by what is called a paste type, punching metal is used. The paste-type negative electrode is mixed with the hydrogen storage alloy (ground powder) of the present invention, the binder described above, and a conductive agent, an antioxidant, a surfactant, a thickener, etc., if necessary, and water as a solvent. The paste is made into a paste, and this paste is applied to a current collector, filled, dried, and then subjected to a roller press or the like.

  The negative electrode for a nickel metal hydride secondary battery of the present invention can be formed with a water repellent layer, a conductive layer, or the like on the surface as necessary. These are performed by a known method. For example, the former is performed by applying and drying a fluororesin dispersion or the like, and the latter is performed by plating or the like.

The nickel metal hydride secondary battery of the present invention uses the negative electrode for a nickel metal hydride secondary battery of the present invention. A publicly known thing can be used for the other composition.
The nickel metal hydride secondary battery of the present invention can have various shapes such as a cylindrical shape, a stacked shape, and a coin shape. Regardless of the shape, the nickel metal hydride secondary battery stores an electrode group in which a negative electrode, a separator, and a positive electrode are stacked in a can body made of stainless steel or the like. In the case of a cylindrical shape, since the can body is normally used as a negative electrode terminal, the negative electrode and the negative electrode terminal are connected by winding the electrode group spirally with the negative electrode outside and inserting the electrode group into the can body. The positive electrode is usually connected to the positive terminal by a lead.

  As the separator, a polymer fiber nonwoven fabric made of nylon, polypropylene, polyethylene or the like, a porous polymer film such as polyethylene, polypropylene, or the like can be used.

  The positive electrode contains nickel oxide, and for example, a non-sintered nickel electrode is used. A non-sintered nickel electrode is made by mixing nickel hydroxide and optionally added cobalt hydroxide, cobalt monoxide, metallic cobalt, etc. together with a binder and water as a solvent to form a paste. It is produced by filling a current collector such as foam metal and drying, and then applying a roller press or the like.

  A 6-8 N potassium hydroxide solution is injected as an alkaline electrolyte into the container in which the electrode group is housed. An alkaline electrolyte to which lithium hydroxide, sodium hydroxide or the like is added can also be used. The container is usually provided with a gasket for sealing the battery, a safety valve that operates when the pressure in the battery rises, and the like.

EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention in detail, this invention is not limited to these.
Example 1
La _0.60 Sm _0.18 Zr _0.02 Mg _0.20 Ni _3.50 Al _0.21 Weighed the raw materials appropriately so as to obtain an alloy (melting point: about 990 ° C.), dissolved in an argon gas atmosphere in a high-frequency melting furnace, did. Subsequently, casting was performed by a strip casting method using a single roll casting apparatus of a copper water-cooled roll at a molten metal pouring temperature of 1,350 ° C. It was 810 degreeC when the temperature of the slab immediately after peeling from a roll was measured with the infrared thermal image measuring device. The slab was cooled by blowing argon gas between the time when the slab was peeled from the cooling roll and until it was collected in a steel container. The thickness of the slab was approximately 0.3 mm. The obtained slab was heat treated in an argon gas atmosphere at 950 ° C., which is about 40 ° C. lower than the melting point of the alloy, for 6 hours.

  The slab after the heat treatment was observed with an EPMA (manufactured by JEOL Ltd., trade name JXA8800) at a magnification of 500 times. The obtained COMP image and element mapping images of Mg and Al are shown in FIGS. The phase with a high Mg concentration was 0.2% and the phase with a high Al concentration was 0.0%. In addition, the equilibrium pressure with an H / M of 0.4 in the hydrogen release curve at 80 ° C. obtained by measurement with a PCT measurement automatic high-pressure Siebelz apparatus (manufactured by Toyobo Engineering) was 0.06 MPa.

-Characterization test-
The electrochemical characteristics (discharge capacity) and battery characteristics (cycle characteristics) of the obtained hydrogen storage alloy were measured as follows. The results are shown in Table 1.
(Discharge capacity)
The obtained hydrogen storage alloy was pulverized by a ball mill to obtain an alloy powder having a D50 of about 60 μm. The alloy powder 0.15 g and the carbonyl nickel powder 0.45 g were mixed well in a mortar, and the mixture was pressed under pressure at 2000 kgf / cm ² to produce a 10 mm diameter pellet. Next, the pellet was sandwiched between nickel wire meshes, spot welded around the periphery, and nickel leads were spot welded to the wire mesh to produce a negative electrode. The obtained negative electrode was immersed in an 8N-KOH aqueous solution together with a sintered nickel electrode as a counter electrode, and a charge / discharge cycle test was performed at a temperature of 25 ° C.
Charging / discharging is performed using a charging / discharging device (trade name BS2500-05R1 manufactured by Keiki Keiki Center Co., Ltd.), charged for 2 hours and 50 minutes at a current of 150 mA per gram of hydrogen storage alloy, paused for 10 minutes, and then charged per gram of hydrogen storage alloy. The cycle in which discharge was performed at a current of 150 mA until −0.7 V with respect to the mercury oxide electrode was repeated, and the maximum discharge capacity was defined as the discharge capacity of the hydrogen storage alloy.

(Cycle characteristics)
1) Production of negative electrode plate 100 parts by mass of the aforementioned alloy powder 0.4 parts by mass of sodium polyacrylate, 0.1 part by mass of carboxymethyl cellulose, and polytetrafluoroethylene dispersion (dispersion medium: water, solid content) 60 parts by mass) After adding 2.5 parts by mass, the mixture was kneaded to obtain a slurry of a negative electrode mixture.
This slurry is applied evenly on both sides of the Ni-plated 60 μm thick Fe punching metal, that is, the thickness is constant, and after drying the slurry, the punching metal is pressed. Thus, a negative electrode plate for an AA size nickel metal hydride secondary battery was obtained.
2) Preparation of positive electrode plate A mixed aqueous solution of nickel sulfate, zinc sulfate and cobalt sulfate was prepared so that Zn was 3% by mass and Co was 1% by mass with respect to metal Ni, and this mixed aqueous solution was stirred. While adding sodium hydroxide aqueous solution gradually. At this time, the pH during the reaction was maintained at 13 to 14 to elute the nickel hydroxide particles, and the nickel hydroxide particles were washed three times with 10 times the amount of pure water, and then dehydrated and dried.
The obtained nickel hydroxide particles were mixed with a 40% by mass HPC dispersion liquid to prepare a slurry of a positive electrode mixture. This slurry was filled in a nickel substrate having a porous structure and dried, and the substrate was rolled and cut to obtain a positive electrode plate for an AA size nickel metal hydride secondary battery.
3) Assembling of the nickel metal hydride secondary battery The negative electrode plate and the positive electrode plate obtained as described above are spirally wound through a separator made of polypropylene or nylon nonwoven fabric to form an electrode group. After the group was accommodated in an outer can, a 30 wt% potassium hydroxide aqueous solution containing lithium and sodium was injected into the outer can to assemble an AA size nickel hydrogen secondary battery with a capacity of 2500 mAh.
4) Measurement of cycle characteristics The battery capacity measurement in which the prepared battery is charged at a current of 0.1 C for 16 hours and then discharged to a final voltage of 0.5 V at a current of 1.0 C is repeated until the battery cannot be discharged. I counted the number. The results are shown in Table 1 with the result of Comparative Example 8 being 100.

Examples 2-13, Comparative Examples 1-7
A slab was obtained in the same manner as in Example 1 except that the temperature difference between the alloy composition, the pouring temperature and the melting point of the alloy was changed to Table 1. The heat treatment was performed for 6 hours at a temperature 40 ° C. lower than the melting point of each alloy.
The obtained slab was treated in the same manner as in Example 1 in the same manner as in Example 1. The area ratio of the phase with high Mg concentration and the phase with high Al concentration, the equilibrium pressure with H / M of 0.4 in the hydrogen release curve at 80 ° C., and the electrochemical characteristics (Discharge capacity) and battery characteristics (cycle characteristics) were measured. The results are shown in Table 1. Moreover, the COMP image of the cross-sectional structure of the hydrogen storage alloy obtained in Example 4 and element mapping images of Mg and Al are shown in FIGS.

Comparative Example 8
An alloy melt was obtained in the same manner as in Example 1 using the raw materials having the compositions shown in Table 1. Subsequently, the pouring temperature of the melt was set to 1,300 ° C., and a water-cooled copper mold was used to form an alloy ingot having a thickness of 5 cm. The obtained ingot was heat-treated at 950 ° C. for 12 hours in an argon gas atmosphere. The center part of the cross section of the alloy ingot was observed with EPMA in the same manner as in Example 1, and the area ratios of the phase with a high Mg concentration and the phase with a high Al concentration were calculated. In the same manner as in Example 1, the equilibrium pressure, electrochemical characteristics (discharge capacity), and battery characteristics (cycle characteristics) of H / M of 0.4 in the hydrogen release curve at 80 ° C. were measured. The results are shown in Table 1. Moreover, the COMP image of the cross-sectional structure of the obtained hydrogen storage alloy and the element mapping images of Mg and Al are shown in FIGS.

Comparative Examples 9-11
An ingot was obtained in the same manner as in Comparative Example 8 except that the temperature difference between the alloy composition, the pouring temperature and the melting point of the alloy was changed to Table 1. The heat treatment was performed for 12 hours at a temperature 40 ° C. lower than the melting point of each alloy.
The obtained ingot was processed in the same manner as in Example 1, and the area ratio of the phase with high Mg concentration and the phase with high Al concentration, the equilibrium pressure with H / M of 0.4 in the hydrogen release curve at 80 ° C., and the electrochemical characteristics. (Discharge capacity) and battery characteristics (cycle characteristics) were measured. The results are shown in Table 1. In addition, FIGS. 10 to 12, 13 to 15, and 16 to 18 show the COMP images of the cross-sectional structures of the hydrogen storage alloys obtained in Comparative Examples 9 to 11 and element mapping images of Mg and Al, respectively.

Claims (11)

Formula (1) R _a Mg _b Ni _c Al _{d Me} (wherein R is a rare earth element including Y, at least one selected from Zr, Hf and Ca, M is an element other than R, Mg, Ni, Al) A is 0.75 ≦ a ≦ 0.85, b is 0.15 ≦ b ≦ 0.25, c is 3.30 ≦ c ≦ 3.65, and d is 0.15. ≦ d ≦ 0.25, e is 0 ≦ e ≦ 0.20, a + b = 1, 0.33 ≦ b + d ≦ 0.45, 3.45 ≦ c + d + e ≦ 3.80). A hydrogen storage alloy having a Mg concentration higher than that of a mother phase confirmed by a COMP image and an element mapping image of Mg and Al of 500 times by EPMA of a cross-sectional structure of the alloy manufactured by a strip casting method. And the total proportion of phases with high Al concentration is 5.0% or less That the hydrogen-absorbing alloy.   2. The hydrogen storage alloy according to claim 1, wherein the total proportion of the phase having a high Mg concentration and the phase having a high Al concentration is 3.0% or less.   The hydrogen storage alloy according to claim 1 or 2, wherein 0.18≤b≤0.20. It is 0.15 <= d <= 0.22, The hydrogen storage alloy in any one of Claims 1-3.   It is 0.40 <b + d <= 0.45, The hydrogen storage alloy in any one of Claims 1-4.   5. The hydrogen storage alloy according to claim 3, wherein R contains La and Sm, and 0.33 ≦ b + d ≦ 0.42.   R is only La and it is 3.60 <= c + d + e <= 3.80, The hydrogen storage alloy in any one of Claims 1-5 characterized by the above-mentioned.   8. The hydrogen occlusion according to any one of 1 to 7, wherein an equilibrium pressure having an H / M of 0.4 in a hydrogen release curve obtained by measurement at 80 ° C. is 0.03 to 0.07 MPa. alloy. Formula (1) R _a Mg _b Ni _c Al _{d Me} (wherein R is a rare earth element including Y, at least one selected from Zr, Hf and Ca, M is an element other than R, Mg, Ni, Al) A is 0.75 ≦ a ≦ 0.85, b is 0.15 ≦ b ≦ 0.25, c is 3.30 ≦ c ≦ 3.65, and d is 0.15. ≦ d ≦ 0.25, e is 0 ≦ e ≦ 0.20, a + b = 1, 0.33 ≦ b + d ≦ 0.45, 3.45 ≦ c + d + e ≦ 3.80). Obtained by heating and melting the raw material to obtain an alloy melt higher than the melting point by 300 ° C. or higher, and then cooling and solidifying the alloy melt by a strip casting method to obtain an alloy. The alloy is heat-treated for 30 minutes to 10 hours in a temperature range 10 to 100 ° C. lower than the melting point of the alloy. Method for producing a hydrogen-absorbing alloy Motomeko 1 wherein.   A negative electrode for a nickel metal hydride secondary battery containing the hydrogen storage alloy according to claim 1.   A nickel metal hydride secondary battery using the negative electrode for a nickel metal hydride secondary battery according to claim 10.