Hydrogen storage alloy and nickel-metal hydride battery

Abstract

The present invention realizes a hydrogen storage alloy capable of obtaining a high-performance nickel-metal hydride battery.　A nickel-metal hydride battery (1) includes a battery element (20) housed in an outer can (10). The battery element (20) has a positive electrode (21), a negative electrode (22), and a separator (23) interposed therebetween. The hydrogen storage alloy is used in the negative electrode (22). As the hydrogen storage alloy in the negative electrode (22), an alloy having a composition of Ln1-xMgxNiy-zAlz is used. Here, Ln includes Y and a rare earth element different from Y, the composition proportion of Y in Ln is not less than 65%, and x, y, and z satisfy 0<x≤0.15, 3.5≤y, and z≤0.25, respectively.

Description

Hydrogen storage alloys and nickel-metal hydride batteries

[0001] The present invention relates to a hydrogen storage alloy and a nickel-metal hydride battery.

[0002] There is known a technology for using a hydrogen storage alloy in the negative electrode of an alkaline storage battery such as a nickel-metal hydride battery, and a technology for using a rare earth-Mg-Ni based hydrogen storage alloy as the hydrogen storage alloy for such an alkaline storage battery (Patent Document 1).

[0003] JP 2013-134903 A

[0004] In the case of conventional hydrogen storage alloys, nickel-metal hydride batteries using the alloys have sometimes been unable to achieve sufficient performance, for example, in terms of dischargeability in low-temperature environments. In one aspect, the present invention aims to provide a hydrogen storage alloy that can be used to obtain high-performance nickel-metal hydride batteries.

[0005] In one embodiment, there is provided a hydrogen storage alloy represented by the following general formula (1): Ln １－ｘ Mg ｘ Ni ｙ－ｚ Al ｚ ... (1) (In the general formula (1), Ln contains Y and a rare earth element different from Y, the composition ratio of Y in Ln is 65% or more, and x, y, and z satisfy the following conditions: 0<x≦0.15, 3.5≦y, z≦0.25, respectively.) In another aspect, there is provided a nickel-metal hydride battery using the above-described hydrogen storage alloy.

[0006] In one aspect, it is possible to realize a hydrogen storage alloy that can provide a high-performance nickel-metal hydride battery. The objects, features, and advantages of the present invention will become apparent from the following description taken in conjunction with the accompanying drawings, which illustrate preferred embodiments of the present invention by way of example.

[0007] FIG. 1 is a diagram illustrating an example of a nickel-metal hydride battery.

[0008] Fig. 1 is a diagram illustrating an example of a nickel-metal hydride battery. Fig. 1 shows a schematic cross-sectional view of a main portion of an example of a nickel-metal hydride battery. The nickel-metal hydride battery 1 shown in Fig. 1 includes an outer can 10, a battery element 20, a positive electrode lead 30, an insulating plate 40, an insulating plate 50, an alkaline electrolyte 60, a sealing plate 70, and a gasket 80.

[0009] The outer can 10 is a cylindrical, conductive container with a bottom and one open end. The outer can 10 is made of a metal material such as stainless steel. The open end of the outer can 10 is subjected to drawing and crimping, and a conductive sealing plate 70 provided with a positive electrode terminal 71 is fixed via a gasket 80. The sealing plate 70 is made of a metal material such as stainless steel. The outer can 10 is sealed by the gasket 80 and the sealing plate 70.

[0010] The battery element 20 is an example of a power generating element housed in the exterior can 10. The battery element 20 includes a sheet-shaped positive electrode 21, a sheet-shaped negative electrode 22, and a sheet-shaped separator 23. The battery element 20 has a configuration in which the positive electrode 21 and the negative electrode 22 are spirally wound with the separator 23 interposed therebetween. For example, the battery element 20 is wound so that the negative electrode 22 is located at the outermost periphery of the battery element 20.

[0011] Here, the positive electrode 21 contains Ni (nickel). The negative electrode 22 contains a hydrogen storage alloy, for example, a rare earth-Mg—Ni-based hydrogen storage alloy. As an example, the negative electrode 22 contains a rare earth-Mg—Ni-based hydrogen storage alloy containing a rare earth element such as La (lanthanum), Mg (magnesium), Ni, and Al (aluminum). The rare earth-Mg—Ni-based hydrogen storage alloy of the negative electrode 22 may contain rare earth elements such as Nd (neodymium), Sm (samarium), Ce (cerium), and Y (yttrium). The rare earth-Mg—Ni-based hydrogen storage alloy of the negative electrode 22 may further contain an element such as Zr (zirconium).

[0012] The separator 23 may be made of a microporous film, a woven fabric, a nonwoven fabric, or the like. For example, a polypropylene nonwoven fabric is used for the separator 23. The battery element 20, in which the positive electrode 21, the negative electrode 22, and the separator 23 are wound, is housed in the outer can 10 together with an alkaline electrolyte 60. The alkaline electrolyte 60 may contain, for example, at least one of KOH (potassium hydroxide), NaOH (sodium hydroxide), and LiOH (lithium hydroxide).

[0013] An insulating plate 40 and an insulating plate 50 are provided inside the outer can 10, for example, on its bottom and on top of the housed battery element 20, respectively. The positive electrode 21 of the battery element 20 housed in the outer can 10 is electrically connected to a positive electrode terminal 71 of a sealing plate 70 that is insulated from the outer can 10 via a gasket 80 and seals the open end of the outer can 10, via a conductive positive electrode lead 30 that penetrates the insulating plate 50. The negative electrode 22 of the battery element 20 housed in the outer can 10 is either in direct contact with the inner wall of the outer can 10, which is insulated from the sealing plate 70 that has the positive electrode terminal 71 via the gasket 80, or is connected to the inner wall of the outer can 10 using a conductive negative electrode lead (not shown) or the like, and is electrically connected to the outer can 10. The outer can 10 (e.g., a part of its bottom surface) functions as a negative electrode terminal.

[0014] In the nickel-metal hydride battery 1 having the above-described configuration, the negative electrode 22 is made of a hydrogen storage alloy represented by the following general formula (1): １－ｘ Mg ｘ Ni ｙ－ｚ Al ｚ In the general formula (1), Ln contains Y and a rare earth element different from Y, the composition ratio of Y in Ln is 65% or more, and x, y, and z satisfy the following conditions: 0<x≦0.15, 3.5≦y, and z≦0.25. For example, x, y, and z satisfy the following conditions: 0<x≦0.15, 3.5≦y<3.8, and 0<z≦0.25.

[0015] In the general formula (1), Ln may contain, for example, La as a rare earth element. In the general formula (1), Ln may further contain Zr. A hydrogen storage alloy represented by the general formula (1) has improved hydrogen absorption and desorption characteristics. For example, as described below, in the hydrogen absorption and desorption characteristics in an 80°C environment, i.e., in a pressure-composition-isotherm diagram or PCT (Pressure-Composition-Temperature) characteristic curve, when the hydrogen storage capacity H / M = 0.4 (H is the number of hydrogen atoms, and M is the total number of atoms of the elements constituting the hydrogen storage alloy), the hydrogen absorption pressure is 0.30 MPa or more and the hydrogen desorption pressure is 0.20 MPa or more.

[0016] The use of a hydrogen storage alloy such as that represented by the above general formula (1) in the negative electrode 22 of the nickel-metal hydride battery 1 improves the battery characteristics of the nickel-metal hydride battery 1. For example, as will be described later, the dischargeability of the nickel-metal hydride battery 1 in a low-temperature environment is improved.

[0017] The structure represented by the general formula (1) provides a hydrogen storage alloy that can be used to obtain a high-performance nickel-metal hydride battery 1. Furthermore, the use of a hydrogen storage alloy represented by the general formula (1) provides a high-performance nickel-metal hydride battery 1 that is excellent in dischargeability in a low-temperature environment.

[0018] An example of a method for manufacturing a nickel-metal hydride battery 1 having the above configuration will be described. <Manufacturing a Nickel-Metal Hydride Battery> (Manufacturing a Hydrogen Storage Alloy) The raw materials for the hydrogen storage alloy to be manufactured, such as Ln, Mg, Ni, and Al, are mixed to form a predetermined alloy composition. Here, Ln includes Y and a rare earth element different from Y, such as La, or further includes Zr. For example, the raw materials for Ln, Mg, Ni, and Al are mixed to form a predetermined alloy composition (see, for example, Examples 1-5 below). In addition, the raw materials for the elements to be mixed are selected depending on the alloy composition of the hydrogen storage alloy to be manufactured (see, for example, Comparative Examples 1-9 below).

[0019] The raw materials of the desired elements are mixed to form a desired alloy composition, which is then melted in a high-frequency induction melting furnace in an Ar (argon) gas atmosphere, poured into a mold, and cooled to room temperature to obtain an alloy ingot containing the desired elements in the desired alloy composition.

[0020] The resulting alloy ingot is filled into a metal container, the interior of which is replaced with Ar gas and then sealed. The metal container is placed in a heat treatment furnace and heat-treated for 10 hours at a temperature of 900°C to 1000°C. After cooling, the ingot is pulverized to obtain a hydrogen storage alloy powder having a predetermined particle size, e.g., a mean diameter by volume (MV) of 25 μm.

[0021] The particle size of the hydrogen storage alloy affects the reaction area and the resistance to cracking when the hydrogen storage alloy is used in the negative electrode 22 of the nickel-metal hydride battery 1, and affects the charge-discharge characteristics of the nickel-metal hydride battery 1 including the negative electrode 22. The particle size of the hydrogen storage alloy is appropriately selected based on the charge-discharge characteristics when used in the negative electrode 22 of the nickel-metal hydride battery 1.

[0022] The hydrogen storage alloy powder obtained as described above may be washed with water, an alkaline aqueous solution, or the like to reduce Cl present on the surface of the hydrogen storage alloy, for example, because Cl present on the surface of the hydrogen storage alloy may change the properties of the binder or thickener used when forming a paste of the negative electrode mixture as described below, which may affect the manufacturability of the negative electrode 22 using the paste and the quality of the nickel-metal hydride battery 1.

[0023] Furthermore, the hydrogen storage alloy powder obtained as described above may be in a form in which Ni, which functions as a catalyst, is present relatively abundantly on the surface of the hydrogen storage alloy, for example, in order to promote the charge-discharge reaction of a nickel-metal hydride battery 1 including the negative electrode 22 using the hydrogen storage alloy powder. For example, by treating the hydrogen storage alloy powder with an acid such as hydrochloric acid, in which Ni is relatively difficult to dissolve, components other than Ni on the surface of the hydrogen storage alloy, such as rare earth elements, Mg, and Al, are dissolved by the acid, leaving the less soluble Ni on the surface, resulting in a hydrogen storage alloy with a relatively Ni-rich surface. After the acid treatment, washing with water or the like as described above may be performed.

[0024] (Negative Electrode Preparation) For example, 100 parts by weight of the hydrogen storage alloy powder obtained as described above is mixed with 0.4 parts by weight of sodium polyacrylate as an anode auxiliary, 0.1 parts by weight of carboxymethyl cellulose as a thickener, 1.0 part by weight of a 50% by weight dispersion of styrene butadiene rubber as a binder, 0.5 parts by weight of Ketjen Black as a conductive material, 0.5 parts by weight of yttrium oxide as an anode additive, and 30 parts by weight of water to prepare a paste of a negative electrode mixture. This paste is evenly applied to both sides of a nickel-plated iron perforated plate as a negative electrode substrate. After drying the paste, the perforated plate with the hydrogen storage alloy powder attached is further rolled to increase the amount of alloy per unit volume and cut to a predetermined size. This results in a sheet-shaped negative electrode 22 containing a hydrogen storage alloy.

[0025] (Positive Electrode Fabrication) While stirring a mixed aqueous solution of nickel sulfate, zinc sulfate, magnesium sulfate, and cobalt sulfate, a sodium hydroxide solution is gradually added to the mixed aqueous solution so that the nickel metal contains 3% zinc, 0.4% magnesium, and 1% cobalt by weight. The pH during the reaction is stabilized at 13-14, and nickel hydroxide is eluted. This mixture is washed three times with 10 times the amount of pure water, followed by dehydration and drying to produce a nickel hydroxide active material. Next, 100 parts by weight of the nickel hydroxide active material is mixed with 10 parts by weight of cobalt hydroxide as a conductive material, 0.5 parts by weight of yttrium oxide and 0.3 parts by weight of zinc oxide as positive electrode additives, and 40 parts by weight of hydroxypropyl cellulose (HPC) dispersion liquid as a binder to produce an active material slurry. This active material slurry is filled into a nickel foam, dried, rolled, and cut to a predetermined size. This results in a sheet-like positive electrode 21 containing nickel.

[0026] (Battery Fabrication) A sheet-like separator 23 is prepared together with sheet-like negative electrode 22 and positive electrode 21. For example, a nonwoven fabric made of polypropylene fibers having sulfonic groups is prepared as the separator 23. The prepared positive electrode 21, negative electrode 22, and separator 23 are used to fabricate a battery element 20. For example, the positive electrode 21 and negative electrode 22 are spirally wound with the separator 23 interposed therebetween, with the negative electrode 22 positioned at the outermost periphery, to fabricate a cylindrical battery element 20.

[0027] The fabricated battery element 20 is inserted and housed in the outer can 10. Before the battery element 20 is housed, an insulating plate 40 is provided on the bottom of the outer can 10. After the battery element 20 is housed, an insulating plate 50 is provided on the top of the battery element 20 inside the outer can 10. The open end of the outer can 10 is subjected to a drawing process to form a drawn portion (beading portion).

[0028] Then, a predetermined alkaline electrolyte 60 is poured into the exterior can 10 containing the battery element 20. For example, the alkaline electrolyte 60 is a mixture of a KOH solution and a LiOH solution in a ratio of 7.0:1.0.

[0029] Thereafter, using the drawn portion of the outer can 10 formed by the drawing process as a seat, a sealing plate 70 connected to the positive electrode 21 of the battery element 20 by a positive electrode lead 30, i.e., a sealing plate 70 equipped with a positive electrode terminal 71, is placed so that a gasket 80 is provided on the outer edge of the sealing plate 70, and a crimping process is applied to the open end of the outer can 10. As a result, the sealing plate 70 is fixed to the outer can 10 via the gasket 80, and a sealed structure is realized by the outer can 10, the gasket 80, and the sealing plate 70.

[0030] Using this method, a nickel-metal hydride battery 1 is manufactured. For example, a nickel-metal hydride battery 1 with a nominal capacity of 1000 mAh is manufactured. The nickel-metal hydride battery 1 may be activated (initial activation) by charging and discharging under predetermined conditions. For example, the nickel-metal hydride battery 1 is activated by being charged at 0.1 A for 16 hours, and then discharged at 0.2 A until the battery voltage reaches 1.0 V, five times.

[0031] Examples and comparative examples will be described below. [Example 1] Using the method described above, La ０．２７０ Y ０．６２１ Zr ０．００９ Mg ０．０９９７ Ni ３．３３ Al ０．１７ A hydrogen storage alloy powder having the alloy composition shown in Table 1 was obtained. Furthermore, a nickel-metal hydride battery 1 was obtained by using the hydrogen storage alloy powder obtained in the above-described method for the negative electrode 22.

[0032] Example 2 Using the method described above, La ０．２７１ Y ０．６２３ Zr ０．００９ Mg ０．０９６７ Ni ３．３３ Al ０．１７ A hydrogen storage alloy powder having the alloy composition shown in Table 1 was obtained. Furthermore, a nickel-metal hydride battery 1 was obtained by using the hydrogen storage alloy powder obtained in the above-described method for the negative electrode 22.

[0033] [Example 3] Using the method described above, La ０．３０５ Y ０．５８５ Zr ０．０１ Mg ０．１０ Ni ３．３３ Al ０．１７ A hydrogen storage alloy powder having the alloy composition shown in Table 1 was obtained. Furthermore, a nickel-metal hydride battery 1 was obtained by using the hydrogen storage alloy powder obtained in the above-described method for the negative electrode 22.

[0034] Example 4 Using the method described above, La ０．３１２ Y ０．５８８ Mg ０．１０ Ni ３．３３ Al ０．１７ A hydrogen storage alloy powder having the alloy composition shown in Table 1 was obtained. Furthermore, a nickel-metal hydride battery 1 was obtained by using the hydrogen storage alloy powder obtained in the above-described method for the negative electrode 22.

[0035] [Example 5] Using the method described above, La ０．２７９ Y ０．６２１ Mg ０．１０ Ni ３．３３ Al ０．１７A hydrogen storage alloy powder having the alloy composition shown in Table 1 was obtained. Furthermore, a nickel-metal hydride battery 1 was obtained by using the hydrogen storage alloy powder obtained in the above-described method for the negative electrode 22.

[0036] Comparative Example 1: Using the method described above, Nd ０．８８ Zr ０．０１ Mg ０．１１ Ni ３．２３ Al ０．１７ A hydrogen storage alloy powder having the alloy composition shown in Table 1 was obtained. Furthermore, a nickel-metal hydride battery 1 was obtained by using the hydrogen storage alloy powder obtained in the above-described method for the negative electrode 22.

[0037] [Comparative Example 2] Using the method described above, La ０．５３ Sm ０．３６ Mg ０．１１ Ni ３．７１ Al ０．０９ A hydrogen storage alloy powder having the alloy composition shown in Table 1 was obtained. Furthermore, a nickel-metal hydride battery 1 was obtained by using the hydrogen storage alloy powder obtained in the above-described method for the negative electrode 22.

[0038] Comparative Example 3: Using the method described above, La ０．２６９ Sm ０．６１９ Zr ０．００９ Mg ０．１０３ Ni ３．３３ Al ０．１７ A hydrogen storage alloy powder having the alloy composition shown in Table 1 was obtained. Furthermore, a nickel-metal hydride battery 1 was obtained by using the hydrogen storage alloy powder obtained in the above-described method for the negative electrode 22.

[0039] Comparative Example 4: Using the method described above, La ０．７７ Y ０．１２ Mg ０．１１ Ni ３．７３ Al ０．１２ A hydrogen storage alloy powder having the alloy composition shown in Table 1 was obtained. Furthermore, a nickel-metal hydride battery 1 was obtained by using the hydrogen storage alloy powder obtained in the above-described method for the negative electrode 22.

[0040] Comparative Example 5: Using the method described above, La ０．６８ Sm ０．０７ Mg ０．２５ Ni ３．４７ Al ０．１０A hydrogen storage alloy powder having the alloy composition shown in Table 1 was obtained. Furthermore, a nickel-metal hydride battery 1 was obtained by using the hydrogen storage alloy powder obtained in the above-described method for the negative electrode 22.

[0041] [Comparative Example 6] Using the method described above, La ０．６８ Ce ０．０７ Mg ０．２５ Ni ３．４７ Al ０．１０ A hydrogen storage alloy powder having the alloy composition shown in Table 1 was obtained. Furthermore, a nickel-metal hydride battery 1 was obtained by using the hydrogen storage alloy powder obtained in the above-described method for the negative electrode 22.

[0042] Comparative Example 7: Using the method described above, La ０．６８ Y ０．０７ Mg ０．２５ Ni ３．４７ Al ０．１０ A hydrogen storage alloy powder having the alloy composition shown in Table 1 was obtained. Furthermore, a nickel-metal hydride battery 1 was obtained by using the hydrogen storage alloy powder obtained in the above-described method for the negative electrode 22.

[0043] [Comparative Example 8] Using the method described above, La ０．３２５ Y ０．５６５ Zr ０．０１ Mg ０．１０ Ni ３．４７ Al ０．１７ A hydrogen storage alloy powder having the alloy composition shown in Table 1 was obtained. Furthermore, a nickel-metal hydride battery 1 was obtained by using the hydrogen storage alloy powder obtained in the above-described method for the negative electrode 22.

[0044] Comparative Example 9: Using the method described above, La ０．３６ Y ０．５４ Mg ０．１０ Ni ３．４７ Al ０．１７ A hydrogen storage alloy powder having the alloy composition shown in Table 1 was obtained. Furthermore, a nickel-metal hydride battery 1 was obtained by using the hydrogen storage alloy powder obtained in the above-described method for the negative electrode 22.

[0045] <Evaluation> (Hydrogen absorption / desorption characteristics) For each of the hydrogen storage alloy powders of Examples 1-5 and Comparative Examples 1-9, in order to obtain a PCT characteristic curve (P: pressure, C: hydrogen storage capacity, T: temperature), which indicates the hydrogen absorption / desorption characteristics, the alloy samples were activated by hydrogenation up to a maximum hydrogen pressure of 1 MPa under solid-gas conditions of 80°C using a PCT characteristic evaluation device, followed by dehydrogenation.

[0046] The activated hydrogen storage alloy powder was hydrogenated in an 80°C environment until the maximum hydrogen pressure reached 1 MPa. The pressure during hydrogen absorption was measured, and the equilibrium pressure at the point where the hydrogen storage capacity H / M was 0.4 (H is the number of hydrogen atoms, and M is the total number of atoms of the elements constituting the hydrogen storage alloy) was determined as the hydrogen absorption pressure P ａ Subsequently, the hydrogenated hydrogen storage alloy powder was hydrogenated, and the pressure at the time of hydrogen release was measured. The equilibrium pressure at the time when the hydrogen storage amount H / M=0.4 was determined as the hydrogen release pressure P ｄ The pressure was set to [MPa].

[0047] The hydrogen absorption pressure P of the hydrogen storage alloy ａ and hydrogen release pressure P ｄ The values ​​of are 0.15<P ａ <0.90, 0.10<P ｄ <0.90. If each value is below this range, the nickel-metal hydride battery 1 including the negative electrode 22 using a hydrogen storage alloy may not achieve the expected battery characteristics. On the other hand, if each value is above this range, the internal pressure within the sealed structure may become too high during charging in the nickel-metal hydride battery 1 including the negative electrode 22 using a hydrogen storage alloy, which may cause leakage of the alkaline electrolyte.

[0048] (Battery Characteristics) Each of the nickel-metal hydride batteries 1 of Examples 1-5 and Comparative Examples 1-9 was charged (ΔV=−10 mV) at 25° C. and 1.0 A, and after a 3-hour rest in an environment of −30° C., was discharged at 3.0 W until the cell voltage reached 0.6 V. After such charging and discharging, the discharge capacity [mAh] (−30° C., 3.0 W) of each of the nickel-metal hydride batteries 1 of Examples 1-5 and Comparative Examples 1-9 was determined.

[0049] The composition and hydrogen absorption pressure P of each of the hydrogen storage alloys of Examples 1 to 5 and Comparative Examples 1 to 9 obtained as described above wereａ [MPa] and hydrogen release pressure P ｄ Table 1 shows the pressure [MPa] and the discharge capacity of each of the nickel-metal hydride batteries 1 of Examples 1 to 5 and Comparative Examples 1 to 9.

[0050]

[0051] In Table 1, the discharge capacity of each nickel-metal hydride battery 1 is shown as a value of discharge capacity (compared to Comparative Example 1) when the discharge capacity of Comparative Example 1 is set to 100. Table 1 also shows the composition ratios [%] of Y, La, and Zr in Ln in each of the hydrogen storage alloys of Examples 1 to 5 and Comparative Examples 1 to 9.

[0052] As can be seen from Table 1, in Example 1-5, in which the composition ratio of Y in Ln in the hydrogen storage alloy is 65% or more, the discharge capacity (-30°C, 3.0 W) of the nickel-metal hydride battery 1 was significantly improved compared to Comparative Example 1-9, in which the composition ratio of Y in Ln is less than 65%.

[0053] Here, AB is one type of hydrogen storage alloy. ２ Type unit and AB ５ A having a superlattice structure in which type units are stacked ２ B ７ There are hydrogen storage alloys of this type. ５ The advantage of the type alloy is that it has stable hydrogen absorption and desorption, and ２ It also has the advantage of being able to store a large amount of hydrogen, which is a characteristic of alloys.

[0054] From Table 1, it can be seen that in the hydrogen storage alloy containing a large amount of Y such as in Example 1-5, the ２ B ７ The discharge performance in a low temperature environment is improved compared to hydrogen storage alloys containing elements such as Nd, Sm, and Ce, which are used as rare earth elements in hydrogen storage alloys of the above type.

[0055] No improvement in discharge performance in a low-temperature environment was observed in the hydrogen storage alloys not containing Y, such as Comparative Examples 1-3, 5, and 6. No improvement in discharge performance in a low-temperature environment was observed in the hydrogen storage alloys containing Y but with a small composition ratio, such as Comparative Examples 4 and 7.

[0056] In the hydrogen storage alloys of Comparative Examples 8 and 9, in which the Y content was greater than in Comparative Examples 4 and 7 but the composition ratio was less than 65%, no improvement in discharge performance was observed in low temperature environments.

[0057] In Example 1-5, in which improvement in discharge performance in a low-temperature environment was observed, the above general formula (1), that is, Ln １－ｘ Mg ｘ Ni ｙ－ｚ Al ｚ The hydrogen storage alloy represented by the formula (1) satisfies the following conditions: 0<x≦0.15, 3.5≦y, z≦0.25. For example, x, y, and z each satisfy the following ranges: 0<x≦0.15, 3.5≦y<3.8, 0<z≦0.25. The hydrogen storage alloy Ln １－ｘ Mg ｘ Ni ｙ－ｚ Al ｚ According to this, in the nickel-metal hydride battery 1 using it, it is possible to realize improved discharge performance in a low-temperature environment.

[0058] In the above general formula (1), when y>3.8, A ２ B ７ There is a possibility that deviations in the mold structure may occur, and durability may decrease if Al is not contained when z = 0. Therefore, among x, y, and z within the ranges of 0 < x ≦ 0.15, 3.5 ≦ y, z ≦ 0.25, it is more preferable that y and z be within the ranges of 3.5 ≦ y < 3.8, 0 < z ≦ 0.25.

[0059] In addition, in Example 1-5, in which improvement in discharge performance in a low temperature environment was observed, in the hydrogen absorption and desorption characteristics in an 80°C environment, the hydrogen absorption pressure P ａ is 0.30 MPa or more and the hydrogen release pressure P ｄ The hydrogen absorption pressure P ａ and hydrogen release pressure P ｄ If the hydrogen storage alloy satisfies these ranges, the nickel-metal hydride battery 1 using it can achieve improved battery characteristics, such as dischargeability in a low-temperature environment.

[0060] The hydrogen storage pressure P ａ and hydrogen release pressure P ｄ It is preferable that both of them are less than 0.90. ａ and hydrogen release pressure P ｄ If the hydrogen storage alloy satisfies these ranges, a nickel-metal hydride battery 1 can be realized that can suppress excessive internal pressure rise within the sealed structure during charging and the resulting leakage of alkaline electrolyte.

[0061] In the above description, an example has been given in which a hydrogen storage alloy such as that represented by the general formula (1) is applied to the negative electrode 22 of a cylindrical nickel-metal hydride battery 1, but the battery shape is not limited to this cylindrical shape. A hydrogen storage alloy such as that represented by the general formula (1) can be applied to the negative electrodes of nickel-metal hydride batteries of various shapes, such as prismatic, gum-shaped, and thin. By using a hydrogen storage alloy such as that represented by the general formula (1) in the negative electrode, high-performance nickel-metal hydride batteries of various shapes can be realized.

[0062] Further, since numerous variations and modifications are possible to those skilled in the art, the present invention is not limited to the exact construction and application shown and described above, and all corresponding modifications and equivalents are deemed to be within the scope of the present invention as defined by the appended claims and their equivalents.

[0063] REFERENCE SIGNS LIST 1 Nickel-metal hydride battery 10 Outer can 20 Battery element 21 Positive electrode 22 Negative electrode 23 Separator 30 Positive electrode lead 40, 50 Insulating plate 60 Alkaline electrolyte 70 Sealing plate 71 Positive electrode terminal 80 Gasket

Claims

1. A hydrogen storage alloy represented by the following general formula (1): Ln １－ｘ Mg ｘ Ni ｙ－ｚ Al ｚ ... (1) [In the general formula (1), Ln contains Y and a rare earth element different from Y, the composition ratio of Y in Ln is 65% or more, and x, y, and z satisfy the following relationships: 0<x≦0.15, 3.5≦y, z≦0.25, respectively.] 2. The hydrogen storage alloy according to claim 1, wherein in said general formula (1), said Ln contains La as said rare earth element.

3. The hydrogen storage alloy according to claim 1, wherein in the general formula (1), the Ln further contains Zr.

4. A hydrogen storage alloy according to claim 1, wherein, in its hydrogen absorption and desorption characteristics in an 80°C environment, when the hydrogen storage capacity H / M is 0.4 (H is the number of hydrogen atoms, and M is the total number of atoms of the elements constituting the hydrogen storage alloy), the hydrogen absorption pressure is 0.30 MPa or more and the hydrogen desorption pressure is 0.20 MPa or more.

5. A nickel-metal hydride battery using the hydrogen storage alloy according to any one of claims 1 to 4.

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