Hydrogen storage alloy for alkaline storage battery, alkaline storage battery using it as a negative electrode, and vehicle

Abstract

The invention provides a hydrogen storage alloy suitable for a negative electrode of an alkaline on-board battery, an alkaline storage battery using this alloy, and a vehicle. The invention provides: a hydrogen storage alloy used for an alkaline storage battery, which has a main phase comprising crystal structures of the A2B7 type, of the A5B 19 -type or AB3 type and represented by the general formula (1): (La 1-a-b Y a R b ) 1-c Mg c Ni d Al e Cr f Fe g(wherein R and the suffixes a, b, c, d, e, f, and g are as follows: R is one or both of Sm and Ce, 0 < a ≤ 0.12, 0 ≤ b ≤ 0.12, 0.13 ≤ c ≤ 0.27, 3.20 ≤ d + e + f + g ≤ 3.75, 0 ≤ e ≤ 0.14, 0 ≤ f ≤ 0.05, and 0 ≤ g ≤ 0.35); an alkaline storage battery using this alloy as a negative electrode; and a vehicle having this alkaline storage battery as a power source for a motor.

Description

TECHNICAL AREA

[0001] The present invention relates to a hydrogen storage alloy used for an alkaline storage battery, and more particularly, to a hydrogen storage alloy suitably used for an alkaline storage battery serving as a power source of a hybrid electric vehicle (HEV), a start-stop vehicle, etc., an alkaline storage battery suitable as a power source of a hybrid electric vehicle (HEV), a start-stop vehicle, etc., and a vehicle equipped with this alkaline storage battery. BACKGROUND

[0002] In recent years, secondary batteries have been widely used in applications such as mobile phones, personal computers, power tools, hybrid electric vehicles (HEVs), and pure electric vehicles (EVs). Alkaline storage batteries are primarily used for these applications. For alkaline storage batteries used in conjunction with vehicles such as hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), and pure electric vehicles (EVs), the high performance and long cycle life characteristics are particularly important. As their use expands to these applications, the requirements for downsizing and weight reduction of alkaline storage batteries are increasing.

[0003] Conventionally, hydrogen storage alloys with an AB5-type crystal structure have been used for negative electrodes of alkaline storage batteries. However, the miniaturization and weight reduction achieved with these alloys are limited, and the development of a new hydrogen storage alloy capable of achieving small size and high capacity has been desired. As a solution, Patent Literatures 1 and 2 propose rare earth-Mg-transition metal-based hydrogen storage alloys containing Mg.

[0004] One approach to downsizing and reducing the weight of an alkaline storage battery is to reduce the amount of hydrogen storage alloy used for the negative electrode. However, reducing the amount of hydrogen storage alloy raises the new problem that the performance of the alkaline storage battery decreases due to the reduction in the number of nickel active sites. To address this problem, Patent Literature 3 proposes an approach that increases the operating voltage by using a hydrogen storage alloy with a high hydrogen equilibrium pressure.

[0005] Several rare earth Mg-Ni-based alloys have been proposed as hydrogen storage alloys. For example, Patent Literature 4 discloses a hydrogen storage alloy with the general formula: Ln 1-x Mg x Ni y A z(wherein Ln is at least one kind of element selected from rare earth elements containing Y, and from Ca, Zr, and Ti; A is at least one kind of element selected from Co, Mn, V, Cr, Nb, Al, Ga, Zn, Sn, Cu, Si, P, and B; and the suffixes x, y, and Z satisfy the conditions of 0.05 ≤ x ≤ 0.25, 0 < z ≤ 1.5, and 2.8 ≤ y + z ≤ 4.0). In this hydrogen storage alloy, Sm is contained in the above-mentioned Ln in a ratio of 20 mol% or more.

[0006] Patent Literature 5 discloses, as a hydrogen storage alloy used for a negative electrode of a nickel-hydrogen secondary battery, an alloy having a composition expressed by the following general formula: (La a Sm b A c ) 1-w Mg w Ni x Al y T z(wherein A and T each represent at least one kind of element selected from a group consisting of Pr, Nd, etc., and a group consisting of V, Nb, etc.; the suffixes a, b, and c satisfy the following relationships expressed as: a > 0, b > 0, 0.1 > c ≥ 0, and a + b + c = 1; and the suffixes w, x, y, and z are in ranges expressed as 0.1 < w ≤ 1, 0.05 ≤ y ≤ 0.35, 0 ≤ z ≤ 0.5, 3.2 ≤ x + y + z ≤ 3.8).

[0007] With the aim of providing an alkaline storage battery with improved cycle characteristics and discharge characteristics, Patent Literature 6 discloses a hydrogen storage alloy having a composition expressed by the following general formula: (A α Ln 1-α ) 1-β Mg β Ni γ-δ-ε Al δ T ε(wherein A represents one or more kinds of elements selected from a group consisting of Pr, Nd, Sm, and Gd and contains at least Sm; Ln represents at least one kind of element selected from a group consisting of La, Ce, Pm, Eu, Tb, Dy, Ho, Er, Tm, Yb, Lu, Ca, Sr, Sc, Y, Ti, Zr, and Hf; T represents at least one kind of element selected from a group consisting of V, Nb, Ta, Cr, Mo, Mn, Fe, Co, Zn, Ga, Sn, In, Cu, Si, P, and B; the suffixes α, β, y, δ, and ε represent numbers satisfying the following: 0.4 ≤ α, 0.05 < β < 0.15, 3.0 ≤ γ ≤ 4.2, 0.15 ≤ δ ≤ 0.30, and 0 ≤ ε ≤ 0.20).

[0008] Patent Literature 7 reports a hydrogen storage alloy electrode which, in order to enable high-rate discharge, uses hydrogen storage alloy particles whose central diameter D50, represented by a 50% transmission rate, is in a range of 8 to 15 μm.

[0009] With the aim of providing a hydrogen storage alloy with excellent cycle life properties, Patent Literature 8 discloses a hydrogen storage alloy having a phase formed by a Gd2Co7-type crystal structure. The disclosed alloy is characterized in that this phase accounts for 10 wt% or more of the entire hydrogen storage alloy, and the hydrogen storage alloy contains yttrium in a ratio of 2 mol% or more but 10 mol% or less based on the entire hydrogen storage alloy.

[0010] Patent Literature 9 discloses a rare earth Mg-Ni-based hydrogen storage alloy that can mitigate the drop in operating voltage and achieve a high operating voltage even after long-term non-use of a nickel-hydrogen secondary battery. Specifically, the hydrogen storage alloy used for a battery has a composition expressed by the following general formula: (La a Nd b A c D d ) 1-w Mg w Ni x Al y T z. According to this disclosure, A, D and T in this formula each represent at least one kind of element selected from a group consisting of Sm and Gd, a group consisting of Pr, Eu, etc., and a group consisting of V, Nb, etc.; the suffixes a, b, c and d satisfy the following relationships expressed as a ≥ 0, b ≥ 0, c > 0, 0.1 > d ≥ 0, and a + b + c + d = 1; and the suffixes w, x, y and z are within ranges expressed as 0 < w ≤ 0.25, 0.05 ≤ y ≤ 0.35, 0 ≤ z < 0.5, and 3.15 ≤ x + y + z ≤ 3.35.

[0011] Patent Literature 10 discloses, as a hydrogen storage alloy for an alkaline storage battery that enables cost reduction while maintaining high performance, an alloy characterized by being represented by the following general formula (Re 1-x Y x ) 1-y-z Zr y Mg z Ni a-b Al b(Re contains only La or at least one kind of element containing La and selected from Nd and Sm, 0 < x ≤ 0.60, 0 ≤ y ≤ 0.02, 0.09 ≤ z ≤ 0.13, 3.40 ≤ a ≤ 3.80, and 0.05 ≤ b ≤ 0.20).

[0012] With the aim of providing a nickel-hydrogen secondary battery that has a high capacity and is excellent in both self-discharge characteristics and cycle life characteristics, Patent Literature 11 discloses a hydrogen storage alloy having a composition represented by the following general formula: (RE 1-x T x ) 1-y Mg y Ni z-a Al a(where RE is at least one element selected from Y, Sc, and rare earth elements; T is at least one element selected from Zr, V, and Ca; and the suffixes x, y, z, and a indicate 0 ≤ x, 0.05 ≤ y ≤ 0.35, 2.8 ≤ z ≤ 3.9, and 0.10 ≤ a ≤ 0.25, respectively). This hydrogen storage alloy has a crystal structure in which an AB2-type subunit and an AB5-type subunit are arranged in layers, and some of the above-mentioned Ni are replaced with Cr.

[0013] Patent Literature 12 aims to provide a hydrogen storage alloy whose pulverization is mitigated, and discloses a hydrogen storage alloy in which the ratio of the strongest peak intensity appearing in a range of 2θ = 31° to 33° to the strongest peak intensity appearing in a range of 2θ = 41° to 44° in an X-ray diffraction measurement using Cu-Kα radiation as an X-ray source is 0.1 or less (including 0). As a specific composition, it has La 1-a-b Y a Mg b Ni c Al d on (a satisfies 0.12 ≤ a ≤ 0.15; b satisfies 0.14 ≤ b ≤ 0.16; c satisfies 3.39 ≤ c ≤ 3.53; and d satisfies 0.13 ≤ d ≤ 0.17).

[0014] With the aim of providing a hydrogen storage alloy with excellent corrosion resistance and durability and a nickel-hydrogen storage battery with excellent cycle life using this hydrogen storage alloy, Patent Literature 13 discloses the following general formula (RE 1-a-b Sm a Mg b ) (Niz 1-c- AlcM d ) x (0.3 < a < 0.6; 0 < b < 0.16; 0.1 < cx < 0.2; 0 ≤ dx ≤ 0.1; 3.2 < x < 3.5; RE is one or more kinds of elements selected from rare earth elements other than Sm and Y, with La being essential; and M is Mn and / or Co).

[0015] In order to provide a hydrogen storage alloy having excellent corrosion resistance and durability and a nickel-hydrogen storage battery having excellent cycle life using this hydrogen storage alloy, Patent Literature 14 discloses a hydrogen storage alloy represented by the following general formula (RE 1-a-b Sm a Mg b ) (Ni 1-c-d Al c M d ) x (0.1 ≤ a ≤ 0.25; 0.1 < b < 0.2; 0.02 < cx < 0.2; 0 ≤ dx ≤ 0.1; 3.6 ≤ x ≤ 3.7; RE is one or more kinds of elements selected from rare earth elements other than Sm and Y; La is essential, and M is Mn and / or Co), and a nickel-hydrogen battery using this hydrogen storage alloy.

[0016] As a hydrogen storage alloy having excellent corrosion resistance, an electrode formed using this hydrogen storage alloy, and an alloy powder used for a nickel-hydrogen storage battery, Patent Literature 15 discloses a hydrogen storage alloy powder for an alkaline storage battery characterized by containing a core of the hydrogen storage alloy having a composition represented by the following general formula: Ln 1-w Mg w Ni x Al y T z(wherein Ln represents at least one kind of element selected from a group consisting of La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Ca, Sr, Sc, Y, Ti, Zr and Hf; T represents at least one kind of element selected from a group consisting of V, Nb, Ta, Cr, Mo, Mn, Fe, Co, Ga, Zn, Sn, In, Cu, Si, P and B; the suffixes w, x, y and z are within the ranges respectively expressed as 0.08 ≤ w ≤ 0.13, 0.05 < y < 0.20, 0 ≤ z ≤ 0.5 and 3.15 ≤ x + y + z ≤ 3.50), and a surface layer formed integrally on a surface of the core and in which the concentration of aluminum is reduced compared to the previously described composition.

[0017] As a hydrogen storage alloy powder for an alkaline storage battery that, when applied to an alkaline storage battery, can mitigate a drop in operating voltage and maintain a high operating voltage even after a long period of non-use, especially after a long period of non-use after a charge-discharge cycle, Patent Literature 16 discloses a hydrogen storage alloy having at least two phases containing La, Ni, and Y or a heavy rare earth element. This hydrogen storage alloy is characterized in that the first phase has a composition represented by the following general formula: R1 a R2 b R3 c Ni d R4 e(wherein R1 is at least one or more kinds of elements in which La is essential; R2 is at least one kind of element selected from a group consisting of Y and heavy rare earth elements; R3 is Ca and / or Mg; R4 is at least one kind of element selected from a group consisting of Co, Mn and Al; and a, b, c, d and e are numerical values ​​satisfying a + b + c = 1, 0 ≤ b ≤ 0.3, 0 ≤ c ≤ 0.4, 3.0 < d + e < 4.0, and 0 ≤ e ≤ 1), and that the second phase has a higher concentration of Y or a heavy rare earth element than the first phase and is dispersed in the first phase.

[0018] In order to provide a sealed nickel-hydrogen storage battery having excellent high-rate discharge characteristics and charge-discharge cycle characteristics, Patent Literature 17 discloses a layer in which a nickel content ratio is higher than that of the base layer components and which has a thickness of 50 nm or more but 400 nm or less, and is disposed on a surface of a hydrogen storage alloy powder used for a negative electrode, and a layer in which a nickel content ratio is higher than that of the base layer components and is disposed on a surface of a crack leading to a surface of the hydrogen storage alloy.

[0019] In order to sufficiently improve the performance and charge-discharge cycle characteristics of an alkaline storage battery in a low-temperature environment, Patent Literature 18 discloses a negative electrode for an alkaline storage battery using a hydrogen storage alloy expressed by the following general formula Ln 1-x Mg x Ni y-a-b Al a M b(wherein Ln is at least one kind of element selected from rare earth elements containing Y, and from Zr and Ti; M is at least one kind of element selected from V, Nb, Ta, Cr, Mo, Mn, Fe, Co, Ga, Zn, Sn, In, Cu, Si, P and B; and the conditions of 0.05 < x ≤ 0.30, 0.05 ≤ a ≤ 0.30, 0 ≤ b ≤ 0.50, and 2.8 ≤ y ≤ 3.9 are satisfied).This negative electrode for an alkaline storage battery is characterized in that three layers, a first layer to a third layer, are stacked on a surface of a bulk phase of the hydrogen storage alloy; the first layer, which is close to the bulk phase, contains a larger amount of oxygen than the second layer, which is on top of the first layer, and contains an element soluble in an alkaline solution in a ratio of 10 atomic% or more; the second layer, which is on top of the first layer, has a higher content of Ni than the above-mentioned bulk phase; and the third layer, which is on top of the second layer, has a content of NiO higher than a content of NiO in the second layer.

[0020] Patent Literature 19 discloses an alloy that can provide a nickel-hydrogen secondary battery capable of achieving compatibility between high-rate discharge characteristics and cycle life characteristics. A negative electrode of the nickel-hydrogen secondary battery contains particles of a rare-earth-Mg-Ni-based hydrogen storage alloy containing a rare-earth element, Mg, and Ni. The particles of the hydrogen storage alloy have a rare-earth hydroxide, which is a hydroxide of the rare-earth element, on their surfaces and a specific surface area of ​​0.1 to 0.5 m². 2 / g.

[0021] Patent Literature 20 discloses a hydrogen storage alloy that uses inexpensive Fe to achieve lower price, higher corrosion resistance, and improved charge acceptance in a rare earth magnesium nickel-based hydrogen storage alloy. Specifically, a hydrogen storage alloy represented by the following general formula (La) is reported. a Nd b A c B d ) 1-v Mg v Ni w Al x Fe y T z(A is at least one kind of element selected from Sm and Gd; B is at least one kind of element selected from Pr, Eu, Tb, Dy, Ho, Er, Tm, Yb, Lu, Sc, Zr, Hf, Ca and Y; and T is at least one kind of element selected from V, Nb, Ta, Cr, Mo, Mn, Co, Ga, Zn, Sn, In, Cu, Si, P and B). The suffixes a, b, c and d in the general formula satisfy the relationships 0 ≤ a, 0 ≤ b, 0 ≤ c, 0 ≤ d < 0.1, a + b + c + d = 1, and 0 ≤ z ≤ 0.5. The molar ratio v of Mg in the general formula satisfies 0.10 ≤ v ≤ 0.25; The molar ratio x of Al satisfies 0.10 ≤ x ≤ 0.20; the molar ratio y of Fe satisfies 0.05 ≤ y ≤ 0.15; and further, 3.45 ≤ w + x + y + z ≤ 3.65 is satisfied.

[0022] On the other hand, the non-patent literature 1 La 0,80-x Y x Mg 0,20 Ni2, 80 Mn 0,10 Co 0,55 Al 0,10(x = 0, 0.05, 0.10), in which La was replaced by Y in the hydrogen storage alloy for the purpose of improving the properties.

[0023] For the same purpose, non-patent literature 2 La 0,63 Y 0,20 Mg 0,17 Ni 3,1 CO 0,3 Al 0,1 .

[0024] Non-patent literature 3 describes the influence of Ce on a RE-Mg-Ni (RE: rare earth element)-based hydrogen storage alloy. Specifically, the following alloys are described: (La 0,5 Nd 0,5 ) 0,8 Mg 0,15 NiAl 0,2 , (La 0,45 Nd 0,45 Ce 0,1 ) 0,85 Mg 0,15 Ni 3,3 Al 0,2 , (La 0,4 Nd 0,4 Ce 0,2 ) 0,85 Mg 0,15 Ni 3,3 Al 0,2 , and (La 0,3 Nd 0,3 Ce 0,4 ) 0,85 Mg 0,15 Ni 3,3 Al 0,2, and the results of their evaluation are reported.

[0025] Non-patent literature 4 and 5 report on a hydrogen storage alloy represented by Mm 0,83 Mg 0,17 Ni 2,94-x A1 0,17 Co 0,2 Fe x (0 ≤ x ≤ 0.2) .

[0026] Non-patent literature 6 reports a hydrogen storage alloy represented by La 0,7 Mg 0,3 Co 0,45 Ni 2,55-x Fe x .

[0027] Non-patent literature 7 reports a hydrogen storage alloy represented by La 0,80 Mg 0,20 Ni 2,85 Al 0,11 M 0,53 (M = Ni, Si, Cr, Cu, Fe).

[0028] Non-patent literature 8 reports the properties of a hydrogen storage alloy represented by La2Ni 6,9-x Al 0,1 Fe x (0 ≤ x ≤ 2, 1). LITERATURE LISTPatent literature Patent Literature 1: Japanese Patent Laid-Open No. 11-323469 Patent Literature 2: International Publication No. WO 01 / 048841 Patent Literature 3: Japanese Patent Laid-Open No. 2005-032573 Patent Literature 4: Japanese Patent Laid-Open No. 2009-074164 Patent Literature 5: Japanese Patent Laid-Open No. 2009-108379 Patent Literature 6: Japanese Patent Laid-Open No. 2009-138220 Patent Literature 7: Japanese Patent Laid-Open No. 2000-182608 Patent Literature 8: International Publication No. WO 2007 / 23901 Patent Literature 9: Japanese Patent Laid-Open No. 2009-228096 Patent Literature 10: Japanese Patent Laid-Open No. 2013-134903 Patent Literature 11: Japanese Patent Laid-Open No. 2014-026844 Patent Literature 12: Japanese Patent Laid-Open No. 2017-532446 Patent Literature 13: Japanese Patent Laid-Open No. 2016-069691 Patent Literature 14: Japanese Patent Laid-Open No. 2016-069692 Patent Literature 15: Japanese Patent Laid-Open No. 2014-114476 Patent Literature 16: Japanese Patent Laid-Open No. 2010-080291 Patent Literature 17: Japanese Patent Laid-Open No. 2004-247288 Patent Literature 18: Japanese Patent Laid-Open No. 2010-108910 Patent Literature 19: Japanese Patent Laid-Open No. 2016-012443 Patent Literature 20: Japanese Patent Laid-Open No. 2011-014258 Non-patent literature Non-patent reference 1: L. Zhiping et al., J. Rare Earth 33, page 397 (2015) Non-patent reference 2: ZJ Gao et al., J. Taiwan Institute Chem. Engineers 89, page 183 (2018) Non-patent reference 3: S. Yasuoka et al., J. Power Sources 346, page 56 (2017) Non-patent literature 4: Tiejun Meng et al., Batteries 2, (2016) 34 Non-Patent Literature 5: Tiejun Meng et al., Batteries 3, (2017) 28 Non-Patent Literature 6: Yang-huan Zhang et al., Materials Characterization 61 (2010) 305 Non-Patent Literature 7: XU Guochang et al., J. Rare Earth 27 (2009) 250 Non-Patent Reference 8: Hideaki Sodeyama et al.: Ibaraki District Conference. Page 137 (jointly organized by the Kanto Branch of the Japan Society of Mechanical Engineers and the Japan Society of Precision Engineering, published on September 28, 2007) SUMMARY OF THE INVENTIONTechnical Problem

[0029] However, in the above-described technologies disclosed in Patent Literature 1 and Patent Literature 2, the alloys have not been optimized enough for the batteries to be incorporated into hybrid electric vehicles.

[0030] In the technology disclosed in Patent Literature 3, a new problem arises that the use of a hydrogen storage alloy with a high hydrogen equilibrium pressure leads to a reduction in the charge / discharge cycle life.

[0031] In the technology disclosed in Patent Literature 4, although the alloy contains a relatively large amount of Sm and thus uses a cheaper element than Pr and Nd, this technology cannot provide a hydrogen storage alloy that is inexpensive and has excellent durability.

[0032] In the technology disclosed in Patent Literature 5, the alloy contains relatively large amounts of La and Sm, thus using less expensive elements than Pr and Nd as the main components. However, this technology cannot provide a hydrogen storage alloy that is inexpensive and has excellent durability. In particular, the implementation examples mention Zr as essential, and the B / A ratio is only 3.6. While this literature mentions that the hydrogen equilibrium pressure reduced by the increased La content is raised to the point where the alloy can be used for a battery, setting a composition rich in inexpensive La is often insufficient.

[0033] The alkaline storage battery using the hydrogen storage alloy disclosed in Patent Literature 6 is unable to achieve the compatibility between the following three features of small size, high performance, and long cycle life, in other words, between the discharge characteristics and the cycle life characteristics, which are challenging for on-board applications, so the alloy is insufficient as a hydrogen storage alloy for on-board alkaline storage batteries.

[0034] The hydrogen storage alloy disclosed in Patent Literature 7 is an AB5 alloy (MmNi 4,0 Co 0,4 Mn 0,3 Al 0,3 While the discharge properties are improved by pulverization, the practical use of this alloy for on-board applications is difficult in terms of durability, etc., and further improvements in properties are required.

[0035] The hydrogen storage alloy disclosed in Patent Literature 8 contains a relatively large amount of Y, 2 to 10 mol% of the hydrogen storage alloy, which makes it expensive. In addition, the hydrogen storage alloy tends to and desorption, pulverization tends to intensify, so that corrosion progresses, indicating that the durability-improving effect is insufficient.

[0036] While the hydrogen storage alloy disclosed in Patent Literature 9 mainly aims to mitigate a drop in operating voltage after a long period of non-use, the basic cycle life and discharge capacity are not well balanced enough, and furthermore, the cost of the constituent rare earth elements is high.

[0037] Although the hydrogen storage alloy disclosed in Patent Literature 10 aims to achieve high performance by including Y as an essential element, it fails to sufficiently reduce costs. Furthermore, the discharge capacity is not sufficiently increased, so when the alloy is used in a battery, the battery does not have sufficient properties. Although low-temperature performance can be ensured, cycle life is also challenging.

[0038] While the hydrogen storage alloy disclosed in Patent Literature 11 aims to realize a nickel-hydrogen battery that has a high capacity and is excellent in both self-discharge and cycle life, it is not sufficient to achieve a high capacity and also needs to be further improved in terms of cycle life.

[0039] Although the hydrogen storage alloy disclosed in Patent Literature 12 aims at high durability by reducing pulverization, the specific composition contains a large amount of Y. Therefore, this alloy poses a challenge in terms of cost as well as a challenge in terms of cycle life because pulverization progresses during hydrogen storage and desorption, which requires further improvement of the properties.

[0040] While the hydrogen storage alloy disclosed in Patent Literature 13 aims to improve the charge-discharge cycle characteristics by improving corrosion resistance and durability, the cycle characteristics achieved by the disclosed hydrogen storage alloy containing a relatively large amount of Sm are still insufficient, and further improvement of the properties, including improvement of durability, is required.

[0041] The hydrogen storage alloy disclosed in Patent Literature 14 aims to improve the cycle life, but the alloy is insufficient to improve the battery properties from the viewpoint of balance with the discharge capacity and therefore needs further improvements in the properties.

[0042] While the hydrogen storage alloy disclosed in Patent Document 15 aims to improve the charge-discharge cycle characteristics by improving corrosion resistance and durability, it is not easy to form the second phase in which the concentration of Y or a heavy rare earth element is controlled, so that truly effective battery characteristics cannot be achieved.

[0043] Although the hydrogen storage alloy disclosed in Patent Literature 16 aims to improve the charge-discharge cycle characteristics by improving corrosion resistance and durability, the disclosed alloy contains Nd and Pr and is relatively expensive. Even if the surface condition is controlled by alkaline or acid treatment, adequate cycle and rate characteristics cannot be achieved.

[0044] While the hydrogen storage alloy shown in Patent Literature 17 aims to improve the performance characteristics and the charge-discharge cycle characteristics at low temperatures, even if the surface condition is controlled by the alkaline or acidic treatment disclosed in this patent, adequate cycle characteristics cannot be achieved, so further improvement of the properties is required.

[0045] The hydrogen storage alloy disclosed in Patent Document 18 aims to improve the performance and low-temperature charge / discharge cycle characteristics. The surface condition of the relatively inexpensive hydrogen storage alloy is controlled by heat treatment of the alloy particle surfaces in air. While low-temperature properties are said to be preferable, the capacity and cycle characteristics are not yet well balanced, so further property improvement is required.

[0046] The hydrogen storage alloy used in Patent Literature 19 aims to improve the charge-discharge cycle characteristics by improving corrosion resistance and durability. While it aims to achieve compatibility between rate characteristics and cycle life characteristics with a limited specific surface area, the disclosed alloy, which contains a large amount of Sm, exhibits insufficient durability after alkaline treatment and therefore requires further property improvement.

[0047] While the technology disclosed in Patent Literature 20 is characterized by the use of inexpensive Fe, the studies are based on an alloy containing expensive Nd. Consequently, the alloy cannot be inexpensive, and durability also needs to be further improved.

[0048] For the hydrogen storage alloy described in Non-Patent Literature 1, the cycle properties are still insufficient, and since a certain amount of Co is included, the cost is another issue to consider.

[0049] The hydrogen storage alloy described in Non-Patent Literature 2 has the lowest effect among the rare earths in which La has been similarly substituted and needs further improvement in its properties.

[0050] Non-Patent Literature 3 concludes that a rare earth Mg-Ni-based alloy containing Ce deteriorates significantly in a battery due to its low hydrogen storage and desorption capacities and its susceptibility to pulverization as a result of repeated hydrogen storage and desorption.

[0051] Non-patent literature 4 and 5 report on Mm 0,83 Mg 0,17 Ni2,94-x Al 0,17 Co 0,2 Fe x (0 ≤ x ≤ 0.2) from material properties to battery properties. However, the cycling properties of the hydrogen storage alloy disclosed in non-patent references 4 and 5 are insufficient for practical use, and this alloy is covalent and not inexpensive, so further cost reduction and high durability must be made compatible.

[0052] In the non-patent literature 6 the properties of La 0,7 Mg 0,3 Co 0,45 Ni 2,55-x Fe x (0 ≤ x ≤ 0.4) is disclosed, but the cycle properties are insufficient and further improvements of the properties are required for practical use.

[0053] In the alloy La 0,80 Mg 0,20 Ni 2,85 Al 0,11 M 0,53(M = Ni, Si, Cr, Cu, Fe) disclosed in Non-Patent Literature 7, the discharge capacity is low and the cycle life is not sufficient, so that an improvement of the properties is desired.

[0054] What about the alloy La2Ni 6,9-x Al 0,1 Fe x Regarding the alloy (0 ≤ x ≤ 2.1) disclosed in Non-Patent Literature 8, although the alloy itself is inexpensive, the properties presented with respect to the alloy are only data on a gas-solid phase reaction related to hydrogen storage and desorption. Therefore, the alloy described in Non-Patent Literature 8 is an alloy that has insufficient properties as a hydrogen storage alloy for an alkaline storage battery. From these technical perspectives, a low-cost hydrogen storage alloy that has preferable properties as an alloy for a battery has been required.

[0055] The present invention has been developed in view of these problems faced by the conventional technologies and aims to provide a hydrogen storage alloy particularly suitable for an on-board nickel-hydrogen battery (alkaline storage battery), a battery using this alloy, and a vehicle equipped with this battery. Problem solving

[0056] In order to achieve the above-mentioned goal, an alloy having a crystal structure whose main phase has the crystal structures of an A2B7 type structure, an A5)B 19-type structure and an AB3-type structure, and which has a specific component composition containing Y (rare earth element). Furthermore, the substitution of Fe is used to achieve low cost and significantly improve the charge / discharge cycle life characteristics. In this way, the discharge capacity and charge / discharge cycle life characteristics of the alkaline storage battery can be balanced with each other at a low cost. This finding leads to the development of the present invention.

[0057] The present invention is, on the one hand, a hydrogen storage alloy used for an alkaline storage battery.

[0058] This hydrogen storage alloy has a main phase that has the crystal structures of an A2B7 type structure, an A5)B 19-type structure and an AB3-type structure and satisfies the conditions of the following general formula (1): [Chemical Formula 1] (La 1-a-b Y a R b ) 1-c Mg c Ni d Al e Cr f Fe g (1), where R and the suffixes a, b, c, d, e, f and g are as follows: R is one or both of the elements Sm and Ce, 0 <a≤0,12, 0≤b≤0.12, 0.13≤c≤0.27, 3.20≤d+e+f+g≤3.75, 0≤e≤0.14, 0≤f≤0.05, and 0≤g≤0.35.

[0059] The hydrogen storage alloy for an alkaline storage battery in which the general formula (1) further satisfies the following condition may be a preferred solution: the suffixes a, b, c, d, e, f and g in the general formula (1) are as follows: 0 <a≤0,10, 0 <b≤0,10, 0.14≤c≤0.26, 3.25≤d+e+f+g≤3.70, 0≤e≤0.13, 0≤f≤0.04, and 0≤g≤0.30.

[0060] The hydrogen storage alloy for an alkaline storage battery according to the present invention specified below may be a preferred solution: (a) The hydrogen storage alloy has a hydrogen storage capacity H / M (H is the number of hydrogen atoms, M is the number of metal atoms) of 0.94 or more when a hydrogen pressure of up to 1 MPa is applied at 80°C, and a hydrogen pressure P0.5 is 0.025 MPa or more but 0.12 MPa or less when the hydrogen storage capacity H / M is 0.5 during hydrogen desorption; (b) the hydrogen storage alloy, the particle size of which has been adjusted to be in a range of 150 µm or more but 1 mm or less, has a volume-average particle diameter MV of 75 µm or more after repeated hydrogen storage and desorption, wherein the volume-average particle diameter MV is measured after repeating five times a cycle in which, for hydrogen storage, a hydrogen pressure of up to 3 MPa is applied and maintained at 80°C for one hour and, for hydrogen desorption, an evacuation is carried out and the pressure is reduced to or below 0.01 MPa at 80°C and maintained at for one hour; (c) in the hydrogen storage desorption properties at 80°C of the hydrogen storage alloy, a value calculated as the plateau slope B during hydrogen desorption after storage and represented by the following relational expression (A) is in a range of 1.3 or more but 3.0 or less: Plateau slope B=[log(P0.7 / P0.3)] / 0.4(A), where P0.7 is a hydrogen pressure [MPa] when the hydrogen storage capacity (H / M) = 0.7, and P0.3 is a hydrogen pressure [MPa] when the hydrogen storage capacity (H / M) = 0.3; (d) in an X-ray diffraction measurement of the hydrogen storage alloy using Cu-Kα radiation as an X-ray source, the ratio ζ / ε of the diffraction intensity ζ of the (101) plane of an AB5 phase to the diffraction intensity ε of the strongest diffraction peak present in a range of a diffraction angle 2θ of 40 to 45° is 0.08 or less; (e) in the hydrogen storage alloy, a layer of an oxide or hydroxide containing Y is present on at least a part of a surface of the hydrogen storage alloy; (f) in the hydrogen storage alloy, the layer of an oxide or hydroxide containing Y present on at least a part of the surface of the hydrogen storage alloy has a thickness of 500 nm or less where the layer is in close contact with surfaces of alloy particles. (g) an oxide or hydroxide present on at least a part of the surface of the hydrogen storage alloy consists mainly of a rare earth metal contained in the hydrogen storage alloy; (h) the BET specific surface area of ​​the hydrogen storage alloy in which an oxide or hydroxide is present on at least part of the surface of the hydrogen storage alloy is more than 0.5 m 2 / G; (i) furthermore, the pore volume is 0.013 cm 3 / g or less and the average pore diameter is 40 nm or less.

[0061] The present invention, on the other hand, provides an alkaline storage battery that uses one of the above-described hydrogen storage alloys for a negative electrode, and that is either a battery that is installed in a hybrid electric vehicle having a motor as a drive source and supplies power to the motor, or a battery that is installed in a motor vehicle with a start-stop function that starts the engine by a starter motor and supplies power to the starter motor.

[0062] Thirdly, the present invention provides a vehicle having, as a power source for the engine, an alkaline storage battery using one of the hydrogen storage alloys described above as a negative electrode. Preferred effects of the invention

[0063] The hydrogen storage alloy for an alkaline storage battery and the alkaline storage battery using this hydrogen storage alloy according to the present invention have a high power density and have a particularly excellent charge-discharge cycle life (durability) and thus excellent discharge capacity characteristics, which enables a sufficiently high discharge even under on-board conditions.

[0064] The hydrogen storage alloy for an alkaline storage battery according to the present invention exhibits specific hydrogen storage properties. The average particle diameter of the alloy particles pulverized from the hydrogen storage alloy for an alkaline storage battery after repeated hydrogen storage and desorption is within a predetermined range. The content of the AB5 phase is controlled to be a certain amount or less. This hydrogen storage alloy exhibits improved durability while maintaining electrical properties, and is therefore preferred.

[0065] That is, the hydrogen storage alloy for an alkaline storage battery according to the present invention can reduce the probability that the alloy develops cracks even under conditions such as hydrogen storage and desorption, and that the cracking intensifies and leads to pulverization.

[0066] Furthermore, in the hydrogen storage alloy for an alkaline storage battery according to the present invention, a layer of an oxide or hydroxide containing Y or consisting mainly of a rare earth element comes into close contact with alloy particles as a surface layer. This makes it possible to reduce the amount of Al, which improves corrosion resistance, and thus increase the discharge capacity of the alkaline storage battery.

[0067] That is, the surface layer formed on at least a part of the surface of the hydrogen storage alloy has excellent alkaline corrosion resistance because it is composed of a hydroxide or oxide mainly formed by an element such as Y or a rare earth element forming part of the alloy.

[0068] In addition, this surface layer formed on the surface of the hydrogen storage alloy has a small pore volume and a small average pore diameter (size), which reduces the probability of crack occurrence and thus can further improve the corrosion resistance of the hydrogen storage alloy.

[0069] The alkaline storage battery according to the present invention can achieve downsizing and weight reduction, and when this alkaline storage battery is installed in a vehicle such as an automobile, a hybrid electric vehicle (HEV), etc., which has high kinematic performance and high fuel efficiency, it can be provided. Short description of the characters [ Fig. 1] Fig.1 is a partially cutaway perspective view of an alkaline storage battery using a hydrogen storage alloy of the present invention. [ Fig. 2] Fig. Figure 2 is an example of DZT properties related to the hydrogen storage alloy of the present invention. [ Fig. 3] Fig. 3 is an example of an X-ray diffraction measurement result regarding the hydrogen storage alloy of the present invention. Description of the embodiments

[0070] An embodiment according to the present invention will be described below. An alkaline storage battery with a hydrogen storage alloy according to the embodiment is described with reference to Fig. 1 described. Fig. 1 is a perspective partial cutaway view showing an embodiment of the battery. As shown in Fig.1, an alkaline storage battery 10 is a storage battery including, within a casing 4, a group of electrodes composed of a nickel positive electrode 1 containing nickel hydroxide (Ni(OH)2) as the main positive electrode active material, a negative electrode 2 containing a hydrogen storage alloy using the hydrogen storage alloy (MH) according to the embodiment as the negative electrode active material, and a separator 3, together with an electrolyte layer (not shown) filled with an alkaline electrolyte solution.

[0071] The alkaline storage battery 10 is a so-called nickel-metal hydride battery (Ni-MH battery; hereinafter also referred to as “nickel-hydrogen battery”) in which the following reactions take place. Positive electrode: NiOOH + H2O + e - = Ni(OH)2+OH - Negative electrode: MH + OH - + e - = M + H2O + e -[Chemical Formula 2] [Hydrogen storage alloy]

[0072] The following describes the hydrogen storage alloy used for the negative electrode of the alkaline storage battery according to the embodiment. The hydrogen storage alloy for an alkaline storage battery (hereinafter also referred to as "hydrogen storage alloy") according to the embodiment is a hydrogen storage alloy used for an alkaline storage battery. This hydrogen storage alloy is characterized by having a main phase that exhibits the crystal structures of an A2B7 type structure, an A5B 19 -type structure and an AB3-type structure, and is represented by the following general formula (1): [Chemical Formula 3] (La 1-a-b Y a R b ) 1-c Mg c Ni d Al e Cr f Fe g (1), where R and the suffixes a, b, c, d, e, f and g are as follows: R is one or both of the elements Sm and Ce, 0 <a≤0,12, 0≤b≤0.12, 0.13≤c≤0.27, 3.20≤d+e+f+g≤3.75, 0≤e≤0.14, 0≤f≤0.05, and 0≤g≤0.35.

[0073] The crystal structures of the A2B7-type structure, the A5B 19 -type structure and the AB3-type structure are each a Ce2Ni 7- type and a Gd2Co7 type; a Pr5Co 19 -Type and a Ce5Co 19 -type; or a CeNi3- Typ and a PuNi3 type.

[0074] In this embodiment, it is preferable that the hydrogen storage alloy is a hydrogen storage alloy for an alkaline storage battery whose general formula (1) further satisfies the following condition: the suffixes a, b, c, d, e, f and g in the general formula (1) are as follows: 0 <a≤0,10, 0 <b≤0,10, 0.14≤c≤0.26, 3.25≤d+e+f+g≤3.70, 0≤e≤0.13, 0≤f≤0.04, and 0 <g≤0,30.

[0075] When used as the negative electrode of an alkaline storage battery, the hydrogen storage alloy represented by general formula (1) imparts high discharge capacity and long charge / discharge cycle life to the alkaline storage battery. Thus, the hydrogen storage alloy represented by general formula (1) contributes to the downsizing, weight reduction, and durability improvement of the alkaline storage battery.

[0076] The following describes reasons for limiting the component composition of the hydrogen storage alloy according to the embodiment.

[0077] Rare earth element: La 1-a-b Y a R b (where 0 < a ≤ 0.12, 0 ≤ b ≤ 0.12, preferably 0 < a ≤ 0.10, 0 < b ≤ 0.10)

[0078] The hydrogen storage alloy according to this embodiment contains rare earth elements as elements of component A of the A2B7 type structure, the A5B 19 -type structure and the AB3-type structure. Of the rare earth elements, the two elements La and Y are essential as basic components for providing hydrogen storage capacity. Since La and Y have different atomic radii, the hydrogen equilibrium pressure can be controlled by the ratio between these components, and the hydrogen equilibrium pressure proportional to the battery voltage can be arbitrarily adjusted. The value a of the atomic ratio of Y among the rare earth elements is in a range greater than 0 but not greater than 0.12.

[0079] When the value a is within this range, a hydrogen equilibrium pressure suitable for an alkaline storage battery can be easily adjusted, and favorable corrosion resistance and properties less susceptible to pulverization of the hydrogen storage alloy can be achieved. As a result, a long service life of the alkaline storage battery can be achieved.

[0080] When the value a exceeds 0.12, the pulverization of the hydrogen storage alloy associated with hydrogen storage and desorption progresses, so that despite the corrosion resistance-enhancing effects, the service life of the alkaline storage battery gradually decreases. The value a is preferably 0.10 or less, and more preferably 0.003 or more. Y plays an important role in improving the durability of the hydrogen storage alloy by being present as an oxide or hydroxide within a surface layer formed by an oxide layer or a hydroxide layer and present on at least a part of the surface of the hydrogen storage alloy.

[0081] On the other hand, R is one or both of Ce and Sm, and together with Y, it contributes to the control of hydrogen equilibrium pressure and the improvement of corrosion resistance of the hydrogen storage alloy. The value b of the total amount of the atomic ratio of R among the rare earth elements is in a range including 0 and not exceeding 0.12. When hydrogen equilibrium pressure control and durability are considered with Y and R in combination, a value b exceeding 0.12 increases the pulverization of the hydrogen storage alloy associated with hydrogen storage and desorption, which may lead to reduced durability of the alkaline storage battery. The value b is preferably 0.10 or less, and more preferably 0.005 or more.

[0082] It is preferable that R is essential together with Y, that is, that one or both of Ce and Sm are essential, and it is even more preferable that Ce is used in particular. In this case, it is preferable that the value b is 0.10 or less to control the properties, including the hydrogen storage desorption properties, of the hydrogen storage alloy that are relevant to battery properties.

[0083] With a high La content composition, the discharge capacity of the alkaline storage battery becomes high, and when La is combined with another element, the discharge capacity characteristics of the alkaline storage battery are further improved. While Pr and Nd are not necessarily used as rare earth elements, they may be present in an unavoidable impurity level. Mg: Mg c (where 0.13 ≤ c ≤ 0.27, preferably 0.14 ≤ c ≤ 0.26)

[0084] Mg is an essential element in this embodiment, which is an element of component A of the A2B7-type structure, the A5)B 19 -type structure and the AB3-type structure. Mg contributes to improving the discharge capacity characteristics and charge-discharge cycle life of an alkaline storage battery using the hydrogen storage alloy. The value c, which represents the atomic ratio of Mg in component A, is in a range of 0.13 or more but 0.27 or less.

[0085] If the value c is below 0.13, the hydrogen desorption capacity of the hydrogen storage alloy decreases, so that the discharge capacity of the alkaline storage battery decreases.

[0086] However, if the value c exceeds 0.27, the pulverization of the hydrogen storage alloy associated with hydrogen storage and desorption will be particularly exacerbated, resulting in a deterioration of the charge-discharge cycle life, i.e., the durability of the alkaline storage battery. The value c is preferably in a range of 0.14 or more but 0.26 or less. Ni: Ni d

[0087] Ni is a major element of component B of the A2B7-type structure, the A5)B 19 -type structure and the AB3-type structure. The value d of the atomic ratio of Ni to component A will be described later. Al: Al e (where 0 ≤ e ≤ 0.14 if Fe is essential, 0.03 ≤ e ≤ 0.13 if Fe is not essential)

[0088] Al is an element that is part of component B of the A2B7-type structure, the A5B 19-type structure and the AB3-type structure. Al is effective in adjusting the hydrogen equilibrium pressure, which is relevant to the battery voltage, and can improve corrosion resistance, thus improving the durability of the hydrogen storage alloy, that is, an effect on the charge-discharge cycle life of the alkaline storage battery.

[0089] To reliably achieve these effects, the value e, which indicates the atomic ratio of Al to component A, is in a range of 0.03 or more but 0.14 or less.

[0090] If the value e is below 0.03, the corrosion resistance of the hydrogen storage alloy is insufficient and consequently the service life of the alkaline storage battery in the charge / discharge cycle is also insufficient.

[0091] However, if the value e exceeds 0.14, the discharge capacity of the alkaline storage battery decreases, and the pulverization of the hydrogen storage alloy associated with hydrogen storage and desorption progresses, resulting in problems with the durability of the storage battery. A preferred value of e is in the range of 0.04 or more but 0.13 or less.

[0092] On the other hand, in the case where Fe is included as an essential element for component B of the hydrogen storage alloy, the corrosion-resistant effect of the hydrogen storage alloy imparted by Al can be realized by Fe. Therefore, the value e is in a range of 0 or more but 0.13 or less.

[0093] In the case where the hydrogen storage alloy according to the embodiment is a powder composed of fine-diameter alloy particles, the Al content in the alloy is sufficient to a lesser extent within the range of the embodiment. Therefore, the Al content in the hydrogen storage alloy can be reduced, and the discharge capacity of the alkaline storage battery can be increased accordingly. Cr: Cr f (where 0 ≤ f ≤ 0.05, preferably 0 ≤ f ≤ 0.04)

[0094] Cr is an element that is part of component B in the A2B7 type structure, the A5B 19-type structure and the AB3-type structure. Cr is effective in adjusting the hydrogen equilibrium pressure, which is relevant to the battery voltage, and, together with Al, contributes to improving the corrosion resistance of the hydrogen storage alloy. In particular, Cr has the effect of improving the durability of the alkaline storage battery, that is, an effect on the charge-discharge cycle life of the alkaline storage battery. To reliably achieve these effects, the value f, which represents the atomic ratio of Cr relative to component A, is in a range that includes 0 and does not exceed 0.05. Although Cr is not absolutely essential, in synergy with Y and Al, it increases the corrosion resistance of the hydrogen storage alloy and improves its service life.

[0095] However, if the amount of Cr exceeds the value f of 0.05, cracking in the hydrogen storage alloy associated with hydrogen storage and desorption is increased, and consequently, the durability of the alkaline storage battery decreases and the charge-discharge cycle life characteristics of the alkaline storage battery become inadequate. The value f is preferably 0.04 or less, and more preferably 0.003 or more.

[0096] When the hydrogen storage alloy according to the embodiment is a powder composed of small-diameter alloy particles, the Cr content contained in the alloy is sufficient to a lesser extent within the scope of the embodiment. Therefore, the Cr content in the hydrogen storage alloy can be reduced, and the discharge capacity of the alkaline storage battery can be increased accordingly. Fe: Fe g (where 0 ≤ g ≤ 0.35)

[0097] Fe is included as component B of the hydrogen storage alloy, whose main phase is selected from the A2B7 type crystal structure and the A5B 19 -type crystal structure, or both. That is, Fe can be included as an essential element in the hydrogen storage alloy according to the present invention. Fe is effective in controlling the hydrogen equilibrium pressure, which is relevant to the battery voltage of the alkaline storage battery, and can significantly improve corrosion resistance, thus having an effect on improving the durability of the hydrogen storage alloy, that is, an effect on the charge / discharge cycle life characteristics of the alkaline storage battery.

[0098] By using Fe and Y as essential elements among the components of the hydrogen storage alloy according to the present invention, the hydrogen equilibrium pressure can be easily adjusted to a pressure suitable for an alkaline storage battery, and high corrosion resistance, high durability, and low price can be achieved.

[0099] In order to reliably exert these effects, the value g, which represents the atomic ratio of Fe in the general formula (1), is in a range of 0 or more but 0.35 or less.

[0100] If the value of g exceeds 0.35, the discharge capacity of the alkaline storage battery decreases. A preferred value of g is above 0 but not exceeding 0.30. In the case of a nickel-hydrogen battery, the hydrogen storage alloy used for the negative electrode is used in an amount 20 to 30% higher than normal, which is called reservoir, within the positive electrode regulations for battery capacity, assuming alkaline corrosion of the hydrogen storage alloy due to an alkaline solution, which is an electrolyte solution.

[0101] On the other hand, adopting the hydrogen storage alloy according to the embodiment, which contains Fe as an essential element for an alkaline storage battery, can maximally mitigate the capacity deterioration of the battery's discharge capacity. That is, in the alkaline storage battery containing the hydrogen storage alloy according to the embodiment, the amount of hydrogen storage alloy in the part corresponding to the reservoir, where an additional amount of the alloy is used, can be significantly reduced, since the discharge capacity decreases less under the assumption of alkaline corrosion.

[0102] That is, when Fe is used as an essential element in the hydrogen storage alloy according to the embodiment by replacing part of the expensive Ni in the component composition with inexpensive Fe, not only the material cost required to manufacture the hydrogen storage alloy but also the amount of the hydrogen storage alloy contained in the alkaline storage battery can be maximally reduced. Consequently, by adopting the hydrogen storage alloy according to the embodiment, which contains inexpensive and readily available Fe as an essential element for an alkaline storage battery, a cost reduction in the manufacturing cost of the alkaline storage battery can be realized. Ratio between component A and component B: 3.20 ≤ d + e + f + g ≤ 3.75 (preferably 3.25 ≤ d + e + f + g ≤ 3.70)

[0103] The stoichiometric ratio, ie the molar ratio of component B (Ni, Al and Cr) to component A of the A2B7 type structure, the A5B 19 -type structure and the AB3-type structure, that is, the value of d + e + f + g shown in the general formula is in a range of 3.20 or more but 3.75 or less.

[0104] When the value of d + e + f + g is less than 3.20, a sub-phase, that is, an AB2 phase, increases in the hydrogen storage alloy, and in particular, the discharge capacity of the alkaline storage battery decreases.

[0105] The AB2 phase formed in the compositional range of the hydrogen storage alloy according to the embodiment has properties such that hydrogen can be stored but not easily desorbed. Consequently, the hydrogen storage capacity of the hydrogen storage alloy decreases, and the discharge capacity of the alkaline storage battery decreases.

[0106] Conversely, if the value of d + e + f + g exceeds 3.75, the AB5 phase in the hydrogen storage alloy increases, and the pulverization of the hydrogen storage alloy powder, which is associated with hydrogen storage and desorption, increases. As a result, the durability of the hydrogen storage alloy, i.e., the cycle life of the alkaline storage battery, decreases. The value of d + e + f + g is preferably in a range of 3.25 or more but 3.70 or less.

[0107] It is preferable that the hydrogen storage alloy according to the embodiment has the above-described composition, and that a 50% mass sub-fraction particle diameter D50 of alloy particles pulverized from this hydrogen storage alloy is in a range of 3 μm or more but 30 μm or less, and that a 90% mass sub-fraction particle diameter D90 thereof is in a range of 8 μm or more but 60 μm or less.

[0108] When the average particle diameter of the alloy particles pulverized from the hydrogen storage alloy according to the embodiment is within the predetermined range, the hydrogen storage alloy has excellent hydrogen storage desorption properties and a long service life. [Hydrogen storage desorption properties of the hydrogen storage alloy]

[0109] The hydrogen storage capacity H / M (H is the number of hydrogen atoms, M is the number of metal atoms) of the hydrogen storage alloy of the embodiment is preferably 0.94 or more when a hydrogen pressure of up to 1 MPa is applied at 80°C.

[0110] Further, it is preferable that the hydrogen pressure is 0.025 MPa or more but 0.12 MPa or less when the hydrogen storage capacity (H / M: the ratio between the number of hydrogen atoms (H) and metal atoms (M)) during hydrogen desorption at 80°C is 0.5 (P0.5, hereinafter referred to as “hydrogen equilibrium pressure”).

[0111] If the hydrogen storage capacity is within this range, the battery can operate smoothly under different temperature conditions. Fig.Figure 2 shows a specific example of pressure-composition-temperature (DPT) properties that measure hydrogen equilibrium pressure and hydrogen storage capacity.

[0112] When improving the properties of a nickel-hydrogen battery, the discharge capacity is largely determined by the component composition of the hydrogen storage alloy. On the other hand, the durability of the hydrogen storage alloy is influenced by the degree of pulverization of the hydrogen storage alloy, which occurs during hydrogen storage and desorption, the elution of hydrogen storage alloy components into an alkaline aqueous solution, etc. This depends on the component composition of the hydrogen storage alloy, the ratio of an alloy phase formed based on heat treatment, and the properties of the alloy phase.

[0113] From these technical perspectives, in the development of a hydrogen storage alloy that meets the requirements of high durability, studies have been intensively conducted to evaluate the cracking of a hydrogen storage alloy due to repeated hydrogen storage and desorption.

[0114] Consequently, to evaluate cracking in a hydrogen storage alloy, alloy particles were used that were mechanically ground from the hydrogen storage alloy and sieved to 150 µm or more but 1 mm or less. Hydrogen was applied at a pressure of up to 3 MPa at 80°C to cause the alloy to store the hydrogen, and then evacuated to cause the alloy to desorb the hydrogen.

[0115] The particle size distribution of the alloy particles after repeating this cycle five times was evaluated, and a volume-average particle diameter (MV) was used as a representative value. This resulted in the discovery of a hydrogen storage alloy with particularly excellent durability. The detailed conditions are as follows. Here, "sieved to 150 µm or more but 1 mm or less" means that they are above a sieve with 150 µm openings and below a sieve with 1 mm openings.

[0116] Specifically, 7 g of the hydrogen storage alloy is placed into a measuring holder of a DZT evaluation device and evacuated at 80°C (0.01 MPa or less) for one hour. Afterward, while maintaining the temperature, a hydrogen storage desorption measurement (DZT property evaluation) is performed in a hydrogen pressure range of 0.01 to 3 MPa.

[0117] Then, the system is evacuated (0.01 MPa) for one hour, and hydrogen gas is introduced at a pressure of up to 3 MPa. This pressure is maintained for one hour to force the hydrogen storage alloy to store hydrogen almost to its maximum capacity. The system is then evacuated (0.01 MPa) for one hour to allow the hydrogen storage alloy to desorb the hydrogen. This cycle is repeated three times.

[0118] Finally, as in the first cycle, a hydrogen storage desorption measurement (DZT property evaluation) is performed in a hydrogen pressure range of 0.01 to 3 MPa. The difference between the hydrogen storage and desorption in the first and fifth cycles and the hydrogen storage and desorption in the second to fourth cycles is the processing time. During the hydrogen storage and desorption in the second to fourth cycles, the hydrogen pressure is applied at a time up to 3 MPa, so the required time is shorter.

[0119] After the hydrogen storage desorption cycle is performed a total of five times, the hydrogen storage alloy powder is sampled, and particle size distribution measurement is performed. Preferably, the range of the volume-average particle diameter (MV) of the alloy particles pulverized from the hydrogen storage alloy after repeated hydrogen storage and desorption is 75 μm or more. The volume-average particle diameter (MV) of the alloy particles within this range is preferable because the pulverization of the hydrogen storage alloy, which accompanies charging and discharging, does not progress when the hydrogen storage alloy is actually incorporated into an alkaline storage battery. Thus, it is found that the hydrogen storage alloy according to the embodiment exhibits excellent durability combined with its advantageous corrosion resistance in an aqueous alkaline solution.

[0120] The volume-average particle diameter MV of the alloy particles can be measured with a laser diffraction particle size distribution meter, and the measuring device used can be, for example, the MT3300EXII from MicrotracBEL Corp.

[0121] Cracking in hydrogen storage alloys is believed to be due to distortion of the alloy's crystal lattice due to the expansion and contraction associated with hydrogen storage and desorption. When the hydrogen storage capacity is low, the expansion and contraction of the crystal lattice are small, making the hydrogen storage alloy less likely to be pulverized.

[0122] On the other hand, a low hydrogen storage capacity of the hydrogen storage alloy is not preferred because the discharge capacity as a battery material becomes low and reaching a certain battery capacity leads to an increase in size and cost of the battery.

[0123] Therefore, as a condition required to realize the volume-average particle diameter MV of the alloy particles pulverized from the hydrogen storage alloy after repeated hydrogen storage and desorption as described above, it is preferable that the value of the index H / M (the atomic ratio between hydrogen H and metal M) of the hydrogen storage capacity at 1 MPa obtained from a DZT measurement at 80°C be set to 0.94 or more. When the hydrogen storage capacity is within this range, the negative electrode alkaline storage battery containing such a hydrogen storage alloy as the negative electrode active material can maintain sufficient discharge capacity, and it can be said that a hydrogen storage alloy with high durability has been obtained.

[0124] As in Fig.As shown in Figure 2, a plateau slope B during hydrogen desorption after storage, expressed by the relational expression (A) below, was calculated based on a hydrogen pressure P0.3 (MPa) when the hydrogen storage capacity H / M = 0.3 and a hydrogen pressure P0.7 (MPa) when the hydrogen storage capacity H / M = 0.7. That is, the plateau slope B is a value calculated by the above-mentioned relational expression (A) by measuring hydrogen pressures when the hydrogen storage capacity H / M = 0.7 and the hydrogen storage capacity H / M = 0.3 on a hydrogen desorption curve. Plateau slope B=[log(P0.7 / P0.3)] / 4.0

[0125] That is, it is preferable that the plateau slope B, which is a value calculated by [log(P0.7 / P0.3)] / 0.4, expressed by the above relational expression (A), is in a range of 1.3 or more but 3.0 or less. If the plateau slope B is less than 1.3, the expansion of the crystal lattice of the hydrogen storage alloy during hydrogen storage is likely to occur in one direction; in other words, the crystal lattice is likely to expand and shrink anisotropically. Due to the strain caused in the crystal lattice of the hydrogen storage alloy, cracking in the hydrogen storage alloy may increase.

[0126] However, if the plateau slope B exceeds 3.0, the hydrogen storage capacity is less likely to increase even when hydrogen pressure is applied, which may lead to a lower discharge capacity of the alkaline storage battery. The plateau slope B value is preferably 1.35 or more, but 2.95 or less. [Ratio of X-ray diffraction intensity]

[0127] In the hydrogen storage alloy of the embodiment, it is preferable that ζ / ε ≤ 0.08 in an X-ray diffraction measurement using Cu-Kα radiation as the X-ray source, where ζ / ε is a ratio of the diffraction intensity (ζ) of the (101) plane of the AB5 phase to the diffraction intensity (ε) of the strongest diffraction peak present in a diffraction angle range of 40 to 45°. If the ratio ζ / ε exceeds 0.08, the service life of the alkaline storage battery may deteriorate during the charge and discharge cycle. The ratio ζ / ε is preferably 0.05 or less.

[0128] Fig. Figure 3 is a diagram showing an example of an X-ray diffraction measurement result regarding the hydrogen storage alloy according to the embodiment. A diffraction line is calculated based on the XRD diagram in Fig.3 specifically. The ratio ζ / ε is a ratio between the height of the diffraction peak indicated by the black square and the height of the strongest diffraction peak indicated by the asterisk. When the ratio ζ / ε is within this range, the proportion of the AB5 phase that reduces the durability of the hydrogen storage alloy is small, so an improvement in the durability of the hydrogen storage alloy can be expected.

[0129] The conditions for X-ray diffraction measurements are as follows. A hydrogen storage alloy powder consisting of alloy particles ground to a particle diameter of less than 75 µm is placed in a sample holder, and the measurement is performed using Cu as the target and only a kβ filter under the following conditions: Tube voltage: 40 kV Tube current: 40 mA Scanning speed: 0.5° / min Scan step: 0.02° Divergence gap (DS): 1° Scattering gap (SS): 1° Receiving gap (RS): none [Alloy surface layer]

[0130] On the surface of the hydrogen storage alloy of the present invention, a surface layer formed by an oxide layer or a hydroxide layer containing an appropriate amount of Y indicated in the general formula (1) is formed in close contact with the alloy particles constituting the hydrogen storage alloy. Thus, the hydrogen storage alloy of the present invention exhibits excellent durability due to the presence of the surface layer formed by an oxide layer or a hydroxide layer containing an appropriate amount of Y.

[0131] This surface layer is formed when an element contained in the hydrogen storage alloy, such as Y, transforms into a metal oxide or a metal hydroxide during the production of a negative electrode active material and is trapped as an oxide layer or hydroxide layer on the surface of the hydrogen storage alloy. It is preferable that the surface layer formed by a Y-containing oxide layer or hydroxide layer is "mainly composed of a rare earth element" contained in the hydrogen storage alloy and contains Mg and Al. "Mainly composed of a rare earth element" here means that an oxide or hydroxide of a rare earth element accounts for more than half by mass of the oxide layer or hydroxide layer formed on the surface of the hydrogen storage alloy.

[0132] The specific BET surface area of ​​the hydrogen storage alloy is preferably more than 0.5 m 2 / g, preferably 0.55 to 7.0 m 2 / g and more preferably 0.6 to 4.0 m 2 / g. If the specific BET surface area is within this range, the hydrogen storage alloy is suitable as a negative electrode active material contained in a negative electrode of an alkaline storage battery. Preferably, the hydrogen storage alloy in which the surface layer is present has a pore volume of 0.013 cm 3 / g or less and an average pore diameter of 40 nm or less. More preferably, the pore volume is in a range of 0.0025 to 0.0125 cm 3 / g and the average pore diameter in a range of 10 to 35 nm. If the pore volume is 0.013 cm 3 / g and the average pore diameter exceeds 40 nm and thus both are too large, the density of the surface layer becomes lower and the probability of crack occurrence increases, which may lead to reduced durability of the hydrogen storage alloy.

[0133] On the other hand, if the pore volume is less than 0.0025 cm 3 / g and the average pore diameter is less than 10 nm, which are both small, the impregnation of the surface layer of the hydrogen storage alloy with an electrolyte solution becomes insufficient, and the hydrogen storage desorption properties deteriorate. The thickness of the surface layer formed by an oxide layer or hydroxide layer in close contact with the alloy particles is 500 nm or less, and preferably in a range of 50 to 450 nm. If the thickness of the surface layer exceeds 500 nm and is too large, the impregnation of the surface layer of the hydrogen storage alloy with an electrolyte solution becomes insufficient, which may lead to a deterioration of the hydrogen storage desorption properties.On the other hand, if no surface layer is formed on the surface of the hydrogen storage alloy of the present invention, the corrosion resistance of the hydrogen storage alloy decreases significantly.

[0134] In the hydrogen storage alloy according to this embodiment, the durability of the alloy itself, that is, the pulverization of the alloy accompanying hydrogen storage and desorption, is mitigated to achieve compatibility between high performance and high durability. Furthermore, in such a hydrogen storage alloy, a surface layer can easily form on the surface of the alloy particles, which is excellent in both hydrogen storage desorption properties and alkaline corrosion resistance. Therefore, the hydrogen storage alloy according to this embodiment is particularly excellent in durability. That is, an alkaline storage battery using this hydrogen storage alloy as a negative electrode active material exhibits high performance characteristics while also exhibiting excellent charge-discharge cycle characteristics. [Manufacturing process of a hydrogen storage alloy]

[0135] Next, a manufacturing method for the hydrogen storage alloy of the present embodiment will be described.

[0136] For the hydrogen storage alloy of this embodiment, metal elements, including rare earth elements (Sm, Y, La, Ce, etc.), magnesium (Mg), nickel (Ni), aluminum (Al), chromium (Cr), and iron (Fe), are weighed in a predetermined molar ratio. These raw materials are then placed in an alumina crucible in a high-frequency induction furnace and melted in an inert gas atmosphere such as argon. They are then poured into a mold to produce a hydrogen storage alloy ingot. Alternatively, the hydrogen storage alloy of this embodiment can also be directly produced as a sample in the form of flakes with a thickness of approximately 200 to 500 μm by a strip casting method.

[0137] Since the hydrogen storage alloy of the present embodiment contains Mg as a main component, which has a low melting point and high vapor pressure, if the raw materials of all the alloy components are melted at once, Mg may evaporate, and it may become difficult to obtain an alloy having the desired chemical composition. Therefore, in producing the hydrogen storage alloy of the present embodiment by a melting method, it is preferable that the alloy components other than Mg are first melted and then the Mg raw materials such as metallic Mg and Mg alloy are introduced into the resulting molten metal. It is desirable that this melting step be carried out in an inert gas atmosphere such as argon or helium.In particular, it is preferred that this step be carried out in a pressureless atmosphere created by adjusting an inert gas containing 80 vol% or more of argon to 0.05 to 0.2 MPa. Preferably, the alloy molten under these conditions is then poured into a water-cooled mold and solidified into an ingot of the hydrogen storage alloy.

[0138] Next, the melting point (T m ) of the obtained ingot of the hydrogen storage alloy. Namely, it is preferable that the hydrogen storage alloy of the embodiment is subjected to a heat treatment in which the ingot cast as described above is heated at a suitable temperature which is 800°C or higher but below the melting point (T m) of the alloy or lower, in an atmosphere of either an inert gas such as argon or helium, or a nitrogen gas, or an atmosphere of a mixture of these gases for three to 50 hours.

[0139] Through this heat treatment, the overall ratio of the A2B7 type, the A5B 19 -type and AB3-type crystal structures as the main phase in the hydrogen storage alloy can be set to 70 mass% or more, and preferably the total ratio of the A2B7-type and the A5B 19 -type crystal structures can be adjusted to 70 mass% or more, while the AB2 phase and AB5 phase, which are subphases generated during casting, can be reduced or eliminated.

[0140] That the crystal structure of the main phase of the obtained hydrogen storage alloy is the A2B7 type structure, A5)B 19The difference between the AB3-type structure and the AB3-type structure can be confirmed by X-ray diffraction measurements using Cu-Kα radiation. The main phase of the hydrogen storage alloy is more than 50 mass%, and preferably 70 mass% or more.

[0141] If the heat treatment temperature is below 800°C, the diffusion of the elements is insufficient, so that partial phases remain, which can cause a reduction in discharge capacity or a deterioration in the battery's charge-discharge cycle characteristics. On the other hand, if the heat treatment temperature is not below the melting point T m minus 20°C (not less than T m-20°C) of the alloy, coarsening or partial melting of the crystal particles of the main phase or evaporation of the Mg component may result, which may lead to a reduction in hydrogen storage capacity due to pulverization or a change in chemical composition. Therefore, the heat treatment temperature is preferably in a range of 800°C to (T m -30°C).

[0142] If the heat treatment holding time is three hours or shorter, the main phase ratio cannot be stably adjusted to 70 mass% or more, and the homogenization of the main phase chemical components becomes insufficient. This causes the expansion and contraction of the crystal lattice formed by the hydrogen storage alloy during hydrogen storage and desorption to become uneven, and the amount of resulting distortions and defects increases, which may also negatively affect the charge-discharge cycle life characteristics of the alkaline storage battery.

[0143] The holding time of the heat treatment is preferably four hours or longer, and more preferably five hours or longer from the viewpoint of homogenizing the main phase of the hydrogen storage alloy and improving its crystallizability.

[0144] However, if the holding time exceeds 50 hours, the amount of evaporated Mg becomes very large and the chemical composition of the hydrogen storage alloy changes, which may lead to the formation of an AB5-type subphase. Furthermore, such a holding time is not preferred because it increases manufacturing costs and may cause a dust explosion due to evaporated fine Mg powder.

[0145] The heat-treated hydrogen storage alloy is pulverized using a dry or wet process. When pulverizing the alloy using a dry process, the alloy is ground using a hammer mill, an ACM pulverizer, or similar equipment. However, when pulverizing the hydrogen storage alloy using a wet process, the alloy is ground using a ball mill, an attritor, or similar equipment. Wet grinding is particularly preferred for obtaining fine powder from the hydrogen storage alloy because it can produce fine powder safely.

[0146] When the hydrogen storage alloy according to the embodiment is used for a battery for on-board applications, the particle diameter of the alloy particles pulverized from the alloy is preferably in a range of 3 μm or more but 30 μm or less, and more preferably in a range of 5 μm or more but 25 μm or less, as a mass-based 50% sub-fraction particle diameter D50, in view of the balance between battery properties, including performance and cycle life. If the particle diameter distribution of the alloy particles is too broad, these properties deteriorate; Therefore, it is preferable that the mass-based 10% sub-size fraction particle diameter D10 is within a range of 0.5 µm or more but 15 µm or less, and that the mass-based 90% sub-size fraction particle diameter D90 is within a range of 8 µm or more but 60 µm or less.Further, it is more preferable that the 10% undersize fraction particle diameter D10 is in a range of 1 µm or more but 10 µm or less, and that the 90% undersize fraction particle diameter D90 is in a range of 10 µm or more but 50 µm or less.

[0147] The particle diameter of the alloy particles can be controlled by adjusting the conditions such as the diameter and amount of the medium and the rotation speed.

[0148] Here, the particle diameter distributions D50, D10, and D90 of the alloy particles described above are values ​​measured with a laser diffraction particle size distribution measuring device. For example, the MT3300EXII from MicrotracBEL Corp. can be used.

[0149] The above-described hydrogen storage alloy according to the present embodiment is an alloy whose main phase is represented by the A2B7 type crystal structure, the A5B 19 -type crystal structure and the AB3-type crystal structure. Specifically, in the A2B7-type crystal structure, a Ce2Ni7 phase, which is hexagonal (2H), and a Gd2Co7 phase, which is rhombohedral (3R), can coexist without problems, and both phases exist, with a larger amount of the former being preferred.

[0150] In the A5B 19 -type crystal structure (a hexagonal Gd5Co 19 -phase or a rhombohedral Pr5Co 19 -phase), a larger amount of the former is preferred. It is preferred that the A2B7 crystal structure, the A5B 19 crystal structure and the AB3 crystal structure together account for at least 70 mass% or more.

[0151] It is even more preferable that the phases of the A2B7 crystal structure and the A5B19 -Crystal structure together account for 70 mass% or more. These crystal structures of the hydrogen storage alloy can be evaluated by Rietveld analysis based on the result of an X-ray diffraction measurement.

[0152] In order to obtain a hydrogen storage alloy to be used as a negative electrode active material of the embodiment in which a layer of an oxide or hydroxide containing Y is in close contact with the surface of the hydrogen storage alloy, the surface of the hydrogen storage alloy should be positively oxidized.

[0153] Hereinafter, taking the hydrogen storage alloy of the embodiment as an example, a method for producing the hydrogen storage alloy according to the embodiment, which is used as a negative electrode active material of an alkaline storage battery, by performing a treatment of the hydrogen storage alloy by an appropriate method (hereinafter referred to as a method for treating the hydrogen storage alloy) will be described.

[0154] The hydrogen storage alloy treatment method has: N-1) a step in which the hydrogen storage alloy is treated with an aqueous alkaline solution; and N-2) a step in which the surface of the hydrogen storage alloy which has undergone step N-1) is oxidized.

[0155] While N-1), the step in which the hydrogen storage alloy is treated with an aqueous alkaline solution (hereinafter simply referred to as “step N-1”), is not an essential step for the oxidation of the hydrogen storage alloy as described later, this step can obtain a more suitable hydrogen storage alloy according to the embodiment, which can be used as a negative electrode active material.

[0156] First, “Step N-1)” is described.

[0157] The hydrogen storage alloy used for step N-1) is a hydrogen storage alloy whose main phase is a phase characterized by the A2B7 type crystal structure, the A5B 19 -type crystal structure and the AB3-type crystal structure is formed, containing rare earth elements such as La, Y and Ce, Mg, Al and Ni.

[0158] When the hydrogen storage alloy is treated in step N-1) with an aqueous alkaline solution in which an alkali metal hydroxide has been dissolved, corrosion progresses from the surface of the alloy.

[0159] Among the components contained in the hydrogen storage alloy, in particular the rare earth elements, Mg and Al, which are prone to oxidation and have high solubility with respect to an aqueous alkaline solution, partially transform into an oxide or a hydroxide in their positions and are partially eluted from the surface of the hydrogen storage alloy.

[0160] Here, Ni exhibits high corrosion resistance and low solubility in an aqueous alkaline solution, and therefore remains in its position. As a result, a layer containing a mixture of metal, an oxide, and a hydroxide forms on the surface of the hydrogen storage alloy.

[0161] Hereinafter, in the hydrogen storage alloy according to the present embodiment, this surface layer newly formed on the surface of the hydrogen storage alloy is referred to as a surface-treated layer. The surface-treated layer is composed of a metal oxide or hydroxide of an alkali metal. It is believed that the performance of the hydrogen storage alloy used as a negative electrode active material of an alkaline storage battery is improved by the presence of this surface-treated layer on the surface of the hydrogen storage alloy.

[0162] Examples of alkali metal hydroxides include lithium hydroxide, sodium hydroxide, and potassium hydroxide, with sodium hydroxide being preferred. In some cases, using an aqueous sodium hydroxide solution as the aqueous alkaline solution results in more favorable battery characteristics of the nickel-hydrogen battery, which is the alkaline storage battery according to the embodiment, compared to using other lithium hydroxide and potassium hydroxide.

[0163] A strongly basic solution is preferably used as the aqueous alkaline solution. The concentration of the alkali metal hydroxide in the aqueous alkaline solution can preferably be in the range of 10 to 60 mass%, and more preferably in the range of 20 to 55 mass%.

[0164] Preferably, step N-1) is carried out by a method in which the hydrogen storage alloy is immersed in the aqueous alkaline solution. In this case, it is preferable that this step be carried out with stirring and heating. The heating temperature range may preferably be, for example, 50 to 150°C, and more preferably, a range may be, for example, 70 to 140°C. The heating time may be determined according to the concentration of the aqueous alkaline solution, the heating temperature, and the stirring condition, and preferably, a range may be, for example, 0.1 to 10 hours, and particularly preferably, a range may be, for example, 0.2 to 5 hours.

[0165] The mass ratio between the hydrogen storage alloy and the amount of aqueous alkaline solution is preferably in the range of 1:0.5 to 1:10, particularly preferably in the range of 1:0.7 to 1:8. If the amount of aqueous alkaline solution is too small, the surface-treated layer may not sufficiently form on the hydrogen storage alloy, while too large an amount of aqueous alkaline solution is disadvantageous in terms of cost.

[0166] At the time of completion of step N-1), the rare earth elements Mg and Al, which have been partially eluted from the hydrogen storage alloy, are present in the alkaline aqueous solution. During the separation of the alkaline aqueous solution and the hydrogen storage alloy, these rare earth elements Mg and Al may adhere to the surface of the hydrogen storage alloy as hydroxides of the rare earth elements Mg and Al.

[0167] In step N-1), following treatment with the aqueous alkaline solution, the hydrogen storage alloy can be rinsed with water. Rinsing with water can remove any aqueous alkaline solution adhering to the surface of the hydrogen storage alloy. The mass ratio of the hydrogen storage alloy to water during rinsing with water is preferably 1:1 to 1:50, particularly preferably 1:2 to 1:30.

[0168] Next, N-2) is described, a step in which the surface of the hydrogen storage alloy subjected to step N-1) (hereinafter referred to simply as “step N-2)”) is oxidized.

[0169] The water rinsing of the hydrogen storage alloy, which can be performed after the above-described treatment with the aqueous alkaline solution in step N-1), can be performed in ambient air as step N-2. For step N-2), a method can be adopted in which the surface of the hydrogen storage alloy is oxidized with atmospheric oxygen by exposing the hydrogen storage alloy to air, or a method can be adopted in which the hydrogen storage alloy is oxidized by bringing it into contact with an oxidizing agent such as hydrogen peroxide.

[0170] It is preferable that both processes be performed while the hydrogen storage alloy is being cooled to avoid excessive heating of the hydrogen storage alloy. In particular, it is preferable that the process be performed while the hydrogen storage alloy is being sprayed with water to cool the hydrogen storage alloy, or that the process be performed after the hydrogen storage alloy has been placed in water or in an aqueous solution containing an oxidizing agent, such as hydrogen peroxide.

[0171] A preferred negative electrode active material of the embodiment, which is produced by passing through steps N-1) and N-2), contains on its surface a layer in which metal, an oxide, and a hydroxide are mixed. A preferred negative electrode active material of the embodiment can be expressed as having on its surface the surface-treated layer in which metal, an oxide, and a hydroxide are mixed.

[0172] By the method described above, a surface layer of an oxide layer or a hydroxide layer containing at least partially Y can be formed on and in close contact with the surface of the hydrogen storage alloy of the embodiment. This improves the corrosion resistance of the hydrogen storage alloy of the embodiment.

[0173] It is preferable that the oxide or hydroxide contained in the surface-treated layer of the hydrogen storage alloy consists mainly of rare earth elements, Mg and Al contained in the hydrogen storage alloy.

[0174] Furthermore, it is preferred that the hydrogen storage alloy in which the surface-treated layer is formed from an oxide layer or hydroxide layer has a pore volume of 0.013 cm 3 / g or less and an average pore diameter of 40 nm or less. If the pore volume is 0.013 cm 3If the pore diameter exceeds 0.1 nm / g, the density of the surface-treated layer becomes lower and the probability of cracking increases. Immersion in an alkaline aqueous solution may accelerate corrosion of the hydrogen storage alloy, resulting in a decrease in the corrosion resistance of the alloy. If the average pore diameter exceeds 40 nm and is too large, immersion in an alkaline aqueous solution will be too severe, resulting in accelerated corrosion of the hydrogen storage alloy, resulting in a decrease in durability.

[0175] If the pore volume is less than 0.0025 cm 3 / g and the average pore diameter is less than 10 nm, the impregnation of the hydrogen storage alloy with an electrolyte solution becomes insufficient, so that the hydrogen storage desorption properties of the alloy may deteriorate. The pore volume is preferably 0.0025 to 0.0125 cm3 / g and the average pore diameter is 10 to 35 nm.

[0176] Furthermore, it is preferable that the surface layer formed by an oxide layer or hydroxide layer containing at least partially Y, formed on the surface of the hydrogen storage alloy according to the embodiment, has a thickness of 500 nm or less where it is in close contact with the surfaces of the alloy particles. If the thickness of the surface layer exceeds 500 nm, the impregnation of the hydrogen storage alloy with an electrolyte solution becomes insufficient, so that the hydrogen storage desorption properties of the alloy may deteriorate.

[0177] On the other hand, if the surface-treated layer is not even formed on at least a portion of the hydrogen storage alloy according to the present embodiment, the corrosion resistance of the alloy decreases significantly. The thickness of the surface layer is preferably 50 to 450 nm.

[0178] An analysis of the surface of the negative electrode active material is as follows. The surface-treated layer formed on the surface of the hydrogen storage alloy was examined using a transmission electron microscope. After the powder of the negative electrode active material was mixed into the epoxy resin, the resin was cured at 120°C for 30 minutes to embed the powder into the resin.

[0179] A flake sample with a size of 100 nm or less is then obtained by flaking using an argon beam. An ion slicer (EM-09100IS) from JEOL Ltd. is used for the flaking process. The alloy is ground thin at an accelerating voltage of 6 kV until pores of a few µm open, and then post-processed at an accelerating voltage of 1.0 kV for 15 minutes. The surface-treated layer formed on the alloy surface is examined using a transmission electron microscope (JEM-2100F from JEOL Ltd.) at an accelerating voltage of 200 kV. Furthermore, an analysis of the elements contained in the surface-treated layer is performed using an energy-dispersive X-ray emission spectrometer (JED-2300 from JEOL Ltd.) installed in this instrument.

[0180] The pore diameter distribution is analyzed using the following technique. After vacuum drying the negative electrode active material at 100°C for two hours, a nitrogen adsorption-desorption isotherm is measured at a liquid nitrogen temperature (77.3 K) of the negative electrode active material using a fully automated gas adsorption analyzer (AS1-MP, Anton Paar GmbH).

[0181] The nitrogen adsorption amount per unit weight of the hydrogen storage alloy on the adsorption-desorption isotherm is calculated to be represented by a volume of gaseous nitrogen at standard state (STP; standard temperature and pressure).

[0182] Here, the standard state of the gas is assumed to be 0°C and 101325 Pa, with the symbol "N" in front of the volume unit. The total pore volume was calculated using the following calculation formula (B), where the nitrogen adsorption amount at a relative pressure (p / p0 = 0.99) on the storage isotherm V [Ncm 3 / g] is: Total pore volume(cm3 / g)=V / 22414×(M / ρ)

[0183] In this formula, the volume of 1 mole of gas in the standard state is 22414 Ncm 3 ; the molecular weight M of nitrogen is 28.013 g / mol; and the density ρ of nitrogen in the liquid phase is 0.808 g / cm 3 .

[0184] Furthermore, using the adsorption-desorption isotherm, the pore diameter distribution in a mesopore region is analyzed by the BJH method and the pore diameter distribution in a micropore mesopore region is analyzed by the DFT method, and the average pore diameter is calculated.

[0185] It is preferable that the BET specific surface area of ​​the hydrogen storage alloy used as the negative electrode active material according to the present embodiment is more than 0.5 m 2 / g. If the BET specific surface area of ​​the hydrogen storage alloy is not more than this, the average pore diameter may become too large. The BET specific surface area of ​​the hydrogen storage alloy is preferably in a range of 0.55 to 7.0 m 2 / g and more preferably in a range of 0.6 to 4.0 m 2 / G.

[0186] Apart from the treatment with aqueous alkaline solution in step N-1) and the surface oxidation in step N-2), an acid treatment step can be combined with these steps.

[0187] In the acid treatment step, an acid treatment is performed on the surface of the hydrogen storage alloy using an aqueous solution of nitric acid, sulfuric acid, hydrochloric acid, or the like. Through the acid treatment step, a hydrogen storage alloy can be obtained that has more favorable battery properties, particularly durability and low-temperature discharge characteristics. This is because the catalytic effect of the hydrogen storage alloy is improved and hydrogen storage desorption can be easily performed because a large number of fine Ni particles are deposited on the surface of the hydrogen storage alloy.

[0188] Therefore, the low-temperature discharge properties improve, and the corrosion resistance improves with the increase of fine Ni particles on the surface, resulting in improved durability. [Alkaline storage battery]

[0189] Hereinafter, an example of the configuration of the alkaline storage battery with a negative electrode using the hydrogen storage alloy of the present invention will be described with reference to Fig. 1 described.

[0190] The alkaline storage battery 10 of the present invention is composed of at least the positive electrode 1, the negative electrode 2, and the separator 3, as well as the electrolyte-filled case 4 (battery case) in which these components are housed. A specific description follows. <Positive Elektrode>

[0191] The positive electrode 1 is typically composed of a layer of a positive electrode active material and a positive electrode current collector. The positive electrode active material layer contains at least one positive electrode active material. The positive electrode active material layer may also contain at least one positive electrode additive, a conductivity aid, a binder, or a thickener.

[0192] The positive electrode active material is not particularly limited as long as the material functions as a battery in combination with the hydrogen storage alloy (negative electrode material) described above, and examples include elemental metals, alloys, and hydroxides.

[0193] A material containing nickel oxide and composed primarily of nickel oxyhydroxide and / or nickel hydroxide can be used as the positive electrode active material. The proportion of nickel oxide in the positive electrode active material is, for example, 90 to 100 mass% and can be 95 to 100 mass%. The average particle diameter of the nickel oxide can be selected, for example, from a range of 3 to 35 µm and is preferably in a range of 3 to 25 µm.

[0194] As the positive electrode active material, a positive electrode active material around which a layer of a conductive aid has been previously formed is preferred. Furthermore, a positive electrode active material around which a layer of cobalt oxyhydroxide has been formed, and the cobalt oxyhydroxide layer has been previously doped with an alkali metal, is preferred.

[0195] The positive electrode additive is added to the positive electrode to improve the battery properties of the nickel-hydrogen battery. The positive electrode additive is not limited as long as it is used as a positive electrode additive for nickel-metal hydride batteries. Specific examples of positive electrode additives include niobium compounds such as Nb2O5; tungsten compounds such as WO2, WO3, Li2WO4, Na2WO4, and K2WO4; ytterbium compounds such as Yb2O3; titanium compounds such as TiO2; yttrium compounds such as Y2O3; zinc compounds such as ZnO; calcium compounds such as CaO, Ca(OH)2, and CaF2; and other rare earth oxides.

[0196] The conductive aid is not particularly limited as long as the positive electrode material can impart electron conductivity. Examples include metal powders such as Ni powder, oxides such as cobalt oxide, and carbon materials such as graphite and carbon nanotubes. While the amount of conductive aid to be added is not particularly limited, for example, based on 100 parts by mass of the positive electrode active material, a range of 0.1 to 50 parts by mass is preferable, and a range of 0.1 to 30 parts by mass is even more preferable.

[0197] The binder has the function of anchoring an active material, etc., to the surface of the current collector. The binder is not limited as long as it is a binder used as a binder for electrodes of nickel-hydrogen batteries. Specific examples of binders include fluorine-containing resins such as polyvinylidene fluoride, polytetrafluoroethylene, and fluororubber; polyolefin resins such as polypropylene and polyethylene; imide-based resins such as polyimide and polyamideimide; cellulose derivatives such as carboxymethylcellulose, methylcellulose, and hydroxypropylcellulose; copolymers such as styrene-butadiene rubber; and (meth)acrylic resins such as polyacrylic acid, polyacrylic acid esters, polymethacrylic acid, and polymethacrylic acid esters containing a (meth)acrylic acid derivative as a monomer unit. Based on 100 parts by mass of the positive electrode active material, the amount of the binder should be, for example,7 parts by mass or less and may be in a range of 0.01 to 5 parts by mass and may further be in a range of 0.05 to 2 parts by mass.

[0198] Further, examples of thickeners include carboxymethylcellulose and its modifications (including salts such as Na salt), cellulose derivatives such as methylcellulose, saponified polymers containing a vinyl acetate unit such as polyvinyl alcohol, and polyalkylene oxide such as polyethylene oxide. One type of these thickeners can be used independently, or two or more types can be used in combination. For example, based on 100 parts by mass of the positive electrode active material, the amount of the thickener is 5 parts by mass or less, and may be in a range of 0.01 to 3 parts by mass, and may further be in a range of 0.05 to 1.5 parts by mass.

[0199] Examples of positive electrode current collector materials include stainless steel, aluminum, nickel, iron, and titanium. Examples of positive electrode current collector shapes include foil, mesh, and porous; any shape is acceptable.

[0200] The positive electrode can be formed by attaching a positive electrode composite material containing a positive electrode active material to a support body (positive electrode current collector). The positive electrode composite material is typically formed by blending the above-described positive electrode active material, the positive electrode additive, the conductive aid, and the binder together into a paste. Water, an organic medium, a mixed medium consisting of a mixture of two or more media selected from these, etc. can be used as the dispersion medium. A positive electrode additive, a conductive aid, a binder, a thickener, etc. can be added as needed, but these (especially the positive electrode additive, the binder, and the thickener) are not mandatory.

[0201] For the positive electrode, the above-mentioned positive electrode composite material paste may be applied to the support body or packed into holes of the support body, depending on the shape of the support body, etc. The positive electrode can be formed by applying or packing the positive electrode composite material paste on or in the support body, drying the paste to remove the dispersion medium, and compressing the obtained dry product in a thickness direction (e.g., by rolling between a pair of rollers). <Negative Elektrode>

[0202] The negative electrode 2 is typically composed of a negative electrode active material layer and a negative electrode current collector. The negative electrode active material layer must contain at least the above-described hydrogen storage alloy of the present invention as the negative electrode active material. The negative electrode active material layer may further contain at least one negative electrode additive, a conductivity aid, a binder, or a thickener.

[0203] The negative electrode additive is added to the negative electrode to improve the battery properties of the nickel-metal hydride battery. The negative electrode additive is not limited as long as it is an additive used as a negative electrode additive for nickel-metal hydride batteries. Specific examples of negative electrode additives include rare earth element fluorides such as CeF3 and YF3, bismuth compounds such as Bi2O3 and BiF3, indium compounds such as In2O3 and InF3, and compounds mentioned as examples of positive electrode additives.

[0204] The conductive aid is not particularly limited as long as the material can impart electron conductivity. Examples include metal powders such as nickel powder, oxides such as cobalt oxide, and carbon materials such as graphite and carbon nanotubes. While the amount of conductive aid to be added is not particularly limited, the amount is preferably in a range of 0.1 to 50 parts by mass, and more preferably in a range of 0.1 to 30 parts by mass, based on 100 parts by mass of the hydrogen storage alloy powder, for example.

[0205] Examples of binders include synthetic rubber such as styrene-butadiene rubber (SBR), cellulose such as carboxymethyl cellulose (CMC), polyols such as polyvinyl alcohol (PVA), and fluororesins such as polyvinylidene fluoride (PVDF). Based on 100 parts by mass of the hydrogen storage alloy powder, the amount of the binder should be 7 parts by mass or less, for example, and can be in a range of 0.01 to 5 parts by mass, and can further be in a range of 0.05 to 2 parts by mass.

[0206] Examples of negative electrode current collector materials include steel, stainless steel, aluminum, nickel, iron, titanium, and carbon. Examples of negative electrode current collector shapes include foil, mesh, and porous; any shape is acceptable.

[0207] To form a negative electrode active material layer on the negative electrode current collector, the components contained in the negative electrode active material layer, including the negative electrode active material, are processed into a paste, which is a negative electrode paste. The negative electrode paste is prepared by adding the above-described negative electrode active material, negative electrode additive, conductive aid, binder, thickener, etc., to a solvent.

[0208] This negative electrode for a nickel-metal hydride battery is manufactured by forming the negative electrode paste containing the hydrogen storage alloy powder of the present invention as a negative electrode active material into a predetermined shape and supporting the formed negative electrode paste by a negative electrode core material (negative electrode current collector), or is manufactured by preparing a negative electrode paste containing the hydrogen storage alloy powder and applying this paste to the negative electrode current collector and drying it. <elektrolytschicht>

[0209] The electrolyte layer is a layer containing an aqueous electrolyte solution located between the positive and negative electrodes. The aqueous electrolyte solution here refers to an electrolyte solution that primarily uses water as a solvent, although this solvent may also contain components other than water. The proportion of water in the total solvent of the electrolyte solution should be 50 mol% or more, but can also be 70 mol% or more, 90 mol% or more, or 100 mol%.

[0210] The aqueous electrolyte solution is preferably an alkaline aqueous solution. Examples of the solute of the alkaline aqueous solution are potassium hydroxide (KOH) and sodium hydroxide (NaOH), and the solute may contain LiOH. The concentration of the solute in the aqueous electrolyte solution is preferably 2 to 10 mol / L, more preferably 3 to 9 mol / L, and even more preferably 4 to 8 mol / L. A well-known additive used for electrolyte solutions for nickel-metal hydride batteries may be added to the aqueous electrolyte solution.

[0211] The electrolyte layer contains separator 3. The incorporation of separator 3 effectively prevents short circuits. Examples of separator 3 include a nonwoven fabric and a porous, resin-containing membrane, such as polyethylene or polypropylene, that has undergone a sulfonation treatment. <Gehäuse>

[0212] The casing 4 is a battery case (cell container) that houses the above-described positive electrode 1, negative electrode 2, and separators 3, and is filled with an electrolyte. The material of the casing 4 can be any material that remains stable to the electrolyte solution without corroding and that can accommodate a gas (oxygen or hydrogen) temporarily generated during charging and the electrolyte solution without leakage, and, for example, a metal casing or a resin casing is commonly used. In the case of a laminated alkaline storage battery 10 having a laminated body in which a plurality of positive electrodes 1 and negative electrodes 2 are laminated with the separators 3 interposed therebetween, the casing 4 may have a structure in which a periphery of the laminated body is sealed by a frame-shaped resin. <batterieanwendungen>

[0213] The alkaline storage battery 10 of the present invention is typically a secondary battery. Since it can be repeatedly charged and discharged, this battery is suitable, for example, as an on-board battery. In this case, the alkaline storage battery 10 is not limited to use as a battery for a hybrid electric vehicle, i.e., a form in which the battery supplies power to a motor for driving the vehicle. The alkaline storage battery 10 can be used in a form in which it supplies power to a starter motor to restart the engine in a motor vehicle with a start-stop function.

[0214] The secondary battery can be used like a primary battery (intended for only one discharge after charging). Regarding the shape of the battery, there are, for example, a coin type, a laminate type, a cylindrical type, and a rectangular type, and any shape can be adopted. [Vehicle]

[0215] The vehicle of the present invention is equipped with an alkaline storage battery that uses the above-described hydrogen storage alloy as a negative electrode as a power source for a motor. By using the alkaline storage battery of the present invention, which is drastically downsized and lightweight compared to conventional batteries, the vehicle of the present invention can achieve improved kinematic performance, reduced fuel consumption, and extended cruising range. EXAMPLES<Beispiel 1>

[0216] The negative electrode cells to be evaluated, each using alloys (hydrogen storage alloys) Nos. 1 to 70 having the component compositions shown in Tables 1-1 to 1-4 below as negative electrode active materials, were manufactured according to a method described below, and experiments were conducted to evaluate their properties.

[0217] Of the alloys shown in Tables 1-1 to 1-4, alloys Nos. 1 to 33 are examples of alloys that satisfy the conditions of the present invention (inventive examples), and alloys Nos. 34 to 70 are examples of alloys that do not satisfy the conditions of the present invention (comparative examples). Alloy No. 34 of the comparative example was used as a reference alloy for evaluating cell properties. (Production of the negative electrode active material)

[0218] Raw materials (La, Y, Ce, Sm, Nd, Pr, Gd, Zr, Mg, Ni, Co, Mn, Al, Fe, etc., each with a purity of 99% or more) of alloys Nos. 1 to 70 shown in Tables 1-1 to 1-4 were melted and cast in an argon atmosphere (Ar: 100 vol%, 0.1 MPa) using a high-frequency induction heating furnace to obtain alloy ingots consisting of the hydrogen storage alloys.

[0219] Subsequently, a heat treatment was carried out in which these alloy ingots were each heated for ten hours in an argon atmosphere (Ar: 90 vol%, 0.1 MPa) at a temperature equal to the melting point of the alloy T m minus 50°C (940 to 1130°C).

[0220] Thereafter, each heat-treated alloy ingot was coarsely ground, then further coarsely ground with a wet ball mill, finely ground until the 50% undersize particle diameter D50 was 16 µm by mass, and filtered to obtain a finely ground filtered product.

[0221] Next, the following treatment was performed as a step in which the hydrogen storage alloy was treated with an aqueous alkaline solution. To 50 parts by mass of the finely ground, filtered product from Example 1, 50 parts by mass of an aqueous sodium hydroxide solution containing 48 mass% sodium hydroxide was added as an aqueous alkaline solution to obtain a suspension. This suspension was heated to 100°C and maintained for two hours, and then cooled to room temperature.

[0222] This suspension was allowed to stand, and the supernatant liquid was removed to separate the hydrogen storage alloy from the aqueous alkaline solution. 800 parts by mass of water was poured onto the top of the hydrogen storage alloy to rinse the hydrogen storage alloy with water. Again, the suspension was allowed to stand, and the supernatant liquid was removed to separate the hydrogen storage alloy from the aqueous alkaline solution.

[0223] Furthermore, as a step for oxidizing the surface of the hydrogen storage alloy, the following treatment was performed after the step described above. To the entire finely ground, filtered product obtained in the previous paragraph, 25 parts by mass of a 10% by mass hydrogen peroxide solution was added, and the mixture was stirred for 20 minutes. 400 parts by mass of water was poured to rinse the hydrogen storage alloy.

[0224] Here, too, the suspension was allowed to stand, and the supernatant liquid was removed to separate the hydrogen storage alloy from the aqueous alkaline solution. 400 parts by mass of water was poured onto the top of the hydrogen storage alloy to rinse it with water. This filtered hydrogen storage alloy was used as the negative electrode active material of the cell for evaluation.

[0225] Regarding AB5 alloy No. 34, which is to be used as a reference for the cells to be evaluated, this alloy was wet-ground into a fine powder with a 50% sub-size particle diameter D50 of 25 µm by mass to be used as a sample (negative electrode active material) of the cell to be evaluated. (Production of cells for evaluation)

[0226] 97.8 parts by mass of the above-described negative electrode active material, 1.5 parts by mass of an acrylic resin emulsion as a binder in solid form, 0.7 parts by mass of carboxymethyl cellulose as a binder, and an appropriate amount of ion-exchanged water were mixed together to prepare a slurry.

[0227] A 20 µm-thick nickel foil was prepared as a negative electrode current collector. The slurry described above was applied to the surface of this nickel foil to form a film. The nickel foil with the applied slurry was dried to remove water, and then the nickel foil was pressed. Thus, a negative electrode was fabricated, in which a negative electrode active material layer was formed on the surface of the negative electrode current collector.

[0228] Nickel hydroxide particles coated with a sodium- and lithium-containing cobalt oxyhydroxide layer formed by a solid solution of zinc and cobalt were prepared as the positive electrode active material used in the cells evaluated in Example 1.

[0229] 94.3 mass parts of the above-mentioned positive electrode active material, 1.0 mass part of cobalt powder as a conductive aid, 3.5 mass parts of acrylic resin emulsion as a solid binder, 0.7 mass part of carboxymethyl cellulose as a binder, 0.5 mass part of Y2O3 as a positive electrode additive, and an appropriate amount of ion-exchanged water were mixed together to prepare a slurry.

[0230] A 20 µm-thick nickel foil was prepared as a positive electrode current collector. The slurry described above was applied to the surface of this nickel foil to form a film. The nickel foil with the applied slurry was dried to remove water, and then the nickel foil was pressed. In this way, a positive electrode was prepared in which a positive electrode active material layer was formed on the surface of the positive electrode current collector. The amount of the positive electrode active material layer on this positive electrode current collector was 28 mg / cm³. 2 , and the density of the positive electrode active material layer was 2.9 g / cm 3 .

[0231] An aqueous solution was prepared as the electrolyte solution in which the concentration of potassium hydroxide was 5.4 mol / L, the concentration of sodium hydroxide was 0.8 mol / L, the concentration of lithium hydroxide was 0.5 mol / L and the concentration of Na2WO4 was 0.16 mol / L.

[0232] A 104 µm thick nonwoven fabric made of polyolefin fibers was produced as a separator and subjected to a sulfonation treatment.

[0233] The separator was held between the positive and negative electrodes to form a group of electrode plates. The group of electrode plates was placed in a resin casing, and the electrolyte solution was poured into it, sealing the casing. In this way, cells were produced for evaluation as nickel-hydrogen batteries. (Various alloy ratings)

[0234] In this example, an X-ray diffraction measurement was performed on a powder milled from each alloy after heat treatment. Regarding the X-ray diffraction measurement conditions, the powder milled to a particle diameter of less than 75 µm was placed in a sample holder, and with Cu as the target, the measurement was performed at a tube voltage of 40 kV, a tube current of 40 mA, a scan speed of 0.5° / min, a scan pitch of 0.02°, a dispersion slit (DS) of 1°, a scattering slit (SS) of 1°, without a receiving slit (RS), and using only a kβ filter.

[0235] Rietveld analysis was performed based on diffraction line data obtained by X-ray diffraction measurements on the ground powders of each alloy. As a result, it was confirmed that in all alloys of Invention Examples Nos. 1 to 33, the main phase was a phase consisting of an A2B7 phase, an A5B 19 phase or an AB3 phase, with the main phase accounting for 70 mass% or more. In particular, it was confirmed that in all the alloys of the Inventive Examples except for the alloy of Inventive Example No. 22, the two phases of the A2B7 phase and the A5B 19 -phase accounted for more than 70 mass%.

[0236] Using the same diffraction line data, the ratio of the diffraction intensity (ζ) of the (101) plane of the AB5 phase to the diffraction intensity (ε) of the strongest diffraction peak in the diffraction angle range of 40 to 45° was evaluated. As a result, it was confirmed that ζ / ε ≤ 0.08 holds in all alloys of the inventive examples.

[0237] The DZT properties of each alloy were evaluated using the following method. First, a lump of the hydrogen storage alloy was ground, and the particle size of the alloy particles formed by the ground hydrogen storage alloy was adjusted through a sieve with openings of 150 μm or more but 1 mm or less in the same manner as described above. The alloy particles of the ground hydrogen storage alloy were filled into a DZT measuring device, and evacuated (0.01 MPa or less) at 80°C for one hour.

[0238] Subsequently, hydrogen gas was introduced at a pressure of 3 MPa at a constant temperature and maintained for 3.5 hours to allow the hydrogen storage alloy to store the hydrogen. Afterward, the hydrogen storage alloy was evacuated for one hour to desorb the hydrogen. An activation treatment was performed.

[0239] Subsequently, hydrogen storage and desorption measurements (DZT property evaluation) were conducted for the alloys of the inventive examples in a hydrogen pressure range of 0.01 to 1 MPa. Tables 1-1 to 1-4 show the hydrogen storage capacity during the application of 1 MPa as H / M and a calculated value of the relational expression (A) [log(P0.7 / P0.3)] / 0.4 as the plateau slope B.

[0240] As can be seen from these tables, the plateau slope B for the alloys of the invention examples is in a range from 1.3 to 3.0.

[0241] An evaluation of crack formation for each alloy due to repeated hydrogen storage and desorption is as follows. A lump of each hydrogen storage alloy was ground to obtain hydrogen storage alloy particles. The particle size of the hydrogen storage alloy particles was then adjusted so that the particles remained above a sieve with 150 μm openings, thus becoming 1 mm or less. Seven grams of the hydrogen storage alloy formed from the alloy particles was filled into a measuring holder of a pressure-composition-temperature (DZT) evaluation device, and evacuation (0.01 MPa or less) was performed at 80°C for one hour. Then, while maintaining the temperature, a hydrogen storage desorption measurement (DZT property evaluation) was performed in a hydrogen pressure range of 0.01 to 3 MPa.

[0242] Next, the hydrogen storage alloy is evacuated (0.01 MPa or less) for one hour, and a hydrogen gas is introduced at a pressure of up to 3 MPa. This is maintained for one hour to allow the hydrogen storage alloy to almost completely store the hydrogen. Then, the alloy is evacuated (0.01 MPa or less) for one hour to allow the hydrogen to desorb. This cycle is repeated three times.

[0243] Finally, as in the first cycle, hydrogen storage desorption measurement (DZT property evaluation) was performed in the hydrogen pressure range of 0.01 to 3 MPa. After this hydrogen storage desorption cycle was performed five times, the hydrogen storage alloy powder was sampled, and particle size distribution measurements were performed. Tables 1-1 to 1-4 show the volume-average particle diameter (MV) of the alloy particles composing the finely pulverized hydrogen storage alloy after repeated hydrogen storage and desorption. As shown in these tables, the alloy particles of the hydrogen storage alloys of the present invention had mean particle diameters of 75 µm or more. [Table 1-1] AlloyNo. Component composition of the hydrogen storage alloy HM P0,5 B ζ / ε MV[µm] 1 (At 0,96 Y 0,01 What 0,02 Sm 0,01 ) 0,76 Mg 0,24 us 3,337 the 0,11 -R 0,003 0,95 0,048 2,10 0,03 87,1 2 (At 0,87 Y 0,03 What 0,01 Sm 0,09 ) 0,77 Mg 0,23 us 3,307 the 0,09 -R 0,003 0,96 0,055 2,43 0,02 94,1 3 (At 0,945 Y 0,02 What 0,025 MS 0,01 ) 0,76 Mg 0,24 us 3,305 the 0,09 -R 0,002 0,95 0,038 2,32 0,02 91,8 4 (At 0,915 Y 0,05 What 0,025 Sm 0,01 ) 0,76 Mg 0,24 us 3,305 the 0,09 -R 0,003 0,97 0,050 1,88 0,02 82,5 5 (At 0,825 Y 0,10 What 0,005 Sm 0,07 ) 0,77 Mg 0,23 us 3,275 the 0,09 -R 0,003 0,98 0,061 2,02 0,00 85,4 6 (La 0,91 Y 0,07 Ce 0,01 Sm 0,01 ) 0,77 Mg 0,23 Ni3, 3275 Al 0,09 Cr 0,005 0,96 0,032 2,58 0,02 97,0 7 (At 0,90 Y 0,03 What 0,01 Sm 0,06 ) 0,77 Mg 0, 23 us 3,305 the 0,09 -R 0,005 0,96 0,045 2,44 0,00 94,1 8 (At 0,89 Y 0,05 What 0,01 Sm 0,05 ) 0,77 Mg 0,23 us 3,305 the 0,09 -R 0,005 0,96 0,056 2,10 0,02 87,1 9 to 0,90 Y 0,03 What 0,05 Sm 0,02 ) 0,77 Mg 0,23 us 3,305 the 0,12 -R 0,005 0,95 0,056 1,90 0,02 83,1 10 to 0,87 Y 0,03 What 0,09 Sm 0,01 ) 0,77 Mg 0,23 us 3,305 the 0,12 -R 0,005 0,95 0,062 1,73 0,03 79,6 11 to 0,90 Y 0,03 What 0,01 Sm 0,06 ) 0,77 Mg 0,23 us 3,27 the 0,09 -R 0,04 0,97 0,035 2,07 0,03 86,6 12 to 0,90 Y 0,03 What 0,01 Sm 0,06 ) 0,77 Mg 0,23 us 3,28 the 0,09 -R 0,02 0,96 0,030 1,93 0,02 83,7 13 to 0,90 Y 0,03 What 0,02 Sm 0,05 ) 0,73 Mg 0,26 us 3,325 the 0,08 -R 0,005 0,99 0,062 2,07 0,04 86,6 14 to 0,90 Y 0,03 What 0,02 Sm 0,05 ) 0,80 Mg 0,20 us 3,345 the 0,07 -R 0,005 0,95 0,050 2,21 0,03 89,5 15 to 0,82 Y 0,08 What 0,01 Sm 0,09 ) 0,85 Mg 0,15 us 3,375 the 0,06 -R 0,005 0,96 0,038 2,71 0,02 99,9 16 (At 0,925 Y 0,05 What 0,025 ) 0,75 Mg 0,25 us 3,448 the 0,09 -R 0,012 1,00 0,065 1,57 0,05 76,2 17 (At 0,95 Y 0,03 What 0,02 ) 0,81 Mg 0,19 us 3,655 the 0,09 -R 0,005 1,01 0,110 1,59 0,05 78,4 18 (At 0,95 Y 0,03 What 0,02 ) 0,83 Mg 0,17 us 3,605 the 0,09 -R 0,005 0,98 0,070 1,98 0,03 88,2 19 (At 0,96 Y 0,02 What 0,02 ) 0,83 Mg 0,17 us 3,555 the 0,09 -R 0,005 0,98 0,063 2,45 0,02 93, 5 20 (At 0,92 Y 0,03 What 0,02 Sm 0,03 ) 0,81 Mg 0,19 us 3,505 the 0,09 -R 0,005 0,99 0,102 2,12 0,02 92, 4 [Table 1-2] AlloyNo. Component composition of the hydrogen storage alloy HM P0,5 B ζ / ε MV [µm] 21 (At 0,925 Y 0,05 What 0,025 ) 0,75 Mg 0,25 us 3,398 the 0,09 -R 0,012 0,99 0,061 1,73 0,02 82,4 22 (At 0,94 Y 0,025 What 0,025 Sm 0,01 ) 0,75 Mg 0,25 us 3,148 the 0,09 -R 0,012 0,94 0,025 2,61 0,00 97,6 23 (At 0,86 Y 0,04 What 0,03 Sm 0,07 ) 0,80 M 0,20 us 3,362 the 0,03 -R 0,008 0,98 0,047 2,81 0,03 104,0 24 (At 0,86 Y 0,04 What 0,07 Sm 0,07 ) 0,80 Mg 0,20 us 3,362 the 0,06 -R 0,008 0,97 0,049 2,69 0,02 99,3 25 (At 0,85 Y 0,07 What 0,02 Sm 0,06 ) 0,80 Mg 0,20 us 3,336 the 0,10 -R 0,004 0,97 0,036 2,10 0,04 87,1 26 (At 0,85 Y 0,07 What 0,02 Sm 0,06 ) 0,80 Mg 0,20 us 3,336 the 0,13 -R 0,004 0,95 0,030 1,76 0,05 80,2 27 (La 0,96 Y 0,02 Ce 0,02 ) 0,77 Mg 0,23 Ni 3,265 Fe 0,10 Al 0,09 Cr 0,005 0,96 0,023 1,72 0,03 82,2 28 (La 0,975 Y 0,02 Ce 0,005 ) 0,80 Mg 0,20 Ni 3,545 Fe 0,02 Al 0,09 Cr 0,005 0,97 0,050 1,89 0,04 84,5 29 (La 0,95 Y 0,02 Ce 0,02 Sm 0,01 ) 0,87 Mg 0,13 Ni 3,645 Fe 0,25 Al 0,09 Cr 0,005 0,93 0,027 2,60 0,03 98,0 30 (La 0,90 Y 0,03 Ce 0,03 Sm 0,04 ) 0,77 Mg 0,23 Ni 3,01 Fe 0,30 Al 0,09 0,93 0,025 1,98 0,04 92,9 31 (La 0,975 Y 0,015 Ce 0,01 ) 0,80 Mg 0,20 Ni 3,545 Fe 0,05 Al 0,09 Cr 0,005 0,97 0,058 1,68 0,03 82,8 32 (La 0,91 Y 0,03 Ce 0,03 Sm 0,03 ) 0,77 Mg 0,23 Ni 3,21 Al 0,03 Fe 0,16 0,95 0,030 2,00 0,04 86,8 33 (La 0,91 Y 0,03 Ce 0,03 Sm 0,03 ) 0,77 Mg 0,23 Ni 3,21 Fe 0,19 0,95 0,028 2,24 0,02 92,9 34 Day 0,9 Ce 0,1 Ni 4,0 Co 0,5 Mr 0,2 Al 0,4 0,82 0,048 0,42 - 40,2 35 La 0,66 Mg 0,34 Ni 3,15 Al 0,12 0,92 0,070 1,18 0,03 51,9 36 (The 0,90 Y 0,03 Sm 0,07 ) 0,77 Mg 0,23 Nor 3,45 Al 0,090 Cr 0,08 0,92 0,057 1,35 0,10 69,8 37 (At 0,72 Y 0,2 What 0,02 Sm 0,06 ) 0,80 Mg 0,20 us 3,336 the 0,11 -R 0,004 0,93 0,070 1,28 0,06 67,0 38 (At 0,64 Y 0,08 What 0,10 Sm 0,18 ) 0,77 Mg 0,22 us 3,275 the 0,09 -R 0,003 0,95 0,080 1,26 0,05 62,0 39 (At 0,825 Y 0,10 What 0,005 Sm 0,07 ) 0,77 Mg 0,22 us 3,197 the 0,2 -R 0,003 0,90 0,025 1,37 0,11 64,6 40 (At 0,94 Y 0,025 What 0,025 Sm 0,01 ) 0,75 Mg 0,25 us 3,05 the 0,09 -R 0,01 0,86 0,022 3,14 0,00 88,6 [Table 1-3] AlloyNo. Component composition of the hydrogen storage alloy HM P0,5 B ζ / ε MV [µm] 41 (At 0,915 Y 0,05 What 0,025 Sm 0,01 ) 0,75 M9 0,25 us 3,548 the 0,09 -R 0,012 0,96 0,087 1,20 0,10 54,8 42 (The 0,25 Sm 0,73 Zr 0,02 ) 0,90 Mg 0,10 Nor 3,20 Al 0,20 0,89 0,081 1,24 0,10 64,8 43 The 0,60 BC 0,30 Mg 0,10 Nor 3,70 Al 0,10 0,94 0,066 1,20 0,12 58,0 44 (The 0,20 Pr 0,39 Nd 0,40 Zr 0,01 ) 0,84 Mg 0,16 Nor 3,15 Al 0,20 0,88 0,105 1,38 0,06 68,4 45 (La 0,83 Y 0,17 ) 0,82 Mg 0,18 Ni 3,32 What 0,14 Mn 0,09 0,92 0,023 1,20 0,10 62,4 46 (La 0,86 Y 0,14 ) 0,88 Mg 0,12 Ni 3,00 What 0,08 Mn 0,08 0,87 0,015 1,22 0,00 78,0 47 (La 0,5 Y 0,5 ) 0,82 Mg 0,18 Ni 3,36 Mn 0,18 0,88 0,090 1,39 0,05 52,0 48 (The 0,765 AND 0,235 ) 0,81 Mg 0,19 Neither 3,67 To the 0,10 0,94 0,084 1,09 0,12 50,2 49 (Day 0,20 Nd 0,27 Sm 0,18 God 0,18 Y 0,17 ) 0,90 Mg 0,10 Ni 2,9 Al 0,20 Co 0,10 0,91 0,048 1,30 0,07 70,0 50 (La 0,4 Y 0,6 ) 0,88 Zr 0,01 Mg 0,11 Ni 3,33 Al 0,17 0,88 0,047 1,11 0,04 48,8 51 (The 0,2 Nd 0,4 Sm 0,39 Zr 0,01 ) 0,89 Mg 0,11 Nor 3,27 Al 0,17 Cr 0,01 0,90 0,087 1,55 0,04 73,2 52 The 0,717 AND 0,13 Mg 0,153 Neither 3,48 To the 0,15 0,92 0,022 1,28 0,10 55,8 53 The 0,3 Y 0,1 Sm 0,49 Mg 0,11 Nor 3,26 Al 0,16 0,91 0,092 1,25 0,05 70,0 54 (The 0,73 Y 0,12 Sm 0,15 ) 0,85 Mg 0,15 Nor 3,48 Al 0,15 0,92 0,060 1,26 0,07 58,6 55 (Day 0,76 Y 0,12 Nd 0,12 ) 0,86 Mg 0,14 Ni 3,46 Al 0,10 Co 0,10 Mr 0,10 0,90 0,027 1,16 0,12 66,6 56 The 0,60 AND 0,35 Mg 0,05 Neither 3,50 To the 0,12 0,91 0,012 1,20 0,11 50,6 57 (The 0,845 AND 0,155 ) 0,84 Mg 3,45 Neither 3,45 To the 0,15 0,92 0,017 1,26 0,09 68,1 58 (Day 0,501 Prof 0,233 Nd 0,249 Zr 0,004 Y 0,013 ) 0,83 Mg 0,17 Ni 3,13 Al 0,17 Co 0,1 0,92 0,070 1,40 0,00 72,5 59 (The 0,975 AND 0,025 ) 0,82 Mg 0,18 Neither 3,55 To the 0,18 0,90 0,023 1,25 0,10 56,8 60 (The 0,22 Nd 0,30 Sm 0,20 Gd 0,20 Y 0,08 ) 0,90 Mg 0,10 Nor 3,18 Al 0,12 0,90 0,095 1,53 0,02 72,0 [Table 1-4] AlloyNo. Component composition of the hydrogen storage alloy HM P0,5 B ζ / ε MV [µm] 61 (Day 0,83 Ce 0,01 Y 0,16 ) 0,86 Mg 0,14 Ni 3,35 Co 0,30 Al 0,15 0,91 0,051 1,27 0,14 60,0 62 Day 0,75 Y 0,05 Mg 0,20 Ni 2,85 Mr 0,10 Co 0,55 Al 0,10 0,94 0,059 1,24 0,10 73,2 63 Day 0,63 Y 0,20 Mg 0,17 Ni 3,1 Co 0,30 Al 0,10 0,91 0,047 1,24 0,06 55,5 64 (At 0,45 when 0,45 What 0,1 ) 0,85 Mg 0,15 us 3,3 the 0,20 0,89 0,078 1,22 0,09 65,6 65 Day 0,7 Mg 0,3 Co 0,45 Ni 2,35 Feb 0,20 0,80 0,032 3,28 0,00 100,1 66 La 2,0 Ni 6,8 Al 0,1 Fe 0,1 (=LaNi 3,4 Al 0,05 Fe 0,05 ) 0,83 0,012 1,84 0,00 115,5 67 La 0,55 Pr 0,06 Nd 0,19 Mg 0,20 Ni 3,27 Fe 0,05 Al 0,08 0,96 0,045 1,32 0,03 91,1 68 MM 0,83 Mg 0,17 Ni 2,84 Al 0,17 Co 0,20 Feb 0,10 0,97 0,130 2,85 0,02 78,8 69 La 0,80 Mg 0,20 Ni 2,85 Al 0,11 Fe 0,53 0,84 0,023 3,30 0,03 100,3 70 (The 0,6 Nd 0,25 Sm 0,1 Zr 0,05 ) 0,85 Mg 0,15 Nor 3,20 Fe 0,10 Al 0,15 0,96 0,088 2,00 0,05 74,2 (Property assessment of cells)

[0244] The evaluation tests of the cells for evaluation based on alloys Nos. 1 to 70 obtained as described above were conducted according to the following procedures. The evaluation temperature was 40°C for all tests. The results are summarized in Table 2-1 to Table 2-4. (1) Electrode discharge capacity

[0245] The electrode discharge capacity of a working electrode was confirmed using the following method. After a 10-hour constant current charge at a current value of 80 mA / g per working electrode active material, a constant current discharge was performed at a current value of 40 mA / g per working electrode active material. The condition for termination of the discharge was that the working electrode potential was -0.5 V. This charge-discharge cycle was repeated 10 times, and the maximum discharge capacity was considered the discharge capacity of the working electrode.

[0246] It was confirmed that the discharge capacity of the working electrode was saturated and stabilized after the ten charge-discharge cycles. Using the discharge capacity of AB5 alloy No. 34, which is shown in Table 1-2, as the reference capacity, a ratio of the measured discharge capacity to this reference capacity was calculated using the relational expression (2) below. Alloys with this ratio greater than 1.15 were rated as excellent, with a higher discharge capacity than the AB5 alloy. [Mathematical Formula 4] Discharge capacity = (discharge capacity of the alloy to be evaluated) (discharge capacity of the AB5 alloy (No. 34)) (2) Cycle life characteristics

[0247] For each cell whose working electrode discharge capacity was confirmed under (1) Electrode Discharge Capacity as described above, the cycle life characteristics of the working electrode were obtained using the following method. If the current required to complete charging or discharging in one hour to the working electrode discharge capacity, as confirmed under (1) Electrode Discharge Capacity as described above, is 1C, performing constant current charging and discharging at a current value of C / 2 in a working electrode charge rate range of 20 to 80% is defined as one cycle. This cycle was repeated 300 times, and the discharge capacity after 300 cycles was measured, and the capacity retention ratio was determined using the following relational expression (3): [Mathematical Formula 5] Capacity maintenance ratio = (discharge capacity in the 100th cycle) (discharge capacity in the 5th cycle)

[0248] For the evaluation of cycle life properties, the capacity retention ratio after 300 cycles of AB5 alloy No. 34, as shown in Table 1-2, was used as a reference for the capacity retention ratio, and a ratio to this ratio was calculated using the following relational expression (4). Alloys with this ratio greater than 1.15 were rated as excellent, with higher cycle life properties than AB5 alloy. [Mathematical Formula 6] Cycle life properties = (capacity maintenance ratio after 300 cycles of the alloy being measured) (capacity maintenance ratio after 300 cycles of the AB5 alloy (No. 34)) (alloy costs)

[0249] For alloy costs, the raw material costs for producing each of the alloys with the component compositions listed in Tables 1-1 to 1-4 by melting metals with a purity of 99% were relatively evaluated. Alloys that were 10% or more cheaper than Alloy No. 34 (reference cost) were rated as excellent; those that were 0 to 10% cheaper were rated as good; those that were more than 0 to 10% more expensive were rated as mediocre; and those that were 10% or more expensive were rated as unsatisfactory. The results are shown in Tables 2-1 to 2-4. As can be seen from these tables, the hydrogen storage alloys of the inventive examples have advantageous values ​​in aspects including properties and cost. [Table 2-1] AlloyNo. Electrode properties Cost Remarks Discharge capacity (ratio to alloy No. 34) Cycle life characteristics (relative to alloy No. 34) 1 1,19 1,30 terrific Invention example 2 1,18 1,24 terrific Invention example 3 1,17 1,25 terrific Invention example 4 1,19 1,26 terrific Invention example 5 1,20 1,24 terrific Invention example 6 1,18 1,22 terrific Invention example 7 1,21 1,36 terrific Invention example 8 1,20 1,35 terrific Invention example 9 1,20 1,25 terrific Invention example 10 1,18 1,26 terrific Invention example 11 1,18 1,17 terrific Invention example 12 1,21 1,30 terrific Invention example 13 1,24 1,35 terrific Invention example 14 1,21 1,24 terrific Invention example 15 1,21 1,23 terrific Invention example 16 1,23 1,29 terrific Invention example 17 1,25 1,20 terrific Invention example 18 1,21 1,24 terrific Invention example 19 1,20 1,27 terrific Invention example 20 1,24 1,28 terrific Invention example [Table 2-2] AlloyNo. Electrode properties Cost Remarks Discharge capacity (ratio to alloy No. 34) Cycle life characteristics (relative to alloy No. 34) 21 1,24 1,24 terrific Invention example 22 1,18 1,38 terrific Invention example 23 1,19 1,38 terrific Invention example 24 1,22 1,28 terrific Invention example 25 1,20 1,28 terrific Invention example 26 1,16 1,25 terrific Invention example 27 1,11 1,68 terrific Invention example 28 1,16 1,48 good Invention example 29 1,06 1,45 terrific Invention example 30 1,10 1,73 terrific Invention example 31 1,16 1,48 terrific Invention example 32 1,12 1,61 terrific Invention example 33 1,12 1,59 terrific Invention example 34 1,00 1,00 Comparison example (reference example) 35 1,11 1,13 terrific Comparison example 36 1,13 1,10 terrific Comparison example 37 1,14 1,12 good Comparison example 38 1,16 1,12 terrific Comparison example 39 1,11 1,15 terrific Comparison example 40 1,08 1,18 terrific Comparison example [Table 2-3] AlloyNo. Electrode properties Cost Remarks Discharge capacity (ratio to alloy No. 34) Cycle life characteristics (relative to alloy No. 34) 41 1,17 1,06 terrific Comparison example 42 1,07 1,14 good Comparison example 43 1,15 1,05 good Comparison example 44 1,07 1,18 insufficient Comparison example 45 1,13 1,02 good Comparison example 46 1,09 1,04 good Comparison example 47 1,11 1,08 mediocre Comparison example 48 1,16 1,02 good Comparison example 49 1,10 1,15 insufficient Comparison example 50 1,08 1,05 terrific Comparison example 51 1,10 1,15 insufficient Comparison example 52 1,11 1,10 terrific Comparison example 53 1,13 1,08 good Comparison example 54 1,13 1,10 good Comparison example 55 1,12 1,13 insufficient Comparison example 56 1,10 1,13 mediocre Comparison example 57 1,12 1,14 terrific Comparison example 58 1,12 1,15 insufficient Comparison example 59 1,10 1,12 terrific Comparison example 60 1,11 1,15 insufficient Comparison example [Table 2-4] AlloyNo. Electrode properties Cost Remarks Discharge capacity (ratio to alloy No. 34) Cycle life characteristics (relative to alloy No. 34) 61 1,12 1,09 mediocre Comparison example 62 1,15 1,08 insufficient Comparison example 63 1,12 1,15 mediocre Comparison example 64 1,08 1,15 insufficient Comparison example 65 0,92 1,35 mediocre Comparison example 66 0,89 0,35 terrific Comparison example 67 1,11 1,32 insufficient Comparison example 68 1,12 1,23 mediocre Comparison example 69 1,01 1,35 terrific Comparison example 70 1,12 1,28 insufficient Comparison example

[0250] As can be seen from Tables 2-1 to 2-4, Alloys Nos. 1 to 33 of the inventive examples exhibit well-balanced, excellent properties, with evaluation values ​​for both discharge capacity and cycle life properties being 1.15 or more compared to those of AB5 Alloy No. 34. In contrast, it can be seen that the evaluation values ​​for both properties of Alloys Nos. 34 to 70 of Comparative Examples are below 1.15, indicating that these hydrogen storage alloys have insufficiently balanced battery properties.

[0251] In the present invention, the presence of the surface-treated layer of the alloy to improve durability and the properties of the alloy itself were discovered in combination, leading to the completion of the invention. The inventive examples are all alloys containing an appropriate amount of Y, while the comparative examples are alloys whose Y content is outside the range of the appropriate amount, alloys that do not contain Y, and alloys to which Y2O3 was externally added.

[0252] Alloys containing Y outside the appropriate amount range are prone to cracking under the influence of hydrogen storage and desorption, and a surface-treated layer that imparts durability to the alloy cannot be sufficiently formed. In addition to these alloys, alloys that do not contain Y are sometimes also improved in durability by the effect of externally added Y2O3, but not enough to achieve the required durability level. This is presumably because a layer has formed inside these alloys, which is different from the surface-treated layer that forms on an alloy containing a corresponding amount of Y. <Beispiel 2>

[0253] As invention examples, hydrogen storage alloys Nos. 7, 8, 21, and 25 shown in Tables 1-1 and 1-2 were subjected to a predetermined treatment, and then powder surface analysis and pore diameter distribution evaluation were performed.

[0254] In the powder surface analysis, the surface-treated layer formed on the alloy surface was examined using a transmission electron microscope. Specifically, each of the hydrogen storage alloys obtained by subjecting Sample Nos. 7, 8, 21, and 25 to the predetermined treatment was mixed with epoxy resin, and then the epoxy resin was cured at 120°C for 30 minutes to embed the alloy in the resin. A sample in the form of flakes of 100 nm or less was obtained by a flaking method using an argon beam.

[0255] An ion slicer (EM-09100IS) from JEOL Ltd. was used for the flaking process. The flaked sample was ground thin at an accelerating voltage of 6 kV until pores of a few µm opened, and then post-processed at an accelerating voltage of 1.0 kV for 15 minutes.

[0256] For the obtained flaky sample, the surface-treated layer formed on the alloy surface was observed using a transmission electron microscope (JEM-2100F, manufactured by JEOL Ltd.) at an accelerating voltage of 200 kV. An energy-dispersive X-ray emission spectrometer (JED-2300, manufactured by JEOL Ltd.) built into the instrument was used to analyze the elements contained in the surface-treated layer.

[0257] As a result, it was confirmed that on the surface of the hydrogen storage alloy, a layer of an oxide or a hydroxide containing at least partially Y was present on and in close contact with the surfaces of the alloy particles.

[0258] It was further confirmed that the thickness of this surface-treated layer in the hydrogen storage alloy No. 7 was 220 nm, and that the thickness of the surface-treated layer became smaller with increasing amount of Y contained in the hydrogen storage alloy.

[0259] On the other hand, the pore diameter distribution was evaluated as follows. Hydrogen storage alloys Nos. 7, 8, 21, and 25, which had undergone the above-mentioned predetermined treatment, were vacuum-dried at 100°C for two hours, and then a nitrogen adsorption-desorption isotherm at a liquid nitrogen temperature (77.3 K) of each hydrogen storage alloy was measured using a fully automatic gas adsorption meter (AS1-MP, Anton Paar GmbH). The nitrogen adsorption amount per unit weight of the hydrogen storage alloy on the adsorption-desorption isotherm was calculated to be represented by a volume of gaseous nitrogen in the standard state. The total pore volume was calculated from the relational expression (B), where the nitrogen adsorption amount at a relative pressure (p / p0 = 0.99) on the adsorption-desorption isotherm was expressed as V [Ncm] 3 / g] was specified.

[0260] Furthermore, using the adsorption-desorption isotherm, the pore diameter distribution in a mesopore region was analyzed using the BJH method, and the pore diameter distribution in a micropore to mesopore region was analyzed using the DFT method, and the mean pore diameter was calculated. The result was a total pore volume of 0.0046 cm 3 / g and an average pore diameter of 25.9 nm. The specific BET surface area was 0.702 m 2 / g. For hydrogen storage alloys No. 8, 21 and 25, the total pore volume ranged from 0.0040 to 0.0125 cm 3 / g and the average pore diameters ranged from 10 to 35 nm. All alloys had specific BET surface areas of 0.790 m 2 / g or more. These measurement results indicate the characteristics of the porous texture of the oxide or hydroxide layer containing at least partially Y, that is, the surface-treated layer formed on the surface of the hydrogen storage alloy and in close contact with the surfaces of the alloy particles.

[0261] As comparative examples, hydrogen storage alloys of Comparative Examples were obtained by the same method as described above, except that Nos. 43 and 48 shown in Tables 1-3 were used. On the surface of each hydrogen storage alloy of Comparative Example, no layer of an oxide or hydroxide containing at least partially Y and in close contact with the surface was present, and there was a proportion of more than 500 nm in the surface-treated layer. Both alloys were outside the ranges of the total pore volume, average pore diameter, and BET specific surface area of ​​the present invention. (Battery properties)

[0262] A nickel-hydrogen battery adjusted to a state of charge (SOC) of 60% using the hydrogen storage alloy subjected to the above-mentioned predetermined treatment was discharged at a rate of 1C for five seconds under conditions of 25°C. The discharge resistance was calculated based on Ohm's law from the amount of voltage change before and after discharge and the current value during discharge.

[0263] The discharge capacity was confirmed according to the method of Example 1. Constant current charging and constant current discharging at a current value of C / 3 were considered one cycle (the final voltage was 1.0 V), and 1800 charge and discharge cycles were performed. The discharge capacity was then measured after the 1800 cycles, and the capacity retention ratio was obtained by the following relational expression (5): [Mathematical Formula 7] Capacity maintenance ratio = (discharge capacity in the 1800th cycle) (discharge capacity in the 1st cycle)

[0264] Table 3 shows the discharge resistance and capacity retention ratio results described above. [Table 3] AlloyNo. Discharge resistance[Ω] Ratio to maintaining capacity [%] Remarks 7 0,16 94,9 Invention example 8 0,16 94,9 Invention example 21 0,17 95,0 Invention example 25 0,15 94,8 Invention example 43 0,15 87,2 Comparison example 48 0,15 86,5 Comparison example

[0265] As shown in Table 3, the negative electrode active materials obtained from the inventive examples, namely, alloys Nos. 7, 8, 21, and 25, exhibit high capacity retention ratios after the durability test while simultaneously exhibiting low discharge resistances. Thus, it can be said that the negative electrode active materials using the alloys of the inventive examples exhibit a high level of compatibility between performance characteristics and durability.

[0266] For these samples, the surface states of the alloys were evaluated in the same way after the durability evaluation. As a result, in the inventive examples, the surface state of the above-described embodiment was observed to be similar to that before the durability evaluation. On the other hand, in the comparative examples, the surface state of the above-described embodiment was not observed. Therefore, it can be said that the effects of Y on durability are different when comparing the case where an appropriate amount of Y is contained in the alloy with the case where Y is added externally as Y2O3. Industrial applicability

[0267] The hydrogen storage alloy of the present invention is superior to a conventionally used AB5-type hydrogen storage alloy in both discharge capacity and cycle life characteristics. Therefore, this hydrogen storage alloy is not only suitable as a negative electrode material for alkaline storage batteries for applications in hybrid electric vehicles and start-stop vehicles, but can also be used for alkaline storage batteries for pure electric vehicles. List of reference symbols 1 Positive electrode 2 Negative electrode 3 Separator 4 Housing (battery housing) 10 alkaline storage batteries QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] JP 11-323469

[0028] WO 01 / 048841

[0028] JP 2005-032573

[0028] JP 2009-074164

[0028] JP 2009-108379

[0028] JP 2009-138220

[0028] JP 2000-182608

[0028] WO 2007 / 23901

[0028] JP 2009-228096

[0028] JP 2013-134903

[0028] JP 2014-026844

[0028] JP 2017-532446

[0028] JP 2016-069691

[0028] JP 2016-069692

[0028] JP 2014-114476

[0028] JP 2010-080291

[0028] JP 2004-247288

[0028] JP 2010-108910

[0028] JP 2016-012443

[0028] JP 2011-014258

[0028] Cited non-patent literature

[0000] L. Zhiping et al., J. Rare Earth 33, page 397 (2015)

[0028] ZJ Gao et al., J. Taiwan Institute Chem. Engineers 89, page 183 (2018

[0028] S. Yasuoka et al., J. Power Sources 346, page 56 (2017

[0028] Tiejun Meng et al., Batteries 2, (2016) 34

[0028] Tiejun Meng et al., Batteries 3, (2017) 28

[0028] Yang-huan Zhang et al., Materials Characterization 61 (2010) 305

[0028] XU Guochang et al., J. Rare Earth 27 (2009) 250

[0028] Hideaki Sodeyama et al.: Ibaraki District Conference. Page 137 (jointly organized by the Kanto Branch of the Japan Society of Mechanical Engineers and the Japan Society of Precision Engineering, published on September 28, 2007

[0028] < / batterieanwendungen> < / elektrolytschicht>

Claims

[1] Hydrogen storage alloy used for an alkaline storage battery, characterized by that the hydrogen storage alloy has a main phase that has the crystal structures of an A2B7 type structure, an A5B 19 -type structure and an AB3-type structure and satisfies the conditions of the following general formula (1): [Chemical Formula 1] (La 1-a-b Y a R b ) 1-c Mg c Ni d Al e Cr f Fe g (1), where R and the suffixes a, b, c, d, e, f and g are as follows: R is one or both of the elements Sm and Ce, 0 <a≤0,12, 0≤b≤0.12, 0.13≤c≤0.27, 3.20≤d+e+f+g+≤3.75, 0≤e≤0.14, 0≤f≤0.50, and 0≤g≤0.

35. [2] A hydrogen storage alloy for an alkaline storage battery according to claim 1, wherein the general formula (1) further satisfies the following condition: the suffixes a, b, c, d, e, f and g in the general formula (1) are as follows: 0 <a≤0,10, 0 <b≤0,10, 0.14≤c≤0.26, 3.25≤d+e+f+g≤3.70, 0≤e≤0.13, 0≤f≤0.04, and 0≤g≤0.

30. [3] The hydrogen storage alloy for an alkaline storage battery according to claim 1, wherein the hydrogen storage alloy has a hydrogen storage capacity H / M (H is the number of hydrogen atoms, M is the number of metal atoms) of 0.94 or more when a hydrogen pressure of up to 1 MPa is applied at 80°C, and wherein a hydrogen pressure P0.5 when the hydrogen storage capacity H / M during hydrogen desorption is 0.5 is 0.025 MPa or more but 0.12 MPa or less. [4] The hydrogen storage alloy for an alkaline storage battery according to claim 1, wherein the hydrogen storage alloy, the particle size of which has been adjusted to be in a range of 150 μm or more but 1 mm or less, has a volume-average particle diameter MV of 75 μm or more after repeated hydrogen storage and desorption, the volume-average particle diameter MV being measured after repeating five times a cycle of applying a hydrogen pressure of up to 3 MPa at 80°C and holding it for one hour for hydrogen storage and evacuating and reducing the pressure to or below 0.01 MPa at 80°C and holding it for one hour for hydrogen desorption. [5] The hydrogen storage alloy for an alkaline storage battery according to claim 1, wherein in the hydrogen storage desorption characteristics of the hydrogen storage alloy at 80°C, a value calculated as a plateau slope B during hydrogen desorption after storage and represented by the following relational expression (A) is in a range of 1.3 or more but 3.0 or less: [Mathematical Formula 1] Plateau slope B=[log(P0.7 / P0.3)] / 0.4 where P0.7 is a hydrogen pressure [MPa] when the hydrogen storage capacity (H / M) = 0.7, and P0.3 is a hydrogen pressure [MPa] when the hydrogen storage capacity (H / M) = 0.

3. [6] The hydrogen storage alloy for an alkaline storage battery according to claim 5, wherein, in an X-ray diffraction measurement of the hydrogen storage alloy using Cu-Ka radiation as an X-ray source, the ratio ζ / ε of the diffraction intensity ζ of the (101) plane of an AB5 phase to the diffraction intensity ε of a strongest diffraction peak present in a range of a diffraction angle 20 of 40 to 45° is 0.08 or less. [7] A hydrogen storage alloy for an alkaline storage battery according to claim 1, wherein in the hydrogen storage alloy, a layer of an oxide or hydroxide containing Y is present on at least a part of a surface of the hydrogen storage alloy. [8] A hydrogen storage alloy for an alkaline storage battery according to claim 7, wherein in the hydrogen storage alloy, the layer of an oxide or hydroxide containing Y present on at least a part of the surface of the hydrogen storage alloy has a thickness of 500 nm or less where the layer is in close contact with surfaces of alloy particles. [9] A hydrogen storage alloy for an alkaline storage battery according to claim 7, wherein an oxide or hydroxide present on at least a part of the surface of the hydrogen storage alloy is mainly composed of a rare earth element contained in the hydrogen storage alloy. [10] A hydrogen storage alloy for an alkaline storage battery according to claim 1, wherein the BET specific surface area of ​​the hydrogen storage alloy in which an oxide or hydroxide is present on at least a part of the surface of the hydrogen storage alloy is more than 0.5 m 2 / g. [11] A hydrogen storage alloy for an alkaline storage battery according to claim 10, further wherein the pore volume is 0.013 cm 3 / g or less and the average pore diameter is 40 nm or less. [12] An alkaline storage battery which uses as a negative electrode the hydrogen storage alloy according to at least one of claims 1 to 11, characterized by that the alkaline storage battery is installed in a hybrid electric vehicle with an engine as a power source and supplies the engine with power. [13] An alkaline storage battery which uses as a negative electrode the hydrogen storage alloy according to at least one of claims 1 to 11, characterized by that the alkaline storage battery is installed in a motor vehicle with a start-stop function that starts an engine through a starter motor and supplies the starter motor with power. [14] Vehicle, characterized by that the vehicle has an alkaline storage battery as a power source for supplying a motor, which uses the hydrogen storage alloy according to at least one of claims 1 to 11 as the negative electrode.

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