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

Abstract

The present invention provides: a hydrogen storage alloy which is suitable for a negative electrode of an in-vehicle alkaline storage battery; an alkaline storage battery which uses this hydrogen storage alloy; and a vehicle. The present invention provides: a hydrogen storage alloy for alkaline storage batteries, the hydrogen storage alloy being used for an alkaline storage battery and having an A2B7 type crystal structure, an A5B19 type crystal structure or a AB3 type crystal structure as a main phase in combination, while being represented by general formula (1) (La1-a-bYaRb)1-cMgcNidAleCrfFeg (wherein R represents one or both of Sm and Ce; and indexes a, b, c, d, e, f and g represent numbers that satisfy 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 which uses this hydrogen storage alloy for alkaline storage batteries in a negative electrode; and a vehicle which comprises this alkaline storage battery as a power supply for a motor.

Description

[Technical Field]

[0001] The present invention relates to a hydrogen storage alloy for use in alkaline storage batteries, and in particular to a hydrogen storage alloy suitable for use in alkaline storage batteries for power sources such as hybrid electric vehicles (HEVs) and vehicles with idling stop systems, an alkaline storage battery suitable for use as a power source for hybrid electric vehicles (HEVs) and vehicles with idling stop systems, and a vehicle equipped with such an alkaline storage battery. [Background technology]

[0002] In recent years, secondary batteries have come to be widely used in, for example, mobile phones, personal computers, power tools, hybrid electric vehicles (HEVs), and electric vehicles (EVs), and alkaline storage batteries are primarily used for these applications. Among these, high output and high durability are particularly important for alkaline storage batteries used in vehicles such as hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), and electric vehicles (EVs). Furthermore, as these applications become more widespread, there is a growing demand for smaller and lighter alkaline storage batteries.

[0003] Conventionally, hydrogen storage alloys with an AB5 crystal structure have been used for the negative electrodes of alkaline storage batteries, but these alloys have limitations in terms of reducing the size and weight of batteries, and there has been a demand for the development of new hydrogen storage alloys that can achieve high capacity in a small size. As a solution to this problem, Patent Documents 1 and 2 propose rare earth-Mg transition metal hydrogen storage alloys that contain Mg.

[0004] Furthermore, one possible method for achieving smaller and lighter alkaline storage batteries is to reduce the amount of hydrogen storage alloy used in the negative electrode, but reducing the amount of hydrogen storage alloy causes a new problem: a decrease in the output of the alkaline storage battery due to a decrease in nickel active sites. To solve this problem, Patent Document 3 proposes a method for increasing the operating voltage by using a hydrogen storage alloy with a high hydrogen equilibrium pressure.

[0005] In addition, several rare earth-Mg-Ni-based alloys have been proposed as hydrogen storage alloys. For example, Patent Document 4 discloses a hydrogen storage alloy represented by the general formula: Ln δ , β , ε , γ-δ-ε Mg x Ni y A z (where Ln is at least one element selected from rare earth elements including Y, Ca, Zr, and Ti, A is at least one element selected from Co, Mn, V, Cr, Nb, Al, Ga, Zn, Sn, Cu, Si, P, and B, and the subscripts 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, a hydrogen storage alloy is disclosed in which Sm is contained in the above Ln at 20 mol% or more.

[0006] In addition, Patent Document 5 discloses a hydrogen storage alloy represented by the general formula: (La a Sm b A c ) 1-w Mg w Ni x Al y T z (where A and T each represent at least one element selected from the group consisting of Pr, Nd, etc. and the group consisting of V, Nb, etc., and the subscripts a, b, and c respectively satisfy the relationships of a > 0, b > 0, 0.1 > c ≧ 0, and a + b + c = 1, and the subscripts w, x, y, and z are respectively in the ranges shown by 0.1 < w ≦ 1, 0.05 ≦ y ≦ 0.35, 0 ≦ z ≦ 0.5, and 3.2 ≦ x + y + z ≦ 3.8). An alloy having the composition shown by this formula is disclosed.

[0007] Patent Document 6 aims to provide an alkaline storage battery with improved cycle characteristics and discharge characteristics, and discloses a general formula: (A α Ln 1-α ​​​​​​​​​​(wherein A represents one or more elements, including at least Sm, selected from the group consisting of Pr, Nd, Sm, and Gd; Ln represents at least one element selected from the 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 element selected from the group consisting of V, Nb, Ta, Cr, Mo, Mn, Fe, Co, Zn, Ga, Sn, In, Cu, Si, P, and B; and the subscripts α, β, γ, δ, and ε represent numbers that satisfy the following relationships: 0.4≦α, 0.05<β<0.15, 3.0≦γ≦4.2, 0.15≦δ≦0.30, and 0≦ε≦0.20, respectively).

[0008] Patent Document 7 reports a hydrogen storage alloy electrode using hydrogen storage alloy particles having a median diameter D50, expressed as 50% penetration, in the range of 8 to 15 μm to enable high-rate discharge.

[0009] Furthermore, Patent Document 8 discloses a hydrogen storage alloy containing a phase having a Gd2Co7 crystal structure, with the aim of providing a hydrogen storage alloy with excellent cycle life characteristics. The alloy is characterized in that the phase accounts for 10% by weight or more of the entire hydrogen storage alloy, and the hydrogen storage alloy contains 2 mol % to 10 mol % of yttrium based on the entire hydrogen storage alloy.

[0010] Furthermore, Patent Document 9 discloses a rare earth-Mg-Ni based hydrogen storage alloy that can suppress the decrease in operating voltage even after a nickel-metal hydride secondary battery has been left unused for a long period of time, thereby providing a high operating voltage. Specifically, the hydrogen storage alloy used in the battery is a rare earth-Mg-Ni based alloy having the general formula: (La a Nd b A c D d ) 1-w Mg w Ni x Al y T zIt has the composition shown therein. In the formula, A, D, and T each represent at least one element selected from the group consisting of Sm and Gd, the group consisting of Pr, Eu, etc., and the group consisting of V, Nb, etc., and the subscripts a, b, c, d satisfy the relationships shown by a≧0, b≧0, c>0, 0.1>d≧0, a + b + c + d = 1 respectively, and the subscripts w, x, y, z are respectively in the ranges shown by 0<w≦0.25, 0.05≦y≦0.35, 0≦z≦0.5, 3.15≦x + y + z≦3.35.

[0011] Also, in Patent Document 10, as a hydrogen storage alloy for an alkaline storage battery that enables cost reduction while maintaining high output, a general formula (Re 1-x Y x ) 1-y-z Zr y Mg z Ni a-b Al b (Re: containing only La or containing La and at least one element selected from Nd and Sm, 0<x≦0.60, 0≦y≦0.02, 0.09≦z≦0.13, 3.40≦a≦3.80, 0.05≦b≦0.20), an alloy characterized by being represented thereby is disclosed.

[0012] Also, in Patent Document 11, for the purpose of providing a nickel-hydrogen secondary battery having high capacity and excellent self-discharge characteristics and cycle life characteristics, a general formula: (RE 1-x T x ) 1-y Mg y Ni z-a Al a (However, in the formula, 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 subscripts x, y, z, a respectively represent 0≦x, 0.05≦y≦0.35, 2.8≦z≦3.9, 0.10≦a≦0.25), having a composition represented thereby, having a crystal structure in which an AB2-type subunit and an AB5-type subunit are laminated, and a hydrogen storage alloy in which a part of the Ni is substituted with Cr is disclosed.

[0013] In addition, Patent Document 12 aims to provide a hydrogen storage alloy with suppressed pulverization. For the maximum peak intensity appearing in the range of 2θ = 41° to 44° by X-ray diffraction measurement using Cu-Kα rays as the X-ray source, the ratio of the maximum peak intensity appearing in the range of 2θ = 31° to 33° is 0.1 or less (including 0), and a hydrogen storage alloy is disclosed. Further, as a specific composition, La 1-a-b Y a Mg b Ni c Al d (where 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) is disclosed.

[0014] In addition, Patent Document 13 aims to provide a hydrogen storage alloy excellent in corrosion resistance and durability, and a nickel-hydrogen storage battery excellent in cycle life using the hydrogen storage alloy. The general formula (RE 1-a-b Sm a Mg b )(Ni 1-c-d Al c M 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 elements selected from rare earth elements other than Sm and Y, and La is essential; M is Mn and / or Co) is disclosed.

[0015] In addition, Patent Document 14 aims to provide a hydrogen storage alloy excellent in corrosion resistance and durability, and a nickel-hydrogen storage battery excellent in cycle life using the hydrogen storage alloy. The 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 elements selected from rare earth elements other than Sm and Y; La is essential, and M is Mn and / or Co) represents a hydrogen storage alloy and a nickel-hydrogen battery using the same are disclosed.

[0016] Further, Patent Document 15 discloses a hydrogen storage alloy excellent in corrosion resistance, an electrode using the same, and an alloy powder for use in a nickel-hydrogen storage battery, having a general formula: Ln 1-w Mg w Ni x Al y T z (However, in the formula, Ln represents at least one element selected from the 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 element selected from the group consisting of V, Nb, Ta, Cr, Mo, Mn, Fe, Co, Ga, Zn, Sn, In, Cu, Si, P and B, and the subscripts w, x, y, z are respectively in the ranges represented by 0.08 ≦ w ≦ 0.13, 0.05 < y < 0.20, 0 ≦ z ≦ 0.5, 3.15 ≦ x + y + z ≦ 3.50.) A hydrogen storage alloy powder for an alkaline storage battery is disclosed, which includes a core of a hydrogen storage alloy having a composition represented by the formula and a surface layer integrally formed on the surface of the core and having a reduced aluminum concentration compared to the composition.

[0017] Further, Patent Document 16 discloses, as a hydrogen storage alloy powder for an alkaline storage battery, which suppresses a decrease in operating voltage and obtains a high operating voltage even after long-term storage, particularly after long-term storage after undergoing charge-discharge cycles when applied to an alkaline storage battery, a hydrogen storage alloy having at least two phases containing La, Ni, and Y or a heavy rare earth element, wherein the first phase has a general formula R1 a R2 b R3 c Ni d R4 e(In the formula, R1 is at least one element that requires La, R2 is at least one element selected from the group consisting of Y and heavy rare earth elements, R3 is Ca and / or Mg, R4 is at least one element selected from the group consisting of Co, Mn, and Al, and a, b, c, d, and e are numerical values that satisfy a + b + c = 1, 0 ≤ b ≤ 0.3, 0 ≤ c ≤ 0.4, 3.0 < d + e < 4.0, and 0 ≤ e ≤ 1.) A hydrogen storage alloy is disclosed that has a composition represented by the formula and in which 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] Also, in Patent Document 17, in order to provide a sealed nickel-hydrogen storage battery excellent in high-rate discharge characteristics and charge-discharge cycle characteristics, a layer with a larger nickel content ratio and a thickness of 50 nm or more and 400 nm or less than that in the mother layer component is arranged on the surface of the hydrogen storage alloy powder used for the negative electrode, and a layer with a larger nickel content ratio than that in the mother layer component is arranged on the surface of cracks communicating with the surface of the hydrogen storage alloy.

[0019] Also, in Patent Document 18, in order to sufficiently improve the output characteristics and charge-discharge cycle characteristics of an alkaline storage battery in a low-temperature environment, the general formula Ln 1-x Mg x Ni y-a-b Al a M b(wherein Ln is at least one element selected from rare earth elements including Y, Zr, and Ti, and M is at least one 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.) The negative electrode for an alkaline storage battery is characterized in that it has three layers, a first layer, a second layer, and a third layer, laminated on the surface, and the first layer, which is closer to the bulk phase, contains a larger amount of oxygen than the second layer located above this first layer, and contains 10 atomic % or more of elements soluble in alkaline solution, and the second layer located above this first layer has a higher Ni content than the bulk phase, and the third layer located above this second layer has a higher NiO content than the NiO content in the second layer.

[0020] Patent Document 19 also describes an alloy that can provide a nickel-hydrogen secondary battery that can achieve both high-rate discharge characteristics and life characteristics, in which the negative electrode of the nickel-hydrogen secondary battery contains particles of a rare earth-Mg-Ni system hydrogen storage alloy containing rare earth elements, Mg, and Ni, and the particles of the hydrogen storage alloy have a rare earth hydroxide, which is a hydroxide of the rare earth element, on the surface thereof, and have a specific surface area of ​​0.1 to 0.5 m. 2 / g.

[0021] Patent Document 20 discloses a rare earth-magnesium-nickel based hydrogen storage alloy that uses inexpensive Fe to reduce the cost, improve corrosion resistance, and improve charge acceptance. a Nd b A c B d ) l-v Mg v Ni w Al x Fe y T z(A is at least one element selected from Sm and Gd, B is at least one element selected from Pr, Eu, Tb, Dy, Ho, Er, Tm, Yb, Lu, Sc, Zr, Hf, Ca, and Y, and T is at least one element selected from V, Nb, Ta, Cr, Mo, Mn, Co, Ga, Zn, Sn, In, Cu, Si, P, and B), and in the general formula The a, b, c, and d have the relationships 0≦a, 0≦b, 0≦c, 0≦d<0.1, a+b+c+d=1, 0≦z≦0.5, and in the general formula, the molar ratio v of Mg is 0.10≦v≦0.25, the molar ratio x of Al is 0.10≦x≦0.20, and the molar ratio y of Fe is 0.05≦y≦0.15. Furthermore, a hydrogen storage alloy has been reported that satisfies the following: 3.45≦w+x+y+z≦3.65.

[0022] On the other hand, Non-Patent Document 1 describes a hydrogen storage alloy in which La is replaced with Y in order to improve its properties. 0.80-x Y x Mg 0.20 Ni 2.85 Mn 0.10 Co 0.55 Al 0.10 (x=0,0.05,0.10) is disclosed.

[0023] In addition, Non-Patent Document 2 describes La 0.63 Y 0.20 Mg 0.17 Ni 3.1 Co 0.3 Al 0.1 has been disclosed.

[0024] Furthermore, Non-Patent Document 3 discloses the influence of Ce on RE-Mg-Ni based hydrogen storage alloys (RE: rare earth elements), specifically, (La 0.5 Nd 0.5 ) 0.85 Mg 0.15 Ni 3.3 Al 0.2 , (La 0.45 Nd 0.45 Ce 0.1 ) 0.85 Mg 0.15 Ni 3.3Al 0.2 , (La 0.4 Nd 0.4 Ce 0.2 ) 0.85 Mg 0.15 Ni 3.3 Al 0.2 , (La 0.3 Nd 0.3 Ce 0.4 ) 0.85 Mg 0.15 Ni 3.3 Al 0.2 The alloy is disclosed and the results of its evaluation are reported.

[0025] Non-patent documents 4 and 5 state that Mm 0.83 Mg 0.17 Ni 2.94-x Al 0.17 Co 0.2 Fe x A hydrogen storage alloy expressed as (0≦x≦0.2) has been reported.

[0026] Non-patent document 6 states that 0.7 Mg 0.3 Co 0.45 Ni 2.55-x Fe x A hydrogen storage alloy represented by the following formula has been reported.

[0027] Non-patent document 7 states that 0.80 Mg 0.20 Ni 2.85 Al 0.11 M 0.53 Hydrogen storage alloys represented by (M=Ni, Si, Cr, Cu, Fe) have been reported.

[0028] Non-patent document 8 states that La2Ni 6.9-x Al 0.1 Fe x The properties of hydrogen storage alloys expressed as (0≦x≦2.1) have been reported. [Prior art documents] [Patent documents]

[0029] [Patent Document 1] Japanese Patent Application Publication No. 11-323469 [Patent Document 2] International Publication No. 01 / 048841 [Patent Document 3] Japanese Patent Application Laid-Open No. 2005-032573 [Patent Document 4] Japanese Patent Application Laid-Open No. 2009-074164 [Patent Document 5] Japanese Patent Application Laid-Open No. 2009-108379 [Patent Document 6] Japanese Patent Application Laid-Open No. 2009-138220 [Patent Document 7] Japanese Patent Application Laid-Open No. 2000-182608 [Patent Document 8] International Publication No. 2007 / 23901 [Patent Document 9] Japanese Patent Application Laid-Open No. 2009-228096 [Patent Document 10] Japanese Patent Application Laid-Open No. 2013-134903 [Patent Document 11] Japanese Patent Application Laid-Open No. 2014-026844 [Patent Document 12] Special Publication No. 2017-532446 [Patent Document 13] Japanese Patent Application Laid-Open No. 2016-069691 [Patent Document 14] Japanese Patent Application Laid-Open No. 2016-069692 [Patent Document 15] Japanese Patent Application Laid-Open No. 2014-114476 [Patent Document 16] Japanese Patent Application Laid-Open No. 2010-080291 [Patent Document 17] Japanese Patent Application Laid-Open No. 2004-247288 [Patent Document 18] Japanese Patent Application Laid-Open No. 2010-108910 [Patent Document 19] Japanese Patent Application Laid-Open No. 2016-012443 [Patent Document 20] Japanese Patent Application Laid-Open No. 2011-014258 [Non-patent literature]

[0030] [Non-Patent Document 1] L.Zhiping et al., J.Rare Earth 33 p397(2015) [Non-patent document 2] ZJGao et al., J.Taiwan Institute Chem. Engineers 89 p183(2018) [Non-patent document 3] S. Yasuoka et al., J. Power Sources 346 p56 (2017) [Non-patent document 4] Tiejun Meng et al.,Batteries 2,(2016)34 [Non-Patent Document 5] Tiejun Meng et al.,Batteries 3,(2017)28 [Non-patent document 6] Yang-huan Zhang et al.,Materials Charactarization 61(2010)305 [Non-Patent Document 7] XU Guochang et al., J.Rare Earth 27 (2009) 250 [Non-patent document 8] Hideaki Sodeyama et al.: Proceedings of the Ibaraki Conference, p.137 (co-hosted by the Kanto Branch of the Japan Society of Mechanical Engineers and the Japan Society for Precision Engineering, published September 28, 2007) Summary of the Invention [Problem to be solved by the invention]

[0031] However, the techniques disclosed in Patent Documents 1 and 2 above did not involve optimizing the alloys, and were not adopted for use in hybrid vehicles.

[0032] Furthermore, in the technology disclosed in Patent Document 3, when a hydrogen storage alloy with a high hydrogen equilibrium pressure is used, a new problem arises in that the charge / discharge cycle life is reduced.

[0033] The technology disclosed in Patent Document 4 uses an alloy containing a relatively large amount of Sm, which is an element cheaper than Pr and Nd, but it does not provide a hydrogen storage alloy that is cheap and has excellent durability.

[0034] The technology disclosed in Patent Document 5 uses alloys containing relatively large amounts of La and Sm, which are cheaper elements than Pr and Nd, but it does not provide a hydrogen storage alloy that is inexpensive and has excellent durability. In particular, Zr is required in the examples, and the B / A ratio disclosed is only 3.6. Furthermore, although it is said that increasing the La content raises the reduced hydrogen equilibrium pressure to a level that can be used in batteries, setting an inexpensive La-rich composition is often insufficient.

[0035] Furthermore, the alkaline storage battery using the hydrogen storage alloy disclosed in Patent Document 6 does not achieve the three characteristics of compactness, high output, and durability, which are important for in-vehicle applications, in other words, does not achieve both discharge characteristics and cycle life characteristics, and is therefore insufficient as a hydrogen storage alloy for in-vehicle alkaline storage batteries.

[0036] The hydrogen storage alloy disclosed in Patent Document 7 is an AB5 alloy (MmNi 4.0 Co 0.4 Mn 0.3 Al 0.3 Although the discharge characteristics are improved by atomization, practical application for automotive use is difficult due to factors such as durability, and further improvements in characteristics are required.

[0037] Furthermore, the hydrogen storage alloy disclosed in Patent Document 8 has a relatively high Y content of 2 to 10 mol % of the hydrogen storage alloy, which increases the cost and relatively accelerates pulverization due to hydrogen absorption and desorption, resulting in accelerated corrosion and insufficient durability improvement.

[0038] Furthermore, the hydrogen storage alloy disclosed in Patent Document 9 was primarily intended to suppress a decrease in operating voltage after long-term storage, but the balance between the basic cycle life and discharge capacity was insufficient, and the rare earth elements that constituted it were expensive.

[0039] Furthermore, the hydrogen storage alloy disclosed in Patent Document 10 requires Y as an essential component and aims to achieve high output, but this does not result in sufficient cost reduction, and the discharge capacity is not sufficiently large. Therefore, when applied to batteries, the characteristics are insufficient, and although output can be obtained at low temperatures, cycle life is also an issue.

[0040] Furthermore, the hydrogen storage alloy disclosed in Patent Document 11 aims to realize a nickel-metal hydride battery that has high capacity and excellent self-discharge characteristics and cycle life characteristics, but it has not achieved high capacity, and the cycle life characteristics also need to be further improved.

[0041] Furthermore, the hydrogen storage alloy disclosed in Patent Document 12 aims to achieve high durability by suppressing pulverization, but the specific composition contains a large amount of Y, which poses a cost issue. In addition, pulverization occurs during hydrogen absorption and desorption, which results in poor cycle life characteristics, and further improvement of the characteristics was necessary.

[0042] Furthermore, the hydrogen storage alloy disclosed in Patent Document 13 aims to improve charge-discharge cycle characteristics by improving corrosion resistance and durability. However, the cycle characteristics of the disclosed hydrogen storage alloy containing a relatively large amount of Sm are still insufficient, and further improvements in characteristics such as corrosion resistance are required.

[0043] Furthermore, the hydrogen storage alloy disclosed in Patent Document 14 aimed to improve cycle life, but in terms of the balance with discharge capacity, it was insufficient to improve battery characteristics, and further improvement of characteristics was necessary.

[0044] Furthermore, the hydrogen storage alloy disclosed in Patent Document 15 aims to improve charge-discharge cycle characteristics by improving corrosion resistance and durability, but it is not easy to produce a second phase with a controlled concentration of Y or heavy rare earth elements, and effective battery characteristics were not actually obtained.

[0045] Furthermore, the hydrogen storage alloy disclosed in Patent Document 16 aims to improve charge-discharge cycle characteristics by improving corrosion resistance and durability, but the disclosed alloy contains Nd and Pr, is relatively expensive, and even when the surface condition is controlled by alkali treatment or acid treatment, sufficient cycle characteristics and rate characteristics are not obtained.

[0046] Furthermore, the hydrogen storage alloy disclosed in Patent Document 17 aims to improve low-temperature output characteristics and charge-discharge cycle characteristics. However, even when the surface condition is controlled by the alkali treatment or acid treatment disclosed in this patent, sufficient cycle characteristics are not obtained, and further improvement of the characteristics is necessary.

[0047] Furthermore, the hydrogen storage alloy disclosed in Patent Document 18 aims to improve output at low temperatures and charge / discharge cycle characteristics. In the case of a relatively inexpensive hydrogen storage alloy, the surface of the alloy particles is heat-treated in air to control the surface condition. Although the low-temperature characteristics are considered to be good, the balance between capacity and cycle characteristics is still insufficient, and further improvement of the characteristics is required.

[0048] Furthermore, the hydrogen storage alloy used in Patent Document 19 aims to improve charge-discharge cycle characteristics by improving corrosion resistance and durability. Although the alloy aims to achieve both rate characteristics and life characteristics with a limited specific surface area, the disclosed alloy, which contains a large amount of Sm, has insufficient durability after alkali treatment, and further improvement of characteristics was necessary.

[0049] Furthermore, although the technology disclosed in Patent Document 20 is characterized by the use of inexpensive Fe, it was based on an alloy containing expensive Nd, and as a result, it was not possible to produce an inexpensive alloy, and further improvement in durability was required.

[0050] Furthermore, the hydrogen storage alloy disclosed in Non-Patent Document 1 still has insufficient cycle characteristics, and since it contains a certain amount of Co, consideration is also needed from the standpoint of cost.

[0051] Furthermore, the hydrogen storage alloy disclosed in Non-Patent Document 2 has the lowest effect among rare earths similarly substituted with La, and further improvement in the properties is required.

[0052] Furthermore, Non-Patent Document 3 concludes that rare earth-Mg-Ni alloys containing Ce have a low hydrogen absorption / release capacity and are prone to pulverization when hydrogen absorption / release is repeated, resulting in significant deterioration in batteries.

[0053] In addition, Non-Patent Documents 4 and 5, Mm 0.83 Mg 0.17 Ni 2.94-x Al 0.17 Co 0.2 Fe x For the hydrogen storage alloys (0≦x≦0.2), everything from material properties to battery properties have been reported. However, the hydrogen storage alloys disclosed in Non-Patent Documents 4 and 5 have cycle characteristics that are insufficient from a practical standpoint, and because they contain Co, they are not inexpensive alloys. Therefore, there was a need to achieve both lower cost and higher durability.

[0054] In addition, Non-Patent Document 6 states that 0.7 Mg 0.3 Co 0.45 Ni 2.55-x Fe x Although the characteristics of (0≦x≦0.4) have been disclosed, the cycle characteristics are insufficient and further improvement of the characteristics is required for practical use.

[0055] In addition, La disclosed in Non-Patent Document 7 0.80 Mg 0.20 Ni 2.85 Al 0.11 M 0.53 The (M=Ni, Si, Cr, Cu, Fe) alloys have a small discharge capacity and insufficient cycle life characteristics, so improvements in these characteristics have been desired.

[0056] In addition, La2Ni disclosed in Non-Patent Document 8 6.9-x Al 0.1 Fe x Although the (0≦x≦2.1) alloy itself is inexpensive, the only properties disclosed for the alloy are data on the gas-solid phase reaction related to hydrogen absorption and desorption. For this reason, the alloy disclosed in Non-Patent Document 8 exhibits insufficient properties as a hydrogen storage alloy for alkaline storage batteries. From this technical perspective, there was a need for an inexpensive hydrogen storage alloy with properties suitable for battery use.

[0057] The present invention has been made in consideration of these problems associated with the prior art, and aims to provide a hydrogen storage alloy that is particularly suitable for in-vehicle nickel-metal hydride batteries (alkaline storage batteries), a battery using the alloy, and a vehicle equipped with the battery. [Means for solving the problem]

[0058] To achieve the above objectives, the A2B7 type structure and the A5B type structure are used as hydrogen storage alloys for the negative electrodes of alkaline storage batteries. 19 The present inventors have developed an alloy having a crystal structure in which the main phase is a combination of the AB3-type and AB4-type crystal structures, and a specific composition containing Y (a rare earth element). Furthermore, by utilizing Fe substitution, the charge-discharge cycle life characteristics are significantly improved at low cost. This finding led to the development of the present invention, based on the finding that it is possible to achieve a good balance between the discharge capacity characteristics and the charge-discharge cycle life characteristics of alkaline storage batteries at low cost.

[0059] The present invention is first directed to a hydrogen storage alloy for use in an alkaline storage battery, the hydrogen storage alloy having an A2B7 structure, an A5B 19 The hydrogen storage alloy for alkaline storage batteries has a crystal structure of the AB3 type structure and the AB4 type structure as a total of its main phases, and satisfies the condition of the following general formula (1). Note [ka] where R and the subscripts a, b, c, d, e, f, and g are R: Sm and / or Ce, 0.01≦ a ≤ 0.12, 0.005 ≦b≦0.12, 0.13≦c≦0.27, 3.20≦d+e+f+g≦3.75 And , 3.01≦d≦3.655、 0≦e≦0.12, 0≦f≦0.05, 0≦g≦0.35 Represents.

[0060] Furthermore, a more preferable means for solving the problems can be a hydrogen storage alloy for alkaline storage batteries in which the general formula (1) satisfies the following conditions: Note The subscripts a, b, c, d, e, f, and g in the general formula (1) represent: 0.01≦ a ≤ 0.10, 0.005≦ b ≤ 0.10, 0.14≦c≦0.26, 3.25≦d+e+f+g≦3.70 And , 3.01≦d≦3.655、 0≦e≦0.12, 0≦f≦0.04, 0 <g≦0.30 Represents.

[0061] The hydrogen storage alloy for alkaline storage batteries according to the present invention comprises: (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 the hydrogen pressure is increased to 1 MPa at 80°C, and a hydrogen pressure P0.5 of 0.025 MPa or more and 0.12 MPa or less when the hydrogen storage capacity H / M is 0.5 during hydrogen release. (A) The hydrogen storage alloy has a particle size adjusted to a range of 150 μm or more and 1 mm or less, and the volume average particle size MV after repeated hydrogen absorption and desorption is 75 μm or more. Here, hydrogen absorption is performed by increasing the hydrogen pressure to 3 MPa at 80°C and maintaining this for 1 hour, and hydrogen desorption is performed by evacuating the sample, reducing the pressure to 0.01 MPa or less at 80°C and maintaining this for 1 hour. This process is repeated five times, and then the volume average particle size MV is measured. (c) In the hydrogen absorption / desorption characteristics of the hydrogen storage alloy at 80°C, the plateau slope B at the time of desorption after hydrogen absorption, which is calculated as expressed by the following relational formula (A), is in the range of 1.3 to 3.0,

number

[0062] Secondly, the present invention provides an alkaline storage battery using any of the above hydrogen storage alloys in a negative electrode, the alkaline storage battery being either mounted on a hybrid vehicle using a motor as a drive source and supplying electric power to the motor, or mounted on a vehicle having an idling stop function that starts the engine using a starter motor and supplying electric power to the starter motor.

[0063] Thirdly, the present invention provides a vehicle having an alkaline storage battery using any one of the above hydrogen storage alloys in the negative electrode as a power supply source for a motor. [Effects of the Invention]

[0064] The hydrogen storage alloy for alkaline storage batteries according to the present invention, and the alkaline storage battery using this hydrogen storage alloy, have high power density and, in particular, excellent charge-discharge cycle life characteristics (durability), and therefore have excellent discharge capacity characteristics and can achieve sufficiently high-rate discharge even under in-vehicle usage conditions.

[0065] Furthermore, the hydrogen storage alloy for alkaline storage batteries according to the present invention is preferable because it has specific hydrogen storage characteristics, the average particle size of the finely divided alloy particles of the hydrogen storage alloy for alkaline storage batteries after repeated hydrogen absorption and release is within a predetermined range, and the AB5 phase is controlled to a predetermined amount or less, thereby maintaining electrical characteristics and improving durability. That is, the hydrogen storage alloy for alkaline storage batteries according to the present invention can suppress cracks that occur in the alloy itself under conditions such as hydrogen absorption and release, and the cracks can be accelerated and the alloy can be prevented from pulverizing.

[0066] Furthermore, in the hydrogen storage alloy for alkaline storage batteries according to the present invention, an oxide layer or hydroxide layer containing Y or mainly containing a rare earth element adheres closely to the alloy particles as a surface layer, so that the amount of Al that improves corrosion resistance can be reduced, and ultimately the discharge capacity of the alkaline storage battery can be increased. In other words, the surface layer formed on at least a portion of the surface of the hydrogen storage alloy is composed of hydroxides or oxides mainly containing elements such as Y or rare earth elements that make up the alloy, and therefore has excellent alkaline corrosion resistance. Furthermore, the surface layer formed on the surface of the hydrogen storage alloy has a small pore volume and average pore diameter (size), which reduces the probability of crack occurrence, thereby further improving the corrosion resistance of the hydrogen storage alloy.

[0067] Furthermore, the alkaline storage battery according to the present invention can be made smaller and lighter, and when it is installed in a vehicle such as an automobile, it can provide a hybrid electric vehicle (HEV) or the like that has high driving performance and low fuel consumption. [Brief explanation of the drawings]

[0068] [Figure 1] 1 is a partially cutaway perspective view illustrating an alkaline storage battery using the hydrogen storage alloy of the present invention. [Figure 2] 1 is an example of the PCT characteristics of the hydrogen storage alloy of the present invention. [Figure 3] 1 shows an example of the results of X-ray diffraction measurement on the hydrogen storage alloy of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0069] An embodiment of the present invention will be described below. An alkaline storage battery using a hydrogen storage alloy according to this embodiment will be described with reference to FIG. 1. FIG. 1 is a partially cutaway perspective view showing an example of such a battery. As shown in FIG. 1, an alkaline storage battery 10 is a storage battery that includes, in a housing 4, an electrode group consisting of a nickel positive electrode 1 having nickel hydroxide (Ni(OH)2) as the main positive electrode active material, a negative electrode 2 including a hydrogen storage alloy having the hydrogen storage alloy (MH) according to this embodiment as the negative electrode active material, and a separator 3, together with an electrolyte layer (not shown) filled with an alkaline electrolyte solution.

[0070] The alkaline storage battery 10 is a so-called nickel-metal hydride battery (Ni-MH battery, hereinafter also referred to as "nickel-metal hydride battery"), in which the following reaction occurs.

[0071] [ka]

[0072] [Hydrogen storage alloy] The hydrogen storage alloy used in the negative electrode of the alkaline storage battery according to this embodiment will be described below. The hydrogen storage alloy for alkaline storage batteries according to this embodiment (hereinafter also referred to as "hydrogen storage alloy") is a hydrogen storage alloy used in alkaline storage batteries, and this hydrogen storage alloy has an A2B7 structure, an A5B 19 The main phase is a crystal structure of the AB3 type structure and the AB4 type structure in total, and is characterized by being represented by the following general formula (1). Note [ka] where R and the subscripts a, b, c, d, e, f, and g are R: Sm and / or Ce, 0.01≦ a ≤ 0.12, 0.005 ≦b≦0.12, 0.13≦c≦0.27, 3.20≦d+e+f+g≦3.75 And , 3.01≦d≦3.655、 0≦e≦ 0.12 , 0≦f≦0.05, 0≦g≦0.35 Represents. Here, A2B7 type structure, A5B 19 The crystal structures of the AB3 and AB4 types are Ce2Ni7 type, Gd2Co7 type, and Pr5Co 19 Mold and Ce5Co 19 type, as well as CeNi3 type and PuNi3 type.

[0073] In the present embodiment, it is preferable that the hydrogen storage alloy is a hydrogen storage alloy for an alkaline storage battery in which the general formula (1) satisfies the following conditions. Record In the general formula (1), the subscripts a, b, c, d, e, f, and g are 0.01≦ a ≤ 0.10, 0.005≦ b ≤ 0.10, 0.14 ≤ c ≤ 0.26, [[ID=X4]]3.25 ≤ d + e + f + g ≤ 3.70 <00006XX>, 3.01≦d≦3.655、 0 ≤ e ≤ 0.12 , 0 ≤ f ≤ 0.04, 0 < g ≤ 0.30 represent. <00006XX> When the hydrogen storage alloy represented by the general formula (1) is used as the negative electrode of an alkaline storage battery, the alkaline storage battery is provided with high discharge capacity and charge-discharge cycle life characteristics. Therefore, the hydrogen storage alloy represented by the general formula (1) contributes to the miniaturization and weight reduction of alkaline storage batteries and the achievement of high durability.

[0075] Hereinafter, the reason for limiting the component composition of the hydrogen storage alloy according to the present embodiment will be described. <00006XX>Rare earth element: La 1-a-b Y a R b (However, 0 < a ≤ 0.12, 0 ≤ b ≤ 0.12, preferably 0 < a ≤ 0.10, 0 < b ≤ 0.10) The hydrogen storage alloy according to the present embodiment contains a rare earth element as an element of the A component of the A2B7 type structure, A5B 19 type structure and AB3 type structure. The rare earth element essentially requires two elements, La and Y, as basic components that provide hydrogen storage ability. Since La and Y have different atomic radii, the hydrogen equilibrium pressure can be controlled by this component ratio, and the hydrogen equilibrium pressure proportional to the battery voltage can be arbitrarily set. The atomic ratio a value of Y in the rare earth element is in the range exceeding 0 and not exceeding 0.12. Note: There seems to be some incorrect or incomplete tags in the original text (like <00006XX> which should be corrected for a proper translation). I've translated as accurately as possible with the given text.Within this range, it is easy to set the hydrogen equilibrium pressure suitable for alkaline storage batteries, and the hydrogen storage alloy has good corrosion resistance and is less likely to pulverize, resulting in high durability of the alkaline storage battery. If the value of a exceeds 0.12, the hydrogen storage alloy will become pulverized as it absorbs and releases hydrogen, and the durability of the alkaline storage battery will gradually decrease, even if the alloy has the effect of improving corrosion resistance. The value of a is preferably 0.10 or less, and more preferably 0.003 or more. Y plays a major role in improving the durability of the hydrogen storage alloy by existing as an oxide or hydroxide in a surface layer composed of an oxide layer or hydroxide layer present on at least a portion of the surface of the hydrogen storage alloy.

[0076] Meanwhile, R is either Ce or Sm, or both, and together with Y, contributes to controlling the hydrogen equilibrium pressure and improving the corrosion resistance of the hydrogen storage alloy. The total atomic ratio b of R among the rare earth elements is in the range of 0 to 0.12. Considering the control of the hydrogen equilibrium pressure and durability of the combined Y and R, if the b value exceeds 0.12, pulverization of the hydrogen storage alloy due to hydrogen absorption and desorption may be promoted, potentially reducing the durability of the alkaline storage battery. The b value is preferably 0.10 or less, and more preferably 0.005 or more.

[0077] It is preferable that R is essential together with Y, that is, either or both of Ce and Sm are essential, and it is particularly preferable to use Ce. In this case, it is preferable that the b value is 0.10 or less in order to control the hydrogen absorption / desorption characteristics of the hydrogen storage alloy, which are related to the battery characteristics.

[0078] A composition with a high La content increases the discharge capacity of an alkaline storage battery, and when La is combined with other elements, the discharge capacity characteristics of the alkaline storage battery are further improved. Furthermore, although Pr and Nd are not actively used as rare earth elements, they may be contained at the level of unavoidable impurities.

[0079] Mg:Mg c (where 0.13≦c≦0.27, preferably 0.14≦c≦0.26) Mg has an A2B7 structure, A5B 19 In this embodiment, Mg is an essential element constituting the A component of the AB3-type and AB3-type structures. Mg contributes to improving the discharge capacity characteristics and charge / discharge cycle life characteristics of alkaline storage batteries using hydrogen storage alloys. The c value, which represents the atomic ratio of Mg in the A component, is in the range of 0.13 to 0.27. If the c value is less than 0.13, the hydrogen release capacity of the hydrogen storage alloy decreases, resulting in a decrease in the discharge capacity of the alkaline storage battery. On the other hand, if the c value exceeds 0.27, pulverization of the hydrogen storage alloy, particularly during hydrogen absorption and desorption, is promoted, resulting in a decrease in the charge-discharge cycle life characteristics, i.e., durability, of the alkaline storage battery. Preferably, the c value is in the range of 0.14 to 0.26.

[0080] Ni:Ni d Ni has an A2B7 structure, A5B 19 It is the main element of the B component in the AB3-type structure and the AB4-type structure. The atomic ratio d of Ni to the A component will be described later.

[0081] Al:Al e (However, if Fe is essential, 0≦e≦0.14, and if Fe is not essential, 0.03≦e≦0.13.) Al has an A2B7 structure, A5B 19 Al is an element contained as the B component in the AB3-type and AB4-type structures. Al is effective in adjusting the hydrogen equilibrium pressure, which is related to the battery voltage, and can also improve corrosion resistance, thereby improving the durability of hydrogen storage alloys, i.e., the charge-discharge cycle life characteristics of alkaline storage batteries. In order to ensure that the above effects are exhibited, the value e, which represents the atomic ratio of Al to the A component, is in the range of 0.03 to 0.14. If the value of e is less than 0.03, the corrosion resistance of the hydrogen storage alloy will be insufficient, and as a result, the charge / discharge cycle life characteristics of the alkaline storage battery will be insufficient. On the other hand, if the e value exceeds 0.14, the discharge capacity of the alkaline storage battery will decrease, and the hydrogen storage alloy will become more pulverized as it absorbs and releases hydrogen, resulting in durability problems. The preferred e value is in the range of 0.04 to 0.13. On the other hand, when the hydrogen storage alloy contains Fe as an essential element in the B component, the corrosion resistance effect of the hydrogen storage alloy imparted by Al can be realized by Fe, and therefore the value of e is in the range of 0 to 0.13. Thus, when the hydrogen storage alloy according to this embodiment is made into a powder consisting of alloy particles with small diameters, the Al content of the alloy is sufficient on the lower side of the range of this embodiment, and therefore the Al content of the hydrogen storage alloy can be reduced, thereby increasing the discharge capacity of the alkaline storage battery.

[0082] Cr:Cr f (where 0≦f≦0.05, preferably 0≦f≦0.04) Cr has an A2B7 structure, A5B 19 Cr is an element contained as the B component in the AB3-type structure and the AB4-type structure. Cr is effective in adjusting the hydrogen equilibrium pressure, which is related to battery voltage, and, together with Al, contributes to improving the corrosion resistance of hydrogen storage alloys. It is particularly effective in improving the durability of alkaline storage batteries, i.e., the charge / discharge cycle life characteristics of alkaline storage batteries. To ensure the above effect, the f value, which represents the atomic ratio of Cr to the A component, should be in the range of 0.05 or less, including 0. While Cr is not essential, its synergistic effect with Y and Al enhances the corrosion resistance of hydrogen storage alloys, improving their durability. However, if the amount of Cr exceeds 0.05 in terms of f-value, cracking of the hydrogen storage alloy due to hydrogen absorption and release is promoted, resulting in a decrease in the durability of the alkaline storage battery and an insufficient charge-discharge cycle life characteristic of the alkaline storage battery. The f-value is preferably 0.04 or less, and more preferably 0.003 or more. When the hydrogen storage alloy according to this embodiment is made into a powder consisting of alloy particles with small diameters, the Cr content of the alloy is sufficient on the lower side of the range of this embodiment, so the Cr content of the hydrogen storage alloy can be reduced, and the discharge capacity of the alkaline storage battery can be increased accordingly.

[0083] Fe:Fe g (where 0≦g≦0.35) Fe has an A2B7 crystal structure and an A5B 19 The hydrogen storage alloy according to the present invention is preferably contained as component B of a hydrogen storage alloy having one or both of the following crystal structures as its main phase: Fe, Fe, Fe-type crystalline structure ... By using Fe and Y as essential constituent elements of the hydrogen storage alloy according to the present invention, the hydrogen equilibrium pressure can be easily controlled to a level suitable for alkaline storage batteries, and high corrosion resistance, high durability, and low cost can be achieved.

[0084] To ensure that the above effects are truly achieved, the g value representing the atomic ratio of Fe in general formula (1) is in the range of 0 to 0.35. If the g-value exceeds 0.35, the discharge capacity of the alkaline storage battery will decrease. The preferred g-value is greater than 0 and equal to or less than 0.30. In the case of nickel-metal hydride batteries, due to the battery capacity restriction on the positive electrode, the hydrogen storage alloy used in the negative electrode is called a reservoir, and is 20 to 30 percent more than usual in anticipation of alkaline corrosion of the hydrogen storage alloy by the alkaline solution used as the electrolyte.

[0085] On the other hand, by employing the hydrogen storage alloy according to this embodiment, which contains Fe as an essential element, in an alkaline storage battery, deterioration in the discharge capacity of the battery can be significantly suppressed. In other words, since the alkaline storage battery including the hydrogen storage alloy according to this embodiment has little deterioration in discharge capacity, it is possible to significantly reduce the amount of hydrogen storage alloy used in this portion, which corresponds to the reservoir and which is normally used in excess in anticipation of alkaline corrosion.

[0086] In other words, by replacing a portion of the expensive Ni in the composition of the hydrogen storage alloy according to this embodiment with inexpensive Fe, making Fe an essential element, it is possible to significantly reduce not only the cost of materials required to manufacture the hydrogen storage alloy but also the amount of hydrogen storage alloy used in alkaline storage batteries. As a result, by employing the hydrogen storage alloy according to this embodiment, which contains inexpensive and easily available Fe as an essential element, in alkaline storage batteries, it is possible to reduce the manufacturing costs of alkaline storage batteries.

[0087] Ratio of component A to component B: 3.20≦d+e+f+g≦3.75 (preferably 3.25≦d+e+f+g≦3.70) A2B7 type structure, A5B 19 The stoichiometric ratio, which is the molar ratio of the B component (Ni, Al, and Cr) to the A component in the AB3 type structure and the AB4 type structure, i.e., the value of d+e+f+g represented by the general formula, is in the range of 3.20 to 3.75. If the value of d+e+f+g is less than 3.20, the subphase, ie, the AB2 phase, increases in the hydrogen storage alloy, and the discharge capacity of the alkaline storage battery in particular decreases. The AB2 phase produced within the composition range of the hydrogen storage alloy of this embodiment has the property of absorbing hydrogen but not releasing it easily, resulting in a decrease in the hydrogen storage capacity of the hydrogen storage alloy and a decrease in the discharge capacity of the alkaline storage battery. On the other hand, if the value of d+e+f+g exceeds 3.75, the AB5 phase increases in the hydrogen storage alloy, and the alloy powder of the hydrogen storage alloy is pulverized more finely as hydrogen is absorbed and released. 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 the range of 3.25 to 3.70.

[0088] The hydrogen storage alloy according to this embodiment preferably has the above-described composition, and the alloy particles obtained by pulverizing the hydrogen storage alloy preferably have a mass-based 50% transmittance particle size D50 in the range of 3 μm or more and 30 μm or less, and a mass-based 90% transmittance particle size D90 in the range of 8 μm or more and 60 μm or less. The hydrogen storage alloy according to this embodiment has excellent hydrogen absorption / desorption properties and durability, because the average particle size of the finely pulverized alloy particles is set within a predetermined range.

[0089] [Hydrogen absorption and desorption characteristics of hydrogen storage alloys] The hydrogen storage alloy of this embodiment preferably 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 pressurized to 1 MPa at 80°C. Furthermore, it is preferable that the hydrogen pressure (P0.5, hereinafter referred to as hydrogen equilibrium pressure) when the hydrogen absorption capacity (H / M: atomic ratio of hydrogen atoms (H) to metal atoms (M)) during hydrogen release at 80°C is 0.5 is 0.025 MPa or more and 0.12 MPa or less. If the hydrogen storage capacity is within this range, the battery can operate without problems under various temperature conditions. Figure 2 shows a specific example of PCT (Pressure-Composition-Temperature) characteristics, which measure the hydrogen equilibrium pressure and hydrogen storage capacity.

[0090] When improving the performance of nickel-metal hydride batteries, the discharge capacity is largely determined by the composition of the hydrogen storage alloy. On the other hand, the durability of the hydrogen storage alloy is affected by the degree of pulverization of the hydrogen storage alloy as it absorbs and releases hydrogen, or the elution of the alloy components into alkaline aqueous solutions. This depends on the composition of the hydrogen storage alloy and the proportion and properties of the alloy phases that are generated based on heat treatment. From this technological point of view, in order to proceed with the development of hydrogen storage alloys that satisfy the demand for high durability, we have conducted extensive research into evaluating the cracking tendency of hydrogen storage alloys due to repeated hydrogen absorption and desorption. As a result, when evaluating the cracking tendency of hydrogen storage alloys, the alloy particles are mechanically crushed and sieved to 150 μm or more and 1 mm or less. Hydrogen is pressurized to 3 MPa at 80°C, allowing the alloy to absorb hydrogen, and then the alloy is released by evacuating to a vacuum. After repeating this process five times, the particle size distribution of the alloy particles was evaluated, and the volume average particle size (MV) was used as a representative value, leading to the discovery of a hydrogen storage alloy with particularly excellent durability. The detailed conditions are as follows: "Sieved to between 150 μm and 1 mm" means that the particles are above the 150 μm mesh sieve and below the 1 mm mesh sieve.

[0091] Specifically, 7 g of hydrogen storage alloy is filled into the measurement holder of the PCT evaluation device, and the device is evacuated to a vacuum (0.01 MPa or less) at 80°C for 1 hour. After that, the temperature is maintained and hydrogen absorption and desorption measurements (PCT characteristic evaluation) are performed at a hydrogen pressure in the range of 0.01 to 3 MPa. After this, the alloy is evacuated to a vacuum (0.01 MPa) for one hour, hydrogen gas is introduced up to 3 MPa, and this is maintained for one hour to allow the alloy to absorb hydrogen almost to the upper limit, and then the alloy is evacuated to a vacuum (0.01 MPa) for one hour to release the hydrogen. This process is repeated three times. Finally, as in the first cycle, hydrogen absorption / desorption measurements (PCT characteristic evaluation) are performed at hydrogen pressures ranging from 0.01 to 3 MPa. The difference between the first and fifth hydrogen absorption / desorption and the second to fourth hydrogen absorption / desorption is the processing time. The second to fourth hydrogen absorption / desorption cycles require a shorter time because the hydrogen pressure is increased to 3 MPa in one go.

[0092] After performing this hydrogen absorption / desorption cycle a total of five times, the hydrogen storage alloy powder is removed and its particle size distribution is measured. The volume average particle diameter MV of the alloy particles obtained by pulverizing the hydrogen storage alloy after repeated hydrogen absorption / desorption is preferably in the range of 75 μm or more. This range of volume average particle diameter MV of the alloy particles is preferable because it prevents the hydrogen storage alloy from pulverizing during charge / discharge when actually incorporated into an alkaline storage battery. In other words, the hydrogen storage alloy according to this embodiment has excellent durability, coupled with good corrosion resistance in alkaline solutions. The volume average particle size MV of the alloy particles can be measured using a laser diffraction particle size distribution measuring device, such as the MT3300EXII model manufactured by Microtrac-Bell.

[0093] The cracking of hydrogen storage alloys is thought to be caused by strain due to the expansion and contraction of the alloy's crystal lattice as it absorbs and releases hydrogen. Therefore, if the amount of hydrogen absorbed is small, the expansion and contraction of the crystal lattice is also small, and as a result, the hydrogen storage alloy is less likely to pulverize. However, on the other hand, if the hydrogen storage capacity of the hydrogen storage alloy is small, the discharge capacity as a battery material will be small, which is undesirable because it will lead to an increase in the size and cost of the battery in order to obtain a certain battery capacity. Therefore, in order to achieve the volume average particle size MV of the alloy particles obtained by pulverizing the hydrogen storage alloy after repeated hydrogen absorption and desorption, it is preferable that the value of the hydrogen storage capacity index H / M (atomic ratio of hydrogen H to metal M) at 1 MPa obtained from PCT measurement at 80°C is 0.94 or more. If the hydrogen storage capacity is within this range, an alkaline storage battery equipped with a negative electrode containing such a hydrogen storage alloy as the negative electrode active material can maintain a sufficient discharge capacity, and therefore it can be said that a highly durable hydrogen storage alloy has been obtained.

[0094] 2, the plateau slope B during hydrogen absorption and desorption, which is represented by the following relational expression (A), was calculated based on the hydrogen pressure P0.3 (MPa) when the hydrogen absorption capacity H / M=0.3 and the hydrogen pressure P0.7 (MPa) when the hydrogen absorption capacity H / M=0.7. That is, the plateau slope B is a value calculated from the hydrogen absorption capacity H / M=0.7 and the hydrogen pressure P0.7 (MPa) when the hydrogen absorption capacity H / M=0.3 on the hydrogen desorption curve, using the above relational expression (A).

[0095]

number

[0096] That is, the plateau slope B, which is the value calculated from [log(P0.7 / P0.3)] / 0.4 shown in the above relational expression (A), is preferably in the range of 1.3 to 3.0. If the plateau slope B is less than 1.3, the crystal lattice of the hydrogen storage alloy is likely to expand in one direction during hydrogen storage, in other words, it is likely to expand and contract anisotropically. Therefore, the strain generated in the crystal lattice of the hydrogen storage alloy may promote cracking of the hydrogen storage alloy. On the other hand, if the plateau slope B exceeds 3.0, the amount of hydrogen storage will be difficult to increase even when hydrogen pressure is applied, which may result in a decrease in the discharge capacity of the alkaline storage battery. Preferably, the plateau slope B value is 1.35 or more and 2.95 or less.

[0097] [X-ray diffraction intensity ratio] In the hydrogen storage alloy of this embodiment, in an X-ray diffraction measurement using Cu-Kα radiation as an X-ray source, 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° is preferably ζ / ε≦0.08. If the ζ / ε ratio exceeds 0.08, the charge / discharge cycle life characteristics of the alkaline storage battery may be reduced. The ζ / ε ratio is more preferably 0.05 or less.

[0098] Figure 3 is a graph showing an example of the results of X-ray diffraction measurement of the hydrogen storage alloy according to this embodiment. To explain the diffraction lines in detail based on the XRD graph in Figure 3, the ζ / ε ratio is the ratio of the height of the diffraction peak indicated by ■ to the height of the strongest diffraction peak indicated by *. If the ζ / ε ratio is within this range, the proportion of the AB5 phase, which reduces the durability of the hydrogen storage alloy, is low, and therefore, improved durability of the hydrogen storage alloy can be expected.

[0099] The X-ray diffraction measurement conditions are as follows: A hydrogen storage alloy powder consisting of alloy particles crushed to a particle size of under 75 μm is set in a sample holder, and measurements are performed using only a kβ filter under the following conditions with Cu as the target. Tube voltage: 40kV Tube current: 40mA Scan speed: 0.5° / min Scan step: 0.02° Divergence slit (DS): 1° Scattering slit (SS): 1° Receiving slit (RS): None

[0100] [Alloy surface layer] On the surface of the hydrogen storage alloy of the present invention, a surface layer consisting of an oxide layer or hydroxide layer containing an appropriate amount of Y as shown in the above general formula (1) is formed in close contact with the alloy particles that constitute the hydrogen storage alloy. Therefore, the hydrogen storage alloy of the present invention has excellent durability due to the presence of the surface layer consisting of an oxide layer or hydroxide layer containing an appropriate amount of Y. This surface layer is formed when elements such as Y already contained inside the hydrogen storage alloy become metal oxides or metal hydroxides during the process of producing the negative electrode active material, and are contained as an oxide or hydroxide layer on the surface of the hydrogen storage alloy. The surface layer consisting of an oxide or hydroxide layer containing Y preferably contains Mg and Al, "mainly composed of rare earth elements" contained in the hydrogen storage alloy. Here, "mainly composed of rare earth elements" means that more than half by mass of the oxide or hydroxide layer formed on the surface of the hydrogen storage alloy is made up of oxides or hydroxides of rare earth elements.

[0101] The BET specific surface area of ​​the hydrogen storage alloy is 0.5m 2 / g or more, and 0.55 to 7.0 m 2 / g is more preferable, and 0.6 to 4.0m 2 / g is more preferable. If the BET specific surface area is within this range, the hydrogen storage alloy is suitable for use as a negative electrode active material contained in the negative electrode of an alkaline storage battery. In addition, the pore volume of the hydrogen storage alloy having a surface layer is 0.013 cm 3 / g or less, and the average pore diameter is preferably 40 nm or less. More preferably, the pore volume is 0.0025 to 0.0125 cm 3 / g and the average pore diameter is in the range of 10 to 35 nm. 3 If the pore size exceeds 1 / g and the average pore diameter exceeds 40 nm, the density of the surface layer will be low, the probability of cracking will increase, and the durability of the hydrogen storage alloy may decrease.

[0102] On the other hand, the pore volume is 0.0025 cm 3 When the surface layer has a surface area of ​​less than 1000 nm, the electrolyte will not sufficiently penetrate the surface layer of the hydrogen storage alloy, resulting in poor hydrogen absorption and desorption properties. The thickness of the surface layer, which is made of an oxide or hydroxide layer in close contact with the alloy particles, is 500 nm or less, and preferably in the range of 50 to 450 nm. When the surface layer is too thick, exceeding 500 nm, the electrolyte will not sufficiently penetrate the surface layer of the hydrogen storage alloy, resulting in poor hydrogen absorption and desorption properties. On the other hand, if a surface layer is not formed on the surface of the hydrogen storage alloy of the present invention, the corrosion resistance of the hydrogen storage alloy will be significantly reduced.

[0103] The hydrogen storage alloy according to this embodiment achieves both high power output and high durability by suppressing the durability of the alloy itself, i.e., by suppressing pulverization of the alloy due to hydrogen absorption and desorption. Furthermore, this hydrogen storage alloy is likely to form a surface layer on the surface of the alloy particles that has both excellent hydrogen absorption and desorption properties and alkaline corrosion resistance. Therefore, the hydrogen storage alloy according to this embodiment is particularly excellent in durability. In other words, an alkaline storage battery using this hydrogen storage alloy as a negative electrode active material achieves high power output characteristics while also having excellent charge-discharge cycle characteristics.

[0104] [Method of manufacturing hydrogen storage alloy] Next, a method for producing the hydrogen storage alloy of this embodiment will be described. The hydrogen storage alloy of this embodiment is prepared by weighing out rare earth elements (such as Sm, Y, La, and Ce) and metallic elements such as magnesium (Mg), nickel (Ni), aluminum (Al), chromium (Cr), and iron (Fe) in a predetermined molar ratio, then placing these raw materials in an alumina crucible placed in a high-frequency induction furnace and melting them in an inert gas atmosphere such as argon gas. The melt is then cast into a mold to produce an ingot of the hydrogen storage alloy. Alternatively, the hydrogen storage alloy of this embodiment may be directly produced as a flake-shaped sample approximately 200 to 500 μm thick using a strip casting method.

[0105] The hydrogen-absorbing alloy of this embodiment contains magnesium as its main component, which has a low melting point and high vapor pressure. Therefore, if all the raw materials for the alloy are melted at once, the magnesium will evaporate, making it difficult to obtain an alloy with the desired chemical composition. Therefore, when producing the hydrogen-absorbing alloy of this embodiment by a melting method, it is preferable to first melt the remaining alloy components (excluding magnesium) and then add magnesium raw materials, such as metallic magnesium and magnesium alloys, to the resulting molten metal. This melting process is preferably carried out in an inert gas atmosphere, such as argon or helium. Specifically, it is preferably carried out in a reduced pressure atmosphere of 0.05 to 0.2 MPa containing an inert gas containing 80 vol% or more of argon gas. The alloy melted under these conditions is then preferably cast into a water-cooled mold and solidified to form a hydrogen-absorbing alloy ingot.

[0106] Next, the melting point (T m The hydrogen storage alloy of this embodiment is produced by heating the ingot after casting to a temperature of 800°C or higher in an atmosphere of an inert gas such as argon or helium, or nitrogen gas, or a mixture of these gases, until the melting point (T m This is because it is preferable to carry out a heat treatment in which the material is maintained at an appropriate temperature of 100°C or less for 3 to 50 hours. This heat treatment resulted in the formation of A2B7 and A5B types as the main phases in the hydrogen storage alloy. 19 The total proportion of the crystalline structures of the A2B7 type and the AB3 type is 70% by mass or more, preferably the A2B7 type and the A5B type. 19 The total ratio of the crystal structure of the mold is set to 70 mass % or more, and the AB2 phase and AB5 phase, which are subphases formed during casting, can be reduced or eliminated. The crystal structure of the main phase of the obtained hydrogen storage alloy is A2B7 type structure or A5B 19 The presence of the AB3 type structure or the AB4 type structure can be confirmed by X-ray diffraction measurement using Cu-Kα radiation. The main phase of the hydrogen storage alloy means more than 50 mass %, and preferably 70 mass % or more.

[0107] If the heat treatment temperature is less than 800°C, the diffusion of the elements will be insufficient, and subphases will remain, which may result in a decrease in the discharge capacity of the battery and a deterioration in the charge-discharge cycle characteristics. m -20℃ or higher (T m If the temperature is higher than -20°C, the crystal grains of the main phase may become coarse or partially melt, or the Mg component may evaporate, resulting in pulverization and a change in the chemical composition, which may decrease the hydrogen storage capacity. Therefore, the heat treatment temperature is preferably set to 800°C or higher (T m -30℃).

[0108] Furthermore, if the heat treatment holding time is less than 3 hours, it is not possible to stably achieve a main phase ratio of 70 mass% or more, and the chemical composition of the main phase will not be sufficiently homogenized. As a result, the crystal lattice that constitutes the hydrogen storage alloy will expand and contract non-uniformly during hydrogen absorption and desorption, increasing the amount of distortion and defects that occur, which may adversely affect the charge-discharge cycle life characteristics of alkaline storage batteries. The holding time for the heat treatment is preferably 4 hours or more, and from the viewpoint of homogenizing the main phase of the hydrogen storage alloy and improving the crystallinity, it is more preferably 5 hours or more. However, if the holding time exceeds 50 hours, the amount of evaporated Mg increases, which may change the chemical composition of the hydrogen storage alloy and result in the formation of an AB5-type subphase. This is also undesirable because it increases the manufacturing cost and may cause a dust explosion due to evaporated Mg fine powder.

[0109] The heat-treated hydrogen storage alloy is pulverized by either a dry method or a wet method. When pulverizing by a dry method, for example, a hammer mill or an ACM pulverizer is used. On the other hand, when pulverizing by a wet method, a ball mill or an attritor is used. In particular, when obtaining a fine powder of a hydrogen storage alloy, wet pulverization is preferable because it can be produced safely.

[0110] When the hydrogen storage alloy according to this embodiment is used in a battery for vehicle applications, the particle size of the pulverized alloy particles is preferably in the range of 3 μm to 30 μm, and more preferably 5 μm to 25 μm, in terms of the mass-based 50% transmission particle size D50, in order to balance battery properties such as output and cycle life characteristics. Furthermore, since the above-mentioned properties deteriorate if the particle size distribution of the alloy particles is too broad, the mass-based 10% transmission particle size D10 is preferably in the range of 0.5 μm to 15 μm, and the 90% transmission particle size D90 is preferably in the range of 8 μm to 60 μm. Furthermore, the 10% transmission particle size D10 is more preferably in the range of 1 μm to 10 μm, and the 90% transmission particle size D90 is more preferably in the range of 10 μm to 50 μm. The particle size of the alloy particles can be controlled by adjusting conditions such as the diameter, amount, and rotation speed of the media. Here, the particle size distributions D50, D10 and D90 of the above-mentioned alloy particles are values ​​measured using a laser diffraction / scattering particle size distribution measuring device, and as the measuring device, for example, the MT3300EXII model manufactured by Microtrack Bell Corporation can be used.

[0111] The hydrogen storage alloy according to the present embodiment has a main phase of the A2B7 type crystal structure, 19 It is an alloy consisting of the AB3 type crystal structure and the AB7 type crystal structure. Specifically, the A2B7 type crystal structure can be either the hexagonal (2H) Ce2Ni7 phase or the rhombohedral (3R) Gd2Co7 phase without any problems, but it is preferable for the former to be present in greater amounts. Also, A5B 19 Gd5Co type crystal structure (hexagonal system) 19 PrCo phase or rhombohedral 19 In the case of the A2B7 type crystal structure, it is preferable that the former is contained in a larger amount, and the A5B 19 It is preferable that the combined amount of the AB3-type crystal structure and the AB4-type crystal structure is at least 70 mass % or more. More preferably, the A2B7 type crystal structure, A5B 19 The total amount of the phases with the type crystal structure is 70 mass % or more. The crystal structure of these hydrogen storage alloys can be evaluated by Rietveld analysis based on the results of X-ray diffraction measurement.

[0112] To obtain a hydrogen storage alloy used as the negative electrode active material of this embodiment in which a layer of oxide or hydroxide containing Y is adhered to the surface of the hydrogen storage alloy, it is preferable to actively oxidize the surface of the hydrogen storage alloy. Below, using the hydrogen storage alloy of this embodiment as an example, we will explain the procedure for treating the hydrogen storage alloy using a suitable method (hereinafter referred to as the hydrogen storage alloy treatment method) to produce the hydrogen storage alloy of this embodiment, which is used as the negative electrode active material of an alkaline storage battery.

[0113] The method for treating hydrogen storage alloys is as follows: N-1) a step of treating the hydrogen storage alloy with an alkaline aqueous solution; N-2) a step of oxidizing the surface of the hydrogen storage alloy after the step N-1); It has. N-1) A step of treating a hydrogen storage alloy with an alkaline aqueous solution (hereinafter simply referred to as "N-1) step") is not an essential step for oxidizing the hydrogen storage alloy, but as will be described later, by undergoing this step, a hydrogen storage alloy that can be more preferably used as the negative electrode active material according to the present embodiment can be obtained.

[0114] First, the "N-1) step" will be explained. The hydrogen storage alloy used in the N-1) process is an alloy with an A2B7 crystal structure, A5B 19 This hydrogen storage alloy has a main phase consisting of a crystalline structure of the AB3 type and a crystalline structure of the AB4 type.

[0115] In step N-1), when the hydrogen storage alloy is treated with an alkaline aqueous solution in which an alkali metal hydroxide is dissolved, corrosion progresses from the surface of the alloy. In particular, rare earth elements, Mg, and Al, which are easily oxidized and highly soluble in alkaline aqueous solutions among the components contained in the hydrogen storage alloy, are partially converted into oxides or hydroxides in situ, and partially eluted from the surface of the hydrogen storage alloy. Here, Ni remains in place due to its high corrosion resistance and low solubility in alkaline aqueous solutions, resulting in the formation of a layer of metal, oxide, and hydroxide on the surface of the hydrogen storage alloy. Hereinafter, in the hydrogen storage alloy according to this embodiment, this newly formed surface layer on the surface of the hydrogen storage alloy will be referred to as the "surface treatment layer." The surface treatment layer is made of a metal oxide or an alkali metal hydroxide. It is believed that the presence of this surface treatment layer formed on the surface of the hydrogen storage alloy improves the performance of the hydrogen storage alloy when used as a negative electrode active material in an alkaline storage battery.

[0116] Examples of alkali metal hydroxides include lithium hydroxide, sodium hydroxide, and potassium hydroxide, and among these, sodium hydroxide is preferred. By using a sodium hydroxide aqueous solution as the alkaline aqueous solution, the battery characteristics of the nickel-metal hydride battery, which is the alkaline storage battery according to this embodiment, may be optimized in some cases compared to when other alkali metal hydroxides such as lithium hydroxide or potassium hydroxide are used.

[0117] The alkaline aqueous solution is preferably a strong base. The concentration of the alkali metal hydroxide in the alkaline aqueous solution is preferably in the range of 10 to 60 mass %, more preferably 20 to 55 mass %, for example.

[0118] Step N-1) is preferably carried out by immersing the hydrogen storage alloy in an alkaline aqueous solution. This is preferably carried out under stirring conditions, and is also preferably carried out under heating conditions. The heating temperature is preferably in the range of 50 to 150°C, and more preferably in the range of 70 to 140°C. The heating time may be determined appropriately depending on the concentration of the alkaline aqueous solution, the heating temperature, and the stirring conditions, and is preferably in the range of 0.1 to 10 hours, and more preferably in the range of 0.2 to 5 hours.

[0119] The relationship between the amounts of the hydrogen storage alloy and the alkaline aqueous solution is preferably in the range of 1:0.5 to 1:10 by mass ratio, more preferably 1:0.7 to 1:8. If the amount of the alkaline aqueous solution is too small, a surface treatment layer may not be formed sufficiently on the hydrogen storage alloy, while if the amount of the alkaline aqueous solution is too large, it will be disadvantageous in terms of cost.

[0120] At the end of step N-1), the alkaline aqueous solution contains rare earth elements, Mg, and Al that have been partially dissolved from 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 when the alkaline aqueous solution and the hydrogen storage alloy are separated.

[0121] In step N-1), the hydrogen storage alloy may be washed with water following the treatment with the alkaline aqueous solution. By washing with water, the alkaline aqueous solution adhering to the surface of the hydrogen storage alloy can be removed. The mass ratio of the hydrogen storage alloy to the amount of water used during washing with water is preferably 1:1 to 1:50, more preferably 1:2 to 1:30.

[0122] Next, N-2) the step of oxidizing the surface of the hydrogen storage alloy after the N-1) step (hereinafter simply referred to as "N-2) step") will be described. The hydrogen storage alloy may be washed with water in the atmosphere after the treatment with the alkaline aqueous solution in the above-mentioned step N-1), but this may be carried out in step N-2). Step N-2 may involve exposing the hydrogen storage alloy to air to oxidize the surface of the hydrogen storage alloy with oxygen in the air, or contacting the hydrogen storage alloy with an oxidizing agent such as hydrogen peroxide to oxidize the alloy. In either method, however, it is preferable to cool the hydrogen storage alloy in order to prevent excessive heat generation in the hydrogen storage alloy. Specifically, it is preferable to cool the hydrogen storage alloy by pouring water over it, or to place the hydrogen storage alloy in water, or to place the hydrogen storage alloy in an aqueous solution containing an oxidizing agent such as hydrogen peroxide.

[0123] The negative electrode active material of the present embodiment, which is preferably manufactured through steps N-1) and N-2), contains a layer on its surface in which a metal, an oxide, and a hydroxide are mixed. Alternatively, the negative electrode active material of the present embodiment can be expressed as having a surface-treated layer on its surface in which a metal, an oxide, and a hydroxide are mixed.

[0124] By undergoing the above process, a surface layer consisting of an oxide layer or hydroxide layer containing Y in at least a part thereof can be formed on the surface of the hydrogen storage alloy of this embodiment, thereby improving the corrosion resistance of the hydrogen storage alloy of this embodiment. The oxide or hydroxide contained in the surface treatment layer of the hydrogen storage alloy is preferably composed mainly of the rare earth elements contained in the hydrogen storage alloy, Mg, and Al.

[0125] Furthermore, the pore volume of the hydrogen storage alloy on which the surface treatment layer consisting of this oxide layer or hydroxide layer is formed is 0.013 cm 3 / g or less, and the average pore diameter is preferably 40 nm or less. 3 If the average pore size exceeds 40 nm, the surface treatment layer will have a low density, and the probability of cracking will increase, which may accelerate corrosion of the hydrogen storage alloy due to immersion in alkaline solution, i.e., reduce the corrosion resistance of the alloy. If the average pore size is too large, exceeding 40 nm, excessive immersion in alkaline solution may accelerate corrosion of the hydrogen storage alloy, i.e., reduce the durability. On the other hand, the pore volume is 0.0025 cm 3 If the pore volume is less than 0.0025 to 0.0125 cm3 / g and the average pore diameter is less than 10 nm, the impregnation of the hydrogen storage alloy with the electrolyte may be insufficient, and the hydrogen absorption / desorption properties of the alloy may be reduced. 3 / g, and the average pore diameter is 10 to 35 nm.

[0126] Furthermore, the surface layer formed on the surface of the hydrogen storage alloy according to this embodiment, which is an oxide or hydroxide layer containing Y in at least a portion thereof, preferably has a thickness of 500 nm or less and is in close contact with the surface of the alloy particles. If the thickness of the surface layer exceeds 500 nm, impregnation of the hydrogen storage alloy with the electrolyte may be insufficient, which may result in a deterioration in the hydrogen absorption / desorption properties of the alloy. On the other hand, if the hydrogen storage alloy according to this embodiment does not have a surface treatment layer formed on at least a portion thereof, the corrosion resistance of the alloy will be significantly reduced.The thickness of the surface layer is preferably 50 to 450 nm.

[0127] The analysis of the negative electrode active material surface is as follows. The surface treatment layer formed on the hydrogen storage alloy surface was observed using a transmission electron microscope. Specifically, the negative electrode active material powder was mixed with epoxy resin, and the resin was cured at 120°C for 30 minutes to embed the material in the resin. Subsequently, a thin flake sample of less than 100 nm was obtained by thinning using an argon beam. For the thinning process, a JEOL ion slicer (EM09100 IS) was used. The sample was thinly polished at an accelerating voltage of 6 kV until pores of several micrometers were formed, and then the sample was finished at an accelerating voltage of 1.0 kV for 15 minutes. The obtained thin flake sample was observed using a transmission electron microscope (JEOL JEM2100F) at an accelerating voltage of 200 kV to examine the surface treatment layer formed on the alloy surface. Furthermore, an energy dispersive X-ray emission spectrometer (JEOL JED2300) equipped on the same instrument was used to perform elemental analysis of the surface treatment layer.

[0128] The pore size distribution is analyzed and evaluated as follows: After the negative electrode active material is vacuum-dried at 100°C for 2 hours, the nitrogen adsorption / desorption isotherm of the negative electrode active material at liquid nitrogen temperature (77.3K) is measured using a fully automatic gas adsorption analyzer (AS1-MP, AntonPaar). The amount of nitrogen adsorbed per unit weight of the hydrogen storage alloy in the adsorption / desorption isotherm is calculated so as to be expressed in terms of the volume of gaseous nitrogen at standard temperature and pressure (STP). Here, the standard state of the gas is 0°C and 101325 Pa, and the symbol "N" is added before the volume unit. The total pore volume is the amount of nitrogen adsorbed at the relative pressure of the adsorption isotherm (p / p = 0.99), V [N cm 3 / g] was calculated using the following formula (B).

[0129]

number

[0130] The BET specific surface area of ​​the hydrogen storage alloy used as the negative electrode active material according to this embodiment is 0.5 m 2 / g. If the BET specific surface area of ​​the hydrogen storage alloy is less than this, the average pore size may become too large. The BET specific surface area of ​​the hydrogen storage alloy is preferably 0.55 to 7.0 m 2 / g is more preferable, and the range is 0.6 to 4.0 m 2 / g range is more preferred. In addition to the alkaline aqueous solution treatment in step N-1) and the surface oxidation step in step N-2), an acid treatment step may be combined. In the acid treatment process, the surface of the hydrogen storage alloy is acid-treated using an aqueous solution of nitric acid, sulfuric acid, hydrochloric acid, etc. The acid treatment process results in a hydrogen storage alloy that exhibits better battery characteristics, particularly durability and low-temperature discharge characteristics. This is because the deposition of many Ni fine particles on the surface of the hydrogen storage alloy improves the catalytic activity of the hydrogen storage alloy, facilitating hydrogen absorption and desorption. Therefore, the discharge characteristics at low temperatures are improved, and the corrosion resistance and durability are improved due to the increase in the amount of Ni fine particles on the surface.

[0131] [Alkaline storage battery] Next, an example of the configuration of an alkaline storage battery having a negative electrode using the hydrogen storage alloy of the present invention will be described with reference to FIG. Here, the alkaline storage battery 10 of the present invention is composed of at least a positive electrode 1, a negative electrode 2, a separator 3, and a casing 4 (battery case) that is filled with an electrolyte and contains these. A specific description will be given below.

[0132] <Positive electrode> The positive electrode 1 is usually composed of a positive electrode active material layer and a positive electrode current collector. The positive electrode active material layer contains at least a positive electrode active material. The positive electrode active material layer may further contain at least one of a positive electrode additive, a conductive aid, a binder, and a thickener. The positive electrode active material is not particularly limited as long as it functions as a battery when combined with the above-mentioned hydrogen storage alloy (negative electrode material), and examples thereof include simple metals, alloys, hydroxides, and the like. The positive electrode active material may contain nickel oxide and be primarily composed of nickel oxyhydroxide and / or nickel hydroxide. The amount of nickel oxide in the positive electrode active material is, for example, 90 to 100 mass %, or may be 95 to 100 mass %. The average particle size of the nickel oxide can be appropriately selected, for example, from the range of 3 to 35 μm, and is preferably from 3 to 25 μm. The positive electrode active material is preferably a positive electrode active material having a layer of a conductive additive formed therearound in advance, or more preferably a positive electrode active material having a layer of cobalt oxyhydroxide formed therearound in advance and having the cobalt oxyhydroxide layer doped with an alkali metal.

[0133] The positive electrode additive is added to the positive electrode of a nickel-metal hydride battery to improve its battery performance. There are no particular limitations on the positive electrode additive, so long as it is used as a positive electrode additive for a nickel-metal hydride battery. Specific positive electrode additives include niobium compounds such as NbO, tungsten compounds such as WO, WO, LiWO, NaWO, and KWO, ytterbium compounds such as YbO, titanium compounds such as TiO, yttrium compounds such as YO, zinc compounds such as ZnO, calcium compounds such as CaO, Ca(OH), and CaF, and other rare earth oxides.

[0134] The conductive additive is not particularly limited as long as it is a material that can impart electronic conductivity to the positive electrode, and examples thereof include metal powders such as Ni powder, oxides such as cobalt oxide, and carbon materials such as graphite and carbon nanotubes. The amount of conductive additive added is not particularly limited, but is preferably in the range of 0.1 to 50 parts by mass, and more preferably in the range of 0.1 to 30 parts by mass, per 100 parts by mass of the positive electrode active material.

[0135] The binder serves to bind the active material and the like to the surface of the current collector. The binder is not limited as long as it is suitable for use as an electrode binder for nickel-metal hydride batteries. Specific binders include fluorine-containing resins such as polyvinylidene fluoride, polytetrafluoroethylene, and fluororubber; polyolefin resins such as polypropylene and polyethylene; imide resins such as polyimide and polyamideimide; cellulose derivatives such as carboxymethyl cellulose, methyl cellulose, and hydroxypropyl cellulose; copolymers such as styrene-butadiene rubber; and (meth)acrylic resins containing (meth)acrylic acid derivatives as monomer units, such as polyacrylic acid, polyacrylic acid esters, polymethacrylic acid, and polymethacrylic acid esters. The amount of binder may be, for example, 7 parts by mass or less, and may be in the range of 0.01 to 5 parts by mass, or even 0.05 to 2 parts by mass, per 100 parts by mass of the positive electrode active material.

[0136] Further examples of thickeners include carboxymethyl cellulose and its modified products (including salts such as sodium salts), cellulose derivatives such as methyl cellulose, saponified polymers having vinyl acetate units such as polyvinyl alcohol, and polyalkylene oxides such as polyethylene oxide. These thickeners may be used alone or in combination of two or more. The amount of thickener is, for example, 5 parts by mass or less, may be in the range of 0.01 to 3 parts by mass, or may be in the range of 0.05 to 1.5 parts by mass, per 100 parts by mass of the positive electrode active material.

[0137] Examples of the material for the positive electrode current collector include stainless steel, aluminum, nickel, iron, titanium, etc. The positive electrode current collector may have any shape, such as a foil, mesh, or porous shape.

[0138] The positive electrode can be formed by attaching a positive electrode mixture containing a positive electrode active material to a support (positive electrode current collector). The positive electrode mixture is usually prepared by forming a paste from the above-mentioned positive electrode active material, positive electrode additive, conductive aid, and binder. The dispersion medium can be water, an organic medium, or a mixed medium containing two or more selected from these. If necessary, a positive electrode additive, conductive aid, binder, thickener, etc. may be added, but these (especially the positive electrode additive, binder, and thickener) are not necessarily added.

[0139] The positive electrode may be formed by applying the positive electrode mixture paste to a support or by filling the pores of the support depending on the shape of the support, etc. The positive electrode can be formed by applying or filling the positive electrode mixture paste to a support, drying to remove the dispersion medium, and compressing the resulting dried product in the thickness direction (for example, by rolling between a pair of rolls).

[0140] <Negative electrode> The negative electrode 2 is usually 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 of a negative electrode additive, a conductive aid, a binder, and a thickener.

[0141] The negative electrode additive is added to the negative electrode to improve the battery characteristics of a nickel-hydride battery. The negative electrode additive is not limited as long as it is used as a negative electrode additive for a nickel-hydride battery. Specific 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 the compounds exemplified as positive electrode additives.

[0142] The conductive additive is not particularly limited as long as it is a material that can impart electronic conductivity, and examples thereof include metal powders such as Ni powder, oxides such as cobalt oxide, and carbon materials such as graphite and carbon nanotubes. The amount of conductive additive added is not particularly limited, but is preferably in the range of 0.1 to 50 parts by mass, and more preferably 0.1 to 30 parts by mass, per 100 parts by mass of the hydrogen storage alloy powder.

[0143] Examples of binders include synthetic rubbers such as styrene-butadiene rubber (SBR), celluloses such as carboxymethyl cellulose (CMC), polyols such as polyvinyl alcohol (PVA), fluororesins such as polyvinylidene fluoride (PVDF), etc. The amount of binder may be, for example, 7 parts by mass or less per 100 parts by mass of the hydrogen storage alloy powder, and may be in the range of 0.01 to 5 parts by mass, or even 0.05 to 2 parts by mass.

[0144] Examples of materials for the negative electrode current collector include steel, stainless steel, aluminum, nickel, iron, titanium, carbon, etc. The negative electrode current collector may have any shape, such as a foil, mesh, or porous shape. To form the negative electrode active material layer on the negative electrode current collector, the components contained in the negative electrode active material layer, such as the negative electrode active material, are made into a paste to prepare a negative electrode paste. The negative electrode paste is prepared by adding the above-mentioned negative electrode active material, negative electrode additive, conductive aid, binder, thickener, etc. to a solvent. This negative electrode for a nickel-metal hydride battery is produced by forming a 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 with a negative electrode core material (negative electrode current collector), or by preparing a negative electrode paste containing the above-mentioned hydrogen storage alloy powder, applying it to a negative electrode current collector, and drying it.

[0145] <Electrolyte layer> The electrolyte layer is a layer formed between the positive electrode and the negative electrode and containing an aqueous electrolyte solution. Here, the aqueous electrolyte solution refers to an electrolyte solution that uses water as the main solvent, but the solvent may contain substances other than water. The proportion of water to the total solvent of the electrolyte solution may be 50 mol% or more, 70 mol% or more, 90 mol% or more, or 100 mol%.

[0146] The aqueous electrolyte is preferably an alkaline aqueous solution. Examples of solutes in the alkaline aqueous solution include potassium hydroxide (KOH) and sodium hydroxide (NaOH), and LiOH may also be included. The concentration of the solute in the aqueous electrolyte is preferably 2 to 10 mol / L, more preferably 3 to 9 mol / L, and even more preferably 4 to 8 mol / L. The aqueous electrolyte may contain known additives used in electrolytes for nickel-hydride batteries.

[0147] The electrolyte layer has a separator 3. By providing the separator 3, it is possible to effectively prevent short circuits. Examples of the separator 3 include a nonwoven fabric or a porous membrane containing a resin such as sulfonated polyethylene or polypropylene.

[0148] <Case> The casing 4 is a battery case (cell container) that houses the positive electrode 1, negative electrode 2, and separator 3 and is filled with an electrolyte. The material used for the battery case 4 is stable and not corroded by the electrolyte, and can retain the gas (oxygen or hydrogen) temporarily generated during charging and the electrolyte without leaking to the outside; for example, a metal case or a resin case is generally used. In addition, in the case of a stacked alkaline storage battery 10 having a stack in which multiple positive electrodes 1 and negative electrodes 2 are stacked with separators 3 interposed therebetween, the casing 4 may have a structure in which the periphery of the stack is sealed with a frame-shaped resin.

[0149] <Battery applications> The alkaline storage battery 10 of the present invention is typically a secondary battery. As such, it can be repeatedly charged and discharged, making it suitable, for example, as an in-vehicle battery. In this case, the alkaline storage battery 10 is not limited to use as a battery for hybrid vehicles that supplies power to a motor that drives the vehicle. The alkaline storage battery 10 may also be used to supply power to a starter motor that restarts the engine in a vehicle with an idling stop function. Secondary batteries also include those used as primary batteries (i.e., used only for one discharge after charging). The shape of the battery may be, for example, a coin type, laminate type, cylindrical type, square type, or the like, and any shape is acceptable.

[0150] [vehicle] The vehicle of the present invention is equipped with an alkaline storage battery using the above-mentioned hydrogen storage alloy in the negative electrode as a power supply source for a motor. By using the alkaline storage battery of the present invention, which is significantly smaller and lighter than conventional batteries, the vehicle of the present invention can improve driving performance, reduce fuel consumption, and extend cruising range. [Example]

[0151] Example 1 Evaluation cells having negative electrodes using alloys Nos. 1 to 70 (hydrogen storage alloys) having the component compositions shown in Tables 1-1 to 1-4 below as negative electrode active materials were fabricated as described below, and experiments were conducted to evaluate their characteristics. Alloys No. 1 to 33 shown in Tables 1-1 to 1-4 are alloy examples (invention examples) that meet the conditions of the present invention, and alloys No. 34 to 70 are alloy examples (comparison examples) that do not meet the conditions of the present invention. Alloy No. 34 of the comparison example was used as a reference alloy for evaluating the cell characteristics.

[0152] (Preparation of negative electrode active material) The raw materials for alloys No. 1 to 70 shown in Tables 1-1 to 1-4 (La, Y, Ce, Sm, Nd, Pr, Gd, Zr, Mg, Ni, Co, Mn, Al, Fe, etc., each with a purity of 99% or more) were melted in a high-frequency induction heating furnace under an argon atmosphere (Ar: 100 vol%, 0.1 MPa) and cast to form alloy ingots consisting of hydrogen storage alloys. Next, these alloy ingots were subjected to heat treatment in an argon atmosphere (Ar: 90 vol%, 0.1 MPa) at a temperature of the melting point Tm of each alloy minus 50°C (940 to 1130°C) for 10 hours. The heat-treated alloy ingot was then coarsely pulverized, further coarsely pulverized in a wet ball mill, and finely pulverized to a 50% mass-based particle size D50 of 16 μm, followed by filtration to obtain a finely pulverized filtered product.

[0153] Thereafter, the hydrogen storage alloy was treated with an alkaline aqueous solution as follows: 50 parts by mass of an aqueous sodium hydroxide solution containing 48% by mass of sodium hydroxide was added to 50 parts by mass of the finely pulverized filtered product of Example 1 to form a suspension. This suspension was heated to 100°C and maintained for 2 hours, and then cooled to room temperature. The suspension was allowed to stand, the supernatant liquid was removed, and the hydrogen storage alloy was separated from the alkaline aqueous solution. 800 parts by mass of water was poured onto the hydrogen storage alloy to wash it. The suspension was again allowed to stand, the supernatant liquid was removed, and the hydrogen storage alloy was separated from the alkaline aqueous solution.

[0154] Furthermore, after the above process, the following process was carried out as a process for oxidizing the surface of the hydrogen storage alloy. 25 parts by mass of 10% by mass of hydrogen peroxide solution was added to the entire amount of the finely pulverized filtered product obtained in the previous paragraph and stirred for 20 minutes. 400 parts by mass of water was poured into the mixture, and the hydrogen storage alloy was washed with water. The suspension was again allowed to stand, and the supernatant was removed to separate the hydrogen storage alloy from the alkaline aqueous solution. 400 parts by mass of water was poured onto the hydrogen storage alloy to wash it. The filtered hydrogen storage alloy was used as the negative electrode active material for the evaluation cell. The AB5 alloy No. 34 used as the reference for the evaluation cell was wet-pulverized into a fine powder having a 50% pass particle size D50 of 25 μm by mass, and used as the sample (negative electrode active material) for the evaluation cell.

[0155] (Preparation of evaluation cells) A slurry was prepared by mixing 97.8 parts by mass of the negative electrode active material, 1.5 parts by mass of an acrylic resin emulsion as a binder (solid content), 0.7 parts by mass of carboxymethyl cellulose as a binder, and an appropriate amount of ion-exchanged water. A nickel foil having a thickness of 20 μm was prepared as a negative electrode current collector. The above slurry was applied to the surface of this nickel foil in the form of a film. The nickel foil coated with the slurry was dried to remove water, and then the nickel foil was pressed to produce a negative electrode in which a negative electrode active material layer was formed on the surface of the negative electrode current collector.

[0156] Nickel hydroxide particles containing zinc and cobalt as a solid solution and coated with a cobalt oxyhydroxide layer containing sodium and lithium were prepared as the positive electrode active material. This was used as the positive electrode active material for the evaluation cell of Example 1. A slurry was produced by mixing 94.3 parts by mass of the positive electrode active material, 1.0 part by mass of cobalt powder as a conductive additive, 3.5 parts by mass (solid content) of an acrylic resin emulsion as a binder, 0.7 parts by mass of carboxymethyl cellulose as a binder, 0.5 parts by mass of YO as a positive electrode additive, and an appropriate amount of ion-exchanged water. A nickel foil having a thickness of 20 μm was prepared as a positive electrode current collector. The above slurry was applied to the surface of this nickel foil in the form of a film. The nickel foil on which the slurry was applied was dried to remove water from the slurry, and then the nickel foil was pressed to produce a positive electrode 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 present on the positive electrode current collector was 28 mg / cm. 2 The density of the positive electrode active material layer is 2.9 g / cm 3 It was.

[0157] As the electrolyte, an aqueous solution containing potassium hydroxide at a concentration of 5.4 mol / L, sodium hydroxide at a concentration of 0.8 mol / L, lithium hydroxide at a concentration of 0.5 mol / L, and Na2WO4 at a concentration of 0.16 mol / L was prepared.

[0158] As a separator, a sulfonated nonwoven fabric made of polyolefin fiber with a thickness of 104 μm was prepared.

[0159] A separator was sandwiched between the positive electrode and the negative electrode to form an electrode assembly, which was then placed in a resin case, into which the above-described electrolyte solution was poured, and the case was sealed to produce a nickel-metal hydride battery for evaluation.

[0160] (Various alloy evaluations) In this example, the alloy was crushed after heat treatment and subjected to X-ray diffraction measurement. The powder crushed to a particle size of under 75 μm was placed in a sample holder, and the target was Cu. The X-ray diffraction measurement conditions were as follows: tube voltage 40 kV, tube current 40 mA, scan speed 0.5° / min, scan step 0.02°, divergence slit (DS) 1°, scattering slit (SS) 1°, no receiving slit (RS), and only a kβ filter was used.

[0161] Each alloy was crushed into powder and subjected to X-ray diffraction measurement, and the resulting diffraction data was subjected to Rietveld analysis. As a result, it was found that the main phases of the alloys Nos. 1 to 33 of the invention were A2B7 and A5B 19 It was confirmed that the main phase consisted of the A2B7 phase or the AB3 phase, and that this constituted 70 mass % or more. In particular, with the exception of alloy No. 22 of the invention example, all of the alloys of the invention example consisted of the A2B7 phase, A5B 19 It was confirmed that the content of the two phases exceeded 70 mass %.

[0162] In addition, using the same diffraction 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 the ratio ζ / ε≦0.08 for all of the alloys of the present invention.

[0163] The PCT characteristics of the alloy were evaluated using the following procedure. First, a block of hydrogen-absorbing alloy was crushed and sieved to a particle size of 150 μm to 1 mm, as described above. The crushed particles of the hydrogen-absorbing alloy were loaded into a PCT measuring device and evacuated (0.01 MPa or less) at 80°C for 1 hour. Next, while maintaining the temperature, hydrogen gas is pressurized to 3 MPa and held for 3.5 hours to store hydrogen in the hydrogen storage alloy, and then the alloy is evacuated to a vacuum for 1 hour to release hydrogen from the hydrogen storage alloy, thereby performing activation treatment. Then, hydrogen absorption / desorption measurements (PCT characteristic evaluation) were performed on the alloys of the examples at hydrogen pressures ranging from 0.01 to 1 MPa. Tables 1-1 to 1-4 show the hydrogen absorption amount at a pressure of 1 MPa as H / M and the plateau slope as B, calculated values ​​from the above relation (A) [log(P0.7 / P0.3)] / 0.4. As is clear from these tables, the plateau slope B of the alloys of the invention examples is in the range of 1.3 to 3.0.

[0164] The cracking susceptibility of the alloy due to repeated hydrogen absorption and desorption was evaluated as follows: A block of hydrogen-absorbing alloy was crushed to produce alloy particles. The particle size of the hydrogen-absorbing alloy particles was then adjusted so that they would remain on a 150 μm sieve and be 1 mm or less. 7 g of the hydrogen-absorbing alloy consisting of alloy particles was loaded into the measurement holder of a PCT (Pressure-Composition-Temperature) evaluation device, and the device was evacuated to a vacuum (0.01 MPa or less) at 80°C for 1 hour. After this, the temperature was maintained and hydrogen absorption and desorption measurements (PCT characteristic evaluation) were performed at a hydrogen pressure ranging from 0.01 to 3 MPa. After this, the alloy is evacuated to a vacuum (below 0.01 MPa) for one hour, hydrogen gas is introduced up to 3 MPa, and this is maintained for one hour, allowing the alloy to absorb almost all of the hydrogen. After this, the alloy is evacuated to a vacuum (below 0.01 MPa) for one hour to release the hydrogen. This process is repeated three times. Finally, hydrogen absorption / desorption measurements (PCT characteristic evaluation) were performed at hydrogen pressures ranging from 0.01 to 3 MPa, as in the first cycle. After five hydrogen absorption / desorption cycles, the hydrogen storage alloy powder was removed and particle size distribution measurements were performed. The volume-average particle diameters MV of the alloy particles constituting the pulverized hydrogen storage alloy after repeated hydrogen absorption / desorption are shown in Tables 1-1 to 1-4. As shown in these tables, the alloy particles of the hydrogen storage alloy according to the present invention have an average particle diameter of 75 μm or more.

[0165] [Table 1-1]

[0166] [Table 1-2]

[0167] [Table 1-3]

[0168] [Table 1-4]

[0169] (Cell characterization) Evaluation tests of the evaluation cells for alloys Nos. 1 to 70 obtained as described above were carried out as follows. The evaluation temperature was 40° C. The results are summarized in Tables 2-1 to 2-4.

[0170] (1) Discharge capacity of the electrode The discharge capacity of the working electrode was confirmed using the following procedure. After 10 hours of constant current charging at a current value of 80 mA / g per active material of the working electrode, constant current discharging was performed at a current value of 40 mA / g per active material of the working electrode. The discharge termination condition was a potential of -0.5 V of the working electrode. The above charge / discharge cycle was repeated 10 times, and the maximum discharge capacity was recorded as the discharge capacity of the working electrode. It was confirmed that the discharge capacity of the working electrode was saturated and stabilized after 10 charge / discharge cycles. The measured discharge capacity was calculated by the ratio to the discharge capacity of the AB5 alloy No. 34 shown in Table 1-2, which was used as the reference capacity, using the following relational expression (2). Those with a ratio of greater than 1.15 were evaluated as having a larger discharge capacity than the AB5 alloy and being superior.

[0171]

number

[0172] (2) Cycle life characteristics Using a cell in which the discharge capacity of the working electrode was confirmed in (1) Electrode Discharge Capacity above, the cycle life characteristics of the working electrode were determined according to the following procedure: When the current value required to complete charge or discharge the working electrode discharge capacity confirmed in (1) Electrode Discharge Capacity above in 1 hour was defined as 1 C, constant-current charging and constant-current discharging were performed at a current value of C / 2 within a working electrode charge rate range of 20 to 80%, and this cycle was repeated 300 times. The discharge capacity after 300 cycles was measured, and the capacity retention rate was calculated using the following relational formula (3).

[0173]

number

[0174]

number

[0175] (Alloy cost) The alloy costs were evaluated relative to the raw material costs of melting 99% pure metal to produce alloys with the composition shown in Tables 1-1 to 1-4. Compared to alloy No. 34 (reference cost), alloys that were 10% or more cheaper were marked with a ◎, alloys that were 0 to 10% cheaper were marked with a ○, alloys that were more than 0% but up to 10% more expensive were marked with a △, and alloys that were 10% or more expensive were marked with an ×. The results are shown in Tables 2-1 to 2-4. As is clear from these tables, the hydrogen storage alloys of the invention examples exhibit good values ​​in terms of both characteristics and cost.

[0176] [Table 2-1]

[0177] [Table 2-2]

[0178] [Table 2-3]

[0179] [Table 2-4]

[0180] As is clear from Tables 2-1 to 2-4, alloys Nos. 1 to 33 of the invention have excellent, well-balanced characteristics, with evaluation values ​​for both discharge capacity and cycle life characteristics of 1.15 or higher, compared to AB5 alloy No. 34. In contrast, alloys Nos. 34 to 70 of the comparative examples have evaluation values ​​for either characteristic of less than 1.15, making them hydrogen storage alloys with poorly balanced battery characteristics.

[0181] The present invention was accomplished by discovering the existence of a surface treatment layer of an alloy specified for improving durability, combined with the properties of the alloy itself. All of the inventive examples were alloys containing an appropriate amount of Y, while the comparative examples were alloys with a Y content outside the appropriate range or no Y at all, and all had Y2O3 added externally. Alloys containing Y outside the appropriate range are susceptible to cracking due to the effects of hydrogen absorption and desorption, and are unable to form a sufficient surface treatment layer that provides durability to the alloy. In addition to these alloys, alloys that do not contain Y may have improved durability due to the effect of externally added Y2O3, but do not reach the required level of durability. This is presumably because a different surface treatment layer is formed inside the alloy than that formed by alloys containing the appropriate amount of Y.

[0182] <Example 2> As examples of the invention, hydrogen storage alloys Nos. 7, 8, 21, and 25 shown in Tables 1-1 and 1-2 were subjected to predetermined treatments, and then powder surface analysis and evaluation of pore size distribution were carried out.

[0183] Powder surface analysis was performed using a transmission electron microscope to observe the surface treatment layer formed on the alloy surface. Specifically, for samples No. 7, 8, 21, and 25, the hydrogen storage alloys were treated as specified, mixed with epoxy resin, and the epoxy resin was cured at 120°C for 30 minutes. After embedding in the resin, the alloys were thinned using an argon beam to obtain flake samples with a thickness of less than 100 nm. For the thinning process, a JEOL ion slicer (EM09100IS) was used to thinly polish the thin sample at an accelerating voltage of 6 kV until pores of several μm were formed in the thin sample, and then finishing was done at an accelerating voltage of 1.0 kV for 15 minutes.

[0184] The obtained thin-film samples were observed using a transmission electron microscope (JEOL JEM2100F) at an accelerating voltage of 200 kV to examine the surface treatment layer formed on the alloy surface. In addition, an energy dispersive X-ray emission spectrometer (JEOL JED2300) equipped on the same microscope was used to perform elemental analysis of the surface treatment layer. As a result, it was confirmed that a layer of oxide or hydroxide containing Y was present on the surface of the hydrogen storage alloy particles, at least in part of which was in close contact with the surface of the alloy particles. Furthermore, it was confirmed that the thickness of this surface treatment layer in the No. 7 hydrogen storage alloy was 220 nm, and that the thickness of the surface treatment layer became thinner as the amount of Y contained in the hydrogen storage alloy increased.

[0185] On the other hand, the pore size distribution was evaluated as follows. The hydrogen storage alloys Nos. 7, 8, 21, and 25, which had undergone the above-mentioned predetermined treatment, were vacuum dried at 100°C for 2 hours, and then the nitrogen adsorption / desorption isotherms of the hydrogen storage alloys at the liquid nitrogen temperature (77.3K) were measured using a fully automatic gas adsorption measurement device (AS1-MP, AntonPaar). The amount of nitrogen adsorbed per unit weight of the hydrogen storage alloy in the adsorption / desorption isotherm was calculated so that it was expressed as the volume of gaseous nitrogen under standard conditions. The total pore volume was calculated by expressing the amount of nitrogen adsorbed V [Ncm] at the relative pressure (p / p = 0.99) in the adsorption / desorption isotherm. 3 / g] was calculated from the above relational formula (B).

[0186] Furthermore, using the adsorption / desorption isotherms, the pore size distribution in the mesopore region was analyzed by the BJH method, and the pore size distribution in the micropore to mesopore region was analyzed by the DFT method, and the average pore size was calculated. As a result, the total pore volume was found to be 0.0046 cm 3 The average pore size was 25.9 nm. The BET specific surface area was 0.702 m 2 For hydrogen storage alloys No. 8, 21, and 25, the total pore volume was 0.0040–0.0125 cm 3 / g, and the average pore diameter was between 10 and 35 nm. The BET specific surface area was 0.790 m 2 These measurement results show the characteristics of the porous structure of the surface treatment layer, which is an oxide or hydroxide layer containing Y at least partially in close contact with the surface of the alloy particles and formed on the surface of the hydrogen storage alloy.

[0187] Comparative hydrogen storage alloys were obtained in the same manner as above, except that Nos. 43 and 48 shown in Table 1-3 were used. The surfaces of the comparative hydrogen storage alloys were free of a closely adhered oxide or hydroxide layer containing Y at least partially, and the surface treatment layer contained portions exceeding 500 nm. Furthermore, the total pore volume, average pore diameter, and BET specific surface area of ​​all alloys were outside the ranges specified in the present invention.

[0188] (Battery characteristics) A nickel-metal hydride battery adjusted to a SOC (State of Charge) of 60% using the hydrogen storage alloy that had undergone the above-mentioned predetermined treatment was discharged at a rate of 1 C for 5 seconds at 25° C. The discharge resistance was calculated based on Ohm's law from the voltage change before and after discharge and the current value during discharge.

[0189] The discharge capacity was confirmed in accordance with the method of Example 1. One cycle (final voltage was 1.0 V) consisted of constant current charging and constant current discharging at a current value of C / 3, and 1800 charge / discharge cycles were performed. After that, the discharge capacity after 1800 cycles was measured, and the capacity retention rate was calculated using the following relational formula (5).

[0190]

number

[0191] The results of the discharge resistance and capacity retention rate are shown in Table 3.

[0192] [Table 3]

[0193] As is clear from Table 3, the negative electrode active materials obtained from the alloys of the invention examples, i.e., Nos. 7, 8, 21, and 25, exhibited high capacity retention after the durability test and low discharge resistance. In other words, it can be said that the negative electrode active materials using the alloys of the invention examples achieve both high levels of output characteristics and durability.

[0194] After evaluating the durability of these samples, the surface condition of the alloy was similarly evaluated. As a result, the surface condition of the inventive example was confirmed to be the same as that of the above embodiment before the durability evaluation. On the other hand, the surface condition of the comparative example could not be confirmed. This indicates that the effect of Y on durability is different when an appropriate amount of Y is contained in the alloy and when Y is externally added as YO. [Industrial Applicability]

[0195] The hydrogen storage alloy of the present invention is superior to the conventionally used AB5-type hydrogen storage alloys in both discharge capacity and cycle life characteristics, and therefore is suitable not only as a negative electrode material for alkaline storage batteries for hybrid vehicles and idle-stop vehicles, but also for alkaline storage batteries for electric vehicles. [Explanation of symbols]

[0196] 1: Positive electrode 2: Negative electrode 3: Separator 4: Housing (battery case) 10: Alkaline storage battery

Claims

1. A hydrogen storage alloy for use in an alkaline storage battery, the hydrogen storage alloy being A ２ B ７ Type structure, A ５ B １９ Mold structure and AB ３ A hydrogen storage alloy for alkaline storage batteries, which has a crystal structure of the above-mentioned type structure as a total main phase and satisfies the condition of the following general formula (1): Note 【Chemistry 1】 where R and the subscripts a, b, c, d, e, f, and g are R: Sm and / or Ce; 0.01≦a≦0.12, 0.005≦b≦0.12, 0.13≦c≦0.27, 3.20≦d+e+f+g≦3.75, 3.01≦d≦3.655, 0≦e≦0.12, 0≦f≦0.05, 0≦g≦0.35 Represents.

2. 2. The hydrogen storage alloy for alkaline storage batteries according to claim 1, wherein the general formula (1) further satisfies the following condition: Note The subscripts a, b, c, d, e, f, and g in the general formula (1) represent: 0.01≦a≦0.10, 0.005≦b≦0.10, 0.14≦c≦0.26, 3.25≦d+e+f+g≦3.70, 3.01≦d≦3.655, 0≦e≦0.12, 0≦f≦0.04, 0<g≦0.30 Represents.

3. 2. The hydrogen storage alloy for alkaline storage batteries according to claim 1, wherein 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 when pressurized to a hydrogen pressure of 1 MPa at 80°C is 0.94 or more, and the hydrogen pressure P0.5 when the hydrogen storage capacity H / M is 0.5 during hydrogen release is 0.025 MPa or more and 0.12 MPa or less.

4. The hydrogen storage alloy has a particle size adjusted to a range of 150 μm or more and 1 mm or less, and has a volume average particle size MV of 75 μm or more after repeated hydrogen absorption and desorption.

2. The hydrogen storage alloy for alkaline storage batteries according to claim 1, wherein hydrogen absorption is performed by increasing the hydrogen pressure to 3 MPa at 80°C and maintaining the pressure for 1 hour, and hydrogen desorption is performed by evacuating the alloy to a vacuum, reducing the pressure to 0.01 MPa or less at 80°C and maintaining the pressure for 1 hour, and this process is repeated five times before measuring the volume average particle size MV.

5. In the hydrogen absorption / desorption characteristics of the hydrogen storage alloy at 80°C, the plateau slope B at the time of desorption after hydrogen absorption, which is calculated by the following relational expression (A), is in the range of 1.3 to 3.0: [Equation 1] Here, P0.7 is the hydrogen pressure [MPa] when the hydrogen storage capacity (H / M) = 0.7, 2. The hydrogen storage alloy for alkaline storage batteries according to claim 1, wherein P0.3 is the hydrogen pressure [MPa] when the hydrogen storage capacity (H / M) is 0.

3.

6. The hydrogen storage alloy is characterized in that, in an X-ray diffraction measurement using Cu-Kα rays as an X-ray source, the AB ratio of the diffraction intensity ε of the strongest diffraction peak in the diffraction angle 2θ range of 40 to 45° is ５ 6. The hydrogen storage alloy for alkaline storage batteries according to claim 5, wherein the ratio ζ / ε of the diffraction intensities ζ of the (101) plane of the phase is 0.08 or less.

7. 2. The hydrogen storage alloy for an alkaline storage battery according to claim 1, wherein a layer of an oxide or hydroxide containing Y is present on at least a portion of the surface of the hydrogen storage alloy.

8. 8. The hydrogen storage alloy for an alkaline storage battery according to claim 7, wherein the layer of the Y-containing oxide or hydroxide present on at least a portion of the surface of the hydrogen storage alloy and adhering closely to the surface of the alloy particles has a thickness of 500 nm or less.

9. 8. The hydrogen storage alloy for alkaline storage batteries according to claim 7, wherein the oxide or hydroxide present on at least a portion of the surface of the hydrogen storage alloy is mainly composed of the rare earth element contained in the hydrogen storage alloy.

10. The hydrogen storage alloy has an oxide or hydroxide on at least a part of its surface, and the BET specific surface area of ​​the hydrogen storage alloy is 0.5 m ２ 2. The hydrogen storage alloy for alkaline storage batteries according to claim 1, wherein the hydrogen storage alloy has a densitometric value greater than 1 / g.

11. Furthermore, the pore volume is 0.013 cm ３ 11. The hydrogen storage alloy for alkaline storage batteries according to claim 10, wherein the average pore diameter is 40 nm or less and the pore size is 100 μm or less.

12. 12. An alkaline storage battery using the hydrogen storage alloy according to claim 1 as a negative electrode, the alkaline storage battery being mounted on a hybrid vehicle using a motor as a drive source to supply power to the motor.

13. 12. An alkaline storage battery using the hydrogen storage alloy according to claim 1 as a negative electrode, the alkaline storage battery being mounted in an automobile having an idling stop function that starts the engine by a starter motor, and supplying power to the starter motor.

14. 12. A vehicle comprising an alkaline storage battery using the hydrogen storage alloy according to claim 1 as a negative electrode, as a power supply source for a motor.

Images