JP7158684B2 - HYDROGEN STORAGE ALLOY FOR ALKALINE STORAGE BATTERY AND ALKALINE STORAGE BATTERY AND VEHICLE USING SAME FOR NEGATIVE - Google Patents

Description

The present invention relates to a hydrogen storage alloy used for alkaline storage batteries, in particular, a hydrogen storage alloy suitable for use in alkaline storage batteries for power sources such as hybrid vehicles (HEV) and idling stop vehicles, and hybrid vehicles (HEV) and idling stop. The present invention relates to an alkaline storage battery suitable as a power source for vehicles and a vehicle equipped with the alkaline storage battery.

In recent years, secondary batteries have come to be widely used, for example, in mobile phones, personal computers, power tools, hybrid vehicles (HEV), electric vehicles (EV), etc. For these applications, alkaline storage batteries are mainly used. is used. Of these, high output and high durability are particularly important for alkaline storage batteries used in vehicles such as hybrid electric vehicles (HEV), plug-in hybrid electric vehicles (PHEV), and electric vehicles (EV). In addition, as the use of alkaline storage batteries increases, there is a growing demand for miniaturization and weight reduction of alkaline storage batteries.

Conventionally, a hydrogen storage alloy with an _AB5 type crystal structure has been used for the negative electrode of alkaline storage batteries. Development of a hydrogen storage alloy has been desired. As a solution to this problem, Patent Documents 1 and 2 propose a rare earth-Mg transition metal based hydrogen storage alloy containing Mg.

In addition, as a method of miniaturization and weight reduction, for example, it is possible to reduce the amount of hydrogen storage alloy used in the negative electrode, but if the amount of hydrogen storage alloy is reduced, a new problem of output decrease due to reduction of nickel active sites will occur. occurs. In order to improve this, Patent Document 3 proposes a method of increasing the operating voltage by using a hydrogen storage alloy with a high hydrogen equilibrium pressure.

Furthermore, in Patent Document 4, it has a crystal structure of the A ₅ B ₁₉ type structure, and the stoichiometric ratio (B/A), which is the molar ratio of the B component to the A component of the A ₅ B ₁₉ type structure, is 3. .8 or more hydrogen-absorbing alloy is used, and the capacity ratio Z (= Y/X), which is the ratio of the capacity Y of the hydrogen-absorbing alloy negative electrode to the capacity X of the nickel positive electrode, is 1.2 or less (1.0 < Z ≤ 1 It is disclosed that both low-temperature output and durability can be achieved by partially charging and discharging the battery of .2).

Also, several rare earth-Mg-Ni alloys have been proposed as hydrogen storage alloys. For example, Patent Document 5 _discloses a general formula: Ln1 _{- xMgxNiyAz} (wherein Ln is at least one element selected from rare earth elements including _Y and Ga, Zr and Ti). and A is at least one element selected from Co, Mn, V, Cr, Nb, Al, Ga, Zn, Sn, Cu, Si, P and B, and subscripts x, y and z are 0.05 ≤ x ≤ 0.25, 0 < z ≤ 1.5, 2.8 ≤ y + z ≤ 4.0), 20 mol of Sm in the above Ln % or more is disclosed.

Further, in Patent Document 6, a hydrogen storage alloy used for the negative electrode of a nickel-metal hydride secondary battery has a general formula: (La _a Sm _{b Ac} ) _1-w Mg _w Ni _{x Aly T z (} wherein A and T represents at least one element selected from the group consisting of Pr, Nd, etc. and the group consisting of V, Nb, etc., and subscripts a, b and c are respectively a>0, b>0, 0.1 >c≧0 and a+b+c=1, where subscripts w, x, y, and z are 0.1<w≦1, 0.05≦y≦0.35, and 0≦z≦0.5, respectively. , 3.2≦x+y+z≦3.8).

Furthermore, in Patent Document 7, a rare earth-Mg-Ni-based hydrogen storage alloy used for the negative electrode of an alkaline storage battery has a general formula: (A _α Ln _1-α ) _1-β Mg _β Ni _γ-δ-ε Al _δ T _ε (Wherein, A represents one or more elements containing at least Sm selected from the group consisting of Pr, Nd, Sm and Gd; Ln represents La, Ce, Pm, Eu, Tb, Dy, Ho, represents at least one element selected from the group consisting of Er, Tm, Yb, Lu, Ca, Sr, Sc, Y, Ti, Zr and Hf, where T is V, Nb, Ta, Cr, Mo, Mn, Fe , Co, Zn, Ga, Sn, In, Cu, Si, P and B, and subscripts α, β, γ, δ and ε are each 0.4≦ α, 0.05 < β < 0.15, 3.0 ≤ γ ≤ 4.2, 0.15 ≤ δ ≤ 0.30, 0 ≤ ε ≤ 0.20). A hydrogen storage alloy having

Furthermore, Patent Document 8 reports a hydrogen-absorbing alloy electrode using hydrogen-absorbing alloy particles having a center diameter D50 in the range of 8 to 15 μm, as represented by a 50% pass rate, in order to enable high-rate discharge. there is

JP-A-11-323469 WO 01/48841 JP-A-2005-32573 JP-A-2009-87631 JP-A-2009-74164 JP 2009-108379 A Japanese Patent Application Laid-Open No. 2009-138220 JP-A-2000-182608

However, the technologies disclosed in Patent Document 1 and Patent Document 2 have not optimized alloys, and have not been installed in hybrid vehicles.

In addition, in the technology disclosed in Patent Document 3, the use of a hydrogen-absorbing alloy with a high hydrogen equilibrium pressure causes a new problem that the charge-discharge cycle life is reduced.

In addition, in the technology disclosed in Patent Document 4, when further miniaturization and weight reduction are attempted, it is necessary to use a high-output battery, that is, a battery with a high energy density, and the maximum discharge per battery capacity is possible. A battery size that considers the current value (limit current value) is required. This is because a simple miniaturization, that is, a simple miniaturization of the battery size, only reduces the battery capacity. However, the technique of Patent Document 4 does not take such consideration into account.

In addition, the hydrogen storage alloys disclosed in Patent Documents 5, 6, and 7 all have large alloy particle sizes, and alkaline storage batteries using these alloys are miniaturized, which is a problem for in-vehicle applications. The three characteristics of high output and durability, in other words, discharge characteristics and cycle life characteristics, have not been achieved at the same time.

Moreover _, the hydrogen storage alloy used in Patent Document 8 is a so-called _{AB5 alloy} ( _{MmNi4.0Co0.4Mn0.3Al0.3} ) _, and the discharge characteristics are improved by atomization. However, for in-vehicle use, further improvements in characteristics such as durability were required.

SUMMARY OF THE INVENTION The present invention has been made in view of these problems of the prior art, and it is an object of the present invention to provide a hydrogen-absorbing alloy particularly suitable for a nickel-metal hydride battery (alkaline storage battery) for vehicle use.

In order to achieve the above object, as a hydrogen storage alloy for the negative electrode of an alkaline storage battery, the main phase has a crystal structure of the A ₂ B ₇ type structure, and by using a fine powder alloy having a specific composition, discharge The inventors have found that both capacity characteristics and charge/discharge cycle life characteristics can be achieved in a well-balanced manner, leading to the development of the present invention.

That is, the present invention provides a fine-grained alloy with a main phase having a crystal structure of A ₂ B ₇ type structure, specifically Ce ₂ Ni ₇ type or Gd ₂ Co ₇ type, and the following general formula (1 ) to provide a hydrogen-absorbing alloy for alkaline storage batteries, characterized by having a composition represented by:
(La _1-a Sm _a ) _1-b Mg _b Ni _c Al _d (1)
Here, the subscripts a, b, c and d in the above formula (1) are
0.60≦a≦0.78,
0.07≤b≤0.18,
0.02≦d≦0.14,
3.25≤c+d≤3.50
satisfy the conditions of

The particle size of the hydrogen storage alloy according to the present invention preferably has a mass-based D50 of 3 μm or more and 20 μm or less, and a mass-based D90 of 8 μm or more and 50 μm or less. Moreover, the hydrogen storage alloy preferably has a layer made of Ni on at least part of the particle surface, and the layer made of Ni is preferably an alkali-treated layer or an acid-treated layer.

Secondly, the present invention is an alkaline storage battery using any one of the above hydrogen-absorbing alloys as a negative electrode, and is mounted in a hybrid vehicle having a motor as a drive source to supply electric power to the motor. Alternatively, there is provided an alkaline storage battery which is mounted in an idling stop vehicle in which an engine is started by a starter motor and which supplies electric power to the starter motor.

Thirdly, the present invention provides a vehicle comprising, as a power supply source for a motor, an alkaline storage battery using any one of the above hydrogen-absorbing alloys as a negative electrode.

The hydrogen-absorbing alloy for alkaline storage batteries of the present invention and alkaline storage batteries using this hydrogen-absorbing alloy have high power density and excellent charge-discharge cycle life. Sufficiently high rate discharge can be achieved even under these conditions.
In addition, by using fine powder with an optimized particle size, it is possible to suppress the progress of alloy cracking and improve durability, so that Al that improves corrosion resistance can be reduced, and discharge capacity is improved. can be increased.
Furthermore, by forming a layer made of Ni on a part of the particle surface by subjecting the surface to surface treatment, progress of alloy corrosion can be suppressed and durability can be further improved.

In addition, according to the alkaline storage battery of the present invention, it is possible to reduce the size and weight, and when it is mounted on a vehicle such as an automobile, it can provide a hybrid electric vehicle (HEV) with high maneuverability and low fuel consumption. become.

1 is a partially cutaway perspective view illustrating an alkaline storage battery using the hydrogen storage alloy of the present invention; FIG.

An alkaline storage battery using the hydrogen storage alloy of the present invention will be described with reference to FIG. 1, which is a partially cutaway perspective view showing an example of a battery. The alkaline storage battery 10 includes a nickel positive electrode 1 whose main positive electrode active material is nickel hydroxide (Ni(OH) ₂ ), a hydrogen storage alloy negative electrode 2 whose negative electrode active material is the hydrogen storage alloy (MH) according to the present invention, The storage battery includes an electrode group including a separator 3 and an electrolyte layer (not shown) filled with an alkaline electrolyte in a housing 4 .

This battery 10 corresponds to a so-called nickel-metal hydride battery (Ni-MH battery), and the following reactions occur.

Positive electrode ^: NiOOH+ _H2O +e-=Ni(OH ⁾ ₂ +OH-
Negative electrode: MH+OH ⁻ =M+H ₂ O+e ⁻

[Hydrogen storage alloy]
The hydrogen storage alloy used for the negative electrode of the alkaline storage battery according to the present invention will be described below.

In the hydrogen storage alloy of the present invention, the main phase is fine grains having a crystal structure of A ₂ B ₇ type structure, specifically Ce ₂ Ni ₇ type or Gd ₂ Co ₇ type, and the following general formula (1) It is necessary to have a component composition represented by
(La _1-a Sm _a ) _1-b Mg _b Ni _c Al _d (1)
Here, the subscripts a, b, c and d in the above formula (1) are
0.60≦a≦0.78,
0.07≤b≤0.18,
0.02≦d≦0.14,
3.25≤c+d≤3.50
satisfy the conditions of

When the alloy represented by the general formula (1) is used as the negative electrode of an alkaline storage battery, it imparts high discharge capacity and cycle life characteristics to the battery. contribute to

The reasons for limiting the chemical composition of the hydrogen storage alloy of the present invention will be described below.
Rare earth element: La _1-a Sm _a (0.60≦a≦0.78)
The hydrogen storage alloy of the present invention contains a rare earth element as an element of the A component of the A ₂ B ₇ type structure. As rare earth elements, two elements, Sm and La, are essential as basic components that provide hydrogen storage capacity. Also, since Sm and La have different atomic radii, the hydrogen equilibrium pressure can be controlled by this component ratio, and the equilibrium pressure required for the battery can be arbitrarily set. The value is the atomic ratio a of Sm to the sum of Sm and La, and must be in the range of 0.60 or more and 0.78 or less. Within this range, it is easy to set the hydrogen equilibrium pressure suitable for the battery. Preferably, the atomic ratio a value of Sm is in the range of 0.62 or more and 0.75 or less.

A composition with a large amount of Sm has improved durability, and when combined with other elements, the durability is further improved. Although Pr, Nd, and Ce are not actively used as rare earth elements, they may be contained at the level of unavoidable impurities.

Mg:Mg _b (where 0.07≤b≤0.18)
Mg is an essential element in the present invention that constitutes the A component element of the A ₂ B ₇ type structure, and contributes to improvement of discharge capacity and cycle life characteristics. The b value, which represents the atomic ratio of Mg in the A component, is in the range of 0.07 or more and 0.18 or less. If the b value is less than 0.07, the hydrogen releasing ability is lowered, so the discharge capacity is lowered. On the other hand, when it exceeds 0.18, cracking especially accompanying hydrogen absorption/desorption is accelerated, and cycle life characteristics, that is, durability is lowered. Preferably, the b value ranges from 0.08 to 0.16.

Ni: _Nic
Ni is the main element of the _B component of the _A2B7 type structure. The atomic ratio c value will be described later.

Al: Al _d (where 0.02≤d≤0.14)
Al is an element contained as an element of the B component of the A ₂ B ₇ type structure, and is effective in adjusting the hydrogen equilibrium pressure related to the battery voltage, and can improve the corrosion resistance and durability of the fine grain hydrogen storage alloy. It is effective in improving, that is, cycle life characteristics. In order to ensure the above effects, the d value, which represents the atomic ratio of Al to the A component, should be in the range of 0.02 or more and 0.14 or less. If the d value is less than 0.02, the corrosion resistance is not sufficient, resulting in an insufficient cycle life. On the other hand, if the d value exceeds 0.14, the discharge capacity will decrease. The d value is preferably in the range of 0.04 or more and 0.10 or less, more preferably 0.04 or more and 0.09 or less. When the hydrogen-absorbing alloy of the present invention is made into a fine-sized powder, it is sufficient for the amount of Al to be on the lower side of the range of the present invention, and the discharge capacity can be increased accordingly.

Ratio of A component and B component: 3.25 ≤ c + d ≤ 3.50
The stoichiometric ratio, which is the molar ratio of the B component (Ni and Al) to the A component of the A ₂ B ₇ type structure, that is, the value of c + d represented by the general formula is in the range of 3.25 or more and 3.50 or less It is necessary to be If it is less than 3.25, the number of subphases, that is, _three AB phases increases, and the discharge capacity in particular decreases. On the other hand, if it exceeds 3.50, the number of AB ₅ phases increases, and cracking accompanying hydrogen absorption/desorption is accelerated, resulting in a decrease in durability, that is, cycle life. It is preferably in the range of 3.28 or more and 3.47 or less.

[Method for producing hydrogen storage alloy]
Next, a method for producing the hydrogen storage alloy of the present invention will be described.

The hydrogen storage alloy of the present invention is obtained by weighing metal elements such as rare earth elements (Sm, La, etc.), magnesium (Mg), nickel (Ni), and aluminum (Al) so as to obtain a predetermined molar ratio. After the raw material is put into an alumina crucible installed in a high-frequency induction furnace and melted in an atmosphere of an inert gas such as argon gas, it is cast into a mold to produce an ingot of a hydrogen-absorbing alloy. Alternatively, a strip casting method may be used to directly prepare a flake-shaped sample with a thickness of about 200 to 500 μm.
The hydrogen storage alloy of the present invention contains Mg with a low melting point and a high vapor pressure as a main component. It may be difficult to obtain an alloy of chemical composition. Therefore, in producing the hydrogen storage alloy of the present invention by the melting method, it is preferable to first melt the alloy components other than Mg, and then add Mg raw materials such as metal Mg and Mg alloys into the melt. preferable. In addition, this dissolving step is preferably performed in an inert gas atmosphere such as argon or helium. Specifically, the inert gas containing 80 vol% or more of argon gas is adjusted to 0.05 to 0.2 MPa. It is preferable to carry out under a reduced pressure atmosphere.

The alloy melted under the above conditions is then preferably cast in a water-cooled mold and solidified to form an ingot of the hydrogen storage alloy. Next, the melting point (T _m ) of each obtained ingot of the hydrogen storage alloy is measured using a DSC (differential scanning calorimeter). This is because the hydrogen-absorbing alloy of the present invention is obtained by exposing the cast ingot to an atmosphere of inert gas such as argon or helium, nitrogen gas, or a mixed gas atmosphere of 900° C. or higher, the melting point of the alloy ( This is because it is preferable to perform heat treatment at a temperature not higher than T _m for 3 to 50 hours. By this heat treatment, the ratio of the main phase having the A ₂ B ₇ type crystal structure in the hydrogen storage alloy is made 50 vol % or more, and the AB ₂ phase, AB ₃ phase, and AB ₅ phase are reduced or eliminated. can be done. It can be confirmed by X-ray diffraction measurement using Cu—Kα rays that the crystal structure of the main phase of the obtained hydrogen-absorbing alloy is the A ₂ B ₇ type structure.

If the heat treatment temperature is less than 900° C., the diffusion of the elements is insufficient, so that the sub-phase remains, which may lead to a decrease in the discharge capacity of the battery and a deterioration in the cycle characteristics. On the other hand, if the heat treatment temperature is −20° C. or higher (T _m −20° C. or higher) than the melting point T _m of the alloy, coarsening of the crystal grains of the main phase and evaporation of the Mg component will occur, resulting in fine powder and chemical composition changes. There is also a possibility that the hydrogen storage capacity may decrease due to the change. Therefore, the heat treatment temperature is preferably in the range of 900° C. to (T _m −30° C.). More preferably, it is in the range of 900°C to (T _m -50°C).

In addition, if the holding time of the heat treatment is 3 hours or less, the ratio of the main phase cannot be stably increased to 50 vol% or more, and the homogenization of the chemical components of the main phase becomes insufficient. Expansion and contraction during release become non-uniform, and the amount of generated distortion and defects increases, which may adversely affect cycle characteristics. The holding time of the heat treatment is preferably 4 hours or longer, and more preferably 5 hours or longer from the viewpoint of homogenizing the main phase and improving the crystallinity. However, if the holding time exceeds 50 hours, the amount of evaporation of Mg increases and the chemical composition changes, and as a result, there is a possibility that an AB ₅ type subphase may be generated. Furthermore, it is not preferable because there is a risk of an increase in manufacturing cost and a dust explosion due to evaporated Mg fine powder.

The heat-treated alloy is pulverized by dry or wet methods. When finely pulverizing by a dry method, for example, it is pulverized using a hammer mill, an ACM pulverizer, or the like. On the other hand, when pulverizing by a wet method, it is pulverized using a bead mill, an attritor, or the like. Especially when obtaining fine powder, wet pulverization is preferable because it can be produced safely.
When the hydrogen-absorbing alloy of the present invention is used in a battery for vehicle use, the particle size of the pulverized alloy particles is 3 μm at a mass-based 50% passage rate particle size D50 in consideration of the balance of battery characteristics such as output and cycle life characteristics. It is preferably in the range of 20 μm or more, more preferably 5 μm or more and 15 μm or less. Furthermore, if the particle size distribution of the alloy particles is too wide, the above characteristics deteriorate, so the mass-based 10% passage particle diameter D10 is in the range of 0.5 μm or more and 9 μm or less, and the 90% passage particle diameter D90 is 8 μm or more. It is preferably in the range of 50 μm or less, more preferably in the range of 1 μm or more and 7 μm or less for D10, and more preferably in the range of 10 μm or more and 40 μm or less for D90. The particle size of the alloy particles can be controlled by adjusting conditions such as the diameter, amount, and number of revolutions of the media.
Here, for the particle size distributions D50, D10 and D90 of the alloy particles described above, values measured by a laser diffraction/scattering particle size distribution measuring device are used. A mold or the like can be used.

The pulverized alloy particles may be subjected to surface treatment such as alkali treatment using an aqueous alkali solution such as KOH or NaOH, or acid treatment using an aqueous solution of nitric acid, sulfuric acid or hydrochloric acid. By applying these surface treatments, a layer made of Ni (alkali-treated layer or acid-treated layer) is formed on at least a part of the surface of the alloy particles, and it is possible to suppress the progress of alloy corrosion and improve durability. Therefore, the cycle characteristics of the battery and the discharge characteristics in a wide temperature range can be improved. In particular, in the case of acid treatment, it is preferable to use hydrochloric acid because it is possible to precipitate Ni with less damage to the alloy surface. In addition, when the alloy is pulverized by a wet method, surface treatment can be performed at the same time.

[Alkaline storage battery]
Next, a configuration example of an alkaline storage battery 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 housing 4 (battery case) that is filled with an electrolyte and accommodates them. A specific description will be given below.

<Positive electrode>
The positive electrode 1 is generally 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 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 hydrogen storage alloy (negative electrode material) described above, and examples thereof include simple metals, alloys, and hydroxides. . As the positive electrode active material, a material containing nickel oxide and mainly composed of nickel oxyhydroxide and/or nickel hydroxide can be used. The amount of nickel oxide in the positive electrode active material is, for example, 90 to 100% by mass, and may be 95 to 100% by mass. The average particle size of the nickel oxide can be appropriately selected, for example, from the range of 3 to 35 μm, preferably from 3 to 25 μm.

The conductive aid is not particularly limited as long as it is a material capable of imparting electronic conductivity, and examples thereof include metal powders such as Ni powder, oxides such as cobalt oxide, graphite, and carbon materials such as carbon nanotubes. can be done. The amount of the conductive aid to be added is not particularly limited, but is preferably in the range of 0.1 to 50 parts by weight, more preferably in the range of 0.1 to 30 parts by weight, based on 100 parts by weight of the positive electrode active material. Examples of binders include synthetic rubbers such as styrene-butadiene rubber (SBR), celluloses such as carboxymethyl cellulose (CMC), polyols such as polyvinyl alcohol (PVA), and fluorine resins such as polyvinylidene fluoride (PVDF). etc. can be mentioned. The amount of the binder may be, for example, 7 parts by mass or less with respect to 100 parts by mass of the positive electrode active material. may be in the range of

Furthermore, examples of thickening agents include carboxymethyl cellulose and modified products thereof (including salts such as Na salts), cellulose derivatives such as methyl cellulose, saponified products of polymers having vinyl acetate units such as polyvinyl alcohol, polyethylene oxide, and the like. and polyalkylene oxides of. These thickeners may be used singly or in combination of two or more. The amount of the thickening agent is, for example, 5 parts by mass or less, may be in the range of 0.01 to 3 parts by mass, and further 0.05 to 1.5 parts by mass with respect to 100 parts by mass of the positive electrode active material. It may be in the range of part.

Examples of materials for the positive electrode current collector include stainless steel, aluminum, nickel, iron, and titanium. The shape of the positive electrode current collector includes, for example, a foil shape, a mesh shape, a porous shape, and the like, and any shape may be used.
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 making it into a paste together with the positive electrode active material, conductive aid, and binder described above. As the dispersion medium, water, an organic medium, or a mixed medium in which two or more media selected from these are mixed can be used. Conductive agents, binders, thickeners and the like may be added as necessary, but these (in particular, binders and thickeners) do not necessarily need to be added.
For the positive electrode, the positive electrode mixture paste may be applied to the support according to the shape of the support, or may be filled in the pores of the support. The positive electrode can be formed by coating or filling a support, drying to remove the dispersion medium, and compressing the resulting dried product in the thickness direction (for example, rolling between a pair of rolls).

<Negative Electrode>
The negative electrode 2 is generally 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 hydrogen storage alloy of the present invention described above as a negative electrode active material. The negative electrode active material layer may further contain at least one of a conductive aid, a binder and a thickener. The conductive aid is not particularly limited as long as it is a material capable of imparting electronic conductivity, and examples thereof include metal powders such as Ni powder, oxides such as cobalt oxide, graphite, and carbon materials such as carbon nanotubes. can be done. The amount of the conductive aid added is not particularly limited, but is preferably in the range of 0.1 to 50 parts by weight, more preferably in the range of 0.1 to 30 parts by weight, based on 100 parts by weight of the hydrogen-absorbing alloy powder. Examples of binders include synthetic rubbers such as styrene-butadiene rubber (SBR), celluloses such as carboxymethyl cellulose (CMC), polyols such as polyvinyl alcohol (PVA), and fluorine resins such as polyvinylidene fluoride (PVDF). etc. can be mentioned. The amount of the binder may be, for example, 7 parts by mass or less with respect to 100 parts by weight of the hydrogen-absorbing alloy powder. It may be a range of parts.

Examples of materials for the negative electrode current collector include steel, stainless steel, aluminum, nickel, iron, titanium, and carbon. Further, the shape of the negative electrode current collector includes, for example, a foil shape, a mesh shape, a porous shape, and the like, and any shape may be used.
Paste is used to form the negative electrode active material layer on the negative electrode current collector. The negative electrode active material, the conductive aid, the binder, the thickener, and the like are contained in this material.
This negative electrode for a nickel-metal hydride battery is produced by molding a negative electrode paste containing the hydrogen-absorbing alloy powder of the present invention into a predetermined shape, and supporting the molded negative electrode paste with a negative electrode core material (negative electrode current collector). Alternatively, it is produced by preparing a negative electrode paste containing the above hydrogen-absorbing alloy powder, applying it to a negative electrode current collector, and drying it.

<Electrolyte layer>
The electrolyte layer is a layer containing an aqueous electrolyte solution formed between the positive electrode and the negative electrode. Here, the water-based electrolytic solution refers to an electrolytic solution using water as a main solvent, and the solvent may contain substances other than water. The ratio of water to the entire solvent of the electrolytic solution may be 50 mol % or more, and may be 70 mol % or more, 90 mol % or more, or 100 mol %.
The aqueous electrolytic solution is preferably an alkaline aqueous solution. Examples of the solute of the alkaline aqueous solution include potassium hydroxide (KOH) and sodium hydroxide (NaOH), which may contain LiOH. The concentration of the solute in the aqueous electrolytic solution is preferably as high as possible.
The electrolyte layer has a separator 3 . A short circuit can be effectively prevented by installing the separator 3 . Examples of the separator 3 include nonwoven fabrics and porous membranes containing resins such as sulfonated polyethylene and polypropylene.

<Case>
The housing 4 is a battery case (cell container) containing the positive electrode 1, the negative electrode 2 and the separator 3 described above and filled with an electrolyte. Any material can be used as long as it is stable without being corroded by the electrolyte, and can retain the gas (oxygen or hydrogen) temporarily generated during charging and the electrolyte without leaking to the outside. A metal case, a resin case, or the like is generally used. When the positive electrode 1 and the negative electrode 2 are a laminated alkaline storage battery 10 having a laminate in which a plurality of separators 3 are interposed, the housing 4 has a structure in which the circumference of the laminate is sealed with a frame-shaped resin. There may be.

<Battery>
Battery 10 of the present invention is typically a secondary battery. Therefore, since it can be repeatedly charged and discharged, it is suitable for use as a vehicle battery, for example. In that case, it is not limited to use as a hybrid vehicle battery that supplies power to a motor for driving a vehicle, but also supplies power to a starter motor for restarting the engine in a vehicle with an idling stop function. You may apply as a form to do. The secondary battery also includes use of a secondary battery as a primary battery (use for the purpose of discharging only once after charging). Moreover, the shape of the battery includes, for example, a coin shape, a laminate shape, a cylindrical shape, a rectangular shape, and the like, and any shape may be used.

<Vehicle>
A vehicle according to the present invention is equipped with an alkaline storage battery using the hydrogen storage alloy as a 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, it is possible to improve exercise performance, reduce fuel consumption, and extend cruising distance.

<Example 1>
No. 1 having the component composition shown in Table 1 below. An evaluation cell using hydrogen storage alloys Nos. 1 to 30 as a negative electrode active material was fabricated in the manner described below, and an experiment was conducted to evaluate its characteristics. In addition, No. shown in Table 1. Alloys Nos. 1 to 14 are alloy examples (invention examples) that meet the conditions of the present invention. Nos. 15 to 30 are alloy examples (comparative examples) that do not satisfy the conditions of the present invention. Moreover, No. of the comparative example. Alloy No. 15 was used as a reference alloy for evaluating cell properties.

(Preparation of negative electrode active material)
No. shown in Table 1. 1 to 30 alloy raw materials (Sm, La, Mg, Ni and Al each with a purity of 99% or more) are melted and cast in an argon atmosphere (Ar: 100 vol%, 0.1 MPa) using a high-frequency induction heating furnace. and ingots. Then, these alloy ingots were subjected to heat treatment in an argon atmosphere (Ar: 90 vol%, 0.1 MPa) at a temperature (940 to 1130° C.) of the melting point T _m −50° C. of each alloy for 10 hours. , coarsely pulverized, and finely pulverized with a wet bead mill to a mass-based D50 of 13 μm to obtain a sample (negative electrode active material) for cell evaluation. However, No. used as a reference for alloy cell evaluation. The AB5 alloy _No. 15 was wet-pulverized into a fine powder of 25 μm in mass-based D50, and used as a sample (negative electrode active material) for cell evaluation. In addition, No. of the invention example of this invention. Alloys 1 to 14 were subjected to X-ray diffraction measurement of pulverized powder after heat treatment, and it was confirmed that the main phase was A ₂ B ₇ phase in all cases.

(Preparation of cell for evaluation)
<Negative Electrode>
The negative electrode active material prepared above, the Ni powder of the conductive agent, and two types of binders (styrene-butadiene rubber (SRB) and carboxymethyl cellulose (CMC)) were mixed in a weight ratio of negative electrode active material:Ni powder: They were mixed so that SBR:CMC=95.5:3.0:1.0:0.5 and kneaded to obtain a paste-like composition. This paste composition was applied to a punching metal, dried at 80° C., and roll-pressed with a load of 15 kN to obtain a negative electrode.

<Positive electrode>
Nickel hydroxide (Ni(OH) ₂ ), metallic cobalt (Co) as a conductive agent, and two types of binders (styrene-butadiene rubber (SBR) and carboxymethyl cellulose (CMC)) are mixed at a mass ratio of Ni (OH) ₂ :Co:SBR:CMC=95.5:2.0:2.0:0.5, and kneaded to form a paste composition. This paste composition was applied to porous nickel, dried at 80° C., and roll-pressed with a load of 15 kN to obtain a positive electrode.

<Electrolyte>
The electrolytic solution used was an alkaline aqueous solution obtained by mixing pure water with potassium hydroxide (KOH) at a concentration of 6 mol/L and adding 0.1 mol/L of LiOH.

<Evaluation cell>
After arranging the above positive electrode as a counter electrode and the above negative electrode as a working electrode in an acrylic housing, the above electrolytic solution was injected to prepare a cell using the Hg/HgO electrode as a reference electrode, and an evaluation test was performed. provided. At this time, the capacity ratio between the working electrode and the counter electrode was adjusted to be working electrode:counter electrode=1:3.

(Evaluation of cell characteristics)
Alloy no. The evaluation test of the evaluation cells of Nos. 1 to 30 was conducted in the following manner. The evaluation temperature at this time was all 25°C.

(1) Discharge Capacity of Electrode The discharge capacity of the electrode of the working electrode was confirmed by the following procedure. After performing constant current charging at a current value of 80 mA/g per active material of the working electrode for 10 hours, constant current discharging was performed at a current value of 40 mA/g per active material of the working electrode. The termination condition of the discharge was the working electrode potential of -0.5V. The above charging and discharging were repeated 10 times, and the maximum discharge capacity was taken 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 capacities are No. 1 shown in Table 1. The discharge capacity of the AB ₅ alloy of No. ₁₅ is used as a reference capacity, and the ratio to it is calculated by the following formula (2). evaluated.
Discharge capacity = (discharge capacity of evaluation alloy) / (discharge capacity of AB ₅ alloy (No. 15))
... (2)

(2) Cycle life characteristics Using a cell in which the discharge capacity of the working electrode was confirmed in (1) Electrode discharge capacity, the cycle life characteristics of the working electrode were obtained by the following procedure.
When the discharge capacity of the electrode of the working electrode confirmed by the discharge capacity of the electrode (1) above is 1 C, and the current value required to complete charging or discharging in 1 hour is 1 C, the charging rate of the working electrode is 20-. In the range of 80%, constant current charging and constant current discharging at a current value of C / 2 is defined as one cycle, and this is repeated 100 cycles, and the discharge capacity after 100 cycles is measured. The capacity retention rate was obtained by the formula.
Capacity retention rate = (discharge capacity at 100th cycle)/(discharge capacity at 1st cycle)
... (3)
The evaluation of the cycle life characteristics was performed on No. 1 shown in Table 1. The capacity retention rate after 100 cycles of the AB ₅ alloy of No. ₁₅ is defined as the reference capacity retention rate, and the ratio to it is calculated by the following formula (4). It was evaluated as having large and excellent characteristics.
Cycle life characteristics=(capacity retention rate of measured alloy after 100 cycles)/(capacity retention rate of AB5 alloy (No. ₁₅ ) after 100 cycles) (4)

As is clear from Table 1, No. of invention examples. 1 to 14 alloys are No. It can be seen that the evaluation values of the discharge capacity and the cycle life characteristics are both 1.10 or more for the AB5 alloy of No. ₁₅ , and have excellent characteristics. In particular, the cycle life characteristics are all evaluated values of 1.20 or more, indicating that they are excellent. On the other hand, No. of the comparative example. It can be seen that the alloys of 15 to 30 have an evaluation value of less than 1.05 for any property.

<Example 2>
(Preparation of negative electrode active material)
A hydrogen storage alloy having a composition of (La _0.30 Sm _0.70 ) _0.90 Mg _0.10 Ni _3.28 Al _0.09 was once evacuated and then heated in an argon atmosphere using a high-frequency induction heating furnace. (Ar: 90 vol%, 0.15 MPa) and cast to form an ingot, which is then placed in an argon atmosphere (Ar: 100 vol%, 0.5 MPa) at 1000°C (alloy melting point T _m -50°C). After performing heat treatment for 10 hours at a temperature of , coarsely pulverized, finely pulverized to the particle size shown in Table 2, and used as a sample (negative electrode active material) for cell evaluation. In addition, the sample No. shown in Table 2 was used. B1-B4 were prepared using a wet bead mill and sample no. B5-B7 were pulverized using an ACM pulverizer.
In addition, as an alloy of a comparative example, an alloy of MmNi _4.0 Co _0.4 Mn _0.3 Al _0.3 (sample No. BZ) was melted in the same manner as above, heat-treated, coarsely pulverized, and then bead milled. to obtain a fine powder having D50 of 11.2 μm on a mass basis, and used as a sample (negative electrode active material) for cell evaluation. Here, Mm is a mixture of rare earth elements consisting of La: 25%, Ce: 50%, Pr: 5%, and Nd: 20% by mass.
As a result of performing X-ray diffraction on the sample obtained above, Sample No. In the alloys B1 to B7, the crystal structure of the main phase is A ₂ B ₇ type, and the sample No. of the comparative example. The alloy of BZ was confirmed to have the _AB5 type crystal structure of the main phase.

(Preparation of cell for evaluation and evaluation of cell characteristics)
Next, using the sample for cell evaluation prepared as described above, an evaluation cell was prepared in the same manner as in Example 1, and the cell characteristics (discharge capacity, cycle life characteristics, ), and the results are compared with sample No. 1, which is a comparative example, in the same manner as in Example 1. Relative evaluation was performed using the measured value of the BZ alloy as a reference value (1.00), and the results are also shown in Table 2.

As is clear from Table 2, the No. 1 suitable for the present invention. The alloys B1 to B7 are No. 1 of the comparative example used as a reference. It can be seen that the evaluation values of the discharge capacity and cycle life characteristics are all 1.10 or more, which is superior to the BZ alloy.

<Example 3>
(Preparation of negative electrode active material)
(La _0.25 Sm _0.75 ) _0.90 Mg _0.10 Ni _3.33 Al _0.07 After evacuating the hydrogen storage alloy, it was heated in an argon atmosphere using a high-frequency induction heating furnace. (Ar: 100 vol%, 0.1 MPa) and cast into an ingot, and then the ingot is heated to 1000 ° C. (alloy melting point T _m −50 ° C.) in an argon atmosphere (Ar: 90 vol% 0.1 MPa). ) for 10 hours, coarsely pulverized, and then finely pulverized to D50=13.4 μm based on mass using a wet bead mill.
Next, the finely pulverized alloy powder was subjected to the following two levels of surface treatment to obtain a sample (negative electrode active material) for cell evaluation.
Alkali treatment: NaOH: immersed in an aqueous sodium hydroxide solution of 40 mass% at 75 ° C. for 2 hours under the condition of a solid-liquid ratio of 1:2 (sample No. C1)
・Acid treatment: immersed in a 1 mol/L hydrochloric acid aqueous solution at 30°C for 2 hours at a solid-liquid ratio of 1:1 (sample No. C2)

(Preparation of cell for evaluation and evaluation of cell characteristics)
Next, using the sample for cell evaluation prepared as described above, an evaluation cell was prepared in the same manner as in Example 1, and the cell characteristics (discharge capacity, cycle life characteristics, ) were evaluated, and the results were compared with sample No. 2 used in the comparative example of Example 2. Relative evaluation was performed using the measured value of the BZ alloy (without surface treatment) as the standard value (1.00), and the results are shown in Table 3.

As can be seen by comparing Tables 3 and 2, the hydrogen-absorbing alloys of the present invention were significantly improved in cycle life characteristics by surface treatment.

Since the hydrogen storage alloy of the present invention is superior to the conventionally used AB ₅ type hydrogen storage alloy in both discharge capacity and cycle life characteristics, it is suitable as a negative electrode material for alkaline storage batteries for hybrid vehicles and idling stop vehicles. In addition, it can be suitably used for alkaline storage batteries for electric vehicles.

1: positive electrode 2: negative electrode 3: separator 4: housing (battery case)
10: Alkaline storage battery

Claims (8)

A fine hydrogen storage alloy for use in alkaline storage batteries,
A hydrogen storage alloy for an alkaline storage battery, wherein the main phase of the hydrogen storage alloy is an A ₂ B ₇ type crystal structure with a volume ratio of 50 vol % or more, and is represented by the following general formula (1): .
(La _1-a Sm _a ) _1-b Mg _b Ni _c Al _d (1)
Here, the subscripts a, b, c and d in the above formula (1) are
0.60≦a≦0.78,
0.07≤b≤0.18,
0.02≦d≦0.14,
3.25≤c+d≤3.50
satisfy the conditions of 2. The hydrogen storage alloy for an alkaline storage battery according to claim 1, wherein the particle size of said hydrogen storage alloy has a mass-based D50 of 3 μm or more and 20 μm or less. 3. The hydrogen-absorbing alloy for an alkaline storage battery according to claim 1, wherein the particle size of said hydrogen-absorbing alloy has a mass-based D90 of 8 μm or more and 50 μm or less. 4. The hydrogen storage alloy for an alkaline storage battery according to any one of claims 1 to 3, wherein said hydrogen storage alloy has a layer made of Ni on at least part of the particle surface. 5. The hydrogen-absorbing alloy for an alkaline storage battery according to claim 4, wherein said Ni layer is an alkali-treated layer or an acid-treated layer. An alkaline storage battery using the hydrogen storage alloy according to any one of claims 1 to 5 as a negative electrode, which is mounted in a hybrid vehicle having a motor as a drive source and supplies electric power to the motor. An alkaline storage battery characterized by: An alkaline storage battery using the hydrogen storage alloy according to any one of claims 1 to 5 as a negative electrode, which is mounted in an automobile having an idling stop function for starting the engine with a starter motor, and electric power is supplied to the starter motor. An alkaline storage battery, characterized in that it supplies A vehicle comprising, as a power supply source for a motor, an alkaline storage battery using the hydrogen storage alloy according to any one of claims 1 to 5 as a negative electrode.

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