WO2020195542A1 - Hydrogen-intercalated alloy for alkaline battery, alkaline battery using same as negative electrode, and vehicle - Google Patents

Abstract

Provided are: a hydrogen-intercalated alloy suitable for a negative electrode of an in-vehicle alkaline battery; an alkaline battery using same; and a vehicle. A fine-grained hydrogen-intercalated alloy used for an alkaline battery, and an alkaline battery using same as a negative electrode are provided, wherein the hydrogen-intercalated alloy has an A₂B₇-type crystal structure as a main phase, and is represented by general formula (La_1-aSm_a)_1-bMg_bNi_cAl_d (in the formula, the subscripts a, b, c, and d satisfy the conditions of 0.60≤a≤0.78, 0.07≤b≤0.18, 0.02≤d≤0.14, and 3.25≤c+d≤3.50). A vehicle having the alkaline battery as a power supply of a motor is provided.

Description

Hydrogen storage alloy for alkaline storage batteries and alkaline storage batteries and vehicles using it as the negative electrode

The present invention relates to a hydrogen storage alloy used for an alkaline storage battery, particularly a hydrogen storage alloy suitable for use in an alkaline storage battery for a power source of a hybrid electric vehicle (HEV) or an idling stop vehicle, and a hybrid electric vehicle (HEV) or an idling stop. It relates to an alkaline storage battery suitable for a power source of a car or the like, and a vehicle equipped with the alkaline storage battery.

In recent years, secondary batteries have come to be widely used in, for example, mobile phones, personal computers, electric tools, hybrid electric vehicles (HEVs), electric vehicles (EVs), etc., and are mainly used for alkaline storage batteries. Is used. Of 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). In addition, as the spread of these applications increases, there is an increasing demand for smaller and lighter alkaline storage batteries.

Conventionally, a negative electrode of an alkaline storage battery, a hydrogen storage alloy of AB ₅ type crystal structure was used, the alloy, there is a limit to the size and weight of the battery, a new hydrogen that can achieve high capacity in a small The development of storage alloys has been desired. Therefore, as a solution to this problem, Patent Document 1 and Patent Document 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 conceivable to reduce the amount of hydrogen storage alloy used for the negative electrode. Occurs. In order to improve this, Patent Document 3 proposes a method of increasing the operating voltage by using a hydrogen storage alloy having a high hydrogen equilibrium pressure.

Furthermore, Patent Document _4, A _{5 B 19} type structure has a crystal structure, stoichiometry is the molar ratio of B component to A component in the _A 5 _{B 19} type structure (B / A) is 3 A capacity ratio Z (= Y / X), which is the ratio of the capacity Y of the hydrogen storage alloy negative electrode to the capacity X of the nickel positive electrode, is 1.2 or less (1.0 <Z ≦ 1) using a hydrogen storage alloy of 8. or more. It is disclosed that low-temperature output and durability can be achieved at the same time by partially charging and discharging the battery of 2).

Further, as hydrogen storage alloys, some rare earth-Mg—Ni based alloys have been proposed. For example, Patent Document 5, the general formula: Ln in _{1-x Mg x Ni y A} z ( wherein, Ln is at least one element selected from the rare earth elements, Ga, Zr and Ti containing Y Yes, 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 are In the hydrogen storage alloy represented by 0.05 ≦ x ≦ 0.25, 0 <z ≦ 1.5, 2.8 ≦ y + z ≦ 4.0), 20 mol of Sm is contained in the above Ln. Hydrogen storage alloys containing% or more are disclosed.

In Patent Document 6, as a hydrogen absorbing alloy used for the negative electrode of nickel-hydrogen secondary battery, the general _{formula: (La a Sm b A c} ) in _{1-w Mg w Ni x Al} y 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 the subscripts a, b, and c represent a> 0, b> 0, 0.1, respectively. The relationships shown by> c ≧ 0 and a + b + c = 1 are satisfied, and the subscripts w, x, y and z are 0.1 <w ≦ 1, 0.05 ≦ y ≦ 0.35 and 0 ≦ z ≦ 0.5, respectively. An alloy having the composition shown in (2) (in the range shown by 3.2 ≦ x + y + z ≦ 3.8) is disclosed.

Further, Patent Document 7 describes a rare earth _- Mg—Ni hydrogen storage alloy used for the negative electrode of an alkaline storage battery as a general formula: (A _α Ln _1-α ) _1-β Mg _β Ni _γ-δ-ε Al _δ T _ε. (In the formula, A represents one or more elements including at least Sm selected from the group consisting of Pr, Nd, Sm and Gd, and 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 represents V, Nb, Ta, Cr, Mo, Mn, Fe. , Co, Zn, Ga, Sn, In, Cu, Si, P and B represent at least one element selected from the group, and the subscripts α, β, γ, δ and ε are 0.4 ≦, respectively. The composition represented by α, 0.05 <β <0.15, 3.0 ≦ γ ≦ 4.2, 0.15 ≦ δ ≦ 0.30, 0 ≦ ε ≦ 0.20) The hydrogen storage alloy having is disclosed.

Further, Patent Document 8 reports a hydrogen storage alloy electrode using hydrogen storage alloy particles having a center diameter D50 represented by a 50% passing rate in the range of 8 to 15 μm in order to enable high rate discharge. There is.

Japanese Unexamined Patent Publication No. 11-323469 International Publication No. 01/48841 Japanese Unexamined Patent Publication No. 2005-32573 Japanese Unexamined Patent Publication No. 2009-87631 Japanese Unexamined Patent Publication No. 2009-74164 Japanese Unexamined Patent Publication No. 2009-108379 JP-A-2009-138220 Japanese Unexamined Patent Publication No. 2000-18260

However, the techniques disclosed in Patent Documents 1 and 2 have not been optimized for alloys and have not been installed in hybrid vehicles.

Further, in the technique disclosed in Patent Document 3, a new problem has arisen in which the charge / discharge cycle life is shortened when a hydrogen storage alloy having a high hydrogen equilibrium pressure is used.

Further, in the technique disclosed in Patent Document 4, in order to further reduce the size and weight, it is necessary to use a high output battery, that is, a battery having a high energy density, and the maximum discharge per battery capacity is possible. A battery size that takes into account 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, in the technique of Patent Document 4, such consideration is not made.

Further, the hydrogen storage alloys disclosed in Patent Document 5, Patent Document 6, and Patent Document 7 all have a large alloy particle size, and an alkaline storage battery using these alloys is a problem for in-vehicle use. The three characteristics of high output and durability, in other words, both discharge characteristics and cycle life characteristics, could not be achieved at the same time, which was insufficient as a hydrogen storage alloy for an in-vehicle alkaline storage battery.

The hydrogen storage alloy used in the Patent Document 8, a so-called AB ₅ alloys _{(MmNi 4.0 Co 0.4 Mn 0.3 Al} 0.3), discharge characteristics by atomization is improved However, for in-vehicle use, it was necessary to further improve the characteristics in terms of durability and the like.

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

To achieve the above object, the hydrogen storage alloy for the negative electrode of an alkaline storage battery, the main phase has the crystal structure of A ₂ B ₇ type structure, and by using a fine powder of an alloy having a specific chemical composition, the discharge We have found that it is possible to achieve both capacitance characteristics and charge / discharge cycle life characteristics in a well-balanced manner, and have developed the present invention.

That is, in the present invention, the main phase is a fine-grained alloy having a crystal structure of A ₂ B ₇ type, specifically, Ce ₂ Ni ₇ type or Gd ₂ Co ₇ type, and the following general formula (1). ), A hydrogen storage alloy for an alkaline storage battery, characterized by having a component composition represented by).
Serial _{(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 equation (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.

The particle size of the hydrogen storage alloy according to the present invention is preferably such that the mass-based D50 is 3 μm or more and 20 μm or less, and the mass-based D90 is 8 μm or more and 50 μm or less. Further, the hydrogen storage alloy preferably has a layer made of Ni on at least a 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 of the above hydrogen storage alloys as a negative electrode, which is mounted on a hybrid vehicle using a motor as a drive source to supply electric power to the motor. Alternatively, the present invention provides an alkaline storage battery, which is mounted on an idling stop vehicle in which an engine is started by a starter motor to supply electric power to the starter motor.

Thirdly, the present invention provides a vehicle characterized by having an alkaline storage battery using any of the above hydrogen storage alloys as a negative electrode as a power supply source to the motor.

The hydrogen storage alloy for the alkaline storage battery of the present invention and the alkaline storage battery using this hydrogen storage alloy have high output density and excellent charge / discharge cycle life, so that they have excellent discharge capacity characteristics and can be used in vehicles. A sufficiently high rate of discharge can be achieved even under conditions.
Further, by using fine powder with an optimized particle size, the progress of alloy cracking can be suppressed and the durability can be improved. Therefore, Al that improves corrosion resistance can be reduced, and eventually the discharge capacity can be increased. Can be increased.
Further, by forming a layer made of Ni on a part of the particle surface by surface treatment, the progress of alloy corrosion can be suppressed and the durability can be further improved.

Further, according to the alkaline storage battery according to 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 is possible to provide a hybrid electric vehicle (HEV) having high kinetic performance and low fuel consumption. Will be.

It is a partial cut-out perspective view which illustrates the alkaline storage battery using the hydrogen storage alloy of this invention.

The 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 the battery. The alkaline storage battery 10 includes a nickel positive electrode 1 using nickel hydroxide (Ni (OH) ₂ ) as the main positive electrode active material, a hydrogen storage alloy negative electrode 2 using the hydrogen storage alloy (MH) according to the present invention as the negative electrode active material, and the negative electrode 2. This is a storage battery in which an electrode group including a separator 3 is provided in a housing 4 together with an electrolyte layer (not shown) filled with an alkaline electrolytic solution.

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

^{_{Cathode: NiOOH + H 2 O + e}} - = Ni (OH) 2 + OH -
_{^{Negative: MH + OH - = M +}} H 2 O + e -

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

The hydrogen storage alloy of the present invention has fine particles having a crystal structure whose main phase is A ₂ B ₇ type, specifically Ce ₂ Ni ₇ type or Gd ₂ Co ₇ type, and has the following general formula (1). It is necessary to have a component composition represented by.
Serial _{(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 equation (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.

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, so that the alkaline storage battery can be made smaller, lighter, and more durable. Contribute to.

Hereinafter, the reason for limiting the component composition of the hydrogen storage alloy of the present invention will be described.
Rare earth _{elements: La 1-a} Sm a (However, 0.60 ≦ a ≦ 0.78)
The hydrogen storage alloy of the present invention, as the element of the A component of the A ₂ B ₇ type structure, containing a rare earth element. As rare earth elements, two elements, Sm and La, are indispensable as basic components that bring about hydrogen storage capacity. In addition, 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 value of Sm with respect to the total of Sm and La, and needs to 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 improves durability, and when combined with other elements, durability is further improved. Further, Pr, Nd, and Ce as rare earth elements are not actively utilized, but may be contained at an unavoidable impurity level.

Mg: Mg _b (where 0.07 ≤ b ≤ 0.18)
Mg is an essential element in the present invention that constitutes the element of the A component of the A ₂ B ₇ type structure, and contributes to the improvement of the discharge capacity and the cycle life characteristics. The b value representing the atomic ratio of Mg in the A component shall be in the range of 0.07 or more and 0.18 or less. If the b value is less than 0.07, the hydrogen release capacity is lowered, so that the discharge capacity is lowered. On the other hand, if it exceeds 0.18, cracking due to hydrogen storage and release is particularly promoted, and the cycle life characteristic, that is, durability is lowered. Preferably, the b value is in the range of 0.08 or more and 0.16 or less.

Ni: Ni _c
Ni is the main element of the B component of the A ₂ B ₇ 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, which is effective for adjusting the hydrogen equilibrium pressure related to the battery voltage, can improve the corrosion resistance, and has the durability of the fine hydrogen storage alloy. It is effective in improving the cycle life characteristics. In order to surely exhibit the above effect, the d value representing the atomic ratio of Al to the component A is set 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 becomes insufficient, and as a result, the cycle life becomes insufficient. On the other hand, if the d value exceeds 0.14, the discharge capacity will decrease. The preferred d value is in the range of 0.04 or more and 0.10 or less, and more preferably 0.04 or more and 0.09 or less. When the hydrogen storage alloy of the present invention is made into a powder having a minute diameter, the amount of Al is sufficient on the side where the range of the present invention is small, and the discharge capacity can be increased accordingly.

Ratio of component A and component B: 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 sub-phases: AB ₃ phase will increasingly, especially discharge capacity decreases. On the other hand, when it exceeds 3.50 increasing AB ₅ phase, it becomes cracked due to hydrogen occlusion and release is accelerated, durability as a result, that is, the cycle life deteriorated. The range is preferably 3.28 or more and 3.47 or less.

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

The hydrogen storage alloy of the present invention weighs rare earth elements (Sm, La, etc.) and metal elements such as magnesium (Mg), nickel (Ni), and aluminum (Al) so as to have a predetermined molar ratio, and then these. The raw material is put into an aluminum crucible installed in a high-frequency induction furnace to dissolve it in an atmosphere of an inert gas such as argon gas, and then cast into a mold to prepare an ingot of a hydrogen storage alloy. Alternatively, a flake-shaped sample having a thickness of about 200 to 500 μm may be directly prepared by using the strip casting method.
Since the hydrogen storage alloy of the present invention contains Mg having a low melting point and a high vapor pressure as a main component, if the raw materials of all alloy components are dissolved at once, Mg evaporates, which is a target. It may be difficult to obtain an alloy with a chemical composition. Therefore, in producing the hydrogen storage alloy of the present invention by the melting method, first, the other alloy components other than Mg are melted, and then Mg raw materials such as metallic Mg and Mg alloy are put into the molten metal. preferable. Further, this dissolution step is preferably performed in an atmosphere of an inert gas such as argon or helium. Specifically, the inert gas containing 80 vol% or more of argon gas was adjusted to 0.05 to 0.2 MPa. It is preferably carried out in 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 a hydrogen storage alloy. Next, the melting point ( _Tm ) of each of the obtained hydrogen storage alloy ingots is measured using a DSC (Differential Scanning Calorimeter). This is because the hydrogen storage alloy of the present invention makes the ingot after casting the melting point of the alloy at 900 ° C. or higher under the atmosphere of either an inert gas such as argon or helium or a nitrogen gas, or a mixed gas atmosphere thereof. This is because it is preferable to perform a heat treatment for holding the temperature at a temperature of T _m ) or less for 3 to 50 hours. By this heat treatment, the ratio of the main phase having an A ₂ B ₇ type crystal structure in the hydrogen storage alloy is set to 50 vol% or more, and the AB ₂ phase, AB ₃ phase, and AB ₅ phase, which are subphases, 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 storage alloy has an 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 subphase 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, when the heat treatment temperature is -20 ° C or higher ( _Tm -20 ° C or higher) from the melting point T _{m of the} alloy, coarsening of the crystal grains of the main phase and evaporation of the Mg component occur, resulting in pulverization and chemical composition. There is also a risk that the hydrogen storage capacity will decrease due to the change. Therefore, the heat treatment temperature is preferably in the range of 900 ° C. to ( _Tm- 30 ° C.). More preferably, it is in the range of 900 ° C. to ( _Tm- 50 ° C.).

Further, if the heat treatment holding time is 3 hours or less, the ratio of the main phase cannot be stably set to 50 vol% or more, and the homogenization of the chemical components of the main phase becomes insufficient. Expansion and contraction at the time of discharge become non-uniform, and the amount of strain and defects generated may increase, which may adversely affect the cycle characteristics. The holding time of the heat treatment is preferably 4 hours or more, and more preferably 5 hours or more from the viewpoint of homogenization of the main phase and improvement of crystallinity. However, if the holding time exceeds 50 hours, the chemical composition changes become much evaporation amount of Mg, As a result, there is a possibility that the AB ₅ type subphase come generated. Further, it is not preferable because it may increase the manufacturing cost and cause a dust explosion due to the evaporated Mg fine powder.

The heat-treated alloy is pulverized by a dry method or a wet method. When pulverizing by the dry method, it is pulverized using, for example, a hammer mill or an ACM palverizer. On the other hand, when pulverizing by the wet method, it is pulverized using a bead mill or an attritor. In particular, when fine powder is obtained, wet pulverization is preferable because it can be produced safely.
When the hydrogen storage alloy of the present invention is used in a battery for in-vehicle use, the particle size of the alloy particles to be pulverized is 3 μm at a mass-based 50% passing rate particle size D50 in terms of the balance of battery characteristics such as output and cycle life characteristics. The range of 20 μm or more is preferable, and the range of 5 μm or more and 15 μm or less is more preferable. Further, if the particle size distribution of the alloy particles is too wide, the above characteristics are deteriorated. Therefore, the mass-based 10% pass rate particle size D10 is in the range of 0.5 μm or more and 9 μm or less, and the 90% pass rate particle size D90 is 8 μm or more. The range is preferably 50 μm or less, D10 is 1 μm or more and 7 μm or less, and D90 is 10 μm or more and 40 μm or less. 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, as the particle size distributions D50, D10 and D90 of the alloy particles described above, the values measured by the laser diffraction / scattering type particle size distribution measuring device are used, and the measuring device is, for example, MT3300EXII manufactured by Microtrac Bell. A mold or the like can be used.

The pulverized alloy particles may be subsequently subjected to surface treatment such as alkali treatment using an alkaline aqueous 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) can be formed on at least a part of the surface of the alloy particles, the progress of alloy corrosion can be suppressed, and the durability is enhanced. Therefore, it is possible to improve the cycle characteristics of the battery and the discharge characteristics in a wide temperature range. In particular, in the case of acid treatment, it is possible to precipitate Ni with less damage to the alloy surface, so it is preferable to use hydrochloric acid. Further, when the alloy is pulverized by the wet method, the surface treatment can be performed at the same time.

[Alkaline battery]
Next, a configuration example of the 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) filled with an electrolyte and accommodating them. Hereinafter, a specific description will be given.

<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 the positive electrode active material. The positive electrode active material layer may further contain at least one of a conductive auxiliary agent, 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, 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 from the range of, for example, 3 to 35 μm, and is preferably in the range of 3 to 25 μm.

The conductive auxiliary agent is not particularly limited as long as it is a material capable of imparting electron 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. Can be done. The amount of the conductive auxiliary agent added is not particularly limited, but is preferably in the range of 0.1 to 50 parts by weight, more preferably 0.1 to 30 parts by weight, based on 100 parts by mass of the positive electrode active material, for example. Examples of the binder include synthetic rubber such as styrene-butadiene rubber (SBR), cellulose such as carboxymethyl cellulose (CMC), polyol such as polyvinyl alcohol (PVA), and fluororesin 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, and even if it is in the range of 0.01 to 5 parts by mass, it is further 0.05 to 2 parts by mass. It may be in the range of.

Further, examples of the thickener include carboxymethyl cellulose and its modified products (including salts such as Na salt), cellulose derivatives such as methyl cellulose, saponified products of polymers having a vinyl acetate unit such as polyvinyl alcohol, and polyethylene oxide. Polyalkylene oxide and the like. These thickeners may be used alone or in combination of two or more. The amount of the thickener 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 a range of parts.

Further, as the material of the positive electrode current collector, for example, stainless steel, aluminum, nickel, iron, titanium and the like can be mentioned. 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 adhering 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 together with the above-mentioned positive electrode active material, conductive auxiliary agent, and binder. As the dispersion medium, water, an organic medium, or a mixed medium in which two or more kinds of media selected from these are mixed can be used. If necessary, a conductive auxiliary agent, a binder, a thickener and the like may be added, but these (particularly, a binder and a thickener) do not necessarily have to be added.
For the positive electrode, the positive electrode mixture paste may be applied to the support depending on the shape of the support, or the pores of the support may be filled. The positive electrode can be formed by applying or filling the support, drying to remove the dispersion medium, and compressing the obtained dried product in the thickness direction (for example, rolling between a pair of rolls).

<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 needs to contain at least the hydrogen storage alloy of the present invention described above as the negative electrode active material. The negative electrode active material layer may further contain at least one of a conductive auxiliary agent, a binder and a thickener. The conductive auxiliary agent is not particularly limited as long as it is a material capable of imparting electron 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. Can be done. The amount of the conductive auxiliary agent added is not particularly limited, but is preferably in the range of 0.1 to 50 parts by weight, more preferably 0.1 to 30 parts by weight, based on 100 parts by weight of the hydrogen storage alloy powder, for example. Examples of the binder include synthetic rubber such as styrene-butadiene rubber (SBR), cellulose such as carboxymethyl cellulose (CMC), polyol such as polyvinyl alcohol (PVA), and fluororesin 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 hydrogen storage alloy powder, and even if it is in the range of 0.01 to 5 parts by mass, it is further 0.05 to 2 parts by mass. It may be a range of parts.

Examples of the material of the negative electrode current collector include steel, stainless steel, aluminum, nickel, iron, titanium, carbon and the like. 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.
To form the negative electrode active material layer on the negative electrode current collector, it is made into a paste. This is prepared by containing the above-mentioned negative electrode active material, conductive auxiliary agent, binder, thickener and the like.
The negative electrode for a nickel hydrogen battery can be produced by molding a negative electrode paste containing the hydrogen storage 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 hydrogen storage 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 aqueous electrolytic solution means an electrolytic solution mainly using water as a solvent, and the solvent may contain a solvent other than water. The ratio of water to the total solvent of the electrolytic solution may be 50 mol% or more, 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 higher the concentration of the solute in the aqueous electrolytic solution, the more preferable it is. For example, it may be 3 mol / L or more, and preferably 5 mol / L or more.
The electrolyte layer has a separator 3. By installing the separator 3, a short circuit can be effectively prevented. Examples of the separator 3 include a non-woven fabric and a porous membrane containing a resin such as polyethylene or polypropylene that has been sulfonated.

<Case>
The housing 4 is a battery case (cell container) that houses the above-mentioned positive electrode 1, negative electrode 2, and separator 3 and is filled with an electrolyte. The material may be stable without being corroded by the electrolytic solution, and may be able to retain the gas (oxygen or hydrogen) temporarily generated during charging and the electrolytic solution without leaking to the outside, for example. A metal case, a resin case, or the like is generally used. Further, in the case of a laminated alkaline storage battery 10 having a laminated body in which a plurality of positive electrodes 1 and 2 are laminated via a separator 3, the housing 4 has a structure in which the periphery of the laminated body is sealed with a frame-shaped resin. There may be.

<Battery>
The battery 10 of the present invention is usually a secondary battery. Therefore, since it can be repeatedly charged and discharged, it is suitable as, for example, an in-vehicle battery. At that time, it is not limited to the use as a hybrid vehicle battery that supplies power to the motor for driving the vehicle, but also supplies power to the starter motor for restarting the engine in a vehicle having an idling stop function. It may be applied as a form to be used. The secondary battery also includes the use as a primary battery of the secondary battery (use for the purpose of discharging only once after charging). The shape of the battery includes, for example, a coin type, a laminated type, a cylindrical type, a square type, and the like, but any shape may be used.

<Vehicle>
The vehicle of the present invention is equipped with an alkaline storage battery using the hydrogen storage alloy as a negative electrode as a power supply source to the motor. By using the alkaline storage battery of the present invention, which is smaller and lighter than the conventional one, it is possible to improve the exercise performance, reduce the fuel consumption, and extend the cruising distance.

<Example 1>
No. having the component composition shown in Table 1 below. Evaluation cells using 1 to 30 hydrogen storage alloys as the negative electrode active material were prepared as described below, and an experiment was conducted to evaluate their characteristics. The No. 1 shown in Table 1 The alloys 1 to 14 are alloy examples (invention examples) that meet the conditions of the present invention, No. Reference numerals 15 to 30 are alloy examples (comparative examples) that do not satisfy the conditions of the present invention. In addition, No. Fifteen alloys were used as reference alloys for evaluating cell properties.

(Preparation of negative electrode active material)
No. 1 shown in Table 1. Raw materials for alloys 1 to 30 (Sm, La, Mg, Ni and Al each having a purity of 99% or more) are melted in an argon atmosphere (Ar: 100 vol%, 0.1 MPa) using a high-frequency induction heating furnace and cast. And made it an ingot. Next, these alloy ingots are subjected to a heat treatment in which they are held in an argon atmosphere (Ar: 90 vol%, 0.1 MPa) at a temperature (940 to 1130 ° C.) of the melting point of each alloy at T _m- 50 ° C. for 10 hours. , Roughly pulverized and finely pulverized with a wet bead mill to a mass-based D50 of 13 μm to prepare a sample (negative electrode active material) for cell evaluation. However, No. 1 used as a standard for alloy cell evaluation. For 15 AB ₅ alloys, and a fine powder of 25μm in D50 of mass by a wet grinding to obtain a sample for the cell evaluation (negative electrode active material). In addition, No. of the invention example of this invention. After the heat treatment, the crushed powders of the alloys 1 to 14 were subjected to X-ray diffraction measurement, and it was confirmed that the main phase of each of them was A ₂ B ₇ phase.

(Preparation of evaluation cell)
<Negative electrode>
The negative electrode active material prepared above, the Ni powder of the conductive auxiliary agent, and the two types of binders (styrene-butadiene rubber (SBR) and carboxymethyl cellulose (CMC)) are mixed in a weight ratio of the negative electrode active material: Ni powder: The mixture was mixed so that SBR: CMC = 95.5: 3.0: 1.0: 0.5 and kneaded to obtain a paste-like composition. This paste-like composition was applied to a punching metal, dried at 80 ° C., and then 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 aid, and two types of binders (styrene-butadiene rubber (SBR) and carboxymethyl cellulose (CMC)) are mixed in a mass ratio of Ni. (OH) ₂ : Co: SBR: CMC = 95.5: 2.0: 2.0: 0.5 was mixed and kneaded to obtain a paste-like composition. This paste-like composition was applied to porous nickel, dried at 80 ° C., and then roll-pressed with a load of 15 kN to obtain a positive electrode.

<Electrolytic solution>
As the electrolytic solution, an alkaline aqueous solution was used in which potassium hydroxide (KOH) was added to pure water to a concentration of 6 mol / L and LiOH was further added to 0.1 mol / L.

<Evaluation cell>
After arranging the positive electrode as the counter electrode and the negative electrode as the working electrode in the acrylic housing, the electrolytic solution is injected to prepare a cell using the Hg / HgO electrode as the reference electrode for evaluation test. Served. At this time, the volume ratio of the working electrode and the counter electrode was adjusted so that the working electrode: the counter electrode = 1: 3.

(Cell characterization)
Alloy No. obtained as described above. The evaluation test of the evaluation cells from 1 to 30 was carried out as follows. The evaluation temperatures at this time were all set to 25 ° C.

(1) Electrode discharge capacity The discharge capacity of the electrode of the working electrode was confirmed by 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 discharge was performed at a current value of 40 mA / g per active material of the working electrode. The end condition of the discharge was an working pole potential of −0.5 V. The above charge / discharge was repeated 10 times, and the maximum value of the discharge capacity was taken as the discharge capacity of the electrode of the working electrode. It has been confirmed that the discharge capacity of the working electrode is saturated and stable after 10 times of charging and discharging.
The measured discharge capacity is No. 1 shown in Table 1. The discharge capacity of 15 AB ₅ alloys is used as the reference capacity, and the ratio to it is calculated by the following formula (2). If this ratio is larger than 1.10, the discharge capacity is larger than that of the AB ₅ alloy and it is superior. evaluated.
(Discharge capacity of AB ₅ alloy (No.15)) ··· (discharge capacity of the evaluation alloy) discharge capacity = / (2)

(2) Cycle life characteristics Using the cell in which the discharge capacity of the electrode of the working electrode was confirmed by the discharge capacity of the above (1) electrode, the cycle life characteristics of the working electrode were determined 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 set to 1C and the current value required to complete charging or discharging in 1 hour, the charging rate of the working electrode is 20-. In the range of 80%, performing constant current charging and constant current discharging at a current value of C / 2 is defined as one cycle, and this is repeated for 100 cycles, and the discharge capacity after 100 cycles is measured. The capacity retention rate was calculated by the formula.
Capacity retention rate = (Discharge capacity in the 100th cycle) / (Discharge capacity in the 1st cycle) ... (3)
The evaluation of the cycle life characteristics was carried out by No. 1 shown in Table 1. The capacity maintenance rate after 100 cycles of AB ₅ alloys 15 and the reference capacity maintenance ratio, to calculate the ratio of it by the following equation (4), what this ratio is greater than 1.10, cycle life than AB ₅ alloys It was evaluated as having great characteristics and being excellent.
= Cycle life characteristics (capacity retention rate after 100 cycles of measurements alloy) / (capacity maintenance rate after 100 cycles of AB ₅ alloys (No.15)) · · · (4)

 

As is clear from Table 1, No. 1 of the invention example. Alloys 1 to 14 are No. Against 15 AB ₅ alloys, any evaluation value of the discharge capacity and the cycle life characteristics seen to have excellent properties with 1.10 or more. In particular, the cycle life characteristics are all evaluated values of 1.20 or more, which shows that they are excellent. On the other hand, No. It can be seen that the evaluation values of any of the characteristics of the alloys of 15 to 30 are less than 1.05.

<Example 2>
(Preparation of negative electrode active material)
(La _0.30 Sm _0.70 ) _0.90 Mg _0.10 Ni _3.28 Al A hydrogen storage alloy having a component composition of _0.09 is evacuated once, and then an argon atmosphere is used using a high-frequency induction heating furnace. lower (Ar: 90vol%, 0.15MPa) was dissolved in, after an ingot by casting, the ingot under argon (Ar: 100vol%, 0.5MPa), the 1000 ° C. (alloy melting point _{T m} - It was subjected to a heat treatment held at a temperature of 50 ° C. for 10 hours, roughly pulverized, and then finely pulverized to the particle size shown in Table 2 to prepare a sample (negative electrode active material) for cell evaluation. The sample numbers shown in Table 2 are shown in Table 2. For B1 to B4, a wet bead mill was used, and sample No. B5 to B7 are finely pulverized using an ACM pulperizer.
Further, as an alloy of the 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 described above, heat-treated, roughly pulverized, and then bead milled. To obtain a fine powder of D50 = 11.2 μm on a mass basis, which was used as a sample for cell evaluation (negative electrode active material). Here, Mm is a mixture of rare earth elements consisting of La: 25%, Ce: 50%, Pr: 5%, and Nd: 20% in mass%.
As a result of performing X-ray diffraction on the obtained sample, the sample No. B1 alloy ~ B7, the crystal structure of the main phase _A 2 _{B 7} type, the sample of Comparative Example No. BZ alloys, the crystal structure of the main phase was confirmed to be ₅ type AB.

 

(Preparation of evaluation cells and evaluation of cell characteristics)
Next, using the cell evaluation sample 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 prepared in the same manner as in Example 1. ), And the results of these are the same as in Example 1, and the sample No. which is a comparative example. 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, No. 1 conforming to the present invention. The alloys of B1 to B7 are No. 2 of the reference comparative example. It can be seen that the evaluation values of the discharge capacity and the cycle life characteristics are all excellent at 1.10 or more with respect 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 After vacuuming a hydrogen storage alloy having a component composition of _0.07 , an argon atmosphere is used using a high-frequency induction heating furnace. After melting at the bottom (Ar: 100 vol%, 0.1 MPa) and casting to make an ingot, this ingot is placed in an argon atmosphere (Ar: 90 vol% 0.1 MPa) at 1000 ° C. (alloy melting point _Tm- 50). It was subjected to a heat treatment held at (° C.) for 10 hours, roughly pulverized, and then finely pulverized to a mass-based D50 = 13.4 μm using a wet bead mill.
Next, the finely pulverized alloy powder was subjected to the following two levels of surface treatment to prepare a sample for cell evaluation (negative electrode active material).
-Alkaline treatment: Immersed in a sodium hydroxide aqueous solution of NaOH: 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 under the condition of a solid-liquid ratio of 1: 1 (Sample No. C2).

(Preparation of evaluation cells and evaluation of cell characteristics)
Next, using the cell evaluation sample 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 prepared in the same manner as in Example 1. ) Was evaluated, and the results were used in the comparative example of Example 2. The measured values of the BZ alloy (without surface treatment) were relatively evaluated as the reference values (1.00), and the results are shown in Table 3.

As can be seen by comparing Table 3 and Table 2, the hydrogen storage alloy of the present invention was found to have a significant improvement in cycle life characteristics by surface treatment.

The hydrogen storage alloy of the present invention is excellent than the discharge capacity and the AB ₅ type both previously used in the cycle life characteristics of hydrogen absorbing alloy, suitable as a negative electrode material for alkaline storage battery of a hybrid vehicle and the idling stop vehicle applications Not only that, it can also be suitably used for an alkaline storage battery for an electric vehicle.

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

Claims (8)

1. A fine hydrogen storage alloy used for alkaline storage batteries.
   Hydrogen storage alloy as the main phase crystal structure of A ₂ B ₇ type structure, and the hydrogen storage alloy for an alkaline storage battery characterized by being represented by the following general formula (1).
   Serial _{(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 equation (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.
2. The hydrogen storage alloy for an alkaline storage battery according to claim 1, wherein the hydrogen storage alloy has a mass-based D50 of 3 μm or more and 20 μm or less.
3. The hydrogen storage alloy for an alkaline storage battery according to claim 1 or 2, wherein the hydrogen storage 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 the hydrogen storage alloy has a layer made of Ni on at least a part of the particle surface.
5. The hydrogen storage alloy for an alkaline storage battery according to claim 4, wherein the layer made of Ni is an alkali-treated layer or an acid-treated layer.
6. An alkaline storage battery using the hydrogen storage alloy according to any one of claims 1 to 5 as a negative electrode.
   An alkaline storage battery that is mounted on a hybrid vehicle that uses a motor as a drive source and supplies electric power to the motor.
7. An alkaline storage battery using the hydrogen storage alloy according to any one of claims 1 to 5 as a negative electrode.
   An alkaline storage battery that is mounted on an automobile having an idling stop function in which an engine is started by a starter motor and supplies electric power to the starter motor.
8. A vehicle characterized by having an alkaline storage battery using the hydrogen storage alloy according to any one of claims 1 to 5 as a negative electrode as a power supply source to the motor.

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