JP5161451B2 - Hydrogen storage alloy, electrode using the same, and nickel metal hydride secondary battery - Google Patents

Description

The present invention relates to a hydrogen storage alloy that realizes a high-capacity nickel-hydrogen secondary battery, a negative electrode using the same, and a high-capacity nickel-hydrogen secondary battery using the negative electrode.

The hydrogen storage alloy is an alloy that can store hydrogen as an energy source safely and easily, and has attracted a great deal of attention for new energy conversion and storage. Applications of hydrogen storage alloys as functional materials include hydrogen storage and transport, heat storage and transport, thermal-mechanical energy conversion, hydrogen separation and purification, hydrogen isotope separation, and hydrogen as the active material Various proposals have been made on batteries, catalysts in synthetic chemistry, and the like.

In particular, a hydrogen storage alloy capable of reversibly storing and releasing hydrogen is actively used as a negative electrode material for secondary batteries. This nickel metal hydride secondary battery is used as a power source for various types of miniaturized and lightweight portable electronic devices. Portable devices have been improved in performance, functionality and size. In order to enable long-time operation of such portable devices, it is necessary to increase the discharge capacity per volume of the secondary battery. is there. In recent years, it has been desired to reduce the weight, that is, increase the discharge capacity per weight, in addition to increasing the discharge capacity per volume.

The LaNi ₅ rare earth hydrogen storage alloy reacts with hydrogen near room temperature and normal pressure and has a relatively high chemical stability. Therefore, research as a hydrogen storage alloy for batteries is currently widely promoted and is commercially available. Used as a negative electrode for secondary batteries.
However, the discharge capacity of a commercially available secondary battery equipped with a negative electrode containing a LaNi ₅ type rare earth hydrogen storage alloy reaches 80% or more of the theoretical capacity, and there is a limit to increasing the capacity beyond this.

By the way, there are many rare earth-Ni intermetallic compounds other than the LaNi ₅ alloy described above. For example, Non-Patent Document 1 discloses that an intermetallic compound containing more rare earth elements than a LaNi ₅ alloy occludes a larger amount of hydrogen near room temperature than a LaNi ₅ type rare earth-based intermetallic compound. . Further, a system in which a La site is a mixture of rare earth and Mg is known in the following two documents. One is La _1-x Mg _x Ni in Non-Patent Document 2.
A hydrogen storage alloy represented by ₂ has been reported. However, this hydrogen storage alloy has a problem that it is difficult to completely release hydrogen when the secondary battery is discharged because the stability with hydrogen is too high and it is difficult to release hydrogen.

On the other hand, Non-Patent Document 3 reports a hydrogen storage alloy whose composition is represented by LaMg ₂ Ni ₉ , but this system also has a problem that the release of hydrogen during charging and discharging is smaller than that of storage.
In Patent Document 1, the _formula, a hydrogen absorbing electrode comprising a hydrogen storage alloy represented by _{Mm 1-x A x Ni a} Co b M c is disclosed. Here, Mm is Misch metal. On the other hand, Patent Document _2, the hydrogen absorbing electrode comprising a hydrogen storage alloy represented by _{La 1-x A x Ni a} Co b M c is disclosed.

However, the secondary battery provided with these hydrogen storage electrodes has a problem that the discharge capacity is low and the cycle life is short. Furthermore, when used for automobile applications, further improvement in discharge characteristics at low temperatures is required.

Patent Document 3 and Patent Document 4 disclose a hydrogen storage electrode containing a hydrogen storage alloy having a composition represented by the following general formula (i) and having a specific antiphase boundary. The crystal structure of this hydrogen storage alloy is a CaCu ₅ type single phase.
(R _1-x L _x ) (Ni _1-y M _y ) _z (i)
In the formula (i), R represents La, Ce, Pr, Nd, or a mixed element thereof. L
Represents Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Y, Sc, Mg, Ca or a mixed element thereof. On the other hand, M is Co, Al, Mn, Fe, Cu, Zr, Ti, Mo, S
i, V, Cr, Nb, Hf, Ta, W, B, C or a mixed element thereof is shown. The atomic ratios x, y, and z are 0.05 ≦ x ≦ 0.4, 0 ≦ y ≦ 0.5, and 3.0 ≦ z <4.5.

This hydrogen storage alloy has a supercooling degree of 50 to 500 ° C. and a cooling rate on a roll having irregularities with an average maximum height of 30 to 150 μm on the surface of a molten alloy having the composition represented by the general formula (i). Manufactured by heat treatment after uniformly solidifying to a thickness of 0.1 to 2 mm under cooling conditions of 1000 to 10000 ° C./second. Also, the alloy obtained when this condition is exceeded is Ca
It has been reported that a LaNi ₅ type single phase cannot be obtained, which is composed of crystal grains of a Cu ₅ type crystal structure and a Ce ₂ Ni ₇ type crystal structure.

However, a secondary battery having a negative electrode containing a hydrogen storage alloy whose composition is expressed by the above-described formula (i), has a specific antiphase boundary, and has a crystal structure of CaCu ₅ structure is particularly used for automobiles. There is a problem that the required discharge capacity at low temperatures and the cycle life are lower.

Furthermore, in Patent Document 5, the composition is represented by the general formula shown in the following (ii), and the space group is P.
A hydrogen storage material having a hexagonal crystal structure of 63 / mmc is disclosed.
_{(R 1-x A x)} 2 (Ni 7-y-z-α-β Mn y Nb z B α C β) n (ii)
However, in said (ii), R is rare earth elements or Misch metal (Mm), A is M
at least one selected from g, Ti, Zr, Th, Hf, Si and Ca, C is Ga
, Ge, In, Sn, Sb, Tl, Pb, and Bi.
X, y, z, α, β, and n are 0 <x ≦ 0.3, 0.3 ≦ y ≦ 1.5, and 0 <z.
≦ 0.3, 0 ≦ α ≦ 1, 0 ≦ β ≦ 1, 0.9 ≦ n ≦ 1.1.

In the hydrogen storage alloy having the composition represented by (ii), the atomic ratio of Mn is 0.135 or more and 0.825 or less when the sum of the atomic ratios of R and A is 1.
However, since this hydrogen storage alloy is inferior in the possibility of hydrogen storage / release reaction, there is a problem that the amount of hydrogen storage / release is small. In addition, a battery equipped with a negative electrode containing this hydrogen storage alloy is inferior in reversibility of the hydrogen storage / release reaction, and the operating voltage is lowered, so that the discharge capacity is lowered.

However, the claims of the patent document 6, the hydrogen-absorbing alloy comprising a phase of an intermetallic compound having a composition represented by A ₅ T ₁₉ is disclosed. Where A is La, Ce, Pr
, Sm, Nd, Mm, Y, Gd, Ca, Mg, Ti, Zr, Hf, and T is B, Bi, Al, Si, Cr, V, Mn, Fe , Co,
At least one element selected from the group consisting of Ni, Cu, Zn, Sn, and Sb.

Patent Document 6 discloses a method described below as a method for producing a hydrogen storage alloy including an intermetallic compound phase having a composition of A ₅ T ₁₉ . First, an alloy including an intermetallic compound phase having an AT ₃ composition and an alloy including an intermetallic compound phase having an AT ₄ composition are mixed and mechanically alloyed. AT ₃ and AT ₄
In addition to the above, an intermetallic compound phase having a composition of A ₅ T ₁₉ is formed. Subsequently, the obtained alloy and an alloy containing an intermetallic compound phase having the composition of AT ₅ are mixed or mechanically alloyed to obtain a hydrogen storage alloy containing an A ₅ T ₁₉ phase and an AT ₅ phase. Get.
In this hydrogen storage alloy, as shown in FIG. 1 of Patent Document 6, the entire crystal grain is composed of a region having a composition represented by A ₅ T ₁₉ .

Further, Patent Document 7 discloses a hydrogen storage alloy represented by the following (iii).
_{R 1-a-b Mg a} T b Ni z-x-y-α M1 x M2 y Mn α (iii)
However, R is at least 1 selected from rare earth elements (the rare earth elements include Y)
Species element, T is at least one element selected from Ca, Ti, Zr and Hf, M1 is at least one element selected from Fe and Co, M2 is Al, Ga, Zn, Sn, Cu,
It is at least one element selected from Si, B, Nb, W, Mo, V, Cr, Ta, Li, P and S, and the atomic ratios a, b, x, y, α and z are 0.15 ≦ a ≦ 0.37, 0 ≦
b ≦ 0.3, 0 ≦ x ≦ 1.3, 0 ≦ y ≦ 0.5, 0 ≦ α ≦ 0.135, 2.5 ≦ z ≦ 4.
2 respectively.
However, in the present invention, it was necessary to develop a hydrogen storage alloy that is more optimal for hybrid vehicles.

Patent Document 8 discloses a hydrogen storage alloy represented by the following (iV). That is,
(Mg _1-a-b R1 _a M1 _b ) Ni _z (iV)
However, R1 is at least one element selected from rare earth elements including Y, M1 is a larger element of electronegativity than Mg (however, the element of R1, Cr, Mn, Fe, Co, Cu
, Zn and Ni), a, b, and z are 0.1 ≦ a ≦ 0.8, 0 <b ≦ 0.9, 1-ab> 0, It is defined as 3 ≦ z ≦ 3.8.
However, this hydrogen storage alloy has not been optimized as a hydrogen storage alloy for hybrid vehicles, and it has been necessary to optimize the hydrogen storage alloy for this application.

The present invention has a problem that hydrogen storage alloy having a composition belonging to a type containing a large amount of La sites compared with LaNi type ₅ is too stable to hydrogen and difficult to release hydrogen. The problem of being susceptible to corrosion and oxidation by the electrolyte is improved, and it provides a hydrogen storage alloy with high hydrogen storage and release. Especially, it is suitable for hybrid vehicles. A life-time hydrogen storage alloy is provided.
The present invention is a battery suitable for a hybrid vehicle and an electric vehicle having excellent running performance such as fuel efficiency.
JP-A-63-271348 JP 62-271349 A Pamphlet of International Publication No. WO97 / 03213 US Pat. No. 5,840,166 Japanese Patent Laid-Open No. 11-29832 JP-A-10-1731 Pamphlet of International Publication No. WO01 / 048841 JP-A-11-323469 Mat. Res. Bull. 11 p.1241 (1976) J. Less-common metals 73 339 (1980) Outline of the 120th Spring Meeting of the Japan Institute of Metals p.289 (1997)

The present invention relates to a hydrogen storage alloy for nickel-metal hydride secondary batteries that has both high capacity, cycle life, and discharge capacity at low temperatures close to −30 ° C., a negative electrode using the same, and a nickel-hydrogen secondary battery The purpose is to provide.

The first invention of the general formula _{(R 1-a A a)} T x Si y M z Z α X β (1)
R: at least one element selected from rare earth elements including Y A: at least one element selected from Ti, Zr, Hf T: at least one element selected from Fe, Co, Ni, Mn, Cu, Cr Element M: at least one element selected from V, Nb, Ta, Mo, W Z: at least one element selected from the group consisting of Sn, Al, Sb and In X: B, C, N, P At least one element selected from 0 ≦ a ≦ 0.3
0.5 ≦ x ≦ 1.2
2.7 ≦ y ≦ 3.2

0 ≦ z ≦ 0.5
0 ≦ α ≦ 0.5
0 ≦ β ≦ 1 (atomic ratio)
A hydrogen storage alloy for a nickel metal hydride secondary battery, characterized in that an intermetallic compound represented by

The second invention of the general formula _{(R 1-a-b A} a D b) T x Si y M z Z α X β (2)
R: at least one element selected from rare earth elements including Y A: at least one element selected from Ti, Zr, Hf D: at least one element selected from Mg, Ca, Sr, Ba T: Fe At least one element selected from Co, Ni, Mn, Cu and Cr M: At least one element selected from V, Nb, Ta, Mo and W Z: From the group consisting of Sn, Al, Sb and In At least one element selected X: at least one element selected from B, C, N, P 0.5 ≦ x ≦ 1.2
2.7 ≦ y ≦ 3.2
0 ≦ z ≦ 0.5

0 ≦ a ≦ 0.3
0 ≦ b ≦ 0.5
0 <a + b ≦ 0.5
0 ≦ α ≦ 0.5
0 ≦ β ≦ 1 (atomic ratio)
A hydrogen storage alloy for a nickel metal hydride secondary battery, characterized in that an intermetallic compound represented by

The hydrogen storage alloy of the present invention is preferably a single-phase intermetallic compound phase, but may have at least one different phase. The former is excellent in charge / discharge cycle life characteristics, and the latter is excellent in high capacity and excellent in initial charge / discharge efficiency. The average crystal grain size of the crystal phase is 10 n
It is preferable that it exists in the range of m-10 micrometers.

The main phase of the present invention preferably has an orthorhombic or tetragonal structure, which is particularly RTS.
An intermetallic compound represented by i ₃ , for example, an intermetallic compound represented by CeCoSi ₃ is preferable.
Further, when R and T are simultaneously used as constituent elements, particularly excellent capacity per unit weight and cycle life characteristics can be obtained.

The negative electrode according to the present invention includes the above-described hydrogen storage alloy for nickel-hydrogen secondary batteries. The nickel metal hydride secondary battery according to the present invention includes a negative electrode including the hydrogen storage alloy for the nickel metal hydride secondary battery, a positive electrode, and an alkaline electrolyte.

According to the present invention, a hydrogen storage alloy capable of realizing a nickel metal hydride secondary battery excellent in both discharge capacity and charge / discharge cycle life, a negative electrode including the alloy, and a nickel metal hydride secondary including the negative electrode A battery can be provided.

The present invention relates to a hydrogen storage alloy for a nickel metal hydride secondary battery, a negative electrode using the same, and a nickel metal hydride secondary battery.
The first invention of the general formula _{(R 1-a A a)} T x Si y M z Z α X β (1)
R: at least one element selected from rare earth elements including Y A: at least one element selected from Ti, Zr, Hf T: at least one element selected from Fe, Co, Ni, Mn, Cu, Cr Element M: at least one element selected from V, Nb, Ta, Mo, W Z: at least one element selected from the group consisting of Sn, Al, Sb and In X: from B, C, N, P At least one element selected 0 ≦ a ≦ 0.3
0.5 ≦ x ≦ 1.2
2.7 ≦ y ≦ 3.2

0 ≦ z ≦ 0.5
0 ≦ α ≦ 0.5
0 ≦ β ≦ 1 (atomic ratio)
A hydrogen storage alloy for a nickel metal hydride secondary battery, characterized in that an intermetallic compound represented by

Here, R is at least one element selected from rare earth elements, preferably La, C
e, Pr, Nd, Sm, Y. R is an element that determines the hydrogen storage capacity.

T is at least one element selected from Fe, Co, Ni, Mn, Cu, and Cr. T
Is an element effective for releasing hydrogen in the hydrogen storage alloy and activating chemical reaction in the electrolytic solution, and the amount x is 0.5 ≦ x ≦ 1.2 in terms of atomic ratio to R. If it is less than 0.5, the crystal structure of the main phase is changed, and it becomes difficult to release the stored hydrogen. On the other hand, even if the ratio exceeds 1.2, the crystal structure of the main phase is different, and the balance between capacity and life is deteriorated. Preferably, 0.55 ≦ x ≦ 1.1
More preferably, 0.6 ≦ x ≦ 1.05. Preferred elements are Ni, Co, and Cu.

The element A is at least one element selected from Ti, Zr, and Hf, and is an effective element for improving the cycle life. The amount a is 0 ≦ a ≦ 0.3, and if it exceeds this, the capacity will be reduced. Preferably it is 0.2 or less.

M is at least one element selected from V, Nb, Ta, Mo, and W, and is an element effective in improving cycle life characteristics. The amount z is 0.5 or less. If it exceeds 0.5, the capacity decreases. Preferably it is 0.3 or less. Preferred elements are Nb and Mo.

Si, like T, is an element effective for releasing hydrogen in the hydrogen storage alloy and activating chemical reactions in the electrolyte. The amount y is 2.7 ≦ y ≦ 3.2. y is an atomic ratio with respect to R;
If it is less than 7, the crystal structure of the main phase changes, making it difficult to release the stored hydrogen, whereas 3.2
If it exceeds 1, the crystal structure of the main phase will change, making it impossible to balance capacity and life.
Preferably, 2.8 ≦ y ≦ 3.1.

Z, like T and Si, is an element effective for releasing hydrogen in the hydrogen storage alloy and activating chemical reactions in the electrolyte. The amount α is 0.5 or less. If it exceeds 0.5, the capacity is lowered and the ratio of the crystal structure of the main phase is lowered, so that the function as a battery material is lowered.

X is at least one selected from B, C, N, and P, and is an element effective in reducing the number of times of activation as a battery. When the amount β exceeds 1, the capacity decreases. Preferably, it is 0.8 or less, more preferably 0.5 or less.

The second alloy of the present invention has a general formula (R _{1 -ab} A _a D _b ) T _x Si _y M _z Z _α X _β (2)
R: at least one element selected from rare earth elements including Y A: at least one element selected from Ti, Zr, Hf D: at least one element selected from Mg, Ca, Sr, Ba T: Fe At least one element selected from Co, Ni, Mn, Cu and Cr M: At least one element selected from V, Nb, Ta, Mo and W Z: From the group consisting of Sn, Al, Sb and In At least one element selected X: at least one element selected from B, C, N, P 0.5 ≦ x ≦ 1.2
2.7 ≦ y ≦ 3.2
0 ≦ z ≦ 0.5

0 ≦ a ≦ 0.3
0 ≦ b ≦ 0.5
0 <a + b ≦ 0.5
0 ≦ α ≦ 0.5
0 ≦ β ≦ 1 (atomic ratio)
A hydrogen storage alloy for a nickel metal hydride secondary battery, characterized in that an intermetallic compound represented by

Although details are unknown, it is considered that the A element and the D element replace the position of the R element.
Here, R is at least one element selected from rare earth elements, preferably La, C
e, Pr, Nd, Sm, Y. R is an element that determines the hydrogen storage capacity.

The element A is at least one element selected from Ti, Zr, and Hf, and is an effective element for improving the cycle life. The amount a is 0 ≦ a ≦ 0.3, and if it exceeds this, the capacity will be reduced. Preferably it is 0.2 or less. The total amount of a and b is 0 <a + b ≦ 0.5
It is.

Further, D is at least one selected from Mg, Ca, Sr, and Ba, and similarly to R, provides hydrogen storage capacity. The amount b is 0 ≦ b ≦ 0.5. Beyond this, the crystal structure of the main phase changes and the balance between capacity and life deteriorates. Preferably it is 0.4 or less. Preferred elements are Mg and Ca.
About T, Si, Z, and X, it is the same as the reason in the hydrogen storage alloy for nickel-hydrogen secondary batteries represented by General formula (1).

In the hydrogen storage alloy according to the present invention, elements such as oxygen, nitrogen, and carbon may be contained as impurities within a range not impairing the properties of the present alloy. These impurities are 1 wt% each.
The following range is preferable.

Orthogonal crystals and tetragonal crystals can be mentioned as the crystal structure of the main phase. Moreover, although the kind of the crystal phase contained in an alloy can be made into 1 type or 2 types or more, an orthorhombic single phase is preferable from a viewpoint of charging / discharging cycle life. Also, among orthorhombic crystals, space group Amm2, and among tetragonal crystals,
I4mm preferably, an orthorhombic As specific preferred crystal form type ₃ DyNiSi is tetragonal can be mentioned ₃ types CeCoSi.

When the hydrogen storage alloy of the present invention is subjected to X-ray diffraction, the spacing between the strongest diffraction lines is 2.75-2.
. When the crystal analysis is performed, the above crystal structure is obtained.

The average crystal grain size of the crystal phase of the present invention is desirably in the range of 10 nm or more and 10 μm or less. This is due to the reason explained below. If the average crystal grain size is less than 10 nm, the rise of the discharge capacity may be significantly delayed. In addition, when the crystal grains are fine, the mechanical strength of the material is increased, so that pulverization and deterioration due to lattice expansion and contraction due to charge and discharge are suppressed, which is thought to lead to an improvement in life. On the other hand, the larger crystal grain size may be the average powder grain size when pulverized to the size of the alloy powder necessary for producing the negative electrode, that is, about 10 μm.

Examples of the method for producing the hydrogen storage alloy of the present invention include a high frequency melting method, an arc melting method, a sintering method, a rapid quenching method, a strip casting method, an atomizing method, a plating method, a CVD method, a sputtering method, and a rolling method. Can be mentioned. Particularly preferred are a rapid quenching method, a strip casting method, a high frequency dissolution method, an atomizing method, and a centrifugal spraying method.

In each of these methods, each material weighed in advance is dissolved in a crucible in an inert atmosphere, and the subsequent cooling process is changed. That is, in the ultra rapid cooling method, molten alloy is injected onto a cooling body that rotates at high speed to obtain a flake sample having a plate thickness of 10 to 100 μm. In the strip casting method, the amount of molten metal supplied per unit time to the cooling body is increased as compared with the ultra rapid cooling method to obtain a flake sample having a plate thickness of 50 to 500 μm. 10 depending on the conditions
Plate thicknesses up to 0 μm can also be obtained. In the strip casting method, the molten metal may be poured onto a rotating cooling plate during casting, and the thickness of the material is controlled by the amount of molten metal supplied and the moving speed of the cooling plate. As a result, the cooling rate can be controlled.

The obtained samples can be homogenized in structure and composition by heat treatment, and this is particularly noticeable in the cast samples. Samples obtained by the strip cast method or the ultra-quenching method are not subjected to heat treatment. Good. In particular, in the sample obtained by the strip cast method, a columnar crystal structure is easily obtained, and this structure is preferable from the viewpoint of life.

The negative electrode material according to the present invention is preferably a spherical powder. Thereby, since the specific surface area of negative electrode material can be made small, the oxygen content of negative electrode material can be decreased and high initial efficiency can be obtained. Moreover, the coatability of the slurry can be improved. Furthermore, it is possible to simplify the production method of the negative electrode material by eliminating the pulverization step. In order to obtain spherical powder, there are an atomizing method, a centrifugal spraying method, and the like.

In the gas atomization method, a raw material prepared to have a predetermined composition is put in a crucible, dissolved in a vacuum or in an inert atmosphere (eg, Ar gas, He gas, nitrogen gas) by a high frequency induction heating furnace, and alloyed through a hot water supply pipe. The molten metal is dropped into the atomizing tank. A gas atomizing nozzle is arranged in the vicinity of the hot water supply pipe, and the atomizing gas passes through the nozzle hole or slit,
It is ejected toward the molten metal being dripped. The molten metal is scattered, solidified and powdered by the energy of the jet gas. The inside of this tank is an inert atmosphere, and oxidation of the generated atomized powder is prevented. The produced powdery alloy is guided to the powder storage device from the lower part of the atomizing tank and stored.

The alloy shape obtained by gas atomization can be changed from a spherical shape to a flat shape by changing the conditions, but in the case of the present invention, it is preferably as spherical as possible. The particle size of the powder produced by the gas atomizing method generally decreases as the energy of the jet gas applied to the molten metal being dropped increases. The energy of the ejected gas can be adjusted by, for example, the pressure of the gas and the size and arrangement of the nozzle holes or slits. Moreover, if the energy of the jet gas is constant, the smaller the amount of molten metal dropped per unit time, the smaller the powder diameter. The dropping amount of the molten metal can be adjusted by the inner diameter of the hot water supply pipe or the pressure applied to the molten metal in the hot water supply pipe. The gas atomization method is characterized in that rapid cooling and pulverization are performed simultaneously.

On the other hand, in the centrifugal spray method, a molten alloy adjusted to a predetermined composition on a high-speed rotating disk is dropped in an inert atmosphere (eg, Ar gas, He gas, nitrogen gas), and finely dispersed from the disk by centrifugal force. The spherical powder is formed by surface tension. in this case,
When the molten alloy and the disk have good wettability, it is difficult to scatter. Therefore, it is preferable to use a ceramic or metal material having relatively low wettability with respect to the molten metal. The inert atmosphere is H from the viewpoint of heat conduction.
Although e gas is preferable, Ar gas can also be used. The diameter of the spherical powder is the amount of molten metal dripping,
It can be controlled by the number of revolutions of the disk, the temperature of the molten metal, etc.

The particle size of the obtained spherical powder is preferably 10 to 200 μm, and particularly preferably 10 to 60 μm as the negative electrode material. Those having a large particle size can be further pulverized. This pulverization is preferably performed in an inert atmosphere. Further, the spherical powder may be crushed with a press after being applied at the time of electrode preparation.
Here, the spherical powder means that the ratio of the major axis to the minor axis of the powder is 5 or less, but the weight of the spherical powder is 50% or more.

Atomized powder can generally be used without heat treatment, but it can also be heat-treated for the purpose of alleviating internal strain generated during rapid cooling. In that case, it is preferable to carry out in an inert atmosphere. The heat treatment temperature is preferably 50 ° C. or more lower than the solidus temperature. More preferably, it is 100 degrees C or less.

Inevitable impurities other than the constituent elements may each be contained in an amount of 1 wt% or less. Inevitable impurities include oxygen, nitrogen, carbon and the like. In addition, the amount of oxygen after pulverization is 30 including the adsorbed amount.
00 ppm or less is preferable.

Further, in the case of an alloy obtained by a normal casting method, excellent electrode characteristics are easily obtained when heat treatment is performed as compared with a cast state.

The hydrogen storage alloy of the present invention may be subjected to surface treatment in order to exhibit its characteristics more.
The method may be any method such as acid treatment or alkali treatment, and it is preferable to relatively increase the Ni concentration in the vicinity of the powder surface. The acid is preferably hydrochloric acid, nitric acid, or oxalic acid,
In the case of alkali treatment, an aqueous potassium hydroxide solution may be used, but an aqueous sodium hydroxide solution may be used. In this case, the concentration of the aqueous solution preferably contains 30 to 80% by weight of alkali hydroxide, and the treatment temperature is preferably room temperature or higher, and 40 ° C. for shortening the treatment time.
As mentioned above, More preferably, it is 60 degreeC or more and a boiling point.

In this case, the process is a process of immersing the hydrogen storage alloy powder in an alkaline aqueous solution,
In some cases, the method comprises a step of washing the surface-treated powder with water.
As for the average particle diameter of the hydrogen storage alloy used for surface treatment, 5-50 micrometers is preferable. If the thickness is less than 5 μm, the hydrogen storage portion decreases due to surface treatment, and as a result, the hydrogen storage amount decreases. On the other hand, 50μ
If it exceeds m, the specific surface area generated by the surface treatment is small, and the high rate discharge and the improvement of the temperature characteristics become insufficient.

Further, the metal salt may be added simultaneously with the surface treatment by addition of ammonia or after delaying the time. The metal that can be used is not particularly limited, but there are alkaline earth metals such as Mg, Ca, and Sr, transition metals such as Ni, Co, and Cu, and rare earth metals including Y, and salts thereof include chlorides,
There are sulfates, nitrates and ammonium salts. The amount of the metal salt used is related to the amount of oxides and / or hydroxides finally formed on the surface of the hydrogen storage alloy.

In the surface treatment of the hydrogen storage alloy using these metal salts, for example, a hydrogen storage alloy powder in which ammonia remains is introduced, and the reaction proceeds in a suspended state by heating and stirring. Further, when the pH is acidic or neutral, an alkali hydroxide or the like is added to make the liquid alkaline.
The temperature in these operations is not particularly limited, and may be performed at an arbitrary liquid temperature from room temperature to 100 ° C., and a desirable liquid temperature is 40 to 80 ° C.

By these operations, metal oxide or metal hydroxide precipitates on the surface of the hydrogen storage alloy powder, so that the life of the hydrogen storage alloy is extended and a hydrogen storage alloy having desired characteristics can be provided.
Surface treatment to the hydrogen storage alloy of the present invention is not limited to electrode activation, self-discharge characteristics, high-rate discharge characteristics and cycle life during known initial charge and discharge, but also temperature characteristics required for batteries used in automobiles. Also realized.

Next, a battery manufacturing method will be described.
1) Negative electrode In this negative electrode, for example, a conductive material is added to the above-mentioned hydrogen storage alloy powder, and the paste is prepared by kneading with a polymer binder and water, filling the conductive material substrate with the paste, and drying. Then, it is produced by molding.

Examples of the conductive substrate on which the hydrogen storage alloy is supported include two-dimensional substrates such as punched metal, expanded metal, and nickel net, and three-dimensional substrates such as felt-like metal porous bodies and sponge-like metal substrates. be able to.

The negative electrode can further contain a binder. Examples of the binder include polyvinyl alcohol, carboxymethyl cellulose, methyl cellulose, sodium polyacrylate, polytetrafluoroethylene, and the like. The negative electrode may contain a conductive material. Examples of the conductive material include carbon black.

Moreover, rare earth metal oxides such as Y ₂ O ₃ , Er ₂ O ₃ , Yb ₂ O ₃ , Sm ₂ O ₃ , Mn ₃ O ₄ , LiMn ₂ O ₄ , Nb ₂ O ₅ , SnO _2, etc. are contained in the paste. An oxide may be added. By including the oxide in the negative electrode, it is possible to improve cycle life at high temperatures. Moreover, the kind of oxide to add can be made into 1 type or 2 types or more. The amount of oxide added is preferably in the range of 0.2 to 5 wt% with respect to the hydrogen storage alloy. A more preferable range is 0.4 to 2 wt%.

2) Positive electrode The positive electrode is only required to be able to be stably charged and discharged in an alkaline electrolyte. For example, a conductive material is added to nickel hydroxide powder as an active material and kneaded with a binder and water. The paste is prepared, filled in a conductive substrate, dried, and then molded.
The nickel hydroxide powder preferably holds a mixture of nickel hydroxide and at least one compound selected from the group consisting of zinc oxide, cobalt oxide, zinc hydroxide and cobalt hydroxide. . A nickel metal hydride secondary battery including a positive electrode including such nickel hydroxide powder and the negative electrode can significantly improve charge / discharge capacity and low-temperature discharge characteristics.

Examples of the conductive material include cobalt oxide, cobalt hydroxide, metallic cobalt, metallic nickel, and carbon.
Examples of the binder include carboxymethylcellulose, methylcellulose, sodium polyacrylate, polytetrafluoroethylene, and polyvinyl alcohol.
Examples of the conductive substrate include a net-like, sponge-like, fiber-like, or felt-like metal porous body made of nickel, stainless steel, or a metal plated with nickel.

3) Separator Examples of the separator include a polypropylene nonwoven fabric, a nylon nonwoven fabric, and a polymer nonwoven fabric such as a nonwoven fabric obtained by mixing polypropylene fibers and nylon fibers.
In particular, a polypropylene nonwoven fabric whose surface is subjected to a hydrophilic treatment is suitable as a separator.

4) Alkaline electrolyte Examples of the alkaline electrolyte include sodium hydroxide aqueous solution, lithium hydroxide aqueous solution, potassium hydroxide aqueous solution, mixed solution of sodium hydroxide aqueous solution and lithium hydroxide aqueous solution,
A mixed solution of a potassium hydroxide aqueous solution and a lithium hydroxide aqueous solution, a mixed solution of potassium hydroxide, lithium hydroxide, a sodium hydroxide aqueous solution, or the like can be used.

The nickel metal hydride secondary battery according to the present invention is manufactured, for example, by the method described below. First, an electrode group is prepared by interposing a separator between the positive electrode and the negative electrode, and after the electrode group is housed in a container, an alkaline electrolyte is injected into the container, and then a sealing process is performed. Next, the secondary battery can be manufactured by first charging after being held at a temperature of room temperature or higher, or by holding at a temperature of room temperature or higher after the initial charging. The average particle size of the hydrogen storage alloy powder of the negative electrode is preferably in the range of 10 to 50 μm. When the average particle size is less than 10 μm, the cycle life is shortened, while when it exceeds 50 μm, the low-temperature characteristics tend to deteriorate. Further, there is a possibility that the paste cannot be uniformly applied to the conductive substrate, and battery characteristics vary.

FIG. 1 shows a cylindrical nickel hydride secondary battery which is an example of a nickel hydride secondary battery according to the present invention. As shown in FIG. 1, a negative electrode 11 containing a hydrogen storage alloy and a positive electrode 12 containing nickel oxide.
The separator 13 having electrical insulation is interposed between the sealed container 14 and the sealed container 14. The sealed container 14 is filled with an alkaline electrolyte.
That is, the hydrogen storage alloy electrode (negative electrode) 11 containing a hydrogen storage alloy is wound in a spiral shape with a separator interposed between the non-sintered nickel electrode (positive electrode) 12 and a cylindrical container 14 with a bottom. Is housed inside. The alkaline electrolyte is accommodated in the container 14. Hole 15 in the center
A circular sealing plate 16 having the above is installed in the upper opening of the container 14. The ring-shaped insulating gasket 17 is disposed between the peripheral edge of the sealing plate 16 and the inner surface of the upper opening of the container 14, and the sealing is performed on the container 14 by caulking to reduce the diameter of the upper opening inward. The plate 16 is airtightly fixed through the gasket 17. The positive electrode lead 18 has one end connected to the positive electrode 12 and the other end connected to the lower surface of the sealing plate 16. A positive electrode terminal 19 having a hat shape is attached on the sealing plate 16 so as to cover the hole 15. The rubber safety valve 20 is disposed so as to close the hole 15 in a space surrounded by the sealing plate 16 and the positive electrode terminal 19. The insulating tube 21 includes the positive terminal 19 and the container 14.
It is attached near the upper end of the container 14 so as to fix the paper 22 placed on the upper end of the container 14.

The nickel metal hydride secondary battery according to the present invention includes an electrode group having a structure in which positive electrodes and negative electrodes are alternately stacked via separators in addition to the cylindrical nickel metal hydride secondary battery as shown in FIG. The present invention can be similarly applied to a prismatic nickel metal hydride secondary battery having a structure in which a liquid is housed in a bottomed rectangular cylindrical container.
According to such a battery, it is possible to satisfy both a low temperature characteristic around −30 ° C. and a cycle life while maintaining a high discharge capacity.

A hybrid vehicle and an electric vehicle according to the present invention will be described.
The hybrid vehicle according to the present invention includes an external combustion engine or an internal combustion engine, an electric drive means such as a motor, and a power source for the electric drive means. The power source includes a nickel metal hydride secondary battery according to the present invention.
In this hybrid vehicle, an external combustion engine or an internal combustion engine drives a generator, an electric drive means drives a wheel by the generated power and the power from the secondary battery, and an external combustion engine or an internal combustion engine. In addition, the driving force of both the electric driving means is properly used to drive the wheel.
The electric vehicle according to the present invention includes the nickel metal hydride secondary battery according to the present invention as a drive power source.
According to such a hybrid vehicle and an electric vehicle according to the present invention, it is possible to improve driving performance such as fuel efficiency.

(Example)
(Examples 1-66 and Comparative Examples 1-13)
The negative electrode active material was prepared by mixing a predetermined amount of elements at the composition ratio shown in Table 1 and prepared by the method described in (A) to (E) below.

(A) Single roll method After the elements mixed in the composition ratio shown in Table 1 below are melted by high frequency melting, they are injected onto a cooling roll (10 m / s) that rotates at high speed to produce flakes having a plate thickness of 20 to 100 μm. Thus, a negative electrode material was obtained.

(B) Strip casting method After the elements mixed in the composition ratios shown in Tables 1 and 2 below are melted by high frequency melting, the molten metal is poured onto a slowly moving cooling roll (1 m / s), and flakes having a thickness of 100 to 500 μm Was used to obtain a negative electrode material.

(C) High-frequency melting method After mixing the elements mixed at the composition ratio shown in Table 1 by high-frequency melting, an alloy ingot was obtained by casting on a water-cooled disk mold at a thickness of about 10 mm. The obtained alloy ingot 6
A negative electrode material was obtained by heat treatment in an inert atmosphere at 00 ° C. for 20 hours.

(D) Gas atomization method The elements mixed in the composition ratio shown in Table 1 below are melted by high-frequency dissolution, and then dropped into a gas atomization chamber through a nozzle, and then high-pressure Ar gas is applied to the resulting mixture to cool and scatter the spherical powder. Obtained.

(E) Centrifugal spray method After the elements mixed in the respective composition ratios are melted by high-frequency dissolution, they are dropped from a disk made of ceramics rotating at high speed in a He atmosphere through a nozzle, and then scattered from the disk.
A spherical powder was obtained.

In any of the examples, it was confirmed from the results of the X-ray diffraction method that the alloy was a substantially single phase crystalline alloy. Further, it was confirmed that the main diffraction line spacing d in the X-ray diffraction pattern was in the range of 2.75 to 2.90 mm, and that the main phase was an orthorhombic structure from the analysis of the crystal structure. In these examples, the main phase has an RTSi ₃ type crystal structure depending on the composition.
Except for the sample prepared by the atomizing method, after coarse pulverization and fine pulverization with a hammer mill, the average particle size was set to 35 μm.

To 100 parts by weight of this alloy powder, 0.5% by weight of nickel powder prepared by a commercially available carbonyl method and 0.5 part by weight of ketjen black powder were added and mixed. To 100 parts by weight of the mixed powder, 1 part by weight of polytetrafluoroethylene, 0.2 part by weight of sodium polyacrylate, 0.2 part by weight of carboxymethyl cellulose, and 50 parts by weight of water are added and stirred to prepare a paste. did. The obtained paste was applied to an iron perforated thin plate whose surface was plated with nickel, and dried to obtain a coated plate. The obtained coated plate was roll-pressed to adjust the thickness, and then cut to a desired size to produce a negative electrode containing a hydrogen storage alloy.

On the other hand, a polyolefin nonwoven fabric in which acrylic acid was graft copolymerized was prepared as a separator.
An electrode group was prepared by winding this negative electrode and a paste type nickel positive electrode prepared by a known technique in a spiral manner with the separator interposed therebetween.
The obtained electrode group and 7 mol of potassium hydroxide aqueous solution, 0.5 mol of sodium hydroxide aqueous solution, and 2.5 ml of alkaline electrolyte containing 0.5 mol of lithium hydroxide aqueous solution were housed in a bottomed cylindrical container, AA having the structure shown in FIG. 1 by sealing.
A cylindrical nickel-metal hydride secondary battery was assembled.

In Comparative Example 1, after melting in an Ar atmosphere using a high-frequency induction heating furnace, a strip-shaped alloy having a thickness of 0.3 to 0.4 mm was produced using a single roll casting apparatus, and the obtained alloy was 850. The sample for evaluation was subjected to heat treatment at 4 ° C. for 4 hours.
In Comparative Example 2, the molten metal melted at high frequency was cast on a cooling plate, and then heat-treated in an Ar atmosphere at 890 ° C. for 12 hours, and used as an evaluation sample.

In Comparative Example 3, 100 g of LaNi ₃ and LaNi ₄ were first mixed and subjected to mechanical alloying in a planetary ball mill containing steel balls for 10 hours at room temperature in an argon atmosphere. Mechanically alloying 100 g LaNi ₅ alloy under the same conditions,
Samples composed of LaNi ₃ , LaNi ₄ , La ₅ Ni ₁₉ , and LaNi ₅ phases were prepared.
In Comparative Example 4, an alloy having the composition shown in the table was prepared in an arc melting furnace in an Ar atmosphere, and then 900 ° C.
Was subjected to heat treatment for 12 hours to obtain a measurement sample.
In Comparative Example 5, after melting in an Ar atmosphere using a high-frequency induction heating furnace, heat treatment was performed at 900 ° C. for 10 hours.

Comparative Examples 6 to 13 were melted in an Ar atmosphere using a high-frequency induction heating furnace and then cooled at a roll peripheral speed of 1 m / s by a single roll method to obtain a flake sample having a plate thickness of 200 to 500 μm. Thereafter, heat treatment was performed at 800 ° C. for 10 hours to obtain a sample for evaluation. In all the comparative materials, the average particle size was adjusted to 35 μm with a hammer mill after coarse pulverization, as in the examples.
Using these samples, a negative electrode was produced in the same manner as in the example, and an AA size cylindrical nickel-hydrogen secondary battery was assembled.

The obtained secondary batteries of Examples 1 to 66 and Comparative Examples 1 to 13 were left at room temperature for 36 hours. Subsequently, after charging for 15 hours at 150 mA, the battery voltage is 0.8 V at a current of 150 mA.
The charging / discharging cycle which discharges until it becomes is performed twice. The cycle test is 1C in an environment of 45 ° C.
Charge with a current of mA, and terminate charging when the voltage drops by 4 mV from the maximum voltage during charging -ΔV
The battery was charged using the method. Thereafter, the battery was discharged at a current of 1 CmA until the battery voltage became 1.0V. Such charge / discharge was repeated, and the number of cycles until the discharge capacity reached 70% of the initial value was measured.

The low temperature characteristics are shown as a ratio between the value measured at room temperature under the above conditions and the value measured under the same conditions at −30 ° C. Furthermore, the high rate discharge characteristic is a ratio of characteristics evaluated at 2C and 0.5C.

As is clear from Tables 1 and 2, the nickel-metal hydride secondary battery using the hydrogen storage alloy of the present invention has excellent characteristics, and is not only for commercially available batteries such as single 2, 3, 4 but also for hybrid vehicles. The battery is suitable for.

(Examples 67 to 90)
In the same manner as in Example 1, hydrogen storage alloys of Examples 67 to 90 were produced. The average particle size is 25
After pulverizing to μm, Examples 67 to 70 were prepared by adding 60% by weight potassium hydroxide aqueous solution to 60%.
The surface treatment was carried out by immersing the hydrogen storage alloy powder in this temperature. Examples 71-74
The surface treatment was performed by immersing the hydrogen storage alloy powder in a 60 wt% sodium hydroxide aqueous solution at 70 ° C. Examples 75-78 set the pH to 2 using hydrochloric acid,
Surface treatment was performed by immersing the hydrogen storage alloy powder in the aqueous solution. Examples 79-82
The surface treatment was performed by immersing the hydrogen storage alloy powder in an aqueous solution set to pH 2 using nitric acid and adjusted to 60 ° C. Examples 83 to 86 were subjected to surface treatment in an aqueous solution set to pH 4 using oxalic acid and adjusted to 50 ° C., and Examples 87 to 90 were subjected to surface treatment with ammonia.
A negative electrode was produced in the same manner as in Example 1 using the obtained hydrogen storage alloy powder. After that, a battery was prepared together with the positive electrode and the separator and subjected to evaluation.

The obtained secondary batteries of Examples 67 to 90 were left at room temperature for 36 hours. Continuing,
After charging at 150 mA for 15 hours, a charge / discharge cycle was performed twice, in which discharging was performed at a current of 150 mA until the battery voltage reached 0.8 V. After this, the charge / discharge cycle is repeated under an environment of 45 ° C.,
The number of cycles until the discharge capacity reaches 80% or less of the discharge capacity of the first cycle was measured, and Table 2 shows the number of cycles and the discharge capacity of the first cycle. The charging process of the charging / discharging cycle was performed by using a -ΔV method in which the charging current was set to 1500 mA and the charging was terminated when the voltage decreased by 10 mV from the maximum voltage during charging. On the other hand, the discharge process is 3000 mA and the battery voltage is 1
. It went until it became 0V.

The numerical evaluation is the initial capacity, the number of charge / discharge cycle life, the low temperature characteristics, and the high rate discharge characteristics.
As is apparent from Table 2, the nickel metal hydride secondary battery using the hydrogen storage alloy of the present invention has excellent characteristics, and is found to be a battery suitable for hybrid vehicles and electric vehicles.

(Examples 91-98)
In the same manner as in Example 1, hydrogen storage alloys of Examples 91 to 98 were produced. Average particle size 25μ
After crushing as m, 1% by weight of rare earth oxide was mixed when producing the negative electrode. Here, the rare earth oxides used are Y ₂ O ₃ , La ₂ O ₃ , CeO ₂ , and Pr ₂ O ₃ in this order.
Preparation and evaluation of the evaluation battery are in accordance with the above examples. The evaluation results are shown in Table 3, and it can be confirmed that this example is particularly excellent in high rate discharge characteristics.

As is apparent from Table 3, the nickel metal hydride secondary battery using the hydrogen storage alloy of the present invention has excellent characteristics, not only for single batteries such as single 2, 3, 4 but also for hybrid vehicles and electric It can be seen that the battery is suitable for automobiles.

1 is a perspective view showing a nickel hydrogen secondary battery according to an embodiment of the present invention, partially broken away.

Explanation of symbols

11 Hydrogen storage alloy electrode (negative electrode)
12 Non-sintered nickel electrode (positive electrode)
13 Separator 14 Container 15 Hole 16 Sealing plate 17 Insulating gasket 18 Positive electrode lead 19 Positive electrode terminal 20 Safety valve 21 Insulating tube 22 Paper

Claims (8)

Formula _{1: (R 1-a A} a) T x Si y M z Z α X β
R: at least one element selected from rare earth elements including Y A: at least one element selected from Ti, Zr, Hf T: at least one element selected from Fe, Co, Ni, Mn, Cu, Cr Element M: at least one element selected from V, Nb, Ta, Mo, W Z: at least one element selected from the group consisting of Sn, Al, Sb and In X: from B, C, N, P At least one element selected 0 ≦ a ≦ 0.3
0.5 ≦ x ≦ 1.2
2.7 ≦ y ≦ 3.2
0 ≦ z ≦ 0.5
0 ≦ α ≦ 0.5
0 ≦ β ≦ 1 (atomic ratio)
Nickel-hydrogen secondary battery hydrogen storage alloy characterized by comprising from intermetallic compound represented in. Formula _{2: (? R 1-a} b A a D b) T x Si y M z Z α X β
R: at least one element selected from rare earth elements including Y A: at least one element selected from Ti, Zr, Hf D: at least one element selected from Mg, Ca, Sr, Ba T: Fe At least one element selected from Co, Ni, Mn, Cu and Cr M: At least one element selected from V, Nb, Ta, Mo and W Z: From the group consisting of Sn, Al, Sb and In At least one element selected X: at least one element selected from B, C, N, P 0.5 ≦ x ≦ 1.2
2.7 ≦ y ≦ 3.2
0 ≦ z ≦ 0.5
0 ≦ a ≦ 0.3
0 ≦ b ≦ 0.5
0 <a + b ≦ 0.5
0 ≦ α ≦ 0.5
0 ≦ β ≦ 1 (atomic ratio)
Nickel-hydrogen secondary battery hydrogen storage alloy characterized by comprising from intermetallic compound represented in. 3. The hydrogen storage alloy for nickel-metal hydride secondary battery according to claim 1, wherein the plane spacing of the strongest diffraction line by X-ray diffraction is 2.75 to 2.90 mm. The hydrogen storage alloy for a nickel-hydrogen secondary battery according to any one of claims 1 to 3, wherein the intermetallic compound has an orthorhombic structure or a tetragonal structure. The hydrogen storage alloy for a nickel metal hydride secondary battery according to claim 4, wherein the intermetallic compound is an intermetallic compound of RTSi ₃ type. 6. The hydrogen storage alloy for nickel metal hydride secondary batteries according to claim 1, wherein the average crystal grain size is 10 nm to 10 [mu] m. A negative electrode comprising the hydrogen storage alloy for nickel-metal hydride secondary battery according to claim 1. A nickel-metal hydride secondary battery comprising the negative electrode according to claim 7, a positive electrode, and an alkaline electrolyte.

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