JP2001291511A - Hydrogen storage alloy electrode, secondary battery, hybrid car and electric vehicle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a hydrogen storage alloy electrode, which has a high capacity, which is superior in low-temperature discharge characteristic and which also enables the capacity to recover at an early stage after stored at a high temperature. SOLUTION: This hydrogen storage alloy contains a first hydrogen storage alloy which has a composition expressed by (RE1-xMgx)NiyAz-wAlw and a second hydrogen storage alloy which has CaCu5-type crystal structure and Al contains not less than 3 mol%. The weight ratio of the first hydrogen storage alloy to the total weight of alloy for the first and the second hydrogen storage alloy exceeds 10% and is less than 90%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a hydrogen storage alloy containing a first hydrogen storage alloy containing magnesium as a constituent element and a second hydrogen storage alloy having a CaCu ₅ type crystal structure containing Al as a constituent element. The present invention relates to an electrode and a secondary battery including the hydrogen storage alloy electrode. This secondary battery is mounted on, for example, a portable electronic device, a hybrid car, or an electric vehicle.

[0002]

2. Description of the Related Art As a hydrogen storage alloy electrode for a nickel-metal hydride battery, one containing a LaNi ₅ -based alloy having a CaCu ₅ type structure as a main phase has been put to practical use. Nickel-metal hydride batteries provided with a hydrogen-absorbing alloy electrode containing a LaNi ₅ -based alloy occupy most of the currently produced nickel-metal hydride batteries and have high versatility. The hydrogen storage capacity of the LaNi ₅ alloy is said to be the ratio of one hydrogen atom to one metal element, and this hydrogen storage capacity is approximately 370 m when converted to an electrochemical capacity.
Ah / g. On the other hand, since the hydrogen storage alloy contained in the battery currently in practical use has a capacity of about 330 mAh / g, it is hardly expected that the capacity density of the battery will be drastically improved by using a LaNi ₅ -based alloy. .

Meanwhile, a secondary battery provided with a negative electrode containing a hydrogen storage alloy having a composition represented by the following formula (A) has been proposed.

(R _1-x Mg _x ) Ni _y A _z (A) where R is a rare earth element containing yttrium, Ca, Z
At least one element selected from r and Ti, A is Co, Mn, Fe, V, Cr, Nb, Al, Ga, Z
At least one element selected from n, Sn, Cu, Si, P and B, x, y and z are each 0 <x <1, 0
It is defined as ≦ z ≦ 1.5, 2.5 ≦ y + z <4.5.

[0005] This hydrogen storage alloy can store more than one hydrogen atom for one metal element, and has a high rate discharge characteristic at a low temperature compared to a CaCu ₅ type hydrogen storage alloy having the same hydrogen equilibrium pressure. Excellent. However, in the case of this hydrogen storage alloy, when the Al content increases, segregation is apt to occur, so that the characteristics of the production lot fluctuate, and an alloy lot with somewhat poor characteristics is produced, and the yield decreases.

In order to ensure the homogeneity of the product in consideration of the variation in the manufacturing conditions during mass production, the Al
It is desirable to keep the content relatively low. However, when the amount of Al substitution in the alloy is reduced, the polarization of the battery appears significantly during charging after storing the nickel-metal hydride battery equipped with an electrode containing the alloy in a discharged state at a high temperature, and the voltage behavior at the end of charging is abnormal. For this reason, there is a problem that it becomes difficult to apply a method of detecting a general voltage change in an alkaline secondary battery and performing charge control (for example, -ΔV control charge). Leaving the device incorporating the battery in a high-temperature environment without using it for a while often occurs in the case of using the actual device. If the charge control cannot be performed, charging is generally stopped in an extremely shallow state to maintain safety, and thus there is a problem that the use time is shorter than the original capacity of the battery. Such a phenomenon can be resolved by restoring the surface state of the electrode while repeating shallow charge / discharge, but improvement is desired so that the electrode can be returned as soon as possible.

[0007]

SUMMARY OF THE INVENTION The present invention has a high capacity,
An object of the present invention is to provide a hydrogen storage alloy electrode and a secondary battery which are excellent in low-temperature discharge characteristics and capable of recovering capacity early after storage at high temperature.

Another object of the present invention is to provide a hybrid car and an electric vehicle having excellent running performance.

[0009]

A hydrogen storage alloy electrode according to the present invention comprises a first electrode having a composition represented by the following formula (1).
And a second hydrogen storage alloy having a CaCu ₅ type crystal structure and containing 3 mol% or more of Al, and occupying the total weight of the first and second hydrogen storage alloys. The weight ratio of the first hydrogen storage alloy is more than 10% and less than 90%.

[0010] _{(RE 1-x Mg x)} Ni y A zw Al w ... (1) where, RE is a rare earth element (the rare earth elements include yttrium), 1 selected from the group consisting of Ca and Zr
A is Co, Mn, Fe, Cu,
At least one element selected from the group consisting of Sn, Zn, Ga, Si and B, and the atomic ratios x, y, z and w are 0.1 ≦ x ≦ 0.6 and 0 ≦ z ≦ 1.5. , 0 ≦ w ≦ 0.1
5, 2.5 ≦ y + z ≦ 4.0.

A secondary battery according to the present invention is a secondary battery comprising a positive electrode, a negative electrode, and an alkaline electrolyte, wherein the negative electrode has a first composition having a composition represented by the following formula (1).
And a second hydrogen storage alloy having a CaCu ₅ type crystal structure and containing 3 mol% or more of Al, and occupying the total weight of the first and second hydrogen storage alloys. The weight ratio of the first hydrogen storage alloy is more than 10% and less than 90%.

[0012] _{(RE 1-x Mg x)} Ni y A zw Al w ... (1) where, RE is a rare earth element (the rare earth elements include yttrium), 1 selected from the group consisting of Ca and Zr
A is Co, Mn, Fe, Cu,
At least one element selected from the group consisting of Sn, Zn, Ga, Si and B, and the atomic ratios x, y, z and w are 0.1 ≦ x ≦ 0.6 and 0 ≦ z ≦ 1.5. , 0 ≦ w ≦ 0.1
5, 2.5 ≦ y + z ≦ 4.0.

[0013] A hybrid car according to the present invention includes an electric driving means and a power supply for the electric driving means, and the power supply includes a secondary battery including a positive electrode, a negative electrode, and an alkaline electrolyte. The negative electrode comprises a first hydrogen storage alloy having a composition represented by the formula (1) and a second hydrogen storage alloy having a CaCu ₅ type crystal structure and containing 3 mol% or more of Al. Wherein the weight ratio of the first hydrogen storage alloy to the total weight of the first and second hydrogen storage alloys is more than 10% and less than 90%.

The electric vehicle according to the present invention includes a secondary battery as a driving power source, the secondary battery includes a positive electrode, a negative electrode, and an alkaline electrolyte.
A first hydrogen storage alloy having a composition represented by the formula:
It has a Cu ₅ type crystal structure and contains 3 mol% of Al.
The weight ratio of the first hydrogen storage alloy to the total weight of the first and second hydrogen storage alloys is more than 10% and less than 90%. It is characterized by the following.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS First, a hydrogen storage alloy electrode according to the present invention will be described.

The hydrogen storage alloy electrode comprises a first hydrogen storage alloy having a composition represented by the following formula (1):
and has a u ₅ type crystal structure, and a second hydrogen-absorbing alloy containing Al 3 mol% or more. The weight ratio of the first hydrogen storage alloy to the total weight of the first and second hydrogen storage alloys is more than 10% and less than 90%.

[0017] _{(RE 1-x Mg x)} Ni y A zw Al w ... (1) where, RE is a rare earth element (the rare earth elements include yttrium), 1 selected from the group consisting of Ca and Zr
A is Co, Mn, Fe, Cu,
At least one element selected from the group consisting of Sn, Zn, Ga, Si and B, and the atomic ratios x, y, z and w are 0.1 ≦ x ≦ 0.6 and 0 ≦ z ≦ 1.5. , 0 ≦ w ≦ 0.1
5, 2.5 ≦ y + z ≦ 4.0.

(1) First Hydrogen Storage Alloy As the RE, at least one element selected from La, Ce, Pr, Nd and Y is used from the viewpoint of reducing the cost of the hydrogen storage alloy electrode. Is preferred. Among them,
More preferably, a misch metal which is a mixture of rare earth elements is used.

As the RE, La, Ce, Pr, Nd
When at least one element selected from Y and Y is used, it is desirable that the amount of Ce in the RE be 20% by weight or less. With this configuration, a high-capacity hydrogen storage alloy can be easily manufactured at low cost.

A more preferred range of the atomic ratio x is 0.15
≤ x ≤ 0.35.

As A, Co and Mn are particularly preferable. A more preferable range of the atomic ratio z is 0 ≦ z ≦ 0.
6. The sum of the atomic ratio y and the atomic ratio z (y + z)
Is more preferably 2.9 ≦ y + z ≦ 3.6.

The reason why the atomic ratio w of Al is defined in the above range is as follows. Atomic ratio w is 0.15
If the ratio exceeds 2, segregation is likely to occur in the hydrogen-absorbing alloy, so that the characteristics of the alloy lot vary and the yield decreases. By setting the atomic ratio w to 0.15 or less, the uniformity of the hydrogen storage alloy during mass production can be ensured. A more preferable range of the atomic ratio w is 0.05 ≦ w ≦ 0.12.
It is. By setting the content within this range, the uniformity of the hydrogen storage alloy during mass production can be further improved.

The first hydrogen storage alloy has a first phase group having a hexagonal crystal system (excluding a phase having a CaCu ₅ type structure) and a second phase group having a rhombohedral crystal system. At least one phase selected from the group consisting of

The first phase group includes a phase having a Ce ₂ Ni ₇ type structure, a phase having a CeNi ₃ type structure, and a phase having a Ce ₂ Ni ₇ type structure.
Desirably, the phase comprises a phase structure or a phase having a crystal structure similar to the CeNi ₃ type structure. On the other hand, the second phase group includes a phase having a Gd ₂ Co ₇ type structure, a phase having a PuNi ₃ type structure, and a phase having a Gd ₂ Co ₇ type structure or PuNi.
It preferably comprises a phase having a crystal structure similar to the type ₃ structure. Here, a phase having a crystal structure similar to the Ce ₂ Ni ₇ type structure, CeNi ₃ type structure, Gd ₂ Co ₇ type structure or PuNi ₃ type structure (hereinafter referred to as a similar crystal phase)
Means a phase that satisfies the condition (a) or (b) described below.

(A) A phase in which a main peak appearing in an X-ray diffraction pattern is similar to a main peak appearing in an X-ray diffraction pattern having a normal structure. Such a similar crystal phase includes, for example, Ce ₂ Ni ₇ type structure, CeNi ₃ type structure, Gd ₂ Co ₇
Examples thereof include a phase having a crystal structure that can be defined by a type structure or a PuNi ₃ type plane index (Miller index). In particular, the similar crystal phase preferably has a crystal structure described in the following (1) or (2).

(1) In X-ray diffraction using CuKα ray, a peak having the highest intensity appears within a range of 2θ of 42.1 ± 1 °, and an intensity ratio represented by the following formula (I) is 80% or less. Crystal structure that satisfies.

I ₃ / I ₄ (I) where I ₄ is the intensity of the peak having the highest intensity in X-ray diffraction using CuKα ray, and I ₃ is that the 2θ in the X-ray diffraction is 31 to 34 °. Is the intensity of the peak appearing in the range. Is the Bragg angle.

(2) 2 in X-ray diffraction using CuKα ray
A crystal structure in which a peak having the highest intensity appears in the range of θ of 42.1 ± 1 °, and a plurality of peaks appearing in the range of 2θ of 31 to 34 ° appear.

(B) In the electron beam diffraction pattern photographed by the transmission electron microscope, the basic lattice reflection point (00L)
A phase in which a regular lattice reflection point exists at 5n equal points of the distance | G _00L | with respect to the origin (000). Here, L and n are natural numbers.

The aforementioned distance | G _00L | is 0.385 n
It is desirable to be within the range of m ^{-1 to} 0.413 nm ^-1 . The most preferred value is 0.4 nm ^-1 .

For example, when n is 1, the distance | G _00L | between the basic grid reflection point (00L) and the origin (000) is set to 5
There are regular grid reflection points at equally dividing positions.

A hydrogen storage alloy having a Ce ₂ Ni ₇ type crystal structure or a Gd ₂ Co ₇ type crystal structure has a basic lattice reflection point (00 L) in the electron diffraction pattern.
A regular lattice reflection point exists at a position that equally divides the distance | G _00L | On the other hand, a hydrogen storage alloy having a CeNi ₃ type crystal structure or a PuNi ₃ type crystal structure has a distance | G _00L between the basic lattice reflection point (00L) and the origin (000) in the electron diffraction pattern.
A regular lattice reflection point exists at a position that bisects |.

Among the similar crystal phases, the aforementioned (a)
Those satisfying both conditions (b) and (b) are preferable.

Here, the “main phase” means that at least one phase selected from the group consisting of the first phase and the second phase occupies the largest volume in the hydrogen storage alloy, or It means that it occupies the largest area in the cross section of the storage alloy. In particular, it is preferable that the volume ratio of the at least one phase selected from the group consisting of the first phase and the second phase in the hydrogen storage alloy is 50% by volume or more. A more preferred range of the volume ratio is 60% by volume or more, further preferably 70% by volume or more.

(2) Second hydrogen storage alloy The Al content in the second alloy is specified in the above range for the following reason. Al content of 3 mol%
If it is less than 1, since it becomes difficult to suppress corrosion of the first hydrogen storage alloy during high-temperature storage, after high-temperature storage,
It is necessary to repeatedly perform charging and discharging to recover the capacity, and it takes a long time to recover the capacity. A more preferable range of the Al content is 3.3 mol% or more, and a further preferable range is 5 mol% or more. As the Al content increases, the effect of suppressing corrosion of the first alloy increases, but the hydrogen storage / release capability of the second alloy may deteriorate. For this reason, the Al content is determined by the hydrogen storage /
The release performance is set so as not to be impaired. In addition, Al
The allowable upper limit of the content varies depending on the composition of the hydrogen storage alloy.

The second alloy comprises one or more rare earth elements,
It is desirable to further include nickel and cobalt. Above all, a hydrogen storage alloy having a composition represented by the following formula (2) is preferable since it has excellent cycle characteristics.

R _α Ni _5-xyz Co _x Al _y M _z (2) where R is one or more rare earth elements (rare earth elements include yttrium), and M is Mn, Fe, C
r, Sn, Cu, B, Zr, Ca, and one or more elements selected from the group consisting of Ca and Y, and the atomic ratios α, x, y, and z are 0.95 <α <1.05, 0. 2 <x <1.
0, 0.18 ≦ y, and 0 ≦ z <1.

As R, it is preferable to use at least one element selected from La, Ce, Pr, Nd and Y from the viewpoint of reducing the cost of the hydrogen storage alloy electrode. Among them, it is more preferable to use misch metal which is a mixture of rare earth elements. As the misch metal, a misch metal rich in Ce (M
m), it is possible to use misch metal (Lm) rich in La.

The second hydrogen storage alloy having the composition represented by the above formula (2) has an atomic ratio y of Al of 0.18 or more,
That is, the Al content is 3 mol% or more. It is more preferable that the atomic ratio y satisfies 0.2 ≦ y, and an even more preferable range is 0.3 ≦ y. The upper limit of the atomic ratio y is preferably 1.0, and more preferably 0.8, from the viewpoint of maintaining the hydrogen storage ability and homogeneity of the second hydrogen storage alloy.

The reason why the weight ratio of the first hydrogen storage alloy to the total weight of the first hydrogen storage alloy and the second hydrogen storage alloy is defined in the above range is as follows. . If the weight ratio of the first hydrogen storage alloy is less than 10%, high low-temperature discharge characteristics cannot be obtained. On the other hand, when the weight ratio of the first hydrogen storage alloy exceeds 90%,
After storage at a high temperature, the number of times of charge / discharge required to recover the capacity increases, and high capacity recovery characteristics cannot be obtained. A more preferred range for the weight ratio is greater than 30% and less than 80%, and a more preferred range is greater than 40% and less than 80%.

The average particle diameter of each of the first hydrogen storage alloy and the second hydrogen storage alloy is preferably in the range of 15 to 80 μm. When the average particle size is less than 15 μm, the surface area of the hydrogen storage alloy increases, so that corrosion of the alloy surface due to the electrolyte solution may increase and the cycle life may be reduced. On the other hand, when the average particle size exceeds 80 μm, the electrode reactivity may be significantly reduced due to the decrease in the surface area of the hydrogen storage alloy. A more desirable range of the average particle size is 3
0 to 60 μm. The first hydrogen storage alloy and the second hydrogen storage alloy
May have the same or different average particle sizes.

In the hydrogen storage alloy electrode according to the present invention, for example, a conductive material is added to the above-mentioned first and second hydrogen storage alloy powders and kneaded with a binder and water to prepare a paste. The paste is filled in a conductive substrate, dried, and then formed by pressure molding.

Examples of the binder include carboxymethylcellulose, methylcellulose, sodium polyacrylate and polytetrafluoroethylene.

[0044] Examples of the conductive material include carbon black.

Examples of the conductive substrate include a two-dimensional substrate such as a punched metal, an expanded metal, and a nickel net, and a three-dimensional substrate such as a felt-like metal porous body and a sponge-like metal substrate. it can.

In the hydrogen storage alloy electrode according to the present invention, the first,
The mixing ratio of the second hydrogen storage alloy and the compositions and crystal structures of the first and second hydrogen storage alloys are measured by the methods described below.

(I) Mixing ratio The weight ratio of the first hydrogen storage alloy to the total weight of the first hydrogen storage alloy and the second hydrogen storage alloy is as follows:
In the powder X-ray diffraction pattern using CuKα ray, 2θ
Can be grasped from the relative intensity of the peak appearing in the range of 31 to 34 °. That is, the first hydrogen storage alloy is Cu
In the powder X-ray diffraction pattern using Kα ray, 2θ is 3
While a peak appears in the range of 1 to 34 °, the second hydrogen storage alloy does not show a peak in the range of 31 to 34 ° in 2θ in the powder X-ray diffraction pattern using CuKα radiation. Therefore, for only the first alloy, the powder X-ray diffraction pattern using CuKα radiation was measured, and 2θ was 31 to 34.
The intensity of the peak appearing in the range of ° is determined, and this is defined as the intensity (reference intensity) when the weight ratio of the first alloy is 100%. On the other hand, the hydrogen storage alloy electrode is disassembled, and a mixed powder of the hydrogen storage alloy is taken out. About this mixed powder, CuKα
The powder X-ray diffraction pattern using X-rays was measured, and 2θ was 31.
By obtaining the intensity of the peak appearing in the range of up to 34 ° and comparing this peak intensity with the above-mentioned reference intensity, the mixing ratio between the first alloy and the second alloy in the electrode can be obtained. For more accurate measurement, the hydrogen-absorbing alloy electrode is embedded in a resin and polished, the cross section of the alloy particles contained in the electrode is exposed on the polished surface, and the cross section of the exposed plurality of alloy particles is energy-dispersive X It is preferable that the mixing ratio of the first alloy and the second alloy is determined by quantitative analysis using a line analyzer.

(II) Composition and Crystal Structure of First Hydrogen Storage Alloy The composition of the first hydrogen storage alloy can be obtained by, for example, a wavelength dispersive X-ray microanalyzer of a scanning electron microscope.

The crystal structure of the main phase of the first hydrogen storage alloy can be determined from an X-ray diffraction pattern using Cu-Kα radiation as an X-ray source.

Further, the occupancy of the main phase of the first hydrogen storage alloy is measured by the method described below. That is, scanning electron micrographs of five arbitrary visual fields are taken, and for each micrograph, the area ratio of the main phase to the alloy area in the visual field (this alloy area is taken as 100%) is determined. The average value of the obtained area ratios is calculated, and this is defined as the volume ratio of the main phase in the hydrogen storage alloy. However, when the hydrogen storage alloy is produced by quenching the molten metal, the crystal grain size becomes as small as about 1 μm or less, so that it may be difficult to observe the main phase with a scanning electron microscope. In this case, a transmission electron microscope is used instead of the scanning electron microscope.

(III) Composition and Crystal Structure of Second Hydrogen Storage Alloy The composition of the second hydrogen storage alloy can be obtained, for example, by a wavelength-dispersive X-ray microanalyzer of a scanning electron microscope.

The crystal structure of the main phase of the second hydrogen storage alloy can be determined from an X-ray diffraction pattern using Cu-Kα radiation as an X-ray source.

The compositions of the first hydrogen storage alloy and the second hydrogen storage alloy contained in the hydrogen storage alloy electrode according to the present invention are different from those before being incorporated in the secondary battery in the stage before being incorporated in the secondary battery. does not change. On the other hand, after incorporating the hydrogen storage alloy electrode according to the present invention into a secondary battery and performing initial charge / discharge, the secondary battery is disassembled to take out the hydrogen storage alloy electrode, and the first hydrogen storage alloy electrode included in this electrode is taken out. When the compositions of the alloy and the second hydrogen storage alloy were measured, both the first hydrogen storage alloy and the second hydrogen storage alloy had a higher Al content near the surface of the alloy particles in contact with the electrolyte than before being incorporated into the electrode.
Although the amount is reduced, the composition is such that the initial amount of Al is maintained at the center of the alloy particles. Therefore, when measuring the composition and the like of the hydrogen storage alloy used for the secondary battery after the initial charge and discharge, the hydrogen storage alloy electrode is subjected to the above-described resin filling polishing, and the center of the cross section of the alloy particle exposed on the polished surface is measured. Part shall be measured.

Next, a secondary battery provided with the hydrogen storage alloy electrode according to the present invention will be described.

This secondary battery has an electrode group including a positive electrode, the above-mentioned hydrogen storage alloy electrode as a negative electrode, a separator interposed between the positive electrode and the negative electrode, and an alkali impregnated in the electrode group. An electrolyte is provided.

Hereinafter, the positive electrode, the negative electrode, the separator, and the electrolyte will be described.

1) Positive electrode This positive electrode is prepared, for example, by adding a conductive material to nickel hydroxide powder as an active material, kneading the mixture with a polymer binder and water to prepare a paste, and applying the paste to a conductive substrate. It is produced by filling, drying, and then molding.

The nickel hydroxide powder comprises zinc oxide,
It may contain at least one compound selected from the group consisting of cobalt oxide, zinc hydroxide and cobalt hydroxide.

Examples of the conductive material include cobalt oxide, cobalt hydroxide, metallic cobalt, metallic nickel, and carbon.

Examples of the polymer binder include carboxymethyl cellulose, methyl cellulose, sodium polyacrylate, and polytetrafluoroethylene.

Examples of the conductive substrate include a mesh-like, sponge-like, fibrous, or felt-like porous metal body made of nickel, stainless steel, or nickel-plated metal.

2) Separator Examples of the separator include a polymer non-woven fabric such as a polypropylene non-woven fabric, a nylon non-woven fabric, and a non-woven fabric obtained by mixing polypropylene fibers and nylon fibers. In particular, a polypropylene nonwoven fabric whose surface has been hydrophilized is suitable as a separator.

3) Alkaline Electrolyte Examples of the alkaline electrolyte include an aqueous solution of sodium hydroxide (NaOH), an aqueous solution of lithium hydroxide (LiOH), an aqueous solution of potassium hydroxide (KOH), and a mixed solution of NaOH and LiOH. , A mixed solution of KOH and LiOH, a mixed solution of KOH, LiOH and NaOH, and the like.

FIG. 1 shows a cylindrical alkaline secondary battery as an example of the secondary battery according to the present invention.

As shown in FIG. 1, an electrode group 5 formed by laminating a positive electrode 2, a separator 3, and a negative electrode 4 and winding them in a spiral shape is accommodated in a bottomed cylindrical container 1. ing. The negative electrode 4 is arranged at the outermost periphery of the electrode group 5 and is in electrical contact with the container 1. The alkaline electrolyte is contained in the container 1. Hole 6 in the center
Is disposed in the upper opening of the container 1. The ring-shaped insulating gasket 8 is disposed between the peripheral edge of the sealing plate 7 and the inner surface of the upper opening of the container 1, and the sealing plate is attached to the container 1 by caulking to reduce the diameter of the upper opening inward. 7 is hermetically fixed via the gasket 8. One end of the positive electrode lead 9 is connected to the positive electrode 2, and the other end is connected to the lower surface of the sealing plate 7. The positive electrode terminal 10 having a hat shape is provided with the sealing plate 7.
It is attached so as to cover the hole 6 above. A rubber safety valve 11 is disposed so as to close the hole 6 in a space surrounded by the sealing plate 7 and the positive electrode terminal 10.
Circular holding plate 12 made of an insulating material having a hole in the center
Are arranged on the positive electrode terminal 10 such that the projections of the positive electrode terminal 10 protrude from the holes of the holding plate 12. The outer tube 13 is provided on the periphery of the holding plate 12,
The side surface of the container 1 and the periphery of the bottom of the container 1 are covered.

The secondary battery according to the present invention includes, in addition to the cylindrical alkaline secondary battery as shown in FIG. 1 described above, an electrode group having a structure in which a positive electrode and a negative electrode are alternately stacked with a separator interposed therebetween. The present invention can be similarly applied to a rectangular alkaline secondary battery having a structure in which an electrolytic solution is contained in a bottomed rectangular cylindrical container.

Next, a hybrid car and an electric vehicle according to the present invention will be described.

The hybrid car 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 supply for the electric drive means. The power supply includes a secondary battery including a positive electrode, a negative electrode, and an alkaline electrolyte. The hydrogen storage alloy electrode according to the present invention is used for the negative electrode.

The “hybrid car” referred to here includes an external combustion engine or an internal combustion engine that drives a generator, and an electric drive unit that drives wheels by electric power generated and electric power from the secondary battery. The one that drives the wheels by selectively using the driving force of both the fuel engine or the internal combustion engine and the electric driving means is included.

The electric vehicle according to the present invention includes a secondary battery as a driving power source. The secondary battery includes a positive electrode, a negative electrode, and an alkaline electrolyte. The hydrogen storage alloy electrode according to the present invention is used for the negative electrode.

The hydrogen storage alloy electrode according to the present invention described above has the first composition having the composition represented by the above formula (1).
And a second hydrogen storage alloy having a CaCu ₅ type crystal structure and containing 3 mol% or more of Al. The weight ratio of the first hydrogen storage alloy to the total weight of the first and second hydrogen storage alloys is as follows:
More than 10% and less than 90%. According to such a hydrogen storage alloy electrode and a secondary battery provided with this electrode, it is possible to suppress the polarization of the battery when it is stored for a long time in a high temperature atmosphere with high capacity, excellent in low temperature and high rate discharge characteristics. The capacity can be easily recovered after such storage. Although the reason for obtaining such an effect is not clear, it is presumed to be due to the operation described below.

That is, a first phase group having a composition represented by the above formula (1) and having a hexagonal crystal system (however,
A first hydrogen storage alloy containing as a main phase at least one phase selected from the group consisting of a second phase group having a rhombohedral crystal system except for a phase having a CaCu ₅ type structure)
Although it shows a higher capacity per volume per weight than a hydrogen storage alloy having a CaCu ₅ type crystal structure,
When an alkaline storage battery provided with a negative electrode containing this alloy is left for a long time in a high-temperature environment, a hydroxyl compound or the like due to the reaction between the alloy constituent elements and the alkaline electrolyte is accumulated on the alloy surface, and a thick oxide film is formed. This oxide film becomes a factor inhibiting the charge / discharge reaction and increases the polarization of the battery. As a result, it becomes difficult to control charging properly after high-temperature storage, so the charging depth becomes shallow to avoid overcharging,
The discharge capacity becomes lower than the original value. After high-temperature storage, the shallow charge / discharge cycle causes the hydrogen-absorbing alloy to crack due to expansion and contraction to form a new surface, and the deposits on the alloy surface are washed away by the movement of the electrolyte and bubbles. To a safe level,
The original discharge capacity can be restored. However, a large number of charge / discharge operations must be performed before the discharge capacity is recovered, and it takes a long time to recover the capacity.

By increasing the Al atomic ratio w of the above-mentioned first hydrogen storage alloy, Al, which is an amphoteric element, can be dissolved in an alkaline electrolyte in a large amount as aluminate ions. Among them, ions of magnesium or a rare earth metal, which is a strong basic alkaline earth metal, can be bonded on the alloy surface to form an insoluble surface film on the alloy surface. As a result, since this surface film functions as a protective film and can suppress the formation of an oxide film during high-temperature storage, the increase in polarization due to long-term storage in a high-temperature environment can be suppressed.

However, in the case of the first hydrogen storage alloy, when the Al atomic ratio w exceeds 0.15, segregation is liable to occur, and the homogeneity is remarkable under the condition that manufacturing conditions are liable to vary, such as manufacturing a lot of lots. May be impaired. If there is significant segregation in the alloy, the hydrogen storage capacity of that part will be reduced, or the volume change at the time of hydrogen absorption will be inhomogeneous, causing problems such as promoting cracking of the alloy,
In some cases the benefits may be lost as higher capacity than the CaCu ₅ type hydrogen storage alloy.

On the other hand, in the second hydrogen storage alloy having a CaCu ₅ type crystal structure, segregation does not occur even if the Al content is relatively large, and an appropriate amount of aluminate ion is contained in the electrolytic solution by surface oxidation. Can be stored and released while supplying hydrogen.

Therefore, a high-capacity first hydrogen storage alloy in which the Al content is kept relatively small to stabilize the characteristics,
When a second hydrogen storage alloy containing a relatively large amount of Al is mixed to form a hydrogen storage alloy electrode, aluminate ions supplied from the second alloy act on the surface of the first alloy to stably and moderately react. It is possible to form a protective film having an appropriate thickness. As a result, it is possible to maintain the characteristics of the first hydrogen storage alloy, that is, high capacity and excellent low-temperature high-rate discharge characteristics, and that the degree of polarization of the battery increases even when stored in a high-temperature atmosphere for a long time. It is possible to obtain a hydrogen storage alloy electrode which is small and easily recovers battery characteristics by charge / discharge.

In the present invention, the cycle characteristics of the second hydrogen storage alloy can be improved by making the composition of the second hydrogen storage alloy represented by the above-mentioned formula (2). The cycle life of the battery can be improved.

In the present invention, the average particle diameter of each of the first hydrogen storage alloy and the second hydrogen storage alloy is 15
By setting the thickness within the range of ~ 80 µm, corrosion by the electrolytic solution can be further suppressed while maintaining high reactivity in the hydrogen storage alloy, so that the low-temperature high-rate discharge characteristics and cycle life of the secondary battery are further improved. be able to.

In addition, a hybrid car and an electric vehicle equipped with a secondary battery having the hydrogen storage alloy electrode according to the present invention as a negative electrode can improve running performance such as fuel efficiency.

[0080]

Embodiments of the present invention will be described below in detail.

(Examples 1 to 7 and Comparative Examples 1 to 4) << Preparation of Negative Electrode >> (Preparation of First Hydrogen Storage Alloy) 45% Lanthanum, 35%
Mish metal, magnesium based on% neodymium, 4% cerium and 10% praseodymium,
Nickel, cobalt, manganese, and aluminum in a molar ratio of 0.7: 0.3: 2.8: 0.5: 0.1: 0.01
Was prepared using an induction melting furnace. This alloy was heat-treated at 900 ° C. for 10 hours in an argon atmosphere, and the composition was changed to RE.
A hydrogen storage alloy ingot represented by _0.7 Mg _0.3 Ni _2.8 Co _0.5 Mn _0.1 Al _0.01 was obtained.

When the crystal structure of the hydrogen storage alloy was observed from an X-ray diffraction pattern using Cu-Kα radiation as an X-ray source, the crystal structure of the main phase was Ce ₂ Ni ₇ type.

Further, with respect to this hydrogen storage alloy, scanning electron micrographs of five arbitrary visual fields were taken. For each micrograph, the area ratio of the main phase to the alloy area in the visual field was determined. Next, the volume ratio of the main phase in the hydrogen storage alloy was obtained by calculating the average value of the area ratio, and the volume ratio was 95% by volume.

Subsequently, this hydrogen storage alloy was mechanically pulverized in an inert atmosphere, and the alloy powder remaining between 400 and 200 mesh was selected by sieving. When the particle size distribution was measured by a laser diffraction / scattering type particle size distribution analyzer, the average particle size corresponding to 50% by weight was 46%.
μm.

(Preparation of second hydrogen storage alloy) 45% lanthanum, 35% neodymium, 4% cerium and 1%
A misch metal whose main component is 0% praseodymium,
A second hydrogen storage alloy ingot containing nickel, cobalt, aluminum, and manganese in the molar ratios shown in Table 1 was prepared using an induction melting furnace, and was prepared in an argon atmosphere at 900 ppm.
A heat treatment was performed at 10 ° C. for 10 hours.

When the crystal structure of the hydrogen storage alloy was observed from an X-ray diffraction pattern using Cu-Kα radiation as an X-ray source, the crystal structure was CaCu ₅ type.

Subsequently, the powder was mechanically pulverized in an inert atmosphere, and the alloy powder remaining between 400 mesh and 200 mesh was selected by sieving. The average particle size was determined in the same manner as described for the first hydrogen storage alloy.
μm.

The obtained first hydrogen storage alloy powder and the second hydrogen storage alloy powder were mixed at a weight ratio shown in Table 1,
A hydrogen storage alloy mixed powder for an electrode was obtained. This alloy powder 10
0.4 parts by weight of sodium polyacrylate, 0.1 parts by weight of carboxymethylcellulose, and a polytetrafluoroethylene dispersion (dispersion medium: water, solid content 60
2.5% by weight), kneaded, and applied evenly and uniformly to both surfaces of a substrate made of a nickel-plated iron perforated plate having a thickness of 60 μm. Subsequently, after drying, pressing, and cutting, a negative electrode for AA size was produced.

(Assembly of Battery) An electrode group was prepared by spirally winding the negative electrode and a non-sintered nickel positive electrode prepared by a known technique via a separator. The obtained electrode group was inserted into a battery can, and 6 mol /
L KOH, 1 mol / L NaOH and 0.5 mol
/ L LiOH mixed aqueous solution was injected, and then sealed to obtain a capacity of 1400 mAh.
Thus, an AA size nickel-metal hydride secondary battery was assembled.

(Examples 8 to 14 and Comparative Examples 5 to 7) The composition of the second hydrogen storage alloy was changed to the composition shown in Table 2 below, and the second hydrogen storage alloy and the first hydrogen storage alloy described above were used. Except for mixing with the alloy in the weight ratio shown in Table 2 below,
A negative electrode was manufactured in the same manner as described in Example 1 described above. Next, a nickel-hydrogen secondary battery was assembled in the same manner as described in Example 1 except that this negative electrode was used.

(Examples 15 to 21 and Comparative Examples 8 to 1)
0) The composition of the second hydrogen storage alloy is changed to that shown in Table 3 below, and the second hydrogen storage alloy and the first hydrogen storage alloy described above are mixed at the weight ratio shown in Table 3 below. Except for the above, a negative electrode was produced in the same manner as described in Example 1 described above. Next, a nickel-hydrogen secondary battery was assembled in the same manner as described in Example 1 except that this negative electrode was used.

(Comparative Examples 11 to 20) The composition of the second hydrogen storage alloy was changed to that shown in Table 4 below, and this second hydrogen storage alloy and the above-described first hydrogen storage alloy were compared with each other in Table 4 below. A negative electrode was produced in the same manner as described in Example 1 except that the components were mixed at the weight ratio shown in Example 1. Next, a nickel-hydrogen secondary battery was assembled in the same manner as described in Example 1 except that this negative electrode was used.

The obtained Examples 1-21 and Comparative Examples 1-2
The secondary battery of No. 0 was charged at room temperature with a current of 140 mA for 13 hours, and then subjected to five charge / discharge cycles of discharging at a current of 140 mA until the battery voltage dropped to 1.0 V. Then, the battery was charged at a current of 1400 mA in an environment of 0 ° C., and −dV control charging was performed with the time when the battery voltage dropped by 8 mV from the peak voltage as a charging end point.
Two cycles of charging and discharging were performed at a current of 1400 mA until the battery voltage dropped to 1.0 V. Thereafter, the secondary battery in the discharged state was stored in a 55 ° C environment for 28 days, and then the secondary battery was returned to a 0 ° C environment, and the charge / discharge using the −dV control described above was repeated. Assuming that the discharge energy (Wh) obtained at the last charge / discharge performed before storage at 55 ° C. was 100%, the discharge energy in charge / discharge after storage was required to recover to 95% or more before storage. The number of charge / discharge cycles is shown in Tables 1 to 4 below.

Examples 1 to 21 and Comparative Examples 1 to 20
After charging the secondary battery at room temperature with a current of 140 mA for 13 hours, the battery was subjected to 5 charge / discharge cycles of discharging at a current of 140 mA until the battery voltage dropped to 1.0 V. Next, after charging at 140 mA for 13 hours, the secondary battery was cooled to −10 ° C., discharged at a current of 1400 mA until the battery voltage dropped to 1.0 V, and the energy (Wh) at the time of discharging was measured. Example 1 with the discharge energy at −10 ° C. of the secondary battery of Comparative Example 1 set to 1.00.
Tables 1 to 4 show the results of displaying the discharge energies of the secondary batteries of Comparative Examples 2 to 21 and Comparative Examples 2 to 20 at -10 ° C.

[0095]

[Table 1]

[0096]

[Table 2]

[0097]

[Table 3]

[0098]

[Table 4]

As is clear from Table 1, the above (1)
A first hydrogen storage alloy having a composition represented by the following formula:
A second type having a Cu5 type structure and containing 3 mol% or more of Al
And a hydrogen storage alloy, wherein the weight ratio of the first alloy is 10%
The secondary batteries of Examples 1 to 7 provided with a hydrogen storage alloy electrode having a hydrogen storage alloy electrode that exceeded 90% and less than 90% had a cycle number until capacity recovery was 3 times or less, and the discharge energy at −10 ° C. was lower than that of Comparative Example 1.
It can be seen that 81% or more of (only the first alloy) can be secured, and the capacity recovery characteristics after storage can be greatly improved while keeping the low-temperature discharge characteristics high.

On the other hand, the secondary battery of Comparative Example 1 containing only the first hydrogen storage alloy and the secondary battery of Comparative Example 2 in which the weight ratio of the first hydrogen storage alloy was 90% were low-temperature discharge. It can be seen that although the energy at the time is high, the number of cycles required for capacity recovery is large. The secondary battery of Comparative Example 3 in which the weight ratio of the first hydrogen storage alloy was 10% and the secondary battery of Comparative Example 4 including only the second hydrogen storage alloy had the number of cycles required for capacity recovery. Although it is small, it can be seen that the energy at the time of low-temperature discharge is low.

Also, from Tables 2 and 3, when the Al content in the second hydrogen storage alloy was changed to 6.7 mol% and 3.3 mol%, the weight ratio of the first alloy was changed. More than 10%,
It is understood that when the content is less than 90%, high low-temperature discharge characteristics can be obtained, and the number of cycles required for capacity recovery can be reduced.

Further, from Table 4, when the Al content in the second hydrogen storage alloy is set to less than 3 mol%, the capacity recovery can be achieved even if the weight ratio of the first alloy is more than 10% and less than 90%. It can be seen that the number of required cycles cannot be reduced.

[0103]

As described above in detail, according to the hydrogen storage alloy electrode and the secondary battery according to the present invention, a high rate discharge at a low temperature is possible, and a charge / discharge cycle required for recovery of discharge energy after storage at a high temperature. A remarkable effect such as the number can be reduced is exhibited. Further, according to the hybrid car and the electric vehicle according to the present invention, remarkable effects such as improvement in running performance such as fuel efficiency can be obtained.

[Brief description of the drawings]

FIG. 1 is a partially cutaway perspective view showing a cylindrical alkaline secondary battery as an example of a secondary battery according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Container, 2 ... Positive electrode, 3 ... Separator, 4 ... Negative electrode, 5 ... Electrode group, 7 ... Sealing plate, 8 ... Insulating gasket.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) // B60K 6/02 B60K 9/00 C (72) Inventor Hideki Yoshida 8 Shinsugita-cho, Isogo-ku, Yokohama-shi, Kanagawa Address Co., Ltd.Toshiba Yokohama Office (72) Inventor Takamichi Inaba 8th Shinsugita-cho, Isogo-ku, Yokohama-shi, Kanagawa Prefecture Co., Ltd. Inside Toshiba Yokohama Office (72) Inventor Junichi Takabayashi 8-8 Shinsugitacho, Isogo-ku, Yokohama, Kanagawa Prefecture Inside Toshiba Yokohama Office (72) Inventor Hideharu Suzuki 3-4-1-10 Minamishinagawa, Shinagawa-ku, Tokyo Toshiba Battery Corporation (72) Inventor Shuichiro Irie 3-4-10 Minamishinagawa, Shinagawa-ku, Tokyo Toshiba Battery Corporation (72) Inventor Take Wada 3-4-10 Minamishinagawa, Shinagawa-ku, Tokyo F-term in Toshiba Battery Corporation (reference) 3D035 AA00 5H028 CC12 EE01 EE05 EE08 HH01 HH05 5H050 AA02 AA08 AA10 BA14 CA03 CB16 CB17 FA05 FA19 HA01 HA02 HA05 5H115 PA12 PA15 PG04 PI16 PI22 PI29 PU25 PU26 UI40

Claims (12)

[Claims] 1. A first hydrogen storage alloy having a composition represented by the following formula (1) and a second hydrogen storage alloy having a CaCu ₅ type crystal structure and containing at least 3 mol% of Al. Wherein the weight ratio of the first hydrogen storage alloy to the total weight of the first and second hydrogen storage alloys is 10%.
% And less than 90%. _{(RE 1-x Mg x)} Ni y A zw Al w ... (1) where, RE is a rare earth element (the rare earth elements include yttrium), 1 selected from the group consisting of Ca and Zr
A is Co, Mn, Fe, Cu,
At least one element selected from the group consisting of Sn, Zn, Ga, Si and B, and the atomic ratios x, y, z and w are 0.1 ≦ x ≦ 0.6 and 0 ≦ z ≦ 1.5. , 0 ≦ w ≦ 0.1
5, 2.5 ≦ y + z ≦ 4.0. 2. The first hydrogen-absorbing alloy has a first phase group having a hexagonal crystal system (excluding a phase having a CaCu ₅ type structure) and a second phase group having a rhombohedral crystal system. 2. The hydrogen storage alloy electrode according to claim 1, comprising at least one type of phase selected from the group consisting of phase groups as a main phase. 3. The hydrogen storage alloy electrode according to claim 1, wherein the second hydrogen storage alloy further contains one or more rare earth elements, nickel and cobalt. 4. The second hydrogen storage alloy according to the following (2):
The composition according to claim 1, wherein the composition has a composition represented by the following formula:
The hydrogen storage alloy electrode as described in the above. R _α Ni _5-xyz Co _x Al _y M _z (2) where R is at least one kind of rare earth element, and M is Mn,
One or more elements selected from the group consisting of Fe, Cr, Sn, Cu, B, Zr, Ca, and Y;
x, y and z are 0.95 <α <1.05, 0.2 <
x <1.0, 0.18 ≦ y, and 0 ≦ z <1. 5. The average particle diameter of each of the first hydrogen storage alloy and the second hydrogen storage alloy is 15 to 80 μm.
2. The hydrogen-absorbing alloy electrode according to claim 1, wherein 6. A positive electrode, a negative electrode, the secondary battery having an alkaline electrolyte, said negative electrode, the following (1) and the first hydrogen-absorbing alloy having a composition represented by the formula, the CaCu ₅ type A second hydrogen storage alloy having a crystal structure and containing 3 mol% or more of Al, wherein the weight ratio of the first hydrogen storage alloy to the total weight of the first and second hydrogen storage alloys is 10%
, And less than 90%. _{(RE 1-x Mg x)} Ni y A zw Al w ... (1) where, RE is a rare earth element (the rare earth elements include yttrium), 1 selected from the group consisting of Ca and Zr
A is Co, Mn, Fe, Cu,
At least one element selected from the group consisting of Sn, Zn, Ga, Si and B, and the atomic ratios x, y, z and w are 0.1 ≦ x ≦ 0.6 and 0 ≦ z ≦ 1.5. , 0 ≦ w ≦ 0.1
5, 2.5 ≦ y + z ≦ 4.0. 7. The first hydrogen-absorbing alloy has a first phase group having a hexagonal crystal system (excluding a phase having a CaCu ₅ type structure) and a second phase group having a rhombohedral crystal system. 7. The secondary battery according to claim 6, wherein at least one type of phase selected from the group consisting of phase groups is included as a main phase. 8. The secondary battery according to claim 6, wherein the second hydrogen storage alloy further contains one or more rare earth elements, nickel and cobalt. 9. The second hydrogen storage alloy according to the following (2):
7. The composition according to claim 6, having a composition represented by the formula:
The secondary battery according to any one of the preceding claims. R _α Ni _5-xyz Co _x Al _y M _z (2) where R is at least one kind of rare earth element, and M is Mn,
One or more elements selected from the group consisting of Fe, Cr, Sn, Cu, B, Zr, Ca, and Y;
x, y and z are 0.95 <α <1.05, 0.2 <
x <1.0, 0.18 ≦ y, and 0 ≦ z <1. 10. The first hydrogen storage alloy and the second hydrogen storage alloy
The average particle size of the hydrogen storage alloy is 15 to 80 μm, respectively.
The secondary battery according to claim 6, wherein m is within a range of m. 11. A hybrid car comprising an electric drive means and a power supply for the electric drive means, wherein the power supply comprises a secondary battery comprising a positive electrode, a negative electrode, and an alkaline electrolyte, Comprises a first hydrogen storage alloy having a composition represented by the following formula (1) and a second hydrogen storage alloy having a CaCu ₅ type crystal structure and containing at least 3 mol% of Al. The weight ratio of the first hydrogen storage alloy to the total weight of the first and second hydrogen storage alloys is 10%
The hybrid car is characterized by exceeding 90% and less than 90%. _{(RE 1-x Mg x)} Ni y A zw Al w ... (1) where, RE is a rare earth element (the rare earth elements include yttrium), 1 selected from the group consisting of Ca and Zr
A is Co, Mn, Fe, Cu,
At least one element selected from the group consisting of Sn, Zn, Ga, Si and B, and the atomic ratios x, y, z and w are 0.1 ≦ x ≦ 0.6 and 0 ≦ z ≦ 1.5. , 0 ≦ w ≦ 0.1
5, 2.5 ≦ y + z ≦ 4.0. 12. An electric vehicle including a secondary battery as a driving power source, wherein the secondary battery includes a positive electrode, a negative electrode, and an alkaline electrolyte, wherein the negative electrode has a composition represented by the following formula (1). And a second hydrogen storage alloy having a CaCu ₅ type crystal structure and containing 3 mol% or more of Al, and wherein the total of the first and second hydrogen storage alloys is The weight ratio of the first hydrogen storage alloy to the weight is 10%
An electric vehicle characterized by exceeding 90% and less than 90%. _{(RE 1-x Mg x)} Ni y A zw Al w ... (1) where, RE is a rare earth element (the rare earth elements include yttrium), 1 selected from the group consisting of Ca and Zr
A is Co, Mn, Fe, Cu,
At least one element selected from the group consisting of Sn, Zn, Ga, Si and B, and the atomic ratios x, y, z and w are 0.1 ≦ x ≦ 0.6 and 0 ≦ z ≦ 1.5. , 0 ≦ w ≦ 0.1
5, 2.5 ≦ y + z ≦ 4.0.