JP2000073132A - Hydrogen storage alloy and secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a hydrogen storage alloy having a considerably improved desorbing property of occluded gaseous hydrogen as well as capacity to occlude the large amt. of the gaseous hydrogen and to provide a metal oxide-hydrogen secondary battery having a high capacity and excellent in a charge-discharge cycle. SOLUTION: This hydrogen storage alloy has a compsn. represented by the formula: MgaR1-a-bTb(Ni1-xMx)z (where R is at least one element selected from rare earth elements including Y, T is at least one element selected from Ca, Ti, Zr and Hf, M is at least one element selected from Co, Mn, Fe, Al, Ga, Zn, C, Sn, Cu, Si, B, Nb, W, Mo, V, Cr, Ta, P and S, 0.2<=a<=0.35, 0<=b<=0.3, 0<=x<=0.6 and 3<=z<=3.8). In the alloy, grains contg. a parallel growth structure are present. Further, the metal oxide-hydrogen secondary battery uses the hydrogen storage alloy as a negative electrode.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hydrogen storage alloy and a secondary battery using the hydrogen storage alloy for a negative electrode.

[0002]

2. Description of the Related Art Hydrogen storage alloys are attracting attention as new energy conversion materials and energy storage materials because they can safely and easily store hydrogen. In other words, hydrogen storage alloys are: 1) storage and transport of hydrogen, storage and transport of heat
Transport, 2) conversion of thermo-mechanical energy, 3) separation and purification of hydrogen, 4) separation of hydrogen isotopes, 5) batteries using hydrogen as active material,
6) Catalysts in synthetic chemistry, 7) Temperature sensors, etc., have been applied to a wide range of new functional materials.

For example, a nickel-metal hydride secondary battery using a hydrogen storage alloy as a negative electrode material has the following requirements.
(b) It is strong against overcharge and overdischarge, (c) It can be charged and discharged at a high rate, (d) It is clean, and (e) It is compatible with nickel cadmium batteries. Therefore, it is attracting attention as a next-generation consumer battery, and its application and practical use are being actively carried out. As described above, the hydrogen storage alloy has various potentials of application mechanically, physically, and chemically, and is therefore cited as one of the key materials in the future industry.

[0004] By the way, metals that occlude hydrogen include:
Metals that can form stable compounds with hydrogen, such as Pd, T
A simple substance such as i, Zr, V, a rare earth metal element, or an alkaline earth element, or an alloy of these metal elements and another metal element can be used. In particular, in the case of the alloy type, the bonding force between the metal and hydrogen is appropriately weakened so that not only the hydrogen storage reaction but also the desorption reaction can be performed relatively easily, and the equilibrium hydrogen pressure (plateau pressure) required for the reaction is reduced. Improving occlusion and release reactions such as size, width of equilibrium region (plateau region), change in equilibrium pressure (flatness) in the process of storing hydrogen,
It has features such as high chemical and physical stability.

[0005] As such a hydrogen storage alloy, the following hydrogen storage alloys are known. In addition, as an electrode material of a battery as one application example, generally,
Rare earth alloys such as LaNi ₅ or MmNi ₅ are used. However, its discharge capacity is 80% of the theoretical capacity
However, there is a limit to increasing the capacity.

(1) Rare earths (LaNi ₅ , MmNi ₅ etc.),
(2) Laves type (ZrV ₂ , ZrMn ₂ etc.), (3) titanium type (TiNi, TiFe etc.), (4) magnesium type (Mg ₂ Ni, Mg
(Ni ₂ etc.), (5) Others (cluster alloy etc.).

[0007]

The magnesium-rare-earth alloy in which a part of the lanthanum element component is substituted with the magnesium element has a feature that it can occlude a large amount of hydrogen gas. For example, La _1-x Mg _x Ni ₂ Has a problem in its function as a hydrogen electrode because the stability of bonding with hydrogen is high and the hydrogen release rate is low. That is, in the case of a magnesium-rare earth alloy, although the theoretical hydrogen storage capacity in the gas phase is large, the hydrogen release property is inferior, and at room temperature, it hardly acts as a battery electrode in an alkaline electrolyte. , Cannot be used for the construction of a hydrogen negative electrode.

Recently, Mg ₂ LaNi ₉ having PuNi ₃ type has been used.
Are reported, but their hydrogen absorption / desorption characteristics are extremely low.

The present invention has been made in view of the above circumstances, and a magnesium-rare earth-based hydrogen storage alloy has a large amount of hydrogen storage capacity, and also has a greatly improved release or release of stored hydrogen. The purpose of the present invention is to provide a hydrogen storage alloy.

Another object of the present invention is to provide a metal oxide / hydrogen secondary battery having a high capacity and an excellent charge / discharge cycle by applying the hydrogen storage alloy having excellent hydrogen storage / release properties to a negative electrode. .

[0011]

According to the first aspect of the present invention, there is provided a compound represented by the following general formula: Mg _a R _{1 -abT b} (Ni _{1 -xM x} ) _z (where R is selected from rare earth elements including Y) At least one element, T is at least one element selected from Ca, Ti, Zr and Hf, M is Co, Mn, Fe, Al, Ga, Zn,
At least one element selected from C, Sn, Cu, Si, B, Nb, W, Mo, V, Cr, Ta, P and S, 0.2 ≦ a ≦ 0.
35, 0 ≦ b ≦ 0.3, 0 ≦ x ≦ 0.6, 3 ≦ z ≦ 3.8), characterized by the presence of crystal grains containing a parallel intergrowth structure It is an occlusion alloy.

According to a second aspect of the present invention, in the hydrogen storage alloy according to the first aspect, the unit cell layer formed by stacking A and B subcells having the Laves phase as A and the CaCu ₅ type structure as B is 2 It is characterized in that a parallel intergrowth structure is formed between more than one kind of periodic structures.

According to a third aspect of the present invention, in the hydrogen storage alloy according to the second aspect, the laminated portion exhibiting a periodic structure has a length of 5 nm to
It is characterized by being formed from a 1 μm unit cell layer.

In the first to third aspects of the present invention,
In the composition represented by the general formula Mg _a R _1-ab T _b (Ni _1-x M _x ) _z , the Mg composition ratio (a), (Mg + R + T)
The ratio (z) to (Ni + M) needs to be selected within the above range. That is, by selecting the Mg composition ratio (a), the ratio (z) between (Mg + R + T) and (Ni + M) within the above range, parallel intergrowths are formed in the alloy main phase. A hydrogen storage alloy that has a high hydrogen storage capacity due to the formation of the parallel intergrowth crystals, while at the same time easily releases hydrogen and can realize a metal oxide / hydrogen secondary battery having a large discharge capacity. Because.

At least one element selected from the rare earth elements containing Y represented by R is preferably La, Ce, Pr, Nd and Y in consideration of cost reduction of the hydrogen storage alloy. It is more preferable to use a misch metal which is a mixed system of rare earth elements, and a misch metal rich in Ce or a misch metal rich in La.

Further, Ca, Ti, Zr and Hf represented by T
At least one element selected from the above is a so-called substitution component, and this substitution component does not reduce the hydrogen storage capacity, but suppresses the improvement and improvement of the hydrogen release property and the miniaturization of the alloy accompanying the release of hydrogen. It is a necessary component to perform. here,
If the substitution amount (b) exceeds 0.3, it is limited to 0.3 or less because improvement and improvement of hydrogen release property and suppression of alloy miniaturization due to hydrogen release cannot be achieved. And this replacement amount
The smaller the amount of (b), the longer the cycle life tends to be. Therefore, it is preferably 0.2 or less.

Furthermore, Co, Mn, Fe, A represented by M
l, Ga, Zn, C, Sn, Cu, Si, B, Nb, W, Mo, V, C
At least one element selected from r, Ta, P, and S is also a substitution component for the Ni component, and this substitution component contributes to the improvement of hydrogen storage / release characteristics. Here, it is presumed that the substitution by the substitution component represented by M facilitates the diffusion of hydrogen invading into the alloy and the occlusion and release of hydrogen, and when used for a negative electrode material of a secondary battery, It exhibits remarkably excellent charge / discharge cycle characteristics. The replacement amount
If (x) exceeds 0.6, the discharge capacity will be reduced.
It is always selected in the range of 0.6 or less, preferably in the range of 0.02 to 0.3.

In the hydrogen storage alloy according to the first to third aspects of the present invention, impurities such as N, O and F are added in a range that does not impair the characteristics of the hydrogen storage alloy, for example, in a range of 1% or less by weight, respectively. It may be contained.

The hydrogen storage alloy according to the first to third aspects of the present invention can be manufactured, for example, as follows. That is, each raw material element component is weighed, and a required hydrogen storage alloy can be manufactured by a molten metal quenching method such as a single roll method or a twin roll method under an inert atmosphere such as an argon gas.
Here, the quenching rate (cooling rate) of the molten metal is less than 1000 ° C / s, preferably less than 800 ° C / s, more preferably 700 ° C / s.
/ S.

Instead of the above-described quenching method, a method is employed in which each raw material element weighed in an inert atmosphere is subjected to high frequency induction melting, then cast into a mold or the like to obtain an alloy ingot, and quenched. You may. Or, RNi ₅ series, R ₂ Ni
₇ system, RNi ₃ system, RNi ₂ system, Ni ₂ Mg system, after the production of the master alloy in an induction dissolution of such MgNi ₂ type were weighed these master alloys so that the required composition, again frequency After induction melting, casting may be performed to obtain an alloy ingot, and the alloy ingot may be rapidly cooled.

Next, the produced alloy is subjected to a temperature of 300 ° C. or more and less than 850 ° C., preferably 400 ° C. or more and less than 800 ° C., for 10 to 1000 hours in a vacuum or an inert atmosphere.
Preferably 50 to 800 hours, more preferably 200 to 600 hours
By performing the heat treatment for a relatively long period of time, it is possible to obtain a hydrogen storage alloy having excellent characteristics such as a hydrogen storage / release speed. If the heat treatment temperature exceeds 850 ℃,
There is a possibility that the hydrogen storage characteristics may be deteriorated.

In the first, second or third aspect of the present invention, "parallel intergrowth" in the alloy means that the length of the a-axis of the hexagonal crystal is substantially the same and the length of the c-axis is different. It is formed by stacking (stacking) two or more types of unit cell layers. That is, assuming that the Laves phase is A and the CaCu ₅ type structure is B, the unit cell layer in the hydrogen storage alloy system according to the present invention is a stack of A and B subcells (Am
Bn: m and n are integers of 1 or more).

Therefore, for example, a LaNi ₃ type (AB) or La ₅ Ni ₁₉ (ABBB) having a length of 10 nm or less in a laminated (unit cell layer) portion showing a periodic structure of La ₂ Ni ₇ type (ABB).
It is possible to form a parallel intergrowth including a periodic structure including a stack of unit cell layers. The formation of the parallel intergrowth improves the durability of the alloy itself against occlusion and release of hydrogen, and improves the cycle characteristics when used as an electrode material for a secondary battery. The "parallel intergrowth" in the alloy
Can be observed by taking a transmission electron microscope image of the (1,1,0) plane of a crystal grain at a magnification of 10,000 to 500,000 times using a transmission electron microscope.

When the average length of the laminated portion showing the periodic structure is 5 nm to 1 μm, the hydrogen storage / release characteristics are improved, which contributes to the provision of a metal oxide / hydrogen secondary battery having a large discharge capacity. Here, although there is a difference depending on the composition system of the hydrogen storage alloy, generally, the average length of the laminated portion showing the periodic structure is preferably 10 nm to 500 nm, more preferably 20 nm.
In the case of up to 200 nm, the storage / release characteristics of hydrogen are further improved, and a metal oxide / hydrogen secondary battery having excellent discharge capacity and cycle characteristics can be provided.

The average length of the laminated portion of the periodic structure is:
Using a transmission electron microscope at a magnification of 400,000 times, (1,1,
0) Plane A transmission electron microscope image of 100 nm × 100 nm is taken at a total of 20 places, and the average value of the length of the laminated portion forming the periodic structure.

According to a fourth aspect of the present invention, there is provided a secondary battery including a hydrogen negative electrode having a hydrogen storage alloy as a main component, a positive electrode, a separator for separating the hydrogen negative electrode and the positive electrode, and an alkaline electrolyte. Is a secondary battery containing the hydrogen storage alloy according to any one of claims 1 to 3.

That is, a fourth aspect of the present invention is that the hydrogen storage alloy according to the first to third aspects of the present invention has excellent hydrogen storage / release characteristics, and also has improved and improved charge / discharge cycle characteristics. It pays attention to. The main point is to provide a metal oxide / hydrogen secondary battery having a large discharge capacity and excellent cycle characteristics by using the hydrogen storage alloy as a constituent material of the hydrogen negative electrode.

[0028]

Embodiments of the present invention will be described below.

[0029]

[Table 1] Each elemental component was weighed so as to form the composition of the hydrogen storage alloy shown in Table 1, and was subjected to high frequency melting under an argon gas atmosphere, and then cast in a mold to produce 20 kinds of alloy ingots. Next, the alloy ingots corresponding to the respective examples were each melted by a high frequency melting method, dropped into a copper single roll surface in an argon gas atmosphere, and cooled at a rapid cooling rate of 600 ° C./s to produce alloy flakes, respectively. did.

Each of the alloy flakes was heat-treated at 700 ° C. for 200 hours in an argon gas atmosphere to produce a corresponding hydrogen storage alloy. In Table 1, Lm is a misch metal composed of La = 90% by weight, Ce = 2% by weight, Pr = 5% by weight, Nd = 3% by weight, and Mm is La = 35% by weight.
Ce = 50.3% by weight, Pr = 5.5% by weight, Nd = 9% by weight, Sm =
It is a misch metal consisting of 0.2% by weight.

As a comparative example, each elemental component was weighed so as to form the composition of the hydrogen storage alloy shown in Table 1.
1000 ° C / s after high frequency melting under argon gas atmosphere
At a rapid cooling rate (Comparative Examples 1 and 2) or 3000 ° C./s (Comparative Examples 3, 4, and 5), and dropped and cooled on the surface of a copper single roll to produce alloy flakes. Then, each alloy flake was subjected to 950 ° C., 3 hours (Comparative Examples 1, 2) or 850 ° C., 4 hours (Comparative Examples 3, 4, 5) under an argon gas atmosphere.
Each of the heat treatments was performed to produce five types of corresponding hydrogen storage alloys.

Using a transmission electron microscope, the above hydrogen storage alloy was imaged at a magnification of 400,000 times at 20 transmission electron microscope images of the (1,0,0) plane of the crystal grains to have a periodic structure. Table 1 also shows the average value of the length of the laminated portion, that is, the average value of the thickness of the region having the La ₂ Ni ₇ type.

Each of the hydrogen storage alloys according to the examples and the comparative examples obtained above was pulverized to produce hydrogen storage alloy powder having a particle size of 100 μm or less. Each of these hydrogen storage alloy powder and electrolytic copper powder were mixed at a weight ratio of 1: 2, and 1 g of this mixture was pressed at a pressure of 10 ton / cm ² for 5 minutes,
Pellets each having a diameter of 10 mm were produced. These pellets were sandwiched between nickel meshes, and the peripheral edges were spot-welded and pressed against each other. Further, nickel lead wires were spot-welded to produce hydrogen storage alloy electrodes (negative electrodes).

The negative electrode prepared above was immersed and arranged in an 8 N aqueous potassium hydroxide solution together with a sintered nickel electrode (positive electrode), and a charge / discharge cycle test was performed at a temperature of 35 ° C. That is, 1 g of the hydrogen storage alloy in the negative electrode
After charging for 5 hours at a current of 100 mA per hour, rest for 10 minutes,
Repeat the cycle of discharging to -0.75 V against the mercury oxide electrode at a current of 100 mA per 1 g of the hydrogen storage alloy in the negative electrode, and the maximum discharge capacity and cycle life (discharge capacity is reduced to 80% of the maximum discharge capacity) Cycle number). Table 2 shows the measurement results.

[0035]

[Table 2] As can be seen from Table 2 above, Mg _a R _1-ab T _b (Ni _1-x
Represented by M _{x) z,} a metal oxide-hydrogen secondary battery (Examples 1 to 20 comprising a negative electrode containing an alloy containing parallel intergrowth in the alloy grain) is, Mg _a R _1-ab T _b (Ni _1-x M _x ) A metal oxide / hydrogen secondary battery having a negative electrode represented by _z and containing no alloy containing parallel intergrowth in alloy crystal grains (Comparative Example 1
Compared with the above (5), both the discharge capacity and the cycle life are excellent, and it can be seen that the hydrogen storage alloy according to the present invention has a large effective hydrogen storage amount.

[0036]

According to the first to third aspects of the present invention, a magnesium-rare earth element having improved storage / release characteristics without impairing a high hydrogen storage capacity as compared with a conventional magnesium-rare earth hydrogen storage alloy. Based hydrogen storage alloy can be provided. Therefore, for example, storage and transport of hydrogen, storage and transport of heat, conversion of thermo-mechanical energy, separation and purification of hydrogen, separation of hydrogen isotopes, batteries using hydrogen as an active material, catalysts in synthetic chemistry, temperature sensors, etc. In addition, the application fields of hydrogen storage alloys will be expanded, and new application fields will be developed.

According to the fourth aspect of the present invention, a metal oxide having a large discharge capacity and excellent cycle characteristics is obtained by utilizing (applying) a hydrogen storage alloy having both high hydrogen storage capacity and storage / release characteristics. -A hydrogen secondary battery is provided.

[0038]

Continued on the front page (72) Inventor Hideki Yoshida 72 Horikawa-cho, Saiwai-ku, Kawasaki-shi, Kanagawa Prefecture Inside the Higashi-shiba Kawasaki Plant (72) Inventor Takamichi Inaba 72 Horikawa-cho, Sachi-ku, Kawasaki-shi, Kanagawa Prefecture Inside the Higashi-Shibakawasaki Plant (72) Inventor Masaaki Yamamoto 72, Horikawa-cho, Saiwai-ku, Kawasaki-shi, Kanagawa Prefecture Inside the Higashishiba Kawasaki Office (72) Inventor Shiro Takeno 8 Shinsugita-cho, Isogo-ku, Yokohama-shi, Kanagawa Prefecture F-term (Toshiba Yokohama Office) Reference) 5H003 AA02 AA04 BB02 BC06 BD00 BD02 5H016 AA02 EE01 HH00 HH13 5H028 AA05 EE01 FF02 FF04 HH00 HH05

Claims (4)

[Claims] 1. General formula Mg _a R _{1 -ab} T _b (Ni _{1 -x} M _x ) _z (wherein R is at least one element selected from rare earth elements including Y, and T is Ca, Ti , Zr and Hf, at least one element selected from the group consisting of Co, Mn, Fe, Al, Ga, Zn,
At least one element selected from C, Sn, Cu, Si, B, Nb, W, Mo, V, Cr, Ta, P and S, 0.2 ≦ a ≦ 0.
35, 0 ≦ b ≦ 0.3, 0 ≦ x ≦ 0.6, 3 ≦ z ≦ 3.8), characterized by the presence of crystal grains containing a parallel intergrowth structure Storage alloy. 2. The Laves phase is A and the CaCu ₅ type structure is B.
The hydrogen storage alloy according to claim 1, wherein the unit cell layer formed by stacking the A and B subcells forms a parallel intergrowth structure between two or more periodic structures. 3. The laminated portion exhibiting a periodic structure has a length of 5 nm to 1 nm.
3. The hydrogen storage alloy according to claim 2, wherein the hydrogen storage alloy is formed from a unit layer of μm. 4. A secondary battery comprising a hydrogen negative electrode comprising a hydrogen storage alloy as a main component, a positive electrode, a separator for separating the hydrogen negative electrode and the positive electrode, and an alkaline electrolyte.
A secondary battery, wherein the hydrogen negative electrode contains the hydrogen storage alloy according to claim 1, 2 or 3.