JP3381264B2 - Hydrogen storage alloy electrode - Google Patents

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 electrode, which can be used as an electrode for batteries such as nickel-hydrogen storage batteries.

[0002]

2. Description of the Related Art Hydrogen storage alloys have been used for various applications, mainly for hydrogen storage, transportation, refining materials, energy conversion materials such as heat and pressure, and electrode materials for alkaline storage batteries.

Many alloy materials have been proposed as the hydrogen storage alloy materials used for these, and typical ones are LaNi ₅ , TiMn _1.5 , and TiF.
e, Mg ₂ Ni, etc. are well known. Further, in recent years, the performance as a hydrogen storage alloy has been further improved by using a multi-component alloy in which new elements such as third, fourth and fifth elements are added based on these materials.

On the other hand, with the recent remarkable development of portable equipment, the demand for batteries used in such equipment is also significant. Further high energy density batteries are required to enable reduction in size and weight. These requirements are the same in the fields of electric vehicles and various mobile power sources. Among various power sources, lead storage batteries and alkaline storage batteries represented by nickel-cadmium storage batteries have been widely used as storage batteries. Recently, attention has been paid to alkaline storage batteries such as nickel-hydrogen storage batteries that use a hydrogen storage alloy that reversibly stores and releases hydrogen as an electrode material.

The hydrogen storage alloy electrode used for this can constitute a battery in the same manner as cadmium, zinc, etc., and the actual dischargeable capacity density can be made larger than that of cadmium, and there is no formation of dendrite such as zinc. Therefore, it is promising as a high energy density, long-life, pollution-free electrode for alkaline storage batteries.

The hydrogen storage alloys used for these electrodes are usually prepared by an arc melting method, a high frequency induction heating melting method or the like. The hydrogen storage alloy obtained by melting is usually pulverized into a powder and formed into an electrode by a method such as a paste coating method, a pressure method, or a sintering method.

As an example for this electrode, there is a sealed nickel-hydrogen storage battery in which a nickel electrode is used for the positive electrode, a hydrogen storage alloy electrode is used for the negative electrode, and a caustic potash solution is used as the electrolytic solution. This battery has a nominal battery voltage of 1.2V and is compatible with nickel-cadmium storage batteries, and has the advantage that it can be handled in the same manner. If the battery size is similar, the energy density is about 1.5 times higher than that of nickel-cadmium storage batteries. It has a feature of high energy density, and is gradually approaching the stage of practical application.

As the hydrogen storage alloy material used for these electrodes, Ca based on LaNi ₅ or MmNi ₅ is used.
Alloy systems having a Cu ₅ structure are well known. An example is MmNi _3.8 Co _0.5 Mn _0.4 Al _0.3 alloy for electrodes. When these alloy systems having a CaCu ₅ structure are electrochemically charged / discharged, the discharge capacity density obtained is about 0.3 Ah per 1 g of the alloy. In order to improve the energy density of the battery, it is essential to increase the capacity of the hydrogen storage alloy used for the electrode. As an alloy system having the possibility of increasing the capacity, an alloy system having the AB ₂ type Laves phase structure is used. Be expected. AB for concrete electrode
Zr as an alloy with ₂ types of Laves phase structure
Examples include Mn _0.6 Cr _0.1 V _0.2 Ni _1.2 alloys and the like, and the discharge capacity density of these alloys is 0.35 to 0.4 Ah / g.
The degree is obtained.

However, by increasing the capacity of the hydrogen storage alloy in this way, a new problem occurs that the cycle life characteristics of the electrode deteriorate.

[0010]

In order to increase the capacity of the hydrogen storage alloy electrode, ZrMn _0.6 Cr _0.1 V _0.2 Ni _1.2
When an alloy system having an AB ₂ type Laves phase structure such as an alloy is used for the electrode, it is possible to achieve higher capacity than the conventional alloy system having a CaCu ₅ structure. However, in this case, the performance as an electrode is largely deteriorated due to repeated charging and discharging, and there is a problem in the life characteristics.

An object of the present invention is to provide an electrode using an alloy system having an AB ₂ type Laves phase structure, which has excellent characteristics in terms of both high capacity and long life of the electrode. To do.

[0012]

The hydrogen-absorbing alloy electrode of the present invention is an alloy having a Laves phase structure in which the main alloy phase of the hydrogen-absorbing alloy is C14 type or C15 type, and the area ratio in the alloy structure is 1 -40% ZrNiα (1 ≦ α
The electrode is constituted by using a hydrogen storage alloy in which a phase mainly having ≦ 1.8) is partially formed. At this time, ZrNiα (1 ≦ α ≦ 1.
The phase mainly composed of 8) is Zr (Ni + M) α (1 ≦ α ≦
1.8), (where M = Mg, Ca, Ti, Hf, V,
Nb, Cr, Mo, Mn, Fe, Co, Pd, Cu, A
g, Zn, Cd, Al, Si, La, Ce, Pr, Nd
It is effective that a pressurized et one or three or more elements of the multicomponent alloy represented by two or more) are selected. Further, the hydrogen storage alloy has a general formula ABβ (1.5 ≦ β ≦ 2.5, A is Z
r alone or Ti, Hf, Ta of 30 atomic% or less,
Y, Ca, Mg, La, Ce, Nd, Nb, Mo, A
Zr and B containing 1, Si are Ni and Mg, Ca, T
i, Hf, V, Nb, Cr, Mo, Mn, Fe, Co,
Pd, Cu, Ag, Zn, Cd, Al, Si, La, C
e, Pr, shown by at least one element) selected N d or et al., the main alloy phase is an alloy having a C14 type or C15-type Laves phase structure, the crystal lattice constant in the case of type C14 is It is effective that a = 4.8 to 5.2Å (angstrom), c = 7.9 to 8.3Å (angstrom), and in the case of C15 type, a = 6.92 to 7.30Å (angstrom). . Furthermore, the hydrogen storage alloy has the general formula Zr (Mnx + My + Niz) β.
(However, x = 0.1 to 0.8, y = 0.1 to 0.8, z
= 1.0 to 1.5, x + y + z = β, 1.5 ≦ β ≦
2.5, M = Fe, Co, Cr, V, Ti, Nb, M
o, Cu, A l or et indicated by selected at least one element or two or more kinds), and alloys thereof to which the main alloy phase has a C14-type or C15-type Laves phase structure, the crystal lattice constant C14 In the case of a mold, a = 4.8 ~
5.2Å (angstrom), c = 7.9 to 8.3Å
(Angstrom), a = 6.92 for C15 type
It is effective that the value is up to 7.30Å (angstrom).

This hydrogen storage alloy has the general formula ABβ (1.
5 ≦ β ≦ 2.5, A is Zr alone or 30 atomic% or less of Ti, Hf, Ta, Y, Ca, Mg, La, Ce, N
Zr and B containing d, Nb, Mo, Al and Si are Ni and Mg, Ca, Ti, Hf, V, Nb, Cr, Mo and M.
n, Fe, Co, Pd, Cu, Ag, Zn, Cd, A
1, at least one element selected from Si, La, Ce, Pr, Nd, etc., and the main alloy phase is C
It is an alloy having a 14-type or C15-type Laves phase structure, and its crystal lattice constant is a =
4.8-5.2 Å (angstrom), c = 7.9-
8.3Å (Angstrom), a = for C15 type
It is preferably 6.92 to 7.30 Å (angstrom).

[0014]

[Function] A main hydrogen absorbing alloy phase is an alloy having a C14 type or C15 type Laves phase structure, and a phase mainly containing ZrNiα (1 ≦ α ≦ 1.8) is partially formed in the alloy structure. If the electrode is formed by using the hydrogen storage alloy described above, the service life can be extended. This is the main phase Lav
The alloy having the es phase structure actively acts on the charge-discharge reaction, but the partially arranged ZrNiα (1 ≦ α ≦
The phase mainly composed of 1.8) is relatively inactive in this charge / discharge reaction. The active Laves phase is accompanied by miniaturization of the alloy due to repeated charging / discharging, and in the worst case, detachment from the electrode occurs. The presence of this inactive phase, which is mainly ZrNiα (1 ≦ α ≦ 1.8), coexists with the active Laves phase to function as a cushioning material, prevent performance deterioration, and improve life characteristics. it is conceivable that.

[0015]

EXAMPLES Examples of the present invention will be described below. Alloys having the compositions shown in (Table 1) were prepared as hydrogen storage alloys. This alloy was prepared by mixing commercially available Zr, Mn, V, Cr, and Ni metallic materials having a purity of 99.5% or more so as to have alloys with the atomic ratios shown in Table 1 and using an argon arc melting furnace. It melt | dissolved 4 times each, reversing. Then, the alloy ingot obtained by melting was subjected to vacuum heat treatment at 1100 ° C. for 12 hours in 10 ⁻³ Pa.

[0016]

[Table 1]

The alloy block thus obtained was used for electrode evaluation and alloy analysis. The alloy evaluation is the X-ray diffraction measurement of the alloy pulverized to 400 mesh or less, and the observation of the alloy structure of the alloy lump.

A list of alloy analysis results of the alloys shown in (Table 1) is shown in (Table 2). As shown in (Table 2), in the results of X-ray diffraction, the main alloy phases were all C15 type La.
It is an alloy having a ves phase structure, and only No. Alloy 5 was a clean single phase. Other alloy phases recognized from this X-ray diffraction were examined by the structure analysis of the alloy ingot. An example of a typical alloy structure photograph is shown in FIG. Innumerable white island-shaped precipitates were observed on the black substrate as shown in Fig. 1,
Analyzing each composition, the base of the alloy structure (black part) is the C15 type Laves phase, and the island-shaped precipitates (white part) are the alloy phases mainly composed of ZrNiα (1 ≦ α ≦ 1.8). It was confirmed that And in this alloy structure Z
The abundance of the ZrNiα phase in the hydrogen storage alloy in which the phase mainly consisting of rNiα (1 ≦ α ≦ 1.8) was partially formed was determined by graphical integration, and as shown in (Table 2), changed.

[0019]

[Table 2]

Next, the electrode characteristics of the alloys shown in Table 1 were evaluated. The electrode used for this evaluation was prepared as follows. First, each alloy was mechanically pulverized to 200 mesh or less, and then a 1% aqueous solution of carboxymethyl cellulose (CMC) and a 2% aqueous solution of polyvinyl alcohol were added to and mixed with the alloy powder to form a paste. A foamed nickel porous body having a thickness of 1 mm and a porosity of 95% was filled almost uniformly with this paste composition and dried to obtain an electrode.
Each of the hydrogen storage alloy electrodes thus obtained was then pressed by a press, cut into pieces having an alloy amount of 2 g, and a lead plate was attached by spot welding.

The results of performing a single plate test on the hydrogen storage alloy electrodes made of the alloys shown in (Table 1) in an open type rich in electrolytic solution will be described.

A caustic potash aqueous solution having a specific gravity of 1.30 was used as an electrolytic solution, and a sintered nickel electrode having an excessive capacity was used as a positive electrode, and a hydrogen storage alloy electrode was used as a negative electrode to change the discharge capacity during charge / discharge cycles. Examined. Charge and discharge conditions are 20
At ℃, charge 0.2A for 5.5 hours, discharge 0.1A
The battery voltage was set to 0.8V. The result is shown in FIG.

In FIG. 2, the vertical axis represents the discharge capacity per gram of alloy. Among the hydrogen storage alloy electrodes tested, those having a large absolute value of discharge capacity were Alloy Nos. 2, 3 and 4. On the other hand, the discharge capacity of all hydrogen storage alloy electrodes gradually decreased with the progress of charge / discharge cycles, but the rate of capacity decrease increased in the order of Alloy No. 1 <2 <3 <4 <5, and No. No. 5 showed the largest decrease in discharge capacity. From this result, ZrNiα (1 ≦ α ≦
It has been found that a hydrogen storage alloy in which a phase mainly containing 1.8) is partially formed, and the more the amount of the ZrNiα phase present in the alloy, the more stable the discharge capacity is maintained in the charge / discharge cycle.

Next, a description will be given of the results of evaluation by constructing a sealed battery using the hydrogen storage alloy electrodes made of the alloys shown in (Table 1).

A cylindrical sealed nickel-hydrogen storage battery in which three layers of a negative electrode, a separator and a positive electrode are spirally formed in a battery case using a known foamed nickel electrode as a counter electrode and a hydrophilic polypropylene non-woven separator. It was created. Then 25g / in a caustic potash solution with a specific gravity of 1.25
An electrolytic solution in which 1 l of lithium hydroxide was dissolved was injected and sealed. This sealed battery was a sub C type and the battery capacity was 2.8 Ah.

Five sealed cells each made of a hydrogen storage alloy electrode made of the alloy shown in Table 1 were prepared and charged and discharged for 5 cycles under relatively mild conditions. It was confirmed that all the batteries had a standard discharge capacity of approximately 2.8 to 2.9 Ah. Then, while measuring the battery internal pressure during charging / discharging, charge at 2.8 A (1
A charging / discharging cycle test was carried out in which the battery was charged at 2.8 A (1 C) for 1.5 hours in C) up to a battery voltage of 0.9 V.

FIG. 3 shows a comparison between the charge / discharge cycle as a result of the charge / discharge cycle test and the discharge capacity of the battery. Figure 3
As is clear from the above, all the batteries maintained stable performance up to about 200 cycles, but the batteries prepared from alloy No. 5 reached the end of their life with a rapid decrease in capacity around 250 cycles. On the other hand, alloys Nos. 1 to 4 showed excellent cycle life performance and maintained a stable discharge capacity even after 400 cycles.

In this charge / discharge cycle test, the relationship between the charge / discharge cycle during charging and the maximum battery internal pressure during charging was examined at the same time. As a result, at the beginning of the charging / discharging cycle, all batteries reach the maximum internal pressure, and at the end of charging, 4 to 5 kg / c.
Although the battery internal pressure was about m ^2, the battery prepared from alloy No. 5 showed a gradual increase in the battery internal pressure from around 200 cycles. It is considered that this increase in battery internal pressure caused a decrease in discharge capacity. From these results, in the tests up to 400 cycles, it is preferable that the ZrNiα phase existing in the alloy is large in order to maintain a stable battery internal pressure. In this case as well, ZrNiα (1 ≦ α ≦
It was found that the partial formation of the phase mainly composed of 1.8) maintains a stable discharge capacity in the charge / discharge cycle.

The above is one embodiment of the present invention. In this embodiment, the hydrogen storage alloy is Zr-Mn-V.
The five-component system of --Cr--Ni was taken up.

However, the present invention is not limited to this embodiment, and those satisfying the following requirements are effective. That is, the hydrogen storage alloy has the general formula ABβ (1.5 ≦ β ≦
2.5, A is Zr alone or Ti of 30 atomic% or less,
Hf, Ta, Y, Ca, Mg, La, Ce, Nd, N
Zr containing b, Mo, Al and Si, B is Ni and M
g, Ca, Ti, Hf, V, Nb, Cr, Mo, Mn,
Fe, Co, Pd, Cu, Ag, Zn, Cd, Al, S
i, La, Ce, Pr, Nd, etc.), whose main alloy phase is a C14-type or C15-type Laves phase structure, and whose crystal lattice constant is C14-type. In the case of a = 4.8-
5.2Å (angstrom), c = 7.9 to 8.3Å
(Angstrom), a = 6.92 for C15 type
~ 7.30Å (Angstrom).

More preferably, the hydrogen storage alloy is particularly Zr (Mnx + My + Niz) β (where x = 0.1 to 0.8, y = 0.1 to 0.8 and z = 1.0).
~ 1.5, x + y + z = β, 1.5 ≦ β ≦ 2.5, M
= Fe, Co, Cr, V, Ti, Nb, Mo, Cu, A
at least one element selected from 1 or two or more kinds), the main alloy phase is an alloy having a C14 type or C15 type Laves phase structure, and the crystal lattice constant is C14 type, a = 4.8-5.2Å
(Angstrom), c = 7.9 to 8.3Å (angstrom), in the case of C15 type, a = 6.92 to 7.3.
It is 0Å (angstrom).

C14 type or C which is an effective alloy
Zr present in alloy structure of type 15 Laves phase structure
The phase mainly composed of Niα (1 ≦ α ≦ 1.8) is more effective in the life characteristics as the abundance is larger, but if the ratio of the original effective alloy phase is decreased, the discharge capacity itself is decreased. .
Therefore, the phase mainly composed of ZrNiα (1 ≦ α ≦ 1.8) is preferably 1 to 40% in terms of the structure area ratio.

In addition, ZrNiα existing in the alloy structure
The phase mainly composed of (1 ≦ α ≦ 1.8) is highly likely to be a binary component of Zr and Ni based on the analysis results so far, but Zr (N
i + M) α (1 ≦ α ≦ 1.8) It is considered possible that the alloy has three or more components. In this case, M = M
g, Ca, Ti, Hf, V, Nb, Cr, Mo, Mn,
Fe, Co, Pd, Cu, Ag, Zn, Cd, Al, S
One or more selected from i, La, Ce, Pr, Nd and the like.

[0034]

INDUSTRIAL APPLICABILITY As described above, according to the present invention, the main alloy phase of the hydrogen storage alloy is Laves of C14 type or C15 type.
It is an alloy with a phase structure, and ZrNi is contained in the alloy structure.
The hydrogen storage alloy electrode is characterized in that the electrode is formed by using a hydrogen storage alloy in which a phase mainly having α (1 ≦ α ≦ 1.8) is partially formed.

As a result, it is possible to provide a high-performance hydrogen storage alloy electrode having an effect of prolonging the life of the electrode and excellent in life characteristics, and a battery using the same.

[Brief description of drawings]

1 is an embodiment of the present invention Zr-Mn-V-Cr
-Photograph of metal structure of Ni-based hydrogen storage alloy

FIG. 2 is a relational diagram of charge / discharge cycles and discharge capacities in a single plate test in an open type rich in electrolyte solution of a hydrogen storage alloy electrode made of the alloy shown in (Table 1) which is an example of the present invention.

FIG. 3 is a diagram showing the relationship between the charge / discharge cycle and the discharge capacity of a battery of a hydrogen-occlusion alloy electrode made of the alloy shown in Table 1 which is an example of the present invention in a cylindrical sealed battery.

Front page continuation (72) Inventor Tsutomu Iwaki 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (56) References JP-A-2-65060 (JP, A) JP-A-1-102855 (JP , A) JP-A-60-241652 (JP, A) Patent 2563638 (JP, B2) (58) Fields investigated (Int.Cl. ⁷ , DB name) H01M 4/38 C22C 1/00-49/14

Claims (4)

(57) [Claims] 1. An alloy having a C14 type or C15 type Laves phase structure as a main alloy phase of a hydrogen storage alloy, and having an area ratio of 1 to 40% ZrNiα in the alloy structure.
A hydrogen storage alloy electrode, characterized in that the electrode is formed by using a hydrogen storage alloy in which a phase mainly having (1 ≦ α ≦ 1.8) is partially formed. 2. ZrNiα (1 ≦ 1 present in the alloy structure)
The phase mainly having α ≦ 1.8) is Zr (Ni + M) α (1
≤α≤1.8), where M = Mg, Ca, Ti, H
f, V, Nb, Cr, Mo, Mn, Fe, Co, Pd,
Cu, Ag, Zn, Cd, Al, Si, La, Ce, P
r, N d or al one or more) of 3 elements or more multicomponent alloy is claim 1 hydrogen storage alloy electrode according represented by selected. 3. A hydrogen storage alloy having a general formula ABβ (1.5 ≦
β ≦ 2.5, A is Zr alone or T of 30 atomic% or less
i, Hf, Ta, Y, Ca, Mg, La, Ce, Nd,
Zr containing Nb, Mo, Al and Si, B is Ni and M
g, Ca, Ti, Hf, V, Nb, Cr, Mo, Mn,
Fe, Co, Pd, Cu, Ag, Zn, Cd, Al, S
i at least 1, La, Ce, Pr, selected N d or al
Is an alloy having a C14-type or C15-type Laves phase structure,
The crystal lattice constant of the C14 type is a = 4.8 to 5.
2Å (angstrom), c = 7.9 to 8.3Å (angstrom), a = 6.92 to C15 type
The hydrogen storage alloy electrode according to claim 1 or 2, which has a thickness of 7.30Å (angstrom). 4. The hydrogen storage alloy has the general formula Zr (Mnx + M
y + Niz) β (where x = 0.1 to 0.8, y =
0.1-0.8, z = 1.0-1.5, x + y + z =
β, 1.5 ≦ β ≦ 2.5, M = Fe, Co, Cr,
V, Ti, Nb, Mo, Cu, indicated by A l or al least one element or more selected), its main alloy phase is an alloy having a C14 type or C15-type Laves phase structure, The crystal lattice constant is a = 4.8 to 5.2Å (angstrom) in the case of C14 type, c
= 7.9 to 8.3Å (Angstrom), a = 6.92 to 7.30Å (Angstrom) for C15 type
The hydrogen storage alloy electrode according to claim 1 or 2.