JPH0265060A - Hydrogen storage electrode - Google Patents

Abstract

PURPOSE:To obtain a hydrogen storage electrode with good battery characteristic and excellent reliability at a low cost by using a hydrogen storage alloy reversibly absorbing or desorbing hydrogen. CONSTITUTION:An alloy expressed by the formula I and having the alloy phase which is practically the Laves phase of an inter-metal compound is used. In the formula I, A is one or two or more elements selected among Zr, Ti, Hf, Ta, Y, Ca, B is V and Fe or one or two or more elements containing V and Fe and selected among Ni, Cr, Mn, Co, Cu, Zn, Al for the remainder, alpha=1.5-2.5, and A and B are elements of different types. This alloy has good homogeneity and no composition drift under the ordinary electrochemical conditions occurring in an alkaline storage battery, thereby the various characteristics for the alkaline storage battery are good, the raw material cost is low, and the workability at the time of manufacture is good. Reliability is high in particular, the cost is low, the battery is safe, the electrode performance such as the discharge capacity and life is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to hydrogen storage electrodes using hydrogen storage alloys that reversibly store and release hydrogen, and alkaline storage batteries, particularly positive electrodes such as nickel electrodes, air electrodes, silver oxide electrodes, etc. This invention relates to hydrogen storage electrodes used as negative electrodes in alkaline storage batteries and the like.

BACKGROUND OF THE INVENTION Lead storage batteries and alkaline storage batteries are generally widely used as general-purpose secondary batteries. Of these, the most commonly used alkaline storage battery is the nickel-cadmium storage battery. However, with the recent development of portable devices, there is a demand for storage batteries (secondary batteries) with higher energy density and lower pollution per weight or volume.

Recently, new battery systems that have been attracting attention include alkaline storage batteries and nickel-hydrogen secondary batteries, which use a hydrogen storage alloy that reversibly absorbs and releases hydrogen as the negative electrode and nickel oxide as the positive electrode.

This material has a substantially higher dischargeable capacity density than cadmium, does not form dendrites, and can be manufactured using almost the same methods as conventional methods. Therefore, it is promising as a secondary battery with high energy density, long life, and low pollution.

Until now, Ti
-Ni system, Zr-Ni system, La (or Mm)-N
i-based or alloys based on these alloys and substituted or added with other elements (e.g. Journal o
f Less-Common Metals 129
(1987) 13-30 and 131 (1987) 311
-319 etc.).

Problems to be Solved by the Invention However, with conventional compositional alloys, it is difficult to obtain a homogeneous alloy suitable as a hydrogen storage alloy without compositional deviation or segregation, and the material cost is relatively high.

The present invention was obtained as a result of searching for an alloy with good characteristics in view of the above-mentioned problems in Laves phase alloys containing ■. The purpose of the present invention is to obtain an electrode using a hydrogen storage alloy that can provide a storage battery with excellent electrode performance.

Means to solve problems The present invention is based on the general formula ABα (where A is Zr).

TL Hf, Ta, Y+ Cat Mg
, La+ CatPr, Mm, Nb, Nd, Mo
, AI, one or more elements selected from Si, B
contains V and Fe or V and Fe, and the remainder NL
Cr+ Mn+ Go+ Cut Zn+
AL Sit Nb+MO, W% Mg+ C
a, Y, Ta, Pd+ Ag+Au+
cd, In+ 5nIBL La+ Ca
t Mm+ Pr+ Nd+ One or more elements selected from Th and Sm, α=1.5 to 2.5
, Mm indicates a mixture of rare earth elements, and A and B are different elements), and ferrovanadium (V-Fe alloy) is used as a starting material for producing an alloy whose alloy phase is substantially the Laves phase of an intermetallic compound. The object of the present invention is to provide an electrode using the hydrogen storage electrode, that is, a hydrogen storage electrode with extremely good battery characteristics, low cost, and excellent reliability.

Effect Hydrogen storage electrodes mainly composed of the above-mentioned alloy have better homogeneity and no compositional deviation than conventional ones under normal electrochemical conditions that occur in alkaline storage batteries, so they have various characteristics as alkaline storage batteries. It has extremely good quality, low raw material costs, and good workability during manufacturing.

Example Specific examples will be described below.

(Example 1) Commercially available ferrovanadium and Z L N 11
Ti, Hf, Ta, Y, Ca, Mg+La, Ce, Mm
, Nb+ Nd, Sm+ Mo+ AL
Sit V+ Cr+Mn+ Fe+Col
Cut Zn+ Sit Nb+ Mo+W,
Using Cd etc. as a raw material, the general formula ZrαVβNirMδ (where α, β.

γ and δ are the atomic ratio of Zr1VN Nis M element, respectively, α=0.5 to 1.5, β=0.01 to 1.2,
γ=0.4~2.5, δ=o, oi~1.8, and β
+γ+δ=1.2-3.7, M: Fe alone or Fe and Mg+ Cat Y+ Hf+ Nb+
Ta.

Cr+ Mo+ W+ Mn+ Go+ p
a, Cat Ag+Atb Zrb cd,
Alt St, In+ Sn+ BL
La+ Cat Mm+ Pr+ NcL
An alloy system represented by Th + one or more elements selected from Sm was selected, and alloys having the compositions shown in Table 2 were synthesized from among them.

Specifically, raw materials such as 7erovanadium were weighed to have the composition shown in Table 1, and directly melted in an argon arc melting furnace or a high frequency induction heating furnace in vacuum or inert gas. A part of the melted alloy sample is used for alloy analysis such as atomic composition, crystal structure, crystal lattice constant, homogeneity, etc., and the rest is used for measuring hydrogen absorption and release in hydrogen gas (mainly P (pressure)). -C (composition) - (temperature) measurement) and for electrode performance evaluation (single electrode test and closed type test).

Table 1 shows an example of the composition and price ratio of vanadium (V) elemental metal and ferrovanadium alloy, which are raw materials for the hydrogen storage alloy of the present invention. As shown in Table 1, elemental vanadium metal requires a complicated process for refining, so its price per unit weight is about 3 to 4 times higher than that of ferrovanadium. In addition, in the conventional manufacturing method of Laves phase ABa-based alloys containing V and Fe, alloys were manufactured by adding electrolytic iron, zirconium, Mond nickel, etc. in the desired mixing ratio to this expensive vanadium. . On the other hand, the manufacturing procedure for the hydrogen storage alloy of the present invention using ferrovanadium as a raw material may be performed in exactly the same manner as the conventional melting method using a high frequency furnace or an arc furnace.

From the analysis results, among the alloys in Table 1, Nos. 1 to 6 are homogeneous, and the main alloy phase is c! It was confirmed that it was a 44-type or C15-type Laves phase. There was almost no compositional deviation. And these alloys are normal P in hydrogen gas.
-C-T characteristic results showed that the hydrogen storage capacity was larger than that of conventional products, and the properties such as reaction rate and equilibrium pressure hysteresis were also good. Alloy Nos. 7 to 11 are conventional alloys for hydrogen storage electrodes shown for comparison. In other words, No. 7 is V
No. 8 is an alloy in which the atomic ratio of Zr is too small. No. 9 is an alloy in which the atomic ratio of Ni is too small. No. 10 is an alloy in which the atomic ratio of M element is too large. The resulting alloy phase is the Laves phase of an intermetallic compound, and its crystal structure is CI4 type with hexagonal symmetry or C1S type with cubic symmetry.
In particular, for the 014 type with hexagonal symmetry, the crystal lattice constants a and C are a = 4.8 to 5.2 A (angstrom) and c = 7.9 to 8.3 A (angstrom), respectively, and the cubic symmetric type The C15 type does not fall within the range of alloys with a crystal lattice constant a of 6.92 to 7.7 OA (angstroms).

No. 11 is a typical example of an alloy having the same alloy composition as No. 001, but without using ferrovanadium.

The performance of the alloys shown in this table as negative electrodes for alkaline storage batteries was first evaluated by a half-cell test using only the negative electrode. The evaluation method and results are shown in FIG. 1 and below. First, the alloy obtained by melting was pulverized into particles of 300 mesh or less, and 5 g of this alloy powder was thoroughly mixed and stirred with 0.5 g of polyethylene powder as a binder and 2 g of carbonyl nickel powder as a conductive agent. , this was used as a nickel mesh (wire diameter 0.2 m) as a conductive core material.
m+16 mesh) was filled in the center and pressed with a press to form a plate shape. This was placed in a vacuum at 120° C. for about 1 hour, heated to melt the polyethylene, and then a lead was attached as a hydrogen storage electrode.

In order to evaluate it as a negative electrode for secondary batteries, we selected a sintered nickel electrode used in commercially available nickel-cadmium storage batteries as the positive electrode (counter electrode), and the amount of this positive electrode was made to be larger than the hydrogen storage alloy negative electrode in terms of electrical capacity. Using a polyamide nonwoven fabric as a separator and a solution prepared by adding 20 g/Q of lithium hydroxide to a caustic potassium aqueous solution with a specific gravity of 1.30 as an electrolyte, charging and discharging at a constant current were repeated at 20°C.

The amount of electricity charged at this time was 500 mAX for 5 hours, the discharge was performed at 300 mA, and 0.8 V or less was cut off. As an example of the results, Table 2 shows the discharge capacity in an open system at the 10th charging/discharging cycle, and Table 2 shows the charging/discharging cycle life characteristics in FIG. In the figure, the horizontal axis is the number of charging stand discharge cycles (
oo), the vertical axis shows the discharge capacity per 1 g in an open system, along with unfavorable alloy examples (in Table 1). Note that the numbers in FIG. 1 match the alloy numbers in Table 2. As is clear from this, the hydrogen storage electrode according to the present invention is No.

1 and No, 11. No, 1~No, 6
Comparing with and No. 10, it has a larger discharge capacity and durability (cycle life characteristics) than conventional alloys.
It turns out that it is excellent. It also had excellent rapid charging and discharging characteristics.

In addition to those shown in Table 2, the alloy related to the hydrogen storage electrode of the present invention has a poly(alloy composition).In this case, naturally, the alloy phase substantially belongs to the Laves phase of the intermetallic compound, and its crystal structure is the C14 type with hexagonal symmetry or (and) the C15 type with cubic symmetry, and especially for the C14 type with hexagonal symmetry, the crystal lattice constants a1C are a=4.8 to 5.2A (angstrom) and c=7, respectively. The crystal lattice constant a of the C15 type with cubic symmetry was 6.92 to 7.70 A (angstrom).

General formula ZraVβNiγMδ (where α, β.

γ and δ are the atomic ratio of Z 1% VN N i 1M element, respectively, α = 0.5 to 1.5, β = 0.01 to 1
゜2, γ = 0.4 ~ 2.5, δ = 0.01 ~ 1.8,
and β+γ+δ=1.2-3.7, M: Fe alone or Fe and Mg, Ca, Y, Hf, N
b+ Ta, Cr+ Mo, w, Mn,
Co+Pd.

Cut Ag+ Au+ Zn, Cd+
Al+ Sit In+ Sn, BL L
a, Ce+ Mm+ Pr, NcLTh+
(one or more elements selected from Sm), the atomic ratio β is less than 0.01 or 1.2
Larger alloys have lower discharge capacity and atomic ratio δ of 0.
．． Alloys smaller than 01 or larger than 1.8 also have a small discharge capacity 1.

Also, the atomic ratio α is 0. Alloys smaller than 5 have insufficient charge capacity, and alloys larger than 1.5 have low discharge capacity. Furthermore, alloys with an atomic ratio γ smaller than 0.4 have problems in terms of durability, and alloys with an atomic ratio γ larger than 2 or 5 have a small charging capacity. Alloys with a value of (β+γ+δ) smaller than 1.2 have a small discharge capacity (■), and alloys with a value larger than 3.7 have a small charging capacity. The reason for these is that the Zr content α and the V content β are particularly involved in the charging amount of electricity, and the more Zr and As a result, the amount of electricity discharged is small. Further, Niff1 is particularly related to charge/discharge cycle characteristics (durability), and the larger the amount of NI, the longer the life span, but the amount of charged electricity tends to decrease. The content δ of the M element is particularly involved in charge/discharge cycle characteristics and discharge potential, and as the amount of M increases, these characteristics improve, but the amount of electricity charged decreases. Moreover, the effect of making Fe an essential element is due to the homogeneity of the alloy,
It is also highly effective industrially and economically.

In this way, Fe and V are used as starting materials for hydrogen storage alloys.
The alloy synthesized using ferrovanadium, which consists of ferrovanadium, has extremely good homogeneity, and hydrogen storage electrodes containing this as the main component also have better performance as negative electrodes for alkaline storage batteries than those made from Fe and V metals alone. It was excellent and the process was simple.

(Example 2) Next, using these hydrogen storage alloy electrodes, a AA-sized sealed cylindrical nickel-hydrogen secondary battery was constructed and evaluated.

Similar to the single electrode test described above, the alloy was crushed to 300 meshes or less, made into a paste with a binder such as polyvinyl alcohol, applied to a nickel-plated punched metal plate, dried, and made into a paste with a width of 3.9 cm and a length of 3.9 cm. It was cut to a length of 26 cm, and lead plates were attached to two predetermined locations by spot welding to obtain a hydrogen storage alloy. As the mating electrode, a well-known foamed nickel electrode was selected, also with a width of 3.90 m1.
It was used with a length of 22 cm. A polyamide nonwoven fabric was used as the separator, and a solution prepared by adding 20 g/l of lithium hydroxide to a caustic potassium aqueous solution having a specific gravity of 1.20 was used as the electrolyte. The nominal capacity is 3.0 Ah.

These batteries were evaluated by a conventional charge/discharge cycle test at 20°C. Charging is 0. IC (10 hour rate) for 15 hours, discharge at 0.2C (5 hour rate), final voltage 0
．． The charge/discharge cycle was repeated at 9V. The results are shown in FIG. In addition, the numbers in the figure correspond to the alloy No. in Table 2.
, is consistent with .

All of the batteries constructed with the hydrogen storage alloy electrode of the present invention have approximately 3.0 to 3.2 A even after 500 cycles or more.
h discharge capacity was maintained, and almost no deterioration in performance was observed.

Effects of the Invention The hydrogen storage electrode of the present invention has good homogeneity of the alloy that is the electrode material, no segregation, and little variation between lots, resulting in stable quality and high reliability (as a result, the discharge capacity is It is possible to supply a storage battery with excellent electrode performance such as cycle life and cycle life.In addition, the raw material cost is low and the manufacturing process is simple, so the price is low.

[Brief explanation of the drawing]

FIG. 1 is a discharge cycle life characteristic diagram of a battery using a hydrogen storage electrode according to an embodiment of the present invention, and FIG. 2 is a discharge cycle life characteristic diagram of a battery using each plate alloy according to the present invention as a negative electrode. . Name of agent: Patent attorney Shigetaka Awano (1 person)

Claims (5)

[Claims] (1) General formula ABα (where A is Zr, Ti, Hf,
Ta, Y, Ca, Mg, La, Ce, Pr, Mm, Nb
, one or more elements selected from Nd, Mo, Al, Si, B contains V and Fe or V and Fe, the balance is Ni, Cr, Mn, Co, Cu, Zn, Al,
Si, Nb, Mo, W, Mg, Ca, Y, Ta, Pd,
Ag, Au, Cd, In, Sn, Bi, La, Ce, M
One or more elements selected from m, Pr, Nd, Th, Sm, α = 1.5 to 2.5, Mm represents a mixture of rare earth elements, and A and B are different elements). The alloy phase substantially belongs to the Laves phase of an intermetallic compound, and the crystal structure is the C14 type with hexagonal symmetry or (and) the C15 type with cubic symmetry, and especially the crystal lattice constant of the C14 type with hexagonal symmetry. a and c are respectively a=4.8-5.2A (angstrom) and c=7.9-8.3A (angstrom), and for the cubic symmetric C15 type, the crystal lattice constant a is 6.92-7. A hydrogen storage electrode comprising a 70A (angstrom) alloy or its hydride as a main hydrogen storage and release material. (2) Ferrovanadium (V
-Fe alloy) according to claim 1. (3) The hydrogen storage electrode according to claim 1, wherein the alloy or its hydride contains at least Ni. (4) The hydrogen storage electrode according to claim 1, wherein the alloy or its hydride contains Zr as A in an amount of at least 30 atomic % or more. (5) The alloy or its hydride substantially has the general formula Zr
αVβNiγMδ (where α, β, γ, and δ are the atomic ratios of Zr, V, Ni, and M elements, respectively, and α=0.5 to 1
．． 5, β=0.01-1.2, γ=0.4-2.5, δ
=0.01-1.8, and β+γ+δ=1.2-3.
7, M: Fe alone or Fe and Mg, Ca, Y, H
f, Nb, Ta, Cr, Mo, W, Mn, Co, Pd,
Cu, Ag, Au, Zn, Cd, Al, Si, In, S
n, Bi, La, Ce, Mm, Pr, Nd, Th, Sm
Claims 1, 2,
4. The hydrogen storage electrode according to 3 or 4.