JP2929716B2 - 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 an electrode using a hydrogen storage alloy, and this electrode can be used for an alkaline storage battery such as a nickel-hydrogen storage battery.

[0002]

2. Description of the Related Art Lead storage batteries and alkaline storage batteries are widely used as various power supplies. Among them, alkaline storage batteries are expected to have high reliability and can be reduced in size and weight, and have been used as small batteries for various portable devices and as large batteries for industrial use. In this alkaline storage battery, an air electrode, a silver oxide electrode, or the like is partially used as a positive electrode, but in most cases, a nickel electrode. This type of alkaline storage battery has been improved in characteristics from the pocket type to the sintered type, and furthermore, it has become possible to seal the battery and the use thereof has been expanded.

On the other hand, as a negative electrode, zinc, iron, hydrogen and the like are targeted in addition to cadmium. Recently, attention has been paid to nickel-hydrogen storage batteries using metal hydrides, ie, hydrogen storage alloy electrodes, in order to achieve even higher energy densities, and many proposals have been made for manufacturing methods and the like.

[0004] As a method for producing a hydrogen storage alloy electrode, there are a paste method of sintering an alloy powder and a method of filling or coating a porous support such as foamed, fibrous, or punched metal. Of these, the paste method is the simplest one. Hydrogen storage alloys are relatively excellent in terms of electron conductivity, like cadmium electrodes and zinc electrodes, so that the possibility of non-sintered electrodes is great. That is, the paste is formed into a paste shape together with a binder, and the paste is filled or coated on a porous conductive plate having a three-dimensional or two-dimensional structure.

Among them, as a hydrogen storage alloy electrode, for example, in order to improve the oxidation resistance of the hydrogen storage alloy powder, and to improve the utilization factor and formability, the surface of the particles is plated with nickel or copper to form a porous body. Techniques for forming a metal layer are known. Further, in order to improve the characteristics, a process has been proposed in which an alloy is heat-treated in a vacuum after being manufactured or immersed in an alkaline solution. Further, when applied to a closed type, addition of a fluorine resin or a catalyst has been attempted in order to improve the absorbability of oxygen gas generated from the positive electrode particularly when overcharged.

[0006]

Problems to be solved by the battery using the hydrogen storage alloy include the need to improve the charge / discharge characteristics at the beginning of the charge / discharge cycle, and to further improve the utilization factor and the high-rate discharge characteristics. is there. Among these, for example, in order to improve the performance of rare earth / nickel alloys, La _0.8 Nd _0.2 Ni
It is known that by producing an alloy having a stoichiometric composition such as _2.9 Co _2.4 Mo _0.1 Si _0.1 , MoCo ₃ precipitates at the grain boundaries of a LaNi ₅ -based alloy, which exhibits a good electrochemical reaction. (PHL Notten and P. H
okkeling, ECSFall Meeting Extended Abstracts, 120,
1990).

However, in this method, a hydrogen storage alloy electrochemically storing and releasing hydrogen and MoCo ₃ as a second phase are simultaneously formed, and the composition range of an intermetallic compound such as a LaNi ₅ base alloy is limited. Although it is considered effective for a relatively narrow alloy system, it is not necessarily effective for an intermetallic compound that is stable over a wide composition range, and it has been difficult to apply this technique to various alloys. Conventionally, addition of Pd black or the like has been attempted for the purpose of improving these characteristics. In this case, although a considerable effect is obtained, a more inexpensive method has been demanded due to cost restrictions.

[0008]

In particular, the general formula of the main hydrogen storage alloy is represented by ABα (α = 1.5 to 2.5), and the alloy phase substantially belongs to the Laves phase of the intermetallic compound. The general formula is applied to the surface of a hydrogen storage alloy powder whose crystal structure is C14 type having a hexagonal symmetry or (and) C15 type having a cubic symmetry.
There deposited by an alloy of a hexagonal structure represented by _3-inch MoCo machine械的granulation method and the like.

[0009]

In particular, in a nickel-metal hydride storage battery using a hydrogen storage alloy whose alloy belongs to the AB ₂ type Laves phase and whose crystal structure is C14 type or (and) cubic symmetrical C15 type having a hexagonal symmetry, The problem is that the discharge capacity is small, and the polarization is relatively large at a rapid charge / discharge current, and the potential characteristics during charge / discharge are degraded. However, by attaching MoCo ₃ onto the hydrogen storage alloy, the electrochemical hydrogen storage reaction during charging can be accelerated, and the charge / discharge efficiency can be significantly improved.

[0010]

EXAMPLE As a hydrogen storage alloy, the main alloy phase was C15.
ZrMn _0.3 Cr _0.3 V, one of the type Laves phase alloys
Using _0.15 Ni _1.25 Go gold. First, the preparation of the electrodes will be described. MoCo ₃ was prepared by arc melting and heat treatment at 950 ° C., which was crushed and passed through 400 mesh. The heat treatment is performed when the target MoC is melted.
Since fairly deviation in composition from o _3, in order to equalize it. The hydrogen-absorbing alloy which was passed through a 100 mesh to, was adjusted to MoCo ₃ becomes 5 wt%, were mixed using a ball mill. When this state was observed with an electron microscope, it was found that MoCo
₃ was partially scattered. After passing this through 200 mesh, a paste was made using a 1% aqueous solution of polyvinyl alcohol (PVA).
Then, the paste was filled into a foamed nickel plate having a porosity of 95% and a thickness of 0.8 mm and pressed to obtain an electrode. This is an example of the present invention, and is referred to as an electrode A. In order to compare the characteristics of this electrode, an electrode according to a conventional method was also manufactured. That is, similarly to the conventional method, ZrMn
An alloy powder obtained by pulverizing a hydrogen storage alloy having a composition of _0.3 Cr _0.3 V _0.15 Ni _1.25 and passing through a 200 mesh was subjected to MoC
The o ₃ without attaching to the electrodes in the previous similar manner. This is referred to as an electrode B as a conventional method.

These electrodes are used as a negative electrode, and a nickel oxide electrode having an excessive electric capacity is disposed at a counter electrode, and a specific gravity of the electrolytic solution is 1.
Using an aqueous solution of 30 potassium hydroxide, charge / discharge was performed in an open system in which the capacity was regulated with a hydrogen-absorbing alloy negative electrode under conditions rich in electrolyte. Charging is 100 per gram of hydrogen storage alloy
mA × 5.5 hours, the discharge was 50 mA per gram of alloy, and the terminal voltage was up to 0.8 V.

As a result, the discharge capacity of the electrode B at the beginning of the charge / discharge cycle is low, and the saturation discharge capacity of the electrode B is 380 mAh / g.
It took 5 cycles or more to reach, but in the case of the electrode A, it reached 95% of the saturated discharge capacity in the first cycle and reached 380 mAh / g of the saturated discharge capacity in the second cycle. Was effective.

Next, the result of forming a sealed battery using this electrode will be described. The electrodes A and B were adjusted to a width of 3.3 cm, a length of 21 cm, and a thickness of 0.50 mm, respectively, and lead plates were attached at two predetermined positions. Then, the resultant was combined with the positive electrode and the separator, spirally formed into three layers in a cylindrical shape, and stored in an SC-size battery case. As the positive electrode at this time, a known foamed nickel electrode was selected and used with a width of 3.3 cm and a length of 16 cm. Also in this case, two lead plates were attached. In addition, a polypropylene nonwoven fabric provided with hydrophilicity was used as the separator. As an electrolyte, lithium hydroxide was added to an aqueous solution of potassium hydroxide having a specific gravity of 1.30.
0 g / l was used after dissolution. This was sealed to obtain a sealed battery. This battery has a nominal capacity of 2.5 A due to positive electrode capacity regulation.
h. The electrode A of the hydrogen storage alloy electrode is
The battery constituted by the above is referred to as a battery A, and the battery similarly constituted by the electrodes B is referred to as a battery B.

A description will now be given of the results of making ten such batteries and evaluating them by a normal charge / discharge cycle test. First, the initial discharge voltage and the capacity were compared. 150% of capacity constant current charge at 5 hour rate, and 1.0 at 5 hour rate
When a constant current discharge was performed up to V, A had an average voltage of 1.28 V and a discharge capacity of about 2.
It was 5 Ah. However, in B, the average discharge voltage is 1.2
At 2 V, the discharge capacity did not reach 2.5 Ah in two cycles, and the discharge capacity increased with the number of cycles, and required four cycles until the discharge capacity became almost constant.

Similarly, charging is performed at a rate of 1 C (1 hour rate) for 150 hours.
To 1%, the discharge is also at 1C (1 hour rate) with a cut-off voltage of 1.
As a result of repeating the charge / discharge cycle at 20 ° C. at 0 V, battery A had an average discharge voltage of 1.23 V, whereas battery B had 1.14 V, and battery A had excellent discharge characteristics due to rapid charge / discharge. Was also found.

Although the above is the case of the AB ₂ type Laves phase alloy, the same excellent results were obtained with the LaNi ₅ base alloy. In addition, although the mixing in the previous example was performed using a ball mill, a uniform mixture was prepared by such mixing, and the second-phase fine particles were compositely fixed on the surface of the hydrogen storage alloy by a high-speed gas stream impact method. A better result could be obtained by the conversion. Furthermore, excellent results were similarly obtained when immobilization by plating or coating was performed. Further, the alloy represented by MoCo ₃ dissolves a metal mixed in a predetermined ratio,
It is made more uniform by applying a heat treatment at １０００1000 ° C.

[0017]

As described above, the hydrogen storage alloy electrode according to the present invention can improve the initial activity, which has been a problem in the past, and improve the charge / discharge efficiency at a very low cost. An occlusion alloy electrode and a battery using the same can be provided.

──────────────────────────────────────────────────の Continuing on the front page (72) Inventor Hajime Sari 1006 Kadoma Kadoma, Osaka Prefecture Inside Matsushita Electric Industrial Co., Ltd. In-company (56) References JP-A-3-173062 (JP, A) JP-A-2-79369 (JP, A) JP-A-2-256161 (JP, A) JP-A-50-111546 (JP, A) (58) Fields surveyed (Int.Cl. ⁶ , DB name) H01M 4/24-4/26 H01M 4/38

Claims (2)

(57) [Claims] 1. A hexagonal crystal structure having a general formula represented by MoCo ₃ , which is completely different from the hydrogen storage alloy powder, on a surface of a main hydrogen storage alloy powder that electrochemically stores and releases hydrogen.
A hydrogen-absorbing alloy electrode comprising an electrode having an alloy having the following characteristics: 2. The main hydrogen storage alloy has a general formula of ABα.
(Α = 1.5-2.5), wherein the alloy phase substantially belongs to the Laves phase of the intermetallic compound, and the crystal structure thereof is at least one of C14 type having hexagonal symmetry and C15 type having cubic symmetry. 2. The hydrogen storage alloy electrode according to claim 1, wherein: