JPH0241864B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention relates to a negative electrode in a storage battery that generates electrical energy through an electrochemical reaction between hydrogen stored in the negative electrode and a positive electrode.

Configuration of conventional examples and their problems The performance of this type of hydrogen storage electrode depends significantly on the temperature characteristics of the hydrogen gas release pressure of the alloy itself that stores hydrogen, which is the active substance, and the theoretical discharge characteristic unique to that alloy. In order to obtain capacity, it had the disadvantage that it could only be used within a certain limited temperature range. For example, the optimum operating temperature range for LaNi ₅ is a temperature somewhat lower than room temperature, and that for CaNi ₅ is in a higher range than for LaNi ₅ .

Purpose of the Invention The purpose of the present invention is to provide a hydrogen storage electrode for an alkaline storage battery that can be used over a wide temperature range and can obtain a substantially constant discharge capacity over a much wider temperature range than conventional ones. .

Structure of the Invention The hydrogen storage electrode of the present invention includes a plurality of hydrogen storage alloys having mutually different hydrogen dissociation equilibrium pressures and different temperature ranges exhibiting maximum discharge capacities, for example, in layers from both sides of a plate-shaped active material support. They are stacked on top of each other and are tightly integrated to minimize the electrical contact resistance between the layers.As a result,
As a hydrogen storage electrode, the dissociation activation energy of hydrogen atoms on the alloy surface is made constant over a wide temperature range.

Description of Examples Commercially available granular lanthanum (purity 99.5% or higher) and commercially available spherical nickel (purity 99.5% or higher) were weighed so that the atomic ratio of lanthanum to nickel was 1:5, and the mixture was placed in a water-cooled copper crucible. A homogeneous button-shaped LaNi ₅ was produced by arc melting in an argon atmosphere.
Also, commercially available granular calcium (purity 99.3% or more)
Commercially available spherical nickel (purity 99.5% or higher) was weighed so that the atomic ratio of calcium to nickel was 1:5, placed in a carbon crucible, and melted under 40kHz high frequency in an argon atmosphere.

The alloy thus obtained was ground into an alloy powder of about 40 μm or less in a dry box in an argon stream. Next, about 6 g of LaNi ₅ was pressurized and filled from one side of the foamed nickel plate serving as the active material support, and then about 4 g of CaNi ₅ was pressurized from the other side, and this was applied at a rate of about 200 kg/cm. After pressurizing at a pressure of ² , in a vacuum electric furnace to a vacuum degree of 10 ^-5 to ^{10 -6} Torr,
It was sintered at a sintering temperature of 950°C and a sintering time of 2 hours to obtain a sintered porous body of alloy powder. The foam metal used here has a size of 5 cm x 5 cm and a thickness of
It is 2.0mm.

The above electrode is designated as a. As a comparative example, electrode b was manufactured using LaNi ₅ alone as the hydrogen storage alloy under the same conditions, and electrode c was manufactured using CaNi ₅ alone.

Next, each of these electrodes was used as a negative electrode, and a known nickel oxide electrode was used as a positive electrode, and each electrode was immersed in an alkaline electrolyte to construct a battery. FIG. 1 is a temperature characteristic diagram of the discharge capacity (Ah/g) of each hydrogen storage electrode. As is clear from this figure, compared to conventional batteries, the battery using the negative electrode according to the present invention has
The temperature dependence of discharge capacity is small, so it can be used in a wide temperature range. Further, in FIG. 1, the discharge capacity of electrode a does not take the intermediate value between b and c as in the conventional case at each temperature, but shows a value higher than the intermediate value. This is thought to be because the hydrogen atoms in the alloy, which were difficult to dissociate in the case of a single alloy, became easier to discharge due to the influence of the other alloy, which was more likely to dissociate, resulting in an increase in capacity.

In addition, in a simple mixture of alloy particles of a plurality of compositions, cracks occur in various parts due to differences in expansion between each particle, resulting in cracking and extremely shortening the life of the electrode. Furthermore, the electrical contact resistance increased, the polarization increased, the discharge potential decreased, and the electrode performance was significantly worse than that of the present invention.

In addition, instead of the electrode formation method using the sintering method described in the example, a paste method was used, that is, a fine alloy powder was mixed with about 10% by weight of fluororesin, the mixture was filled into a nickel foam metal, and after pressurizing, For electrodes formed by a method of heat treatment for about 1 hour at about 300°C, which is slightly higher than the melting point of fluororesin, in an argon gas stream, the discharge capacity of the CaNi ₅ electrode was slightly improved compared to the characteristics shown in Figure 1. The capacitance of the electrodes using CaNi ₅ and LaNi ₅ increased slightly, but the effect of expanding the usable temperature range was exactly the same.

FIG. 2 shows a schematic diagram of an example of a hydrogen storage electrode formed in an integrated multilayer structure. 1 is a first hydrogen-absorbing alloy powder sintered body, and 2 is a second hydrogen-absorbing alloy powder sintered body, which are firmly integrated and bonded together with a skeleton 3 of nickel foam metal. Furthermore, the interface between the two types of alloys is not clearly defined, but rather gradually changes from one alloy composition to the other alloy composition.

In this way, by integrating multiple hydrogen storage alloys into a multilayer structure, we can improve the temperature dependence of discharge capacity and expand the operating temperature range without impairing the characteristics of each element. It can be achieved.
This property is the result of an effect that cannot be obtained simply from the average value of the properties of each base alloy, and the reason is that the electrolyte concentration, components, and other charge/discharge conditions are determined. Under the ambient temperature conditions, there is a causal relationship between the ease of charging and discharging and the hydrogen storage and desorption properties, and when several types of alloys are integrated, it is possible to find an alloy that is easy to charge and discharge that meets the conditions. This is thought to be because even other alloys that do not meet the conditions function as hydrogen inlets and outlets, making charging and discharging easier without impairing the theoretical hydrogen storage capacity.

Here, the pressure (100-300Kg/ ^cm2 ) and temperature (900-1200℃) in the sintering method when forming an integrated multilayer structure, the amount of synthetic resin (10-20%) in the paste method, etc. Heat treatment temperature (200~350
℃) can be determined to an optimal value depending on the type of hydrogen storage alloy and the amount of filling.

Furthermore, as a result of examining the charge/discharge cycle life characteristics of a battery using the hydrogen storage electrode of the present invention, it was found that the life span was improved by about 10% compared to conventional batteries. This is because in single alloys, bonding and destruction between particles caused by expansion and contraction of the electrode due to hydrogen absorption and release are directional, and as a result, the physical strength of the electrode decreases as the number of cycles increases. This seems to be because, in contrast to the increase in electrical resistance, in the case of the electrode of the present invention, alloys with different characteristics acted in a direction to mutually relieve stress and strain.

Effects of the Invention As described above, the present invention can provide a battery that can be used over a wide range of temperatures and can be used in a temperature range that is not possible with hydrogen storage electrodes using only a single alloy. can.

[Brief explanation of drawings]

FIG. 1 is a temperature-dependent characteristic diagram of discharge capacity of various hydrogen storage electrodes, and FIG. 2 is a schematic diagram of an integrated multilayer structure electrode. 1, 2...Hydrogen storage alloy powder sintered body having mutually different properties, 3...Structure of foamed metal.

Claims (1)

[Claims] 1. A hydrogen storage electrode configured into a multilayer structure in which a plurality of hydrogen storage alloys having mutually different hydrogen dissociation equilibrium pressures are layered in parallel to an electrode support.