JPS6231947A - Manufacture of hydrogen occlusion electrode - Google Patents

Abstract

PURPOSE:To increase the initial performance and reduce the manhour of production process by performing the hydrogenation and micronization of alloy at the same time regardless of high temperature heat treatment. CONSTITUTION:For example, materials are weighed so as to constitute a specified composition and placed in a crucible, then melted to prepare an alloy. The alloy is placed in a vacuum heat treating furnace and heat-treated under a specified vacuum condition at a specified temperature for a specified time. The alloy is put into a pressure resistant, sealed container, and hydrogen is occluded into the alloy, then hydrogen is discharged from the alloy. This cycle is repeated several times until the alloy is crushed to fine powder, then hydrogen is removed to obtain a hydrogenated alloy powder. The fine alloy powder is immersed in a specified solution, then washed and dried. The alloy powder is mixed with a binder, and the mixture is press-filled into a foam metal, and dried to obtain a hydrogen occlusion electrode.

Description

[Detailed description of the invention] Industrial applications The present invention reversibly stores hydrogen as a negative electrode material.

The present invention relates to a method of manufacturing a hydrogen storage electrode using a hydrogen-emitting alloy, and provides a pollution-free alkaline storage battery with high energy density.

BACKGROUND OF THE INVENTION Since conventional batteries such as lead-lead oxide batteries and nickel-cadmium batteries have oxide electrodes, they have a relatively low energy density per unit of weight and volume. Therefore, in order to improve the energy storage capacity, an electrode has been proposed in which a hydrogen storage alloy that reversibly stores and releases hydrogen is used as a negative electrode, and the stored hydrogen is used as an active material. For example, in Japanese Patent Application Laid-Open No. 51-13934, as a hydrogen storage alloy,
La i5. Negative electrode materials such as LaCo5 are shown.

Furthermore, other metals, Ni, and C are added to this La portion.
3. Multi-component alloys in which other metals are partially substituted have also been proposed, but these have issues that need to be improved, such as discharge characteristics at high temperatures and cycle life. On the other hand, since a hydrogen storage alloy containing hydrogen as an active material cannot be used in its lump form, it must be mechanically pulverized into a fine powder that can pass through 400 meshes (37 μm or less). This manufacturing process required a lot of time.

Problems to be Solved by the Invention Among the above alloys, multi-component alloys in which La is replaced with other metals, or Ni and Co are replaced with other metals, may vary depending on the melting conditions. may create strain inside the alloy, or may be difficult to form an alloy phase with excellent homogeneity. This appears in the flatness of the hydrogen dissociation pressure,
The pressure gradient when dissociating hydrogen increases. When this phenomenon is used as a negative electrode, it also affects the voltage flatness of discharge performance, resulting in a problem that the discharge performance deteriorates. Furthermore, when an electrode is constructed using the multi-component alloy mentioned above, the metal in the heterogeneous portion may dissolve into the alkaline aqueous solution (electrolyte) due to repeated charging and discharging of the battery, or the dissolved metal may precipitate. . By repeating this melting and precipitation, the metal passes through the separator, causing a slight short circuit between the positive electrode and the negative electrode, which significantly deteriorates the battery characteristics. Therefore, it is an object of the present invention to completely eliminate this heterogeneous portion, improve discharge characteristics, prevent performance deterioration due to minute short circuit phenomena, and manufacture a hydrogen storage electrode with a long cycle life.

However, by repeating charge/discharge cycles, the alloy particles become even finer, and new surfaces appear even though the alloy surface has been modified in advance, causing dissolution in the electrolyte and separator Surface precipitation phenomena may occur. Therefore, problems may occur when the cycle life is further extended. At the same time, this hydrogen storage alloy is pressurized and integrated into an electrode support to create a negative electrode, and a positive electrode and separator are used to construct a battery. 1. It requires a lot of labor and time, which leads to an increase in manufacturing costs. A simpler manufacturing method was desired.

Therefore, an object of the present invention is to simultaneously hydrogenate and pulverize an alloy, regardless of the presence or absence of high-temperature heat treatment, to improve the initial properties and reduce the number of steps in the manufacturing process.

Means for Solving the Problems The present invention provides hydrogen storage alloys that reversibly store and release hydrogen, and alloys containing any of the aforementioned alloys that are heat-treated in a temperature range of 950 to 1260''C. A process in which hydrogenation treatment and pulverization are performed multiple times at the same time,
After degassing the hydrogen, surface treating the hydrogenated alloy fine powder with an alkaline aqueous solution (alkali treatment), and then binding the hydrogenated alloy fine powder which has been at least washed with water and dried. This is a method for manufacturing a hydrogen storage electrode, which comprises a step of integrating the hydrogen storage electrode with the agent into an electrode support under pressure.

Furthermore, the hydrogen storage alloy and the high-temperature heat-treated alloy are hydrogenated and pulverized by hydrogenation at the same time, and then the hydrogenated fine powder is integrated with a binding agent 6 into an electrode support under pressure. The present invention relates to a method for manufacturing a hydrogen storage electrode, which comprises a step of impregnating the integrated electrode substrate with an aqueous alkali solution (alkali treatment), and then performing at least washing with water and drying.

Function LaNi5 and LaCo5 here have a B5 type open intermetallic compound structure. However, La, Sui, C.

When forming a so-called multi-element alloy in which other metals are substituted, the alloy also contains inhomogeneous parts when melted, and the hydrogen dissociation pressure does not show a constant curve, but changes with a somewhat large slope. do. This gradient of hydrogen dissociation pressure also affects electrode performance (stability of discharge potential). At the same time, problems arise, such as the fact that this heterogeneous (distorted) portion tends to dissolve into the electrolyte.

This dissolution and precipitation of metal has a great effect on the cycle life, and is a problem in manufacturing alkaline storage batteries of excellent quality. The degree of this problem becomes even greater in high-temperature conditions, and improvements are needed from a practical standpoint.

Therefore, in the high-temperature heat treatment process, we further improve the homogeneity during melting, significantly reduce the internal strain and inhomogeneous parts of the alloy, and furthermore, by applying alkali treatment, we are able to improve the melting properties of easily melted metals on the surface of the alloy powder. By removing in advance and modifying the alloy surface with OH groups,
Dissolution in the electrolyte will be significantly reduced. However, Mitsuru.

Due to the discharge cycle, there is a possibility that it will become even finer, and there is also a risk that some of it will dissolve or precipitate.
In addition to simplifying the crushing process, by using a finely powdered alloy that has been hydrogenated in advance (in a degassed state), the mutual effect of these factors results in excellent characteristics including initial discharge performance, and also increases cycle resistance at high temperatures. It is possible to manufacture an alkaline storage battery using a long-life hydrogen storage electrode as a negative electrode.

Example The present invention will be explained in detail below.

Commercially available Mm (Mitshu Metal i La: 60.06
:26, Nd near, Pr other about 28), Ni
(purity of 99 cm or more) and Co (purity of 99 cm or more) were weighed to a certain composition ratio, placed in a water-cooled copper crucible, and heated and melted in an arc melting furnace to form MmNi5Cjo2.
An alloy was produced. Next, this alloy was placed in a vacuum heat treatment furnace and maintained at a vacuum of 10 Torr and a temperature of 1000° C. for 7 hours to perform high temperature heat treatment.

This alloy sample is placed in a pressure-resistant sealable container, hydrogen is applied to absorb hydrogen, and after completion of the operation, hydrogen is released several times to crush the alloy into fine particles (30 μm or less) and degas it. Hydrogen is removed to form a hydrogenated fine alloy powder, and this hydrogenated fine powder is heated to 30% of the temperature of 50'C.
After being immersed in a KOH aqueous solution for 24 hours, the electrode was washed with water, dried, and then filled with a binder such as polyvinyl alcohol into a foamed metal under pressure, and then dried, and the resulting hydrogen storage electrode was used as a human body.

The above-mentioned hydrogenated alloy fine powder is prepared, and the hydrogenated fine powder is pressurized and filled into a foamed metal together with a binder such as polyvinyl alcohol.
A hydrogen storage electrode manufactured by immersing in a 0% KOH aqueous solution for 24 hours, washing with water, and drying was designated as B.

For comparison, as a conventional method, a hydrogen storage electrode that does not include all steps of heat treatment, hydrogenation treatment, and alkali treatment was designated as C. A nickel oxide electrode made by a known method was used as a positive electrode, which is a counter electrode, and a cylindrical (size AA size) alkaline storage battery was constructed with a separator interposed therebetween. Charging current 0.1
C (10 hour rate) discharge current was 0.2 C (6 hour rate), the amount of charged electricity was 130% (overcharge) of the positive electrode capacity, and the discharge end voltage was 1.OV. The negative electrode capacity was 1.3 times the positive electrode capacity, and the positive electrode capacity was 2 μh, and tests were conducted according to the positive electrode rule. Battery cycle life test temperature is 46°
The capacitance was measured at 20'C. The initial discharge characteristics were determined at the 6th cycle, and the discharge potentials were compared. The cycle life was determined by measuring the discharge capacity every 10 cycles.

Figure 1 shows the discharge performance in the second charge/discharge cycle. Battery C has a lower discharge voltage and a smaller discharge capacity than the other batteries B. and B are the discharge voltage and the capacity is 1OA.

There is almost no difference. The reason why Human B is superior to C is that the hydrogen dissociation pressure of Human B is more flat and higher than that of C. Since the electrodes are sufficiently activated, hydrogen storage progresses efficiently, and a sufficient hydrogen storage capacity can be secured. In this respect, battery C has poor hydrogen storage efficiency and cannot secure sufficient capacity, and its capacity decreases due to the negative electrode rule. In this respect, first, the heat treatment effect and the hydrogenation treatment effect appear. In terms of the manufacturing process, the simplification of the manufacturing process significantly reduces manufacturing man-hours, contributing to lower battery costs. If the degree of cost reduction is calculated from the number of man-hours, it can be saved approximately. It is possible to reduce electrode manufacturing costs by 20 to 30%.

Figure 2 shows the cycle life at 46°C. The capacity of battery C decreased to 60% of the initial capacity (6 cycles) after 50 cycles.

This is clearly a decrease in capacity due to a micro-short circuit phenomenon (metal deposition and falling off) within the battery, which can also be seen from the behavior of the charging voltage. In addition, there is almost a large difference between the electrodes M and B, and although the test has been carried out up to 100 cycles, there is hardly any decrease in capacity. When left for a certain period of time, the capacity drop of C is greater than that of humans and B, so it is thought that the self-discharge of electrode C is greater. On the other hand, the electrode of type B has excellent characteristics from the viewpoint of self-discharge. The effect of alkali treatment is seen in the improvement of this property.

When an alloy that is not subjected to high-temperature heat treatment is subjected to both hydrogenation treatment and alkali treatment, the initial discharge performance is poor. In particular, the discharge voltage is low from the middle to the end of the charging and discharging cycles. There are some areas where the homogeneity of the alloy is not good, and there are large gaps in the flatness of the hydrogen dissociation pressure. However, it exhibits much better cycle life characteristics than the C electrode.

Due to hydrogenation, the degree of further fragmentation of the alloy powder over the cycle life is small, so it is thought that there is little promotion of partial dissolution precipitation due to exposure of new and unmodified surfaces of the alloy. . Here, we have described an example in which a heat-treated alloy was hydrogenated and subjected to alkali treatment, but as mentioned earlier, by using both hydrogenation and alkali treatment on an unheat-treated alloy, the alloy pulverization process and hydrogen This saves the time required for conversion and reduces the number of manufacturing steps. Therefore, by hydrogenating an unheated or heat-treated alloy in advance, activation by hydrogenation and pulverization can be performed simultaneously, which greatly contributes to improving initial performance and simplifying the manufacturing process. In the hydrogenation process,
After absorbing hydrogen, it is dehydrogenated in vacuum at a high temperature (200'C or higher), and then the hydrogenated alloy powder is taken out and used as an electrode sample, allowing safe work.

The heat treatment temperature range will be explained using the phase diagram of La (rare earth) and N1 in FIG. 3.

Below 950'C, the melting point corresponds to the alloy phase of LaNi to LaNi 2, and the melting point of LaNi 5 is 1325°C, so intermetallic diffusion is not sufficient in AB5 type alloys similar to this alloy system. As a result, homogenization has progressed.
It is difficult to heat, and the effect of heat treatment is also small. On the other hand, at temperatures above 1250°C, the melting point decreases to 13A-1246°C when LaNi 5 transitions to the Ni IJ notch, which is not preferred in alloy systems similar to LaNi 5. Furthermore, if a metal with a high vapor pressure is added, there may be problems such as a shift in the composition of the alloy, so the appropriate heat treatment temperature is 1250° C. or lower.

In particular, the optimum heat treatment temperature for hydrogen storage alloys mainly composed of rare earth metals and N1 is 950 to 1150°C. On the other hand, the optimum heat treatment temperature for a hydrogen storage alloy mainly composed of T1 and Ni is 1050 to 1250'O. Although the heat treatment conditions differ depending on the type of alloy as described above, the appropriate temperature range for the heat treatment conditions included in a part of the present invention is 960 to 1250'C.

As described above, the present invention has a long cycle life at high temperatures, excellent initial discharge characteristics, and is highly effective against self-discharge.Furthermore, the manufacturing process is simplified, resulting in lower costs. The present invention provides a method for manufacturing a hydrogen storage electrode that is highly practical in that it can be reduced in size.

[Brief explanation of the drawing]

14,,-7 Figure 1 is a comparison of the early discharge characteristics of batteries using the present invention and conventional hydrogen storage electrodes, and Figure 2 is a comparison of the cycle life of batteries using the present invention and conventional hydrogen storage electrodes. FIG. 3, which is a diagram comparing the characteristics, is a phase diagram of La and Ni alloys. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure 0 0.5 /, θ
t, s z,. (Electric 7 volume! (hah) Fig. 2 2.0 --; Go -----------------\\\
B ゝ＼ , J゛・, 4= Figure 3 N + (wt%)

Claims (2)

[Claims] (1) A hydrogen storage alloy that reversibly stores and releases hydrogen, and an alloy containing any of the aforementioned alloys that have been heat-treated in a temperature range of 950 to 1,250°C, are subjected to hydrogen storage and release multiple times. and a step of surface-treating the fine powder of the hydrogenated alloy with an alkaline aqueous solution (alkali treatment) after degassing the hydrogen, and then at least washing and drying the hydrogen-treated alloy. 1. A method for producing a hydrogen storage electrode, comprising the step of pressurizing and integrating fine powder of a chemical alloy into an electrode support together with a binder. (2) Hydrogen storage alloys that reversibly absorb and release hydrogen and heat-treated said alloys are simultaneously hydrogenated and finely pulverized, and then this hydrogenated fine powder is added to an electrode support together with a binder. A method for manufacturing a hydrogen storage electrode, comprising a step of pressurizing the integrated electrode substrate, a step of impregnating the integrated electrode substrate with an alkaline aqueous solution (alkali treatment), and then a step of at least washing with water and drying.