JPH03216959A - Manufacturing method for battery electrodes - Google Patents

Abstract

PURPOSE:To obtain an electrode for a battery with high performance and a long life by manufacturing spherical hydrogen storage alloy powder by the extremely quick cooling method, and leaving it in a hot alkaline solution as it is or after it is machined into an electrode to obtain the electrode made of a hydrogen storage alloy. CONSTITUTION:Spherical hydrogen storage alloy powder preferably with the grain diameter 20-100mum is manufactured by the extremely quick cooling method, the spherical alloy powder is left for a fixed period in an alkaline solution, preferably a hot alkaline solution, in the grain state or after it is machined into an electrode, and it is used as the electrode for a battery. The elution of a specific metal element from the hydrogen storage alloy can be prevented, and the hydrogen storage alloy electrode with high performance and a long life and the battery using it are obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a battery electrode using a hydrogen storage alloy that electrochemically absorbs and releases hydrogen.

BACKGROUND OF THE INVENTION Among various power sources, lead-acid batteries and alkaline batteries, such as nickel-cadmium batteries, are widely used as storage batteries.

In recent years, expectations for high energy density have increased,
Therefore, attention has been focused on alkaline storage batteries that use hydrogen storage alloys that reversibly absorb and release hydrogen.

The hydrogen storage alloy electrode used for this purpose can be used in batteries in the same manner as cadmium or zinc, has a higher actual dischargeable capacity density than cadmium, and does not deform or form dendrites like zinc. It is expected to be used as a negative electrode for alkaline storage batteries, which has high energy density, long life, and is non-polluting.

This hydrogen storage alloy electrode is partially produced by pulverizing a hydrogen storage alloy and sintering it. However, it is mainly produced using punched metal, expanded metal, or foamed metal as a conductive core material. Non-sintering methods have been adopted, such as a paste method in which metal fibers are coated or filled with hydrogen-absorbing alloy powder in the form of a paste, and a pressure method in which pressure molding is performed using a press or the like.

Usually, this hydrogen storage alloy electrode is made by subjecting the hydrogen storage alloy obtained by melting to heat treatment for homogenization, and then mechanically or by absorbing and releasing hydrogen gas to form a fine powder having a particle size of 100 microns or less. This is used as an electrode using a non-sintering manufacturing method such as a paste method or a pressurization method, and this serves as a negative electrode. Together with a positive electrode such as nickel oxide, a separator made of non-woven fabric such as polyolefin, and an alkaline electrolyte, a sealed or open alkaline storage battery is constructed. do.

One of the problems with the hydrogen storage alloy electrode obtained in this way is that due to repeated charging and discharging of the battery, some of the specific elements that make up the hydrogen storage alloy will be eluted into the electrolyte, causing a The catalytic properties of the alloy may deteriorate, causing an increase in the internal pressure of the battery, making rapid charging characteristics impossible, and even shortening the life of the battery. For example, M m N 1 s - w based on rare earth and nickel, which is known as a hydrogen storage alloy electrode material.
M x alloy (M = M nl A L C 01
Cu, etc.), it is known that Mn and Go elute. Conventionally, after constructing a battery using this alloy constituent element, the powder or electrode of the hydrogen storage alloy is left in a hot alkali for a certain period of time to pre-treat the eluted materials in order to prevent later elution, and the battery is constructed. That was proposed. However, even after this treatment in alkali, the elution is still insufficient, and a solution to this problem has been desired.

Problems to be Solved by the Invention An important problem is to prevent the elution of specific metal elements from the hydrogen storage alloy during the manufacturing process of the hydrogen storage alloy electrode and during the operation of a battery using this electrode.

In view of the above problems, an object of the present invention is to provide a high-performance, long-life hydrogen storage alloy electrode and a method for manufacturing a battery electrode using the same.

Means for Solving the Problems The present invention involves producing a spherical hydrogen storage alloy having a particle size of 20 to 100 microns by an ultra-quenching method, and then applying an alkali to the spherical alloy either in the particle state or after processing it into an electrode. It is characterized by being left in a solution, preferably a hot alkaline solution, for a certain period of time, and then used as an electrode for a battery.

Effect The present invention uses the method described above to reduce the elution of specific metal elements that were conventionally eluted from hydrogen storage alloys even when the composition of the alloy is the same when manufacturing electrodes or when charging and discharging a battery. It is possible to maintain extremely stable performance for a long period of time.

The reason for this is that the homogeneity of the alloy was insufficient in the conventional method, and in some cases segregation was observed in the alloy, but this was probably due to the ultra-quenching and spherical alloy particles, which caused the chemical change on the particle surface. This is due to improved physical stability and suppression of segregation and other formations.

The method of ultra-quenching and preparing spherical alloy particles is to heat and melt the raw materials for alloy creation, introduce the melt into a disk rotating at high speed, and use the centrifugal force of the disk to ultra-quickly cool the material. Either a centrifugal spraying method for obtaining spherical alloy powder or a gas spraying method for obtaining spherical alloy powder by spraying high-pressure inert gas onto the molten metal is preferred.
Spherical hydrogen storage alloys with a particle size of 0 microns solidify instantly during melting, so the alloy particles themselves are extremely homogeneous, and the heat treatment process for homogenization that was previously performed can be omitted. It was also found that excellent performance could be obtained. Similarly, the hydrogen storage alloy that constitutes the electrode has conventionally required a pulverization process using a mechanical pulverization method or a hydrogen gas activated pulverization method, but according to the present invention, the required particle size can be adjusted at the time of alloy production. There are also advantages such as eliminating the need for

Example Examples of the present invention will be described below.

Mm (misch metal) commercially available as a hydrogen storage alloy,
Each raw material for NL COI Mnl Al is weighed to a certain composition ratio, melted in a high-frequency induction heating melting furnace, and the resulting molten metal is ultra-quenched using a centrifugal spray method to form spherical MmN i 3. own cos. sMns. 4A 11
1.3 alloy was produced. In other words, the molten metal is poured in small amounts from the crucible containing the molten metal in an inert gas at approximately 20.00 Orp.
The mixture was dropped onto a disk rotating at high speed at m to obtain a powder.

When the alloy powder thus obtained was examined, it was found that it formed very fine spherical particles with an average particle size of 60 microns, and the alloy structure and elemental analysis showed that it had extremely good homogeneity and had properties as a hydrogen storage alloy. was also excellent.

The alloy particles thus obtained were subjected to hot alkali treatment. In other words, a potassium hydroxide aqueous solution with a specific gravity of 1.30 is
It was heated to 0°C and soaked for 5 hours, and then washed with water.

Next, this alloy particle is made of carboxymethyl cellulose (C
Mix and stir with a dilute aqueous solution of MC) to make a paste stick, and use it as an electrode support with an average bore size of 150 microns and a porosity of 9.
A foamed nickel sheet having a thickness of 5% and a thickness of 1.0 mm was filled. This was dried at 120''C and pressurized with a roller press, and the surface was further coated with fluorocarbon resin powder to form a hydrogen storage alloy electrode.This is an embodiment of the present invention and will be referred to as electrode A.

In order to compare the characteristics of this electrode, an electrode was also fabricated using a conventional method. That is, as a conventional method, the same MmN i s.
*co@. sM n@. 4A 1 m. The molten metal was melted to have a composition of S alloy, and the molten metal was cast by a conventional method to produce an alloy ingot. This alloy was then heat treated in a vacuum and then mechanically ground using a ball mill so that the average particle size was 80 microns. The alloy powder thus obtained was subjected to the same hot alkali treatment as before, and then made into an electrode in the same manner.

This is referred to as electrode B as a conventional method.

These electrodes are used as negative electrodes, a nickel oxide electrode with excessive capacitance is arranged as the counter electrode, and a potassium hydroxide aqueous solution with a specific gravity of 1.30 is used as the electrolyte. Charging and discharging was performed in a regulated open system. Charging was carried out at 100 mA for 4 hours per 1 g of alloy, and discharging was carried out at 50 mA per 1 g of alloy until the terminal voltage reached 0.8 V.

As a result, Electrode A maintained a nearly constant discharge capacity despite long-term charging and discharging tests of up to 300 cycles, confirming its excellent stability of performance. On the other hand, for electrode B, the initial cycle discharge capacity was almost the same as electrode A, but from around the 30th to 50th cycle, a decrease in the discharge capacity was observed, albeit very slightly, as the charge/discharge cycles progressed.

After 300 cycles, the electrolyte from each cell was sampled and a quantitative analysis of the metal elements was performed.Mn. Although Co was detected, electrode A was Mn compared to electrode B.
in! /l4, Co had a low value of I/22. Also 3
When the electrode was disassembled after 00 cycles and the hydrogen storage alloy was analyzed, no major change was observed in electrode A, but in electrode B, the alloy surface had a considerable amount of Nf.
In addition, many alloy constituent elements separated and changed into oxides and hydroxides.

Next, the results of constructing a sealed nickel-hydrogen storage battery using these electrodes will be explained. Previous electrode A.
Each B has a width of 3. 3cms length 21cm1
The thickness was adjusted to 0.50 mm, and lead plates were attached to two predetermined locations. Then, in combination with the positive electrode and the separator, it was made into a cylindrical three-layered spiral cane and stored in an SC-sized battery case. As the positive electrode at this time, a well-known foamed nickel electrode was selected and used with a width of 3.3 cm and a length of 16 cm.

In this case as well, lead plates were attached at two locations. Moreover, a polypropylene nonwoven fabric imparted with hydrophilic properties was used for the separator. As the electrolytic solution, 30 g/l of lithium hydroxide was dissolved in an aqueous potassium hydroxide solution having a specific gravity of 1.20.

This was sealed to form a sealed battery. This battery has a nominal capacity of 2.5 Ah due to positive electrode capacity regulations. In this sealed battery, a battery composed of electrode A, which is a hydrogen storage alloy electrode, is battery A1.
A battery similarly configured with electrode B will be referred to as battery B.

The results of making 10 of each of these batteries and performing a normal charge/discharge cycle test will be described.

Charge up to 150% at IC (1 hour rate) and discharge at 0.
End voltage 1.5C (2 hour rate). Ov and repeated charge/discharge cycles at 20°C. As a result A. Both batteries B had a discharge capacity of approximately 2.8Ah at the beginning of the cycle, but after charging and discharging tests up to 500 cycles, internal damage was observed in battery B with two batteries. Ta. This phenomenon was not observed in battery A. Further, the average discharge capacity after 500 cycles was maintained at 2.6 Ah for battery A, while the capacity for battery B decreased to 2.3 Ah.

As another test, battery A. After fully charging B at 20℃, store it at a temperature of 60℃ for 2 weeks, then further charge it at 20℃.
The discharge capacity was examined at a temperature of

As a result, for battery A, the average discharge capacity was 4
5% capacity was maintained. Among batteries B, 3 out of 10 batteries had a capacity of 0, and the remaining 8 batteries had an average capacity of 23%, indicating that battery A was clearly superior in storage performance.

In this example, the hydrogen storage alloy is based on rare earth elements and nickel, and Mn. ALC 01C
An alloy having a CaCus type structure to which elements such as u are added is shown. The degree of elution varies depending on the alloy type, but
Such an effect can be seen, for example, in ZrMns. aCrs. 4N
Similar results were obtained for A B 2 type Laves phase alloys such as i 1.2.

As a method for producing this hydrogen storage alloy, either a centrifugal atomization method or a gas atomization method is preferable. Hydrogen storage alloys are particularly based on rare earths and nickel, with Mnt
C added with elements such as Al+ Co+ Cu
This is particularly effective in the case of alloys having an aCui type structure.

Furthermore, when this electrode was used, similar effects were obtained in open-type batteries.

Effects of the Invention As described above, the method for manufacturing battery electrodes of the present invention makes it possible to prevent the elution of specific metal elements that were conventionally eluted from hydrogen storage alloys, resulting in high performance and long-life hydrogen storage. An alloy electrode and a battery using the same can be provided.

Claims (3)

[Claims] (1) A spherical hydrogen-absorbing alloy powder is produced by an ultra-quenching method, and the hydrogen-absorbing alloy is left in an alkaline solution, preferably a hot alkaline solution, either as a powder or after being processed into an electrode. A method for producing an electrode for a battery, characterized in that the electrode is used as an electrode. (2) The method for producing a battery electrode according to claim 1, wherein the hydrogen storage alloy is produced by either a centrifugal atomization method or a gas atomization method. (3) The method for manufacturing a battery electrode according to claim 1, wherein the particle size of the spherical alloy is 20 to 100 microns.