JP2982195B2 - Manufacturing method of battery electrode - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a battery electrode using a hydrogen storage alloy that electrochemically stores and releases hydrogen.

2. Description of the Related Art Among various power sources, as storage batteries, lead storage batteries and alkaline storage batteries typified by nickel-cadmium storage batteries are widely used.

In recent years, expectations for high energy density have increased, and attention has been paid to alkaline storage batteries using a hydrogen storage alloy that reversibly stores and releases hydrogen.

The hydrogen storage alloy electrode used for this can be used to construct a battery with the same handling as cadmium and zinc, etc., because the actual dischargeable capacity density can be larger than cadmium, and there is no deformation like zinc and no dendrite formation. It is promising as a high energy density, long life, non-polluting negative electrode for alkaline storage batteries.

As the hydrogen storage alloy electrode, a sintering method in which a part of the hydrogen storage alloy is pulverized and sintered is known, but mainly a punching metal, an expanded metal, a foamed metal as a conductive core material, A non-sintering type, such as a paste type in which a hydrogen storage alloy powder is applied to a metal fiber or the like in the form of a paste or filled, or a pressure type in which pressure molding is performed by a press or the like, is employed.

Normally, the hydrogen storage alloy electrode is subjected to a heat treatment for homogenization of the hydrogen storage alloy obtained by melting, and further made into a fine powder having a particle diameter of 100 μm or less by mechanical or hydrogen gas storage / release. This is used as an electrode by a non-sintering method such as a paste method or a pressure method, and this is used as a negative electrode. I do.

One of the problems with the hydrogen storage alloy electrode obtained in this way is that, by repeating charge and discharge of the battery, specific elements constituting the hydrogen storage alloy are partially eluted into the electrolyte solution, causing a short circuit inside the battery. This causes the catalyst characteristics of the alloy to decrease, causing an increase in the internal pressure of the battery, making it impossible to perform quick charge characteristics, and further reducing the life of the battery. For example, an MmNi _5-x M _x- based alloy (M = Mn, A) based on rare earth and nickel known as a hydrogen storage alloy electrode material
l, Co, Cu, etc.), the elution of Mn, Co is known. Conventionally, a powder or electrode of a hydrogen-absorbing alloy is left in a hot alkali for a certain period of time to treat the eluted material in advance to form a battery with the purpose of preventing the later elution after the battery is formed from the alloy constituent elements. That had been proposed. However, the elution is still insufficient even after the alkali treatment, and there has been a demand for a solution.

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

In view of the above problems, an object of the present invention is to provide a high-performance and 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 produces a spherical hydrogen storage alloy containing at least Mn or Co having a particle diameter of 20 to 100 μm by a super-quenching method, and this spherical alloy is used in a state of particles or an electrode. It is characterized in that it is left in an alkaline solution, preferably in a hot alkaline solution for a certain period of time after any of the processing, and is used as an electrode for a battery.

Effect The present invention provides the above-described method, in which the metal composition is the same even when the electrode is manufactured or when the battery is configured to perform charge / discharge, even though the alloy composition is the same, the specific metal element that has conventionally eluted from the hydrogen storage alloy is almost eluted. And extremely stable performance can be maintained for a long period of time.

The reason for this is that the conventional method lacked the homogeneity of the alloy and sometimes caused segregation in the alloy, but this was probably due to the rapid quenching and the formation of spherical alloy particles. And the formation of segregation was suppressed.

As a means for adjusting the ultra-quenched and spherical alloy particles, the raw material for alloy preparation is heated and melted, and the molten metal is introduced into a disk or the like rotating at a high speed, and the ultra-quenched spherical particles are centrifugally exerted by the disk. Either a centrifugal spraying method for obtaining an alloy powder or a gas spraying method obtained by blowing a high-pressure inert gas onto the molten metal is preferable.

In addition, 20-100 prepared by the rapid quenching method
Spherical hydrogen storage alloys with a micron particle size have extremely high homogeneity of the alloy particles themselves because the molten metal solidifies instantaneously during melting, so even if the heat treatment process for homogenization that had been performed so far was omitted. It has been found that excellent performance can be obtained. Similarly, as a hydrogen storage alloy constituting an electrode, a pulverizing step by a mechanical pulverization method and a hydrogen gas activated pulverization method has been required so far, but according to the present invention, Advantages can be obtained, such as the ability to adjust the particle size at the time of alloy preparation and the elimination of a pulverizing step.

Examples Hereinafter, examples of the present invention will be described.

Commercially available hydrogen storage alloys such as Mm (Misch metal), Ni,
Each raw material of Co, Mn, Al is weighed to a certain composition ratio, melted by high frequency induction heating melting furnace, and the resulting molten metal is ultra-quenched and spherical MmNi _3.8 Co _0.5 Mn _0.4 Al _0.3 alloy by centrifugal spray method. Manufactured. That is, in an inert gas, the molten metal was dropped little by little from a crucible containing the molten metal on a disk rotating at a high speed of about 20,000 rpm to obtain a powder. Examination of the alloy powder obtained in this way revealed that very fine spherical particles with an average particle size of 60 microns were formed, and the alloy structure and elemental analysis showed extremely good homogeneity and properties as a hydrogen storage alloy. Was also excellent.

The alloy particles thus obtained were subjected to a hot alkali treatment. That is, an aqueous solution of potassium hydroxide having a specific gravity of 1.30 is heated to 80 ° C.
And soaked for 5 hours, and then washed with water.

Next, the alloy particles are mixed and stirred with a dilute aqueous solution of carboxymethyl cellulose (CMC) to form a paste, and as an electrode support, an average pore size of 150 microns and a porosity of 95 are used.
%, And filled into a foamed nickel sheet having a thickness of 1.0 mm. This was dried at 120 ° C., pressed with a roller press, and further coated with a fluorine resin powder on the surface to obtain a hydrogen storage alloy electrode. This is one embodiment of the present invention and is referred to as electrode A.

In order to compare the characteristics of this electrode, an electrode according to a conventional method was also manufactured. That is, as a conventional method, the same high-frequency induction heating and melting furnace was used to obtain the same MmNi _3.8 Co _0.5 Mn
_The alloy was melted so as to have a composition of _0.4 Al _0.3 , and the melt was cast by an ordinary method to produce an alloy lump. Next, the alloy was heat-treated in a vacuum, and then mechanically pulverized by a ball mill so that the average particle size became 60 μm. The alloy powder thus obtained is subjected to the same thermal alkali treatment as above,
Thereafter, electrodes were formed in the same manner. This is referred to as an electrode B as a conventional method.

Using these electrodes as negative electrodes, disposing a nickel oxide electrode with excess electric capacity at the counter electrode, using an aqueous solution of potassium hydroxide with a specific gravity of 1.30 for the electrolyte, and regulating the capacity with a hydrogen storage alloy negative electrode under conditions where the electrolyte is abundant Charging and discharging were performed in the open system. Charging is 100mA per 1g of alloy x 4 hours, discharging is 1g of alloy
The terminal voltage was set to 0.8 V at 50 mA per unit.

As a result, the electrode A maintained an almost constant discharge capacity despite the long-term charge / discharge test up to 300 cycles, and confirmed excellent performance stability. One electrode B
The discharge capacity in the initial cycle was almost the same as that of the electrode A, but the discharge capacity decreased with the lapse of the charge / discharge cycle, although very little from about 30 to 50 cycles. After 300 cycles, each cell's electrolyte was sampled and quantitative analysis of metal elements was performed.Mn and Co, which were considered to be eluted from the alloy, were detected from the electrolyte composed of A and B electrodes. However, electrode A is 1/1 of Mn with respect to electrode B.
4. Co was a low value of 1/22. After 300 cycles, the electrode was disassembled and the hydrogen storage alloy was analyzed. No significant change was observed in electrode A, but in electrode B, the alloy surface became considerably rich in Ni, and alloy constituent elements were separated. As a result, many changes in the state to oxygenates and hydroxides were observed.

Next, the results of configuring a sealed nickel-hydrogen storage battery using these electrodes 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, and lead plates were attached at two predetermined positions. Then, in combination with the positive electrode and the separator, it is spirally formed into three layers in a cylindrical shape.
It was 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, 30 g / l of lithium hydroxide was dissolved in an aqueous solution of potassium hydroxide having a specific gravity of 1.20 and used. This was sealed to obtain a sealed battery. This battery has a nominal capacity of 2.5 Ah under the positive electrode capacity regulation. In this sealed battery, a battery constituted by the electrode A of the hydrogen storage alloy electrode is referred to as a battery A, and a battery constituted similarly by the electrode B is referred to as a battery B.

The results of making 10 batteries each and evaluating them by a normal charge / discharge cycle test will be described.

Charge up to 150% at 1C (1 hour rate), 0.5C at discharge
The charge / discharge cycle at 20 ° C. was repeated at a final voltage of 1.0 V (2 hours). As a result, both batteries A and B achieved a discharge capacity of approximately 2.6 Ah at the beginning of the cycle, but charge-discharge tests up to 500 cycles showed that battery B had two internal short circuits. Was. This phenomenon was not observed in battery A. In addition, the average discharge capacity after 500 cycles also maintained 2.6 Ah for Battery A, while the battery B showed a decrease in capacity to 2.3 Ah.

As another test, after fully charging batteries A and B at 20 ° C, 60 ° C
At 2 ° C. for 2 weeks, and then the discharge capacity was further examined at a temperature of 20 ° C. to evaluate the high-temperature storage characteristics.

As a result, in battery A, the discharge capacity before the test was on average
45% capacity was maintained. In battery B, 3 out of 10 batteries have completely zero capacity, and the remaining 8 batteries have an average capacity of 23%,
Obviously, Battery A was excellent in storage performance.

In this example, an alloy having a CaCu _5- type structure based on a rare earth and nickel as a hydrogen storage alloy and added with elements such as Mn, Al, Co, and Cu was described. The extent of dissolution may vary depending on alloy species, such effect was obtained also for such AB ₂ type Laves phase alloys such as ZrMn _0.4 Cr _0.4 Ni _1.2.

As a method for producing the hydrogen storage alloy, either a centrifugal spray method or a gas spray method is preferable. And hydrogen storage alloys are particularly based on rare earths and nickel, with Mn, A
This is particularly effective in the case of an alloy having a CaCu _5- type structure to which elements such as l, Co, and Cu are added.

When this electrode was used, the same effect was obtained in an open type battery.

Effect of the Invention As described above, the method for manufacturing a battery electrode of the present invention makes it possible to prevent the elution of a specific metal element that has conventionally eluted from a hydrogen storage alloy, and provides a high performance and long life hydrogen storage. An alloy electrode and a battery using the same can be provided.

────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tsutomu Iwaki 1006 Kazuma Kadoma, Kazuma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (56) References JP-A-1-132048 (JP, A) JP-A-62- 294107 (JP, A) JP-A-1-152204 (JP, A) JP-A-1-130468 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) H01M 4/38 H01M 4 / 24-4/26

Claims (3)

(57) [Claims] 1. A hydrogen storage alloy containing at least Mn or Co is converted into a spherical powder by a super-quenching method, and the powder is maintained in a spherical shape, or after being processed into an electrode, in an alkaline solution, or A method for producing an electrode for a battery, comprising using a hydrogen storage alloy left in a hot alkaline solution as an electrode. 2. The method for producing an electrode for a battery according to claim 1, wherein the hydrogen storage alloy is produced by a centrifugal spraying method or a gas spraying method. 3. The method according to claim 1, wherein the spherical alloy has a particle size of 20 to 100 microns.