JPH0763007B2 - Manufacturing method of hydrogen storage electrode - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing a hydrogen storage electrode used as a negative electrode of an alkaline storage battery such as a nickel-hydrogen storage battery.

2. Description of the Related Art Conventionally, electrodes of this type have not yet been put to practical use, but the following method has been proposed as a manufacturing method thereof. That is, a molten metal of a hydrogen storage alloy is produced in an arc melting furnace or a high frequency melting furnace, and is poured into a mold in the case of a high frequency melting furnace to be naturally cooled, or in the case of an arc melting furnace is cooled by water in a copper crucible. After producing the occlusion alloy, the alloy lump is roughly crushed, and then the kneaded product of the powder and the binder finely crushed in a ball mill or the like is applied or filled on the electrode support, and then pressure integration is performed. There is a method of producing a hydrogen storage electrode.

Problems to be Solved by the Invention In such a conventionally proposed manufacturing method, when a hydrogen storage electrode is used as a negative electrode and a sealed nickel-metal hydride storage battery is configured by combining it with a nickel positive electrode, nickel currently in practical use is used.・ Compared to the cadmium storage battery, there was a problem that it was inferior in high-rate discharge characteristics at low temperature and large in self-discharge.

The present invention solves such problems at the same time, by a simple manufacturing method, to improve high rate discharge characteristics at low temperature,
Further, the purpose is to reduce self-discharge.

Means for Solving the Problem In order to solve this problem, the present invention provides a step of cooling a molten metal of a hydrogen storage alloy by a liquid quenching method to produce a thin piece or a thin strip, and a step of forming the thin piece or the thin strip in an inert gas or A step of heat-treating in a vacuum; a step of finely crushing the heat-treated flakes or a ribbon; a step of applying or kneading a kneaded product of the crushed powder and a binder to an electrode support and then drying; It has a step of applying a pressure operation to a desired thickness.

Action This manufacturing method increases the number of homogeneous parts of CaCu ₅ type crystals effective for hydrogen storage and release in hydrogen storage alloys,
Since the flakes or strips are produced, the orientation of the crystals is aligned, and as a result, various battery characteristics are improved. The inhomogeneous phase metal, which is ineffective in absorbing and releasing hydrogen in the hydrogen storage alloy, dissolves after repeated charge and discharge in the alkaline electrolyte or when stored at a relatively high temperature and exists as a metal ion in the electrolyte. As a result, the self-discharge rate of the battery is increased.

Moreover, when an alloy is melted in an arc melting furnace or a high-frequency melting furnace and naturally cooled to produce a hydrogen-absorbing alloy, the orientation of the crystal grains is disordered and, as a result, the hydrogen absorbed in the alloy is electrochemically generated. When a high rate discharge is performed at a low temperature, the diffusion of hydrogen in the solid phase is delayed, the overvoltage increases, and the battery voltage decreases.

From the above, by using a hydrogen storage electrode composed of a hydrogen storage alloy powder having good homogeneity and crystallographically oriented, it is possible to obtain a storage battery having good self-discharge characteristics and excellent low-rate high-rate discharge characteristics. Become.

Examples Hereinafter, the present invention will be described with reference to Examples. The liquid quenching method includes a high-frequency melting part that creates a hydrogen-absorbing alloy melt, and a twin-roll method that rotates at the same high speed as when an amorphous alloy is used to quench the alloy melt (cooling speed 10 ⁴ ~ 10 ⁵ K / sec) was used. Commercially available misch metal Mm
(A mixture of rare earth elements such as Ce45wt%, La30wt%, Nd5w
t% Other rare earth elements 20 wt%) and Ni, Al, Co, Mn samples are Mm
The composition ratio of Ni _3.55 Mn _0.4 Al _0.3 Co _0.75 was measured and mixed. These samples were melted in a high-frequency furnace capable of rapid cooling by the twin roll method described above, and the molten metal of the alloy was poured between twin rolls rotating at a high speed (the gap between the rolls was 10 μm) to obtain a thickness of 10-15 μm. Thin pieces of hydrogen storage alloy of MmNi _3.55 Mn _0.4 Al _0.3 Co _0.75 were obtained. This thin piece is placed under vacuum (10 ^-3 to 10 ^-4
Torr) at 1050 ° C. for 6 hours, and then the flakes were pulverized in a ball mill into powder of 38 μm or less. Then 1.
The mixture was kneaded with a 5 wt% aqueous solution of polyvinyl alcohol to form a paste, which was filled in a foamed nickel porous body, dried, and subjected to a pressure operation to obtain a hydrogen storage electrode (A) of the present invention used for a negative electrode.

As a comparative example, MmNi prepared by the liquid quenching method as described above.
A thin piece of _3.55 Mn _0.4 Al _0.3 Co _0.75 was prepared by the same method as described above without heat treatment in vacuum, and the alloy was melted in a high frequency melting furnace and a hydrogen storage electrode, and then naturally cooled without quenching. The hydrogen storage electrode (C) prepared by the same method as described above was used for the alloy prepared by the usual alloy manufacturing method.

Next, a foamed type obtained by a known method as a nickel oxide positive electrode (nickel positive electrode (size 39 × 60 × 0.75 mm) was used, a separator was made of polyamide nonwoven fabric, and a specific gravity of 40 g / mol of lithium hydroxide was dissolved in the electrolytic solution. Using 1.30 KOH aqueous solution,
In combination with the negative electrode (size 39 × 80 × 0.5 mm), a sealed nickel-hydrogen storage battery of AA size having a nominal capacity of 1000 mAh was constructed so as to regulate the capacity of the positive electrode. These batteries
Charged at 0.1cmA for 15 hours at a constant temperature of 20 ℃, discharged at 0.2c
After performing 10 charge / discharge cycles under the condition of mA, the high rate discharge characteristics at low temperature were measured. To measure the discharge characteristics,
After charging at 0.1 cmA for 15 hours and at 20 ° C., it was left in an atmosphere at 0 ° C. for 2 hours and discharged at each discharge rate of 1 cmA, 2 cmA and 3 cmA.

FIG. 1 shows the relationship between the discharge rate and the capacity ratio. The capacity ratio is the capacity discharged at a discharge rate of 0.2 cmA up to 1.0 V at 0 ° C.
It was 100%. The final voltage at each discharge rate was 1.0V. As is clear from FIG. 1, the capacity ratio of the battery using the electrode (C) as the negative electrode is 35% at 3 cmA. In this case, the battery capacity is regulated by the positive electrode, but since the overvoltage at the time of high rate discharge at 0 ° C of the negative electrode is large, the battery voltage drops and up to 1.0 V at the high rate discharge compared to the capacity of 0.2 cmA. The capacity ratio is decreased due to the decrease in the capacity. The hydrogen storage alloy powder of the electrode (C) is obtained by crushing an alloy lump produced by natural cooling, and as a result of analysis by the X-ray diffraction method, the orientation of crystal grains is randomly arranged. From this, the hydrogen in the alloy is
When discharged at a high rate at ° C, the diffusion of hydrogen in the solid phase is delayed and the overvoltage increases.

However, the capacity ratio of the battery using the electrode (A) of the present invention as the negative electrode was 75% at 3 cmA, and it is understood that the discharge characteristics are more than doubled as compared with the battery using the electrode (C). The powder produced by the production method of the present invention used for the electrode (A) is a thin piece having a thickness of 10 to 15 μm by the liquid quenching method, and the crystal of the alloy is azimuthally aligned from the result of X-ray diffraction.
Hydrogen occluded in the alloy at the time of high rate discharge smoothly diffuses into the solid phase, the overvoltage of the negative electrode is reduced, the decrease of the battery voltage is suppressed, and the high rate discharge characteristics at 0 ° C. are improved.

Further, the electrode (B) using the alloy powder, which does not include a heat treatment step in the alloy manufacturing method, is inferior in discharge characteristics to the electrode (A) of the present invention. When the alloy produced by the liquid quenching method is used for the electrode without heat treatment, the flatness of the discharge potential becomes worse than that of the electrode (A). Therefore, the high rate discharge at 0 ℃ is 1.0V
It is inferior to the electrode (A) in comparison with the capacity up to. However, since the electrode (B) is also manufactured by the liquid quenching method,
Since the crystals are azimuthally arranged, the discharge characteristics are improved as compared with the electrode (C).

Next, we examined the thickness of the flakes and found that the thickness was 40
It was found that the discharge characteristic was inferior to that of the electrode (A) when the thin piece manufactured so as to have a thickness of ˜45 μm was used. This MmNi
The crystal of _3.55 Mn _0.4 Al _0.3 Co _0.75 alloy has the above-mentioned 10-15 μm.
The orientation is the same as that of the flakes, but since the thickness of the flakes is thick, the process of hydrogen diffusion in the solid phase becomes rate-determining when discharging at 3 cmA at 0 ° C, and the overvoltage during discharging increases. As a result, the battery voltage drops. Therefore, the thickness of the flakes is 40
μm or less is preferable.

FIG. 2 shows the results of examining the self-discharge characteristics of the battery using the same electrodes (A), (B), and (C) as described above. Regarding self-discharge characteristics, after charging 150% at 0.1 cmA to the nominal capacity at 20 ° C, it was left in an atmosphere at 45 ° C. As is clear from FIG. 2, the self-discharge of the battery using the electrode (C) made of the alloy powder prepared by natural cooling in the high frequency melting furnace is 14 days.
It can be seen that when left in an atmosphere of 45 ° C, the capacity retention rate becomes 12.5% and self-discharge is 87.5%. Even if the alloy produced by natural cooling was treated at 1050 ° C. for 6 hours, it was found from the results of the microstructure photograph and the X-ray diffraction that a heterogeneous phase that is ineffective in hydrogen absorption and desorption was present. This heterogeneous phase is M
Consisting of n, Co, Al, Ni and rare earth elements, these metals dissolve in the electrolytic solution when they are repeatedly charged and discharged in an alkaline electrolytic solution or when stored in an atmosphere of 45 ° C, and as metal ions. Exists. Therefore, these ions participate in the self-discharge reaction and increase the self-discharge rate. However, since the electrode (A) of the present invention is formed into a thin piece by the liquid quenching method and heat-treated at 1050 ° C. for 6 hours, the observation result by the microstructure photograph shows that it has a very homogeneous CaCu ₅ type crystal structure. Has become. Therefore, repeated charge / discharge and 45 ° C
Mn, Al, Co, Ni and rare earth elements are hardly dissolved even if left in the atmosphere of, and the capacity retention rate is 75% even when left at 45 ° C for 14 days. Compared with, the self-discharge rate is reduced to about 1/6. The battery using the electrode (A) produced by the production method of the present invention exhibits very good self-discharge characteristics. Further, when the electrode (B) which is not heat-treated is used for the alloy produced by the liquid quenching method, the capacity retention rate is 50% after 14 days, which is inferior to the electrode (A). This is due to the presence of a slightly inhomogeneous phase without heat treatment.
As described above, the self-discharge rate increases. Regarding the heat treatment temperature, the alloy melts at a temperature of 1200 ° C or higher, and there is no effect at a temperature of 800 ° C or lower. Therefore, heat treatment is 800-1
It is preferable to apply in the temperature range of 200 ° C.

Note the MmNi ₅ in this embodiment Mn, Al, was used substituted alloys Co, LaNi ₅ alloy, the same effect if the hydrogen storage alloy such as Ti-based alloy is obtained. Further, in the production of the flakes, even if an apparatus such as sputtering or vapor deposition is used, an alloy with the same orientation is obtained, high rate discharge characteristics and self-discharge are improved, and the same effects as above are obtained.

As described above, according to the present invention, after the hydrogen storage alloy is cooled by the liquid quenching method, a step of producing flakes or ribbons,
A step of heat-treating in an inert gas or vacuum, a step of finely pulverizing, a step of applying or kneading the kneaded material of the powder and the binder to the electrode support, and then drying, and a pressing operation on the electrode. By providing the manufacturing method including the step of subjecting to a desired thickness, a high-rate discharge characteristic is excellent, and an excellent battery with less self-discharge can be provided.

[Brief description of drawings]

FIG. 1 is a diagram showing the relationship between the discharge rate and the capacity ratio in the battery shown in the example of the present invention, and FIG. 2 is a diagram showing the relationship between the storage period and the capacity retention rate in the battery shown in the example.

Claims (3)

[Claims] 1. A step of cooling a molten metal of a hydrogen storage alloy capable of reversibly storing and releasing hydrogen by a liquid quenching method to produce flakes or strips, and a step of heat-treating this in an inert gas or in a vacuum. A step of finely pulverizing the flakes or strips, a step of applying or kneading a kneaded product of the pulverized powder and a binder to an electrode support and then drying, and applying a pressure operation to the electrode, A method of manufacturing a hydrogen storage electrode, comprising a step of setting a desired thickness. 2. The method for producing a hydrogen storage electrode according to claim 1, wherein the thickness of the thin piece or the thin strip is 40 μm or less. 3. The method for producing a hydrogen storage electrode according to claim 1, wherein the heat treatment temperature is in the range of 800 to 1200 ° C.