JPH08120365A - Hydrogen storage alloy and its production - Google Patents

Abstract

PURPOSE: To suppress pulverizing of hydrogen storage alloy by crystal orientation effect after pulverizing in the initial phase while easily pulverizing in the initial phase of storage/discharge of hydrogen. CONSTITUTION: An alloy molten metal 10 in a container 5 is jetted from the tip of a nozzle 6, an inert gas containing the fine powder of hydrogen storage material having the crystal structure different from that of molten metal is blown to the jet flow from an introducing pipe 9, the fine powder is taken into the inside of jet flow to be rapidly solidified. The hydrogen storage material is constituted so that a second alloy grain having the crystal structure different from that of a first alloy coexists in the crystal boundary of a first alloy in which the crystal is oriented in the fixed direction.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hydrogen storage alloy, a method for producing the same, and an electrode.

[0002]

2. Description of the Related Art A hydrogen storage alloy expands and contracts as it absorbs and releases hydrogen, so that the stress at that time causes crushing, and pulverization proceeds as the cycle progresses. This pulverization causes a decrease in the thermal conductivity of the hydrogen storage alloy packed bed and a reduction in the cycle life of the hydrogen storage alloy.

Therefore, it is possible to suppress pulverization of the hydrogen storage alloy,
In order to improve the thermal conductivity, a hydrogen storage alloy in which crystals are oriented in the c-axis direction by rapidly solidifying molten alloy has been proposed (Ikuo Yonezu et al .; Electrochemistry; 58 (No.8), 1990, pp742-7
47). In this document, it is reported that when the crystals are aligned in a certain direction, the stress at the time of expansion and contraction is relaxed, and this suppresses pulverization.

This crystal-oriented alloy is hard to be pulverized,
Although there is an advantage that the absorption / desorption cycle life of hydrogen is improved, there is a problem that the initial activation is poor and high rate discharge cannot be obtained at the initial stage of the cycle because the initial hydrogenation and pulverization is also suppressed.

[0005]

The object of the present invention is to facilitate hydrogenation and pulverization at the beginning of the hydrogen absorption / desorption cycle, while suppressing the progress of pulverization due to the crystal orientation effect after pulverization at the beginning of the cycle. The present invention provides a hydrogen storage alloy, a method for producing the same, and an electrode using the hydrogen storage alloy.

[0006]

Means for Solving the Problems The method for producing a hydrogen-absorbing alloy of the present invention is to cause a molten metal of a hydrogen-absorbing alloy in a container to be ejected from a tip of a nozzle arranged in the lower part of the container, and into the ejected flow, After the fine powder of the hydrogen storage alloy having a crystal structure different from that of the alloy is taken in, it is rapidly solidified. Specifically, an inert gas containing fine powder of a hydrogen storage alloy having a crystal structure different from the crystal structure of the hydrogen storage alloy in the container is sprayed, and the molten alloy is passed through the atmosphere of the inert gas. After the fine powder is taken into the molten alloy, the molten alloy is rapidly cooled and solidified.

In the hydrogen storage alloy of the present invention, the second hydrogen storage alloy having a crystal structure different from the crystal structure of the first alloy in the grain boundaries of the first hydrogen storage alloy in which the crystals are oriented in a certain direction. It has a structure in which alloy particles are mixed.

In the hydrogen storage alloy electrode of the present invention, the second hydrogen having a crystal structure different from the crystal structure of the first alloy is present in the crystal grain boundaries of the first hydrogen storage alloy in which the crystals are oriented in a certain direction. An alloy having a structure in which particles of a storage alloy are mixed is provided as a material for storing and releasing hydrogen.

[0009]

In the method for producing a hydrogen storage alloy of the present invention, since the fine powder is taken in immediately before the molten alloy is rapidly cooled, the molten alloy is then rapidly cooled, and when the crystal grains are aligned in a certain direction, It solidifies in the state in which fine particles are mixed in the grain boundaries.

Since the crystal structure of the first hydrogen storage alloy in which the crystals are oriented in a certain direction is different from that of the second hydrogen storage alloy in which solid particles are introduced into the molten alloy, the expansion at the time of storage and release of hydrogen. , The amount of shrinkage is different. Therefore, in the initial stage of the cycle, a large stress acts on the grain boundaries having different crystal structures, and this acts as a starting point of cracking, causing crushing.

During pulverization in the initial stage of the cycle, the hydrogen storage alloy is divided into crystal groups having the same crystal structure and orientation. In these crystal groups, even if the cycle is repeated thereafter, the stress of the crystal grain boundary is relaxed by the crystal orientation effect, and the pulverization is suppressed.

[0012]

EXAMPLES The present invention will be described in more detail based on examples. Zr, Ni, V, and Mn alloy component metals were weighed and mixed in predetermined amounts and melted in an arc melting furnace in an argon gas atmosphere, and ZrNi _0.7 V _0.5 Mn _0.8 and ZrNi _1.5 V
Two kinds of _0.5 alloy ingots (about 20 g) were prepared.
ZrNi _0.7 V _0.5 Mn _0.8 has a C14 type hexagonal crystal structure, and ZrNi _1.5 V _0.5 has a C15 type cubic crystal structure. C14 type cubic ZrNi _0.7 V _0.5 Mn _0.8 is used as the first alloy for crystal orientation, and C15 type hexagonal ZrNi _1.5 V _0.5 is used as the second alloy mixed in the grain boundaries of the first alloy. Was used. ZrNi _0.7 V _0.5 Mn _0.8
Alloy is used as it is in the ingot, ZrNi _1.5 V _0.5
Alloy was crushed into a fine powder having an average particle size of about 2 μm or less under an argon gas atmosphere.

[0013] In the embodiment example, application of the crystal orientation was performed by chill roll method. FIG. 1 is a schematic explanatory diagram when an alloy ribbon is produced using a quenching roll device. The apparatus of FIG. 1 will be described. The inside of the apparatus is composed of an upper melting chamber (1) and a lower quenching chamber (2). The inside of the melting chamber (1) is formed so as to be kept in a hermetically sealed state, and an argon gas introduction pipe (3) is arranged on the upper side surface and an arc torch (4) is arranged on the ceiling part. A container (5) is provided in the lower part of the dissolution chamber (1), and the container has a nozzle (6) in the lower part. The nozzle (13) is exposed to the quenching chamber (2).
In the quench chamber (2), a copper roll (7) is rotatably arranged below the nozzle (6), and an argon gas exhaust pipe is installed on the lower side surface.
(8) is deployed. Further, in order to incorporate the fine powder of the second alloy into the molten alloy ejected from the nozzle (6) toward the roll (7), an argon gas introduction pipe for carrying the fine alloy powder is introduced.
(9) is deployed on the side.

An ingot of ZrNi _0.7 V _0.5 Mn _0.8 is put in a container (5) and melted by an arc torch (4) to prepare a molten alloy (10). Prior to melting, the valve (12) was once opened and the melting chamber (1) was set to an argon gas atmosphere.
2) Close. After melting the alloy ingot, the valve (12) is opened again to pressurize the inside of the melting chamber (1), and the molten alloy (10) in the container (5) is passed through the nozzle (6) to a diameter of about 30 cm. Eject toward the rotating roll (7). The hole diameter of the nozzle (6) is about 2 mm. Just before the molten alloy (10) spouts from the nozzle (6),
The valve (15) is opened and argon gas is sprayed below the nozzle (6) through the introduction pipe (9). The average particle size is about 2 μm
The fine powder (17) of ZrNi _1.5 V _0.5 pulverized below is loaded in the argon gas passage of the introduction pipe (9) in advance. ZrNi
_{The 0.7} V _0.5 Mn _0.8 alloy melt was ejected from the nozzle (6),
ZrNi _1.5 carried by argon gas from the inlet pipe (9)
After taking in V _0.5 fine powder, it is rapidly cooled by a rotating roll (7) and immediately solidified to produce an alloy ribbon (20).

The test condition is that the number of rotations of the copper roll is 500.
The pressure of the argon gas supplied from the inlet tube (9) is about 2.5 kg / cm ² . ZrNi _0.7 V loaded in container (5)
_0.5 Mn _0.8 is 20 g. The amount of ZrNi _1.5 V _0.5 fine powder was 1 g (Invention Example 1), 10 g (Invention Example 2), and no fine powder was included (Comparative Example 1). The obtained alloy ribbon (20)
Has a thickness of about 50 μm and a width of about 3 mm.

[0016] The above test game gold performs a powder X-ray analysis, C14 phase and _{(ZrNi 0.7 V 0. 5 Mn 0.8} ) C15
The mixed amount of the C15 phase was obtained from the peak intensity ratio of the phases (ZrNi _1.5 V _0.5 ). The content of the C15 phase was 1.3 atom% in Invention Example 1 and 8.6 atom% in Invention Example 2. The crystal structure of Inventive Example 1 is schematically shown in FIG. In FIG.
Reference A is ZrNi _0.7 V _0.5 Mn _0.8 alloy, Reference B is Zr
It shows Ni _1.5 V _0.5 . The ZrNi _0.7 V _0.5 Mn _0.8 alloy is crystallographically oriented, and ZrNi _1.5 V _0.5 fine particles are mixed in the crystal grain boundaries.

Preparation of test electrodes The alloys prepared in Invention Example 1, Invention Example 2 and Comparative Example 1 were crushed to an average particle size of about 50 μm. With this hydrogen storage alloy powder,
Ni powder as a conductive agent and polytetrafluoroethylene (PTFE) as a binder in a weight ratio of 1: 2: 0.
The mixture was mixed at a ratio of 3 and rolled to obtain an alloy paste.

Then, a predetermined amount of this alloy paste was wrapped in nickel mesh and pressed at a pressure of 1.2 ton / cm ² to prepare a disk-shaped hydrogen storage alloy test electrode having a diameter of 20 mm.

A test cell was assembled using the test electrode thus prepared as a negative electrode, and was heated at room temperature (25 ° C.) to 50 mA.
After charging for 8 hours at / g for 1 hour and then for 1 hour at 50 mA / g, discharge to a discharge end voltage of 1 V and pause for 1 hour. mAh / g) was investigated. The electrolyte used was 3
It is 0% by weight of KOH. Table 1 shows the relationship between the discharge capacity measurement result at the first cycle and the maximum capacity.

[0020]

[Table 1]

As is clear from the results shown in Table 1, Invention Example 1
Also, it is shown that the test electrode of Inventive Example 2 can obtain a higher discharge capacity at the stage of one cycle than the test electrode of Comparative Example 1, and it can be seen that the Invention Example is excellent in initial activation. . This is because a large stress acts on the grain boundaries having different crystal structures from each other, which acts as a starting point of cracking to cause crushing, and an active surface appears. By this pulverization, the hydrogen storage alloy is divided into crystal groups having the same crystal structure and orientation. In these crystal groups, even if the cycle is repeated thereafter, the stress of the crystal grain boundary is relaxed by the crystal orientation effect, and the pulverization is suppressed.

FIG. 3 shows the relationship between the mixed amount of the C15 phase and C1 / Cmax. As is clear from FIG. 3, when the amount of the C15 phase mixed is up to about 1.3 atomic%, the initial activation is remarkably improved with the increase of the mixed amount. From these results, although the amount of the particles of the second hydrogen storage alloy mixed in the crystal grain boundaries of the first hydrogen storage alloy is effective even if the amount is small, it is preferably about 0.5 atomic% or more, more preferably It is preferable to set it to about 1 atomic% or more. If the amount of the second hydrogen storage alloy mixed is too large, the crystal orientation effect of the first hydrogen storage alloy will be impaired, so the upper limit is 10.
It is desirable that the content be at most atomic%.

FIG. 4 shows the relationship between the number of charge / discharge cycles and the discharge capacity.
Is shown in. As is clear from FIG. 4, in Comparative Example 1, it took about 7 cycles to reach the maximum capacity, whereas in Invention Example 1 and Invention Example 2, the maximum capacity was reached at about 3 to 4 cycles. It shows that the alloy of the present invention has excellent initial activation. Regarding the change in discharge capacity after reaching the maximum capacity, no substantial difference is observed between the invention example and the comparative example.

The method for producing the hydrogen storage alloy of the present invention is not limited to the quenching roll method, but can be applied to, for example, the atomizing method. In the case of the atomization method, the molten alloy in the nozzle is ejected into the inert gas flowing at a high speed in the lower position of the nozzle, so fine powder of hydrogen-absorbing alloy having a crystal structure different from that of the molten alloy. May be contained in an inert gas that flows at high speed.

The supply of the fine powder of the second alloy is not limited to the method of including it in an inert gas such as argon gas. For example, it is also possible to stir the alloy powder with a fan or the like in a quenching chamber and float the alloy powder, and then jet the molten alloy into the atmosphere. The inert gas is not limited to argon gas, and other gas that can be used in the technical field can be used.

[0026]

EFFECT OF THE INVENTION Hydrogen is easily pulverized at the initial stage of hydrogen absorption / desorption cycle, and initial activation is easily performed. Therefore, high rate discharge characteristics can be achieved at the beginning of the charging / discharging cycle. Further, after the cycle has passed, the progress of pulverization is suppressed due to the crystal orientation effect, so that a long life can be obtained. Therefore, the battery using the hydrogen storage alloy electrode of the present invention can be improved in characteristics such as increased capacity, and its industrial value is great.

[Brief description of drawings]

FIG. 1 is a schematic explanatory diagram when an alloy ribbon is produced using a quenching roll device.

FIG. 2 is a diagram schematically showing a crystal structure of a hydrogen storage alloy of the present invention.

FIG. 3 is a graph showing the relationship between the mixed amount of C15 phase and C1 / Cmax.

FIG. 4 is a graph showing the relationship between the number of charge / discharge cycles and the discharge capacity.

[Explanation of symbols]

 (1) Melting chamber (2) Quenching chamber (5) Container (6) Nozzle (10) First molten hydrogen storage alloy melt (17) Second fine hydrogen storage alloy powder

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Shin Fujita, 2-5-5 Keihan Hondori, Moriguchi City, Osaka Prefecture Sanyo Electric Co., Ltd. (72) Ikuro Yonezu, 2-5 Keihan Hondori, Moriguchi City, Osaka Prefecture No. 5 Sanyo Electric Co., Ltd.

Claims (3)

[Claims] 1. A method for producing a hydrogen storage alloy in which a molten metal of a hydrogen storage alloy in a container is jetted from a tip of a nozzle arranged in a lower portion of the container to rapidly solidify the molten alloy, immediately before the molten alloy solidifies. A method for producing a hydrogen storage alloy, characterized in that fine powder of a hydrogen storage alloy having a crystal structure different from that of the alloy is taken into the jet flow. 2. The particles of the second hydrogen storage alloy having a crystal structure different from the crystal structure of the first alloy are mixed in the crystal grain boundaries of the first hydrogen storage alloy in which the crystals are oriented in a certain direction. A hydrogen storage alloy with excellent initial activation. 3. Particles of a second hydrogen storage alloy having a crystal structure different from the crystal structure of the first alloy are mixed in the crystal grain boundaries of the first hydrogen storage alloy in which the crystals are oriented in a certain direction. A hydrogen storage alloy electrode, comprising an alloy having a structure as a hydrogen storage and release material.