JPH08106904A - Manufacture of hydrogen storage alloy electrode - Google Patents

Abstract

PURPOSE: To provide a manufacturing process of a hydrogen storage alloy electrode having high mechanical strength and current collecting capability of a sintered electrode, not need a large facilities such as a high temperature furnace and an atmosphere control device, capable of manufacturing in a short time, or with high productivity. CONSTITUTION: In a manufacturing process of a hydrogen storage alloy electrode, an alloy particle capable of absorbing/desorbing hydrogen or a mixture with an alloy particle which does not absorb hydrogen or a metal particle is pressed to form a molding 2. The molding 2 is interposed between a pair of electrodes 11, and a current of 10A/mm<2> or more is passed across the electrodes 11 for 0.1-10sec to melt bond hydrogen storage alloy particles themselves, the hydrogen storage alloy particle with the alloy particle not absorb hydrogen, or with the metal particle.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a hydrogen storage electrode used for a negative electrode of a battery using a so-called hydrogen storage alloy that stores and releases hydrogen reversibly.

[0002]

2. Description of the Related Art Conventionally, nickel-cadmium (Ni / Cd) batteries and lead (Pb / H ₂ SO ₄ ) storage batteries have been used as secondary batteries. Nickel-cadmium batteries and lead-acid batteries can be discharged with a large current and can be rapidly charged, and are used as a power source for many cordless devices. However, with the miniaturization, weight reduction, portability and high performance of electronic devices, development of a lightweight, high capacity, high energy density secondary battery is desired. A metal-hydrogen battery typified by a nickel-hydrogen battery attracts attention as a battery that achieves this object.

The metal-hydrogen battery is, for example, a nickel-hydrogen battery, which uses a hydrogen storage alloy as a reversible electrode (negative electrode).
The battery has a structure in which a nickel positive electrode plate and a hydrogen storage alloy negative electrode plate are spirally wound as a material, and an aqueous potassium hydroxide solution is used as an electrolytic solution. The theoretical voltage of the nickel-hydride battery is 1.318V, which is almost the same as the nickel-cadmium battery (1.32V), and the operating voltage is approximately 1.2V for both batteries, and both batteries are compatible with the equipment. Can be used with. The energy density per weight of the nickel-hydride battery is not so different from that of the nickel-cadmium battery, but the energy density per volume is
It is about 1.5 to 2 times that of nickel-cadmium batteries. Nickel-hydride batteries are easy to seal and have the characteristics of being resistant to overcharge and overdischarge.

Battery performance such as cycle life and charge / discharge performance of the metal-hydrogen battery largely depends on the characteristics of the hydrogen storage alloy which is the negative electrode material, and the conductivity of the entire negative electrode and the bonding strength between the particles constituting the electrode. Etc. particularly affect the battery performance.

A conventional method for producing a hydrogen-absorbing alloy electrode is to first pressure-mold alloy particles that absorb and release hydrogen, and then burn the alloy particles in a vacuum, an inert gas atmosphere or a hydrogen atmosphere at a temperature below the melting point of the alloy. By binding, a porous alloy electrode is produced. As another method, cold-press the hydrogen-absorbing alloy powder in a mold, and then inactive gas.
3ton / cm ² at about 600 ℃ in an atmosphere (eg, argon gas)
There is also known a method of forming an electrode sample by hot-pressing in, followed by cooling in the presence of argon (Japanese Patent Publication No. 56-
36786). As another method for producing a hydrogen-absorbing alloy electrode, the hydrogen-absorbing alloy powder is roughly pulverized, then made into a fine powder by a ball mill or the like, and then mixed with a polyvinyl alcohol (PVA) resin solution, and this paste-like alloy is punched metal ( It is applied on both sides of a perforated plate), dried under pressure, and then attached with lead wires to form electrodes (Japanese Patent Publication No. 6-42367).

[0006]

However, the conventional method for producing a hydrogen storage alloy electrode has the following problems. The hydrogen storage electrode manufactured by the sintering or hot pressing manufacturing method has excellent mechanical strength of the electrode, and the electric capacity of the electrode is unlikely to decrease due to repeated charge / discharge cycles. It is necessary to control the atmosphere such as an active gas atmosphere or a hydrogen atmosphere, and sintering and hot pressing require large-scale equipment such as a high temperature furnace and an atmosphere control device. In addition, it takes several minutes for hot pressing to manufacture the electrode and several hours for sintering. Further, according to the sintering method, the alloy particles forming the electrode have a small fusion area in a contact area between the alloy particles and a fusion area in a large contact area due to the applied pressure and the heating value. Since the area is large, the resistance value of the fused portion of the particles varies, and the conductivity of the electrode becomes non-uniform.

This will be described with reference to FIGS. 6 and 7. As shown in FIG. 6, when the alloy particles (6) are pressurized, a contact state as shown in (a) or (b) is obtained. (a) is an enlarged cross-sectional view of a portion (61) where the contact area (t ₁ ) between the alloy particles (6) and (6) is small, and (b) shows the alloy particles (6) and (6). It is an expanded sectional view of a place (62) where the contact area (s ₁ ) is large. 6 (a) or
When the alloy particles (6) in the contact state as shown in (b) are heated by sintering, as shown in (a) and (b) of FIG. , The electrical resistance of the particle contact point (particle material, contact area between particles, contact pressure,
It will be fused regardless of the degree of surface coating). That is, the contact area (t _{1 in} FIG. 6A) is small (6
In 1), the fusion area (t ₂ ) remains small, and in the area (62) where the contact area (s _{1 in} FIG. 6B) is large, the fusion area (s ₂ ) also remains large. . Therefore, the area of the fused portion becomes non-uniform, the resistance value of the fused portion of the particles varies as described above, and the conductivity of the electrode becomes non-uniform.

In addition, although the paste-coated electrode is excellent in continuous workability in manufacturing, the mechanical strength of the electrode is weak and the adhesion between the active material and the current collector is deteriorated due to repeated charge / discharge cycles. However, there is a problem that the cycle life is shortened.
An object of the present invention is to provide a hydrogen storage alloy electrode which has excellent mechanical strength and electric capacity of a sintered electrode, does not require large-scale equipment such as a high temperature furnace and an atmosphere control device, and can be manufactured in a shorter time. It is intended to clarify the manufacturing method of.

[0009]

In order to solve the above-mentioned problems, in the method for producing a hydrogen-absorbing alloy electrode of the present invention, alloy particles that absorb and release hydrogen are used alone or alloys that do not absorb hydrogen. After mixing with particles or metal particles, pressure is applied to form a molded body (2), and the molded body (2) is used as a pair of electrodes (11).
It is sandwiched between them and a current of 10 A / mm ² or more is passed between the electrodes (11) for 0.1 seconds or more and 10 seconds or less, so that the hydrogen storage alloy particles in the molded body (2) or the hydrogen storage alloy particles and hydrogen are separated from each other. The alloy particles or metal particles that do not occlude are fused together.

[0010]

[Function] As described above, the electric resistance when an electric current flows at the contact point between particles, the material of particles, the contact area between particles,
Since it varies depending on the contact pressure, the degree of the surface coating, etc., even if the contact area is large, the electric resistance may be large depending on the degree of the surface coating. In the method for producing a hydrogen storage alloy electrode of the present invention, between hydrogen storage alloy particles, or for fusion between hydrogen storage alloy particles and alloy particles or metal particles that do not store hydrogen, 10 A / mm ² or more It uses electric current. Normally, when a small current is passed between the alloy particles, the current only flows in the portion having a small electric resistance between the particles (hereinafter referred to as the “current-carrying portion”). However, 1
When an electric current of 0 A / mm ² or more is applied to the molded body, the electric current is preferentially passed through the energizing portion, and the contact portion is of course heated and fused, but the portion with a large electric resistance (hereinafter, `` Difficult-to-power section '')
The electric current also passes through. When a current is passed through the hard-to-carry part, the heat is generated, and the particles melt and the particles bond to each other.

[0011]

As in the case of sintering, the structure of the electrode produced by the method of the present invention is a porous body, and the particles are
It is joined by fusion. The electric resistance of the fused portion is lower than the electric resistance before the fusion. Because, the particle contact portion before fusion, the surface is formed a coating by oxidation or the like, the conductivity is poor, but when the particle contact portion is fused particles are locally integrated with each other, the resistance of the coating is Because it will disappear. When an electric current is applied to the molded body, the hard-to-carry portion between the particles forming the molded body is less likely to pass an electric current than the electric current-carrying portion. However, when the electric current is passed, the resistance is large and the heating is easy. When a current of less than 10 A / mm ^{2 is} passed through the molded body, the current is passed only to the current-carrying part, but when a current of 10 A / mm ² or more is passed through the molded body, not only the current-carrying part but also the hard-to-carry part The electric current also passes through. Therefore, an electric current is preferentially passed through the electrifying portion to generate heat and fuse, but the hard-to-conduct portion also produces heat and fuses when energized to reduce the electrical resistance between particles.
Therefore, the maximum value of the electric resistance of the fused portion of the alloy particles is decreased on average, and the total resistance value of the electrode is decreased. Therefore, the electric resistance of the entire electrode becomes uniform, the utilization rate of alloy particles in the electrode increases, and the capacity of the electrode increases.

The above phenomenon will be described with reference to FIGS. 6 and 8. Here, the electrical resistance of the particles shall be determined only by the contact area between the particles. As shown in FIG. 6, the alloy particles (6) are brought into a contact state as shown in (a) or (b) when pressurized. (a) is the contact area between alloy particles (6) and (6)
FIG. 3B is an enlarged cross-sectional view of a portion (61) where (t ₁ ) is small and symbolically shows a difficult-to-energize portion.
(6) An enlarged cross-sectional view of a portion (62) where the contact area (s ₁ ) between the two is large, and which symbolically shows the Du current-carrying portion. When a current of 10 A / mm ² or more is applied to the alloy particles (6), the current flows preferentially to the part where the current easily flows, that is, the current-carrying part (62), and the contact part between the particles is fused. However, the current also flows to the portion where the current hardly flows, that is, the hard-to-carry portion (61). Hard-to-carry part
The current flowing through (61) generates heat due to the resistance of the contact portion, and the particles are fused to each other. The contact area between particles is due to fusion
The energizing part (62) becomes s ₃ as shown in (b) of FIG.
The hard-to-carry part (61) becomes t ₃ as shown in FIG.
Comparing the area size of the fusion-bonded portion (s _{2 of} FIG. 7) by the above-mentioned sintering with the area size of s ₁ of FIG. 6 and s _{3 of} FIG.
s ₁ <s ₂ ≒ s ₃ next, t ₂ in FIG. 7, t ₁ and 8 of Figure 6
Comparing the size of the area with t _{3 of} t ₁ , t ₁ <t ₂ << t ₃
Becomes Therefore, since the fusion area becomes larger on average than the fusion by conventional sintering, the variation in the resistance value of the particle contact portion becomes smaller, and the resistance value of the entire electrode becomes uniform and By increasing the area on average, the resistance value decreases on average, and the total resistance value of the entire electrode also decreases. Therefore, the electron conductivity and the electric capacity of the electrode are improved.

The mechanical strength of the electrode produced by the manufacturing method of the present invention is equal to or higher than that of the conventional sintered electrode. Superior to paste-coated electrodes. Further, the manufacturing of the electrode does not require a large-scale facility, and since continuous work is possible, it is excellent in mass productivity. Further, since heating and fusing of the molded body can be performed in an extremely short time, the molten portion of the metal is less likely to be covered with the oxide film such as oxygen or nitrogen. Therefore, the electrodes can be manufactured in the atmosphere.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail below with reference to the drawings. An apparatus (1) used for manufacturing the hydrogen storage alloy electrode of the present invention will be described with reference to FIG. The device
(1) is used for the purpose of explanation, and the present invention is not limited to being applied only to the device (1). FIG. 1 shows an electrode manufacturing apparatus (1) including a device electrode portion (11) provided with a pair of opposing columnar copper electrodes (11a) (11b) that can be moved toward and away from each other, and the device electrode portion (11). Power supply (1
2) and the copper electrodes (11a) and (11b) respectively.
The distance between a) and (11b) is variable, and the copper electrodes (11a) and (11b)
Lifting / pressurizing means (1
3a) and (13b). The copper electrodes (11a) (11b) are
It is a cylindrical copper electrode with a diameter of 30 mm, and each has a conductor (14a)
It is connected to (14b) and leads to the power supply (12). In addition, the copper electrodes (11a) (11b) are provided on the outer end faces of the copper electrodes (11a) (11b), respectively.
Elevating / pressurizing means (13a) (13b) for varying the distance between b) and pressing the copper electrodes (11a) (11b) inward are provided.

A molded body (2) containing hydrogen-absorbing alloy particles is sandwiched between the electrodes (11a) and (11b) of the device (1). The molded body (2) was produced by the following method. Commercially available misch metal Mm (mixture of rare earth elements such as La, Ce, Nd, Pr, etc.), Ni, Co, AI and Mn each have a constant element ratio Mm: Ni: Co: Al: Mn of 1: 3.1: 0.9: 0. .
After weighing, mixing and pressing so that it becomes 4: 0.6, it is heated and melted in an arc melting furnace, and MmNi _3.1 Co _0.9 A
An l _0.4 Mn _0.6 alloy is prepared. The alloy is mechanically crushed to obtain alloy powder of 25 μm to 150 μm. The alloy powder is formed into a pellet having a diameter of 20 mm and a thickness of 2 mm, and pressure-molded at a pressure of 1 ton / cm ² to prepare a molded body (2). The molded body (2) is sandwiched between the copper electrodes (11a) and (11b), and the lifting / pressurizing means (13a) (13a)
According to b), the pressure is increased to about 0.5 ton / cm ² , and
Five pulses of electric current are applied from the power supply (12) for 0.5 seconds at 1 second intervals so that the current flowing on the contact surface between each copper electrode (11a) (11b) and the molded body (2) becomes 50 A / mm ² (Fig. 9). ). By the above operation,
Electrode A (3) is produced by the method for producing a hydrogen storage alloy of the present invention.

The capacity and cycle life performance of the electrode A (3) is shown by using it as the negative electrode of the test cell A (4). As shown in FIG. 3, the test cell A (4) includes a cylindrical closed container (41), a positive electrode (42) and a negative electrode A (30) suspended and supported inside the closed container (41). Airtight container (41)
Pressure gauge (45) and relief valve (relief valve) (4
It consists of a relief pipe (44) for deploying 6). The cylindrical airtight container (41) is insulative and filled with a 30 wt% potassium hydroxide aqueous solution L therein.
0) and the positive electrode (42) are immersed, and the upper space of the potassium hydroxide aqueous solution L is filled with nitrogen gas, and the negative electrode A (30) is filled with the potassium hydroxide aqueous solution at a predetermined pressure (0.5 MPa)
It is supposed to take place. Moreover, the upper lid (5
Three holes (52) (53) (54) are opened in 1).

As shown in FIG. 2, the electrode A (3) is
In order to use (3) as the negative electrode A of the battery, it is wrapped with a nickel mesh (31) and a negative electrode lead (32) composed of a nickel plate is welded at one end. The negative electrode A (30) is suspended and supported by the negative electrode lead (32) from the hole (53) of the upper lid (51) of the hermetically sealed container (41) so as to be disposed in the substantially cylindrical center of the hermetically sealed container (41). ing. The negative electrode lead (32) is connected to the negative electrode lead terminal (34) on the upper surface of the upper lid (51).

As the positive electrode (42), a known cylindrical sintered nickel electrode having a theoretical capacity sufficiently larger than that of the negative electrode A (30) is used. A positive electrode lead (43) is welded to the ring end of the positive electrode (42). The other end of the positive electrode lead (43) is connected to the upper lid (5
It fits into the hole (54) of 1) and the center of the positive electrode (42) and the closed container (4
1) The centers of the cylinders are substantially coincident with each other, and the negative electrode A (30) is suspended and supported so as to be located at the substantially center of the cylinder. Positive electrode lead (43)
Are connected to the positive electrode lead terminal (47) on the upper surface of the upper lid (51).

Further, by connecting to the hole (52) of the closed container (41),
The relief pipe (44) is projected. The relief pipe (44)
The pressure gauge (45) measures the internal pressure of the closed container (41) and the relief valve (46) for preventing the internal pressure of the closed container (41) from rising above a predetermined pressure.

In order to compare the performance of the electrode A (3), a conventional paste type electrode B was manufactured. Paste type electrode B
Is MmNi _3.1 Co _0.9 Al _0.4 M similar to the electrode A (3).
The n _0.6 alloy is mechanically crushed to obtain an alloy powder having a particle size of 25 μm to 150 μm. The weight of PVA (polyvinyl alcohol) as a binder was 1 wt% with respect to the weight of the alloy in 10 g of the alloy powder.
PVA aqueous solution and 12g of nickel powder as conductive agent
Are mixed to prepare an alloy paste. Apply the alloy paste to both sides of nickel punching metal, and
After drying for 24 hours, it is rolled to obtain a paste type electrode B having a thickness of 1.5 mm. The paste type electrode B was cut into 15 mm squares, and a negative electrode lead (32) made of a nickel plate was welded to one end of the paste type electrode B to prepare a paste type negative electrode B. A comparative cell B having the same structure as the test cell A (4) but having only the negative electrode as the paste type negative electrode B is assembled.

A test cell A (4) using the electrode A (3),
By the comparison cell B using the conventional paste type electrode B,
A charge / discharge cycle test was performed for comparison. The test methods and results are shown below.

In the test method, charging and discharging are performed from the negative electrode lead terminal (34) and the positive electrode lead terminal (47) of the test cell A (4) and the comparison cell B respectively as one cycle, and the discharge capacity of each cell is specified. The number of cycles when the value becomes less than or equal to the value is compared as the cycle life. One cycle of charge / discharge is 30 mA (30 mA / g) per 1 g for 13 hours, and discharge current is 4
Discharge at 0mA / g until the final discharge voltage reaches 1V.

The results of the above test are shown in FIG. FIG. 4 shows the number of cycles on the horizontal axis and the discharge capacity on the vertical axis.
The data of (4) is shown by a solid line, and the data of the comparison cell B is shown by a dotted line. The test cell A (4) has an initial stage as compared with the comparison cell B.
Large discharge capacity (up to 3 cycles). This means that the activation of the electrode is faster than that of the paste type electrode B. Further, it can be seen that the discharge capacity after the completion of activation is constant in the test cell A (4) and the cycle life is long, but the discharge capacity of the comparison cell B is rapidly deteriorated as the cycle progresses and the life is short. .

Further, regarding the hydrogen storage alloy electrode according to the production method of the present invention, various changes were made to the production conditions, and the optimum production conditions were determined. First, regarding the alloy particle diameter, the diameter of the alloy particles is preferably about 10 μm to 500 μm. When the particle size is larger than 500 μm, the particles are likely to drop off from the electrode during charging / discharging, and the packing density during processing is lowered, and the capacity is also lowered. If the particle size is smaller than 10 μm,
Integration during processing becomes difficult.

Further, a metal or an alloy different from the hydrogen storage alloy (eg Ni) may be added to the hydrogen storage alloy particles. In this case, the conductivity of the electrode is further improved, or the catalytic action for hydrogen storage / release reaction is enhanced, so that the electrode is highly activated and the cycle life is improved. However, the packing density of the electrode is relatively lower than that in the case where it is not added. Therefore, when it is desired to prioritize high activation and cycle life of the electrode, it may be added as necessary.

Furthermore, when the molded body is pressed between the copper electrodes and a current is passed, a current of 10 A / mm ² to 10,000 A / mm ² is suitable, and preferably 50 A / mm ² to 5,000 A / It is within the range of mm ² . Further, the energization time is suitably 0.1 to 10 seconds, preferably 0.5 to 2 seconds. Further, the number of energizing pulses is appropriately 1 to 30 times, and preferably,
It is within the range of 5 to 20 times. Further, the interval between pulses is suitably 0.5 to 10 seconds, preferably 1 to 5 seconds. If the current is too large or the energization time is too long, the alloy structure is deformed and the characteristics deteriorate. On the other hand, if the current is too small or the energization time is too short, the alloy particles do not fuse with each other, and a sufficient effect cannot be obtained.

The description of the above embodiments is for the purpose of illustrating the present invention, and should not be construed as limiting the invention described in the claims or reducing the scope thereof. The configuration of each part of the present invention is not limited to the above-mentioned embodiment, and it goes without saying that various modifications can be made within the technical scope described in the claims.

In this embodiment, a copper electrode is used as the device electrode of the electrode manufacturing apparatus (1), but copper is excellent in conductivity,
Since it is difficult to adhere to other metals, it is possible to use metals other than copper. Also, electrode manufacturing equipment (1)
The sheet-shaped electrode (33) is replaced by a roll-shaped rotatable electrode (15) provided with a rotation driving means (16) as shown in FIG. 5, instead of the copper electrode on the disk. It can also be made. Furthermore, in the examples, the compact of the hydrogen storage alloy sandwiched between the copper electrodes is pressed, but this is to reduce the electrical resistance of the contact portion between the compact and the copper electrode, and during particle fusion. Since it is performed to prevent the current from becoming difficult to flow when the volume of the molded body is reduced, the processing can be performed without applying pressure.

[Brief description of drawings]

FIG. 1 is a conceptual diagram of an electrode manufacturing apparatus.

FIG. 2 is a perspective view when an electrode A is processed into a negative electrode A.

FIG. 3 is a perspective view of a partial cross section of a test cell A including a negative electrode A.

FIG. 4 is a graph of the results of the cycle life test of test cell A and comparative cell B.

FIG. 5 is a conceptual diagram of an electrode manufacturing apparatus when a roll-shaped apparatus electrode is used.

FIG. 6 is a cross-sectional view of a contact portion between alloy particles before fusion, in which (a) is an enlarged cross-sectional view of a portion having a large electric resistance;
(b) is an enlarged sectional view of a portion having a small electric resistance.

FIG. 7 is a cross-sectional view of a fusion-bonded portion when alloy particles are fused by sintering, (a) is an enlarged cross-sectional view of a fusion-bonded portion of a portion having high electric resistance, and (b) is FIG. 4 is an enlarged cross-sectional view of a fusion-bonded portion of a portion having low electric resistance.

FIG. 8 is a cross-sectional view of a fused portion when alloy particles are fused with each other by an electric current, (a) is an enlarged sectional view of a fused portion of a portion having a large electric resistance, and (b) is FIG. 4 is an enlarged cross-sectional view of a fusion-bonded portion in a portion having low electric resistance.

FIG. 9 is a diagram showing a pulse of a current passed through a molded body.

[Explanation of symbols]

 (1) Electrode manufacturing device (11) Device electrode part (13) Lifting / pressurizing means (2) Molded body (3) Electrode A (30) Negative electrode A (4) Test cell A (6) Alloy particles

 ─────────────────────────────────────────────────── ─── 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 (1)

[Claims] 1. An alloy particle that absorbs and releases hydrogen, alone or after mixing with alloy particles or metal particles that do not absorb hydrogen, and then pressurizing the molded body (2) to obtain the molded body (2).
Is sandwiched between a pair of electrodes (11), and a current of 10 A / mm ² or more is passed between the electrodes (11) for 0.1 second or more and 10 seconds or less, so that the hydrogen storage alloy particles in the molded body (2), or A method for producing a hydrogen storage alloy electrode, comprising fusing hydrogen storage alloy particles and alloy particles or metal particles that do not store hydrogen together.