JPH10208738A - Manufacture of hydrogen storage alloy electrode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method of a hydrogen storage alloy electrode with which the cycle life of a nickel-hydrogen secondary battery is prolonged. SOLUTION: This method comprises a process P1 of producing a hydrogen storage alloy powder by atomization method, a process P2 of producing a paste by adding a binder and water to the produced hydrogen storage alloy powder, a process P3 of forming a hydrogen storage alloy layer on the surface of a collector by applying the produced paste to the surface of a collector and drying the paste, and a process P4 of shaping the hydrogen storage alloy layer by applying pressure to the formed hydrogen storage alloy layer in a manner that the thickness of the hydrogen storage alloy layer after pressure application is thinner by 1-25% than the thickness of the hydrogen storage alloy layer before pressure application and the content of the hydrogen storage alloy in the hydrogen storage alloy layer is 4.5-6.5g/cm<3> after the pressure application.

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 alloy electrode used as a negative electrode of a hydrogen secondary battery.

[0002]

2. Description of the Related Art FIG. 3 shows a structure of a nickel-hydrogen secondary battery of a positive electrode dominated type, in which a positive electrode (11), a negative electrode (12), a separator (13), a positive electrode lead (14), and a negative electrode lead ( 15), the positive electrode external terminal (16), the negative electrode can (17), the sealing lid (18), etc., constitute an alkaline storage battery having a sealed structure. Positive electrode (11) and negative electrode
(12) is housed in a negative electrode can (17) in a state of being spirally wound with a separator (13) interposed therebetween, and the positive electrode (11) is sealed via a positive electrode lead (14). In (18), the negative electrode (12) is connected to a negative electrode can (17) via a negative electrode lead (15). At the joint between the negative electrode can (17) and the sealing lid (18), an insulating packing (20) is attached to seal the battery. Coil spring between positive external terminal (16) and sealing lid (18)
(19) is provided so that when the battery internal pressure rises abnormally, the coil spring (19) is compressed and the gas inside the battery is released to the atmosphere.

A hydrogen storage alloy electrode used as a negative electrode of a nickel-hydrogen secondary battery is manufactured as follows. First, a hydrogen storage alloy block is mechanically pulverized to produce a hydrogen storage alloy powder. Next, a paste is prepared by adding a binder and water to the hydrogen storage alloy powder, and the paste is applied to both surfaces of a nickel-plated punched metal, and the paste is dried to form a punched metal. A hydrogen storage alloy layer is formed on both sides. Then, the punched metal on which the hydrogen storage alloy layer is formed is cut to obtain a hydrogen storage alloy electrode piece having a predetermined shape. In addition, as a method for producing the hydrogen storage alloy powder, a gas atomizing method (for example, see Japanese Patent Application Laid-Open No. 6-212213) can be adopted.

Meanwhile, in a conventional nickel-hydrogen secondary battery using a hydrogen storage alloy electrode as a negative electrode, there is a problem that the cycle life is short because dry-out occurs in the separator due to repeated charging and discharging. Dryout of this separator, the electrolyte in the separator penetrates into the negative electrode because the hydrogen storage alloy electrode has a porous structure,
This is a phenomenon that occurs because the thickness of the electrode increases, the separator is pressed by the electrode surface, and the electrolyte in the separator further moves to the negative electrode side.

Therefore, the applicant has applied a paste of a hydrogen storage alloy to both surfaces of a punching metal, dried the paste to form a hydrogen storage alloy layer, and then pressurized the hydrogen storage alloy layer. A method of manufacturing a hydrogen storage alloy electrode in which the thickness of the hydrogen storage alloy layer after pressurization is reduced by 10% or more with respect to the thickness of the hydrogen storage alloy layer before pressurization has been proposed (Japanese Patent Application Laid-Open No. HEI 9-258572). 7-57771). In a nickel-hydrogen secondary battery using the hydrogen storage alloy electrode obtained by the manufacturing method as a negative electrode, the porosity of the hydrogen storage alloy electrode is small, so that even when charge and discharge are repeated, the electrolyte to the hydrogen storage alloy electrode And the dryout of the separator is suppressed.

[0006]

However, the above-mentioned manufacturing method proposed by the present applicant is directed to a hydrogen storage alloy electrode using a hydrogen storage alloy powder obtained by mechanically pulverizing a hydrogen storage alloy lump as a material. However, it is clear that the method is extremely effective, but is not necessarily effective for a hydrogen storage alloy electrode using a hydrogen storage alloy powder produced by an atomizing method as a material. That is, the hydrogen storage alloy layer is pressurized and formed so that the thickness of the hydrogen storage alloy layer after pressurization becomes 10% or more, for example, 30% thinner than the thickness of the hydrogen storage alloy layer before pressurization. In this case, the cycle life may be shortened.

Therefore, an object of the present invention is to provide a hydrogen-absorbing alloy electrode using a hydrogen-absorbing alloy powder produced by an atomizing method as a material, and to provide a cycle life of a hydrogen-nickel secondary battery using the hydrogen-absorbing alloy electrode as a negative electrode. It is an object of the present invention to provide a method for producing a hydrogen storage alloy electrode capable of improving the above.

[0008]

The method of manufacturing a hydrogen storage alloy electrode according to the present invention comprises a step P1 of preparing a hydrogen storage alloy powder by an atomizing method, and a step of preparing a binder and water to the prepared hydrogen storage alloy powder. In addition, a step P2 of preparing a paste
And applying the prepared paste to the surface of the current collector, drying the paste to form a hydrogen storage alloy layer on the current collector surface, and pressing the formed hydrogen storage alloy layer. Te, 1% to 25% with thinner the thickness of the thickness of the hydrogen storage alloy layer after pressing is pressurization hydrogen storage alloy layer of hydrogen storage alloy layer after pressing is 1 cm ³ per 4. Forming a hydrogen storage alloy layer so as to contain 5 to 6.5 g of the hydrogen storage alloy.

More specifically, the current collector is made of a punched metal plated with nickel. In the step P3, a hydrogen storage alloy layer is formed on both surfaces of the punched metal. In the step P4, the hydrogen storage alloy layer is pressurized so that the thickness of the hydrogen storage alloy layer after pressurization is preferably 1 to 9% smaller than the thickness of the hydrogen storage alloy layer before pressurization. or,
The rate of addition of the binder is relative to the hydrogen storage alloy powder.
Preferably 0.9% or less, more preferably 0.2-0.8.
Set to%.

In the method for producing a hydrogen storage alloy electrode, the hydrogen storage alloy powder produced by the atomization method in the step P1 (hereinafter referred to as atomized alloy powder) is replaced with the hydrogen storage alloy powder produced by a mechanical pulverization method. (Hereinafter referred to as crushed alloy powder), and the shape of the particles is spherical, substantially spherical, or egg-shaped. For this reason, the atomized alloy powder has high fluidity in the paste prepared in the subsequent step P2, and requires less water to be added. As a result, even before pressurization, the alloy packing density of the hydrogen storage alloy layer becomes relatively high, and the thickness of the paste to be applied becomes small. Therefore, the process P4
When applying pressure, the pressing force may be smaller than that of the hydrogen storage alloy layer made of the pulverized alloy powder, and it is possible to achieve a high alloy packing density at a relatively low rolling reduction, and thereby the porosity of the hydrogen storage alloy layer Becomes sufficiently small.

According to the results of an experiment described later, by applying pressure so that the thickness of the hydrogen storage alloy layer after pressurization becomes 1% or more smaller than the thickness of the hydrogen storage alloy layer before pressurization, The porosity of the hydrogen storage alloy layer becomes sufficiently small, and the cycle life is extended. However, the thickness of the hydrogen storage alloy layer after pressurization is 25 times the thickness of the hydrogen storage alloy layer before pressurization.
%, The rolling reduction becomes excessive and the hydrogen storage alloy particles are cracked, and the alloy is remarkably pulverized by repeated charge and discharge. Therefore, the cycle life is shortened by the oxidation of the alloy particles.

The amount of the hydrogen storage alloy contained per 1 cm ³ of the hydrogen storage alloy layer after pressurization (alloy packing density) is 4.5 g / c.
If the value is less than c, the rolling is insufficient and the porosity of the hydrogen storage alloy layer is high, which causes the separator to dry out. On the other hand, when the alloy packing density exceeds 6.5 g, the rolling reduction becomes excessive and the hydrogen storage alloy particles are broken, and the cycle life is shortened due to the pulverization of the alloy.

[0013]

According to the method of manufacturing a hydrogen storage alloy electrode according to the present invention, when manufacturing a hydrogen storage alloy electrode using a hydrogen storage alloy powder produced by an atomizing method as a material, the hydrogen storage alloy electrode is used as a negative electrode. The cycle life of the nickel-hydrogen secondary battery can be improved.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention for manufacturing a hydrogen storage alloy electrode used as a negative electrode of a nickel-hydrogen secondary battery shown in FIG. 3 will be specifically described with reference to the drawings. FIG. 1 shows a method of manufacturing a hydrogen storage alloy electrode according to the present invention. First, in step P1, an alloy material adjusted to have a predetermined composition is melted, and the molten metal is powdered by a gas atomizing method. For example, average particle size 5
A 0 μm hydrogen storage alloy powder is obtained. As the hydrogen storage alloy, an AB ₅ type alloy, for example, LaNi ₅ , MmNi _5-x M _x
In addition to (Mm: misch metal, M: Mn, Al, Co, etc.), hydrogen storage alloys having various known compositions can be used.

Next, in step P2, the hydrogen storage alloy powder is
A paste is prepared by mixing polytetrafluoroethylene powder as a binder and water. Here, the addition amount of the binder is set to 0.9% by weight or less, preferably 0.2 to 0.8% by weight with respect to the hydrogen storage alloy powder. Subsequently, in a process P3, this paste is applied to both surfaces of a nickel-plated punching metal (current collector) and dried at room temperature for 24 hours or more, so that a predetermined thickness of hydrogen is applied to both surfaces of the punching metal. An electrode body on which the occlusion alloy layer is formed is obtained.

Thereafter, in step P4, the electrode body is pressed by well-known press rolling or roll rolling. At this time, the thickness of the hydrogen storage alloy layer after pressurization is 1 to 25% smaller than the thickness of the hydrogen storage alloy layer before pressurization, preferably 1% or more,
The electrode body is pressurized so that the thickness becomes less than 10% and the packing density of the hydrogen storage alloy after pressurization becomes 4.5 to 6.5 g / cc.

Then, the electrode body after pressurization is cut into a band shape of a predetermined size to produce a hydrogen storage alloy electrode. The hydrogen-absorbing alloy electrode obtained in this manner was connected to a nickel-
Installed as a negative electrode in a hydrogen secondary battery. Incidentally, a sintered nickel electrode can be used as the positive electrode, an alkali-resistant nonwoven fabric can be used as the separator, and a 30% by weight aqueous solution of potassium hydroxide can be used as the electrolytic solution.

Next, the contents of an experiment conducted to confirm the performance of the hydrogen storage alloy electrode according to the present invention and the results thereof will be described. (1) Experiment 1 composition using a hydrogen absorbing alloy _{MmNi 3.2 Co 1.0 Mn 0.6 Al 0.2} , by a gas atomizing method, average particle size 50
A μm hydrogen storage alloy powder was produced. To this alloy powder,
Polytetrafluoroethylene powder is added to
% By weight, and further water was added to prepare a paste.
Thereafter, the paste was applied to both surfaces of a nickel-plated 0.06 mm-thick punching metal, dried at room temperature for 24 hours or more, and as shown in FIG.
An electrode body in which the hydrogen storage alloy layers (2) and (3) were formed on both surfaces of the current collector (1) was produced. Then, the electrode body was cut into a predetermined shape, and a plurality of electrode pieces thus obtained were pressed by a hydraulic press as shown in FIG. 2B.

In the pressing of the electrode pieces, different pressures are applied to the respective electrode pieces so that the rolling rate represented by the following equation 1 varies variously within the range of 0 to 30%, and a plurality of types of rolling rates different from each other are applied. A hydrogen storage alloy electrode was produced.

## EQU1 ## Rolling ratio (%) = ｛(d1 + d2) − (d1 ′ + d
2 ′)｝ / (d1 + d2) × 100 where d1 and d2 are the hydrogen storage alloy layer (2) before pressing.
The thickness (3), d1 'and d2' are the thicknesses of the hydrogen storage alloy layers (2) and (3) after pressurization (see FIG. 2). In addition, in any of the electrodes, extension of the current collector (1) due to pressurization was not recognized.

The hydrogen-absorbing alloy electrodes thus obtained are shown in Comparative Example 1, Tables 1 to 8 and Comparative Example 2 in Table 1 below. The alloy packing density of the hydrogen storage alloy layer after pressurization was 4.5 g to 6.5 g per 1 cc of the alloy excluding the current collector and the binder in all the electrodes.

Similarly, a plurality of types of hydrogen storage alloy electrodes having different rolling rates were produced using hydrogen storage alloy powder obtained by mechanically pulverizing a hydrogen storage alloy block having the same composition as a material. The hydrogen storage alloy electrode obtained in this manner is shown in Table 1 below.
Are shown in Comparative Examples 3 to 7.

[0022]

[Table 1]

The above-mentioned hydrogen-absorbing gold electrode and a known sintered nickel electrode are spirally wound with an alkali-resistant separator interposed therebetween, and the resultant is accommodated in a negative electrode can. After injecting, seal, nominal capacity 1000
A nickel-hydrogen secondary battery of mAh was produced.

Evaluation of Charge / Discharge Cycle Characteristics The battery of the present invention and the battery of the comparative example were charged at 100 mA for 16 hours to be fully charged, and then discharged at 200 mA to a final voltage of 1 V. A cycle test was performed to examine the cycle life of each battery.
The cycle life is 5 times the discharge capacity with respect to the initial discharge capacity.
It was represented by the number of charge / discharge cycles at the time when it reached 0%. The results are shown in Table 2 below.

Evaluation of Internal Pressure Characteristics during Battery Charging A hole having a diameter of 1 mm was opened at the bottom of the battery after sealing, and charging was performed at a current value of 1 A in a state where a pressure transmitter was connected to the hole.
The change in internal pressure was measured by capturing gas generated from the battery with a pressure transmitter. The internal pressure characteristics were evaluated based on the time required to reach 15 kgf / cm ² , which is the gas discharge pressure of the battery. The longer the internal pressure characteristic, the more rapid charging with a large current is possible, and the more the dryout of the separator accompanying the repetition of the charge / discharge cycle is suppressed. The evaluation results of the internal pressure characteristics are also shown in Table 2 below.

[0026]

[Table 2]

As is apparent from Table 2, in the batteries (Battery Nos. B-1 to B-8) using the electrodes 1 to 8 of the present invention using the atomized alloy powder as a material, the reduction ratio was 1% or more. For example, a cycle life exceeding 500 cycles has been achieved. On the other hand, in the batteries using the comparative example electrodes 3 to 7 using the crushed alloy powder as a material (battery numbers D-1 to D-5), if the rolling ratio is not 10% or more, the cycle life exceeding 500 cycles is not achieved. I can't get it. This is because the atomized alloy powder is more homogeneous than the crushed alloy powder and the shape of the particles is spherical or spherical (tears or eggs), so even before pressurization, the alloy packing density of the hydrogen storage alloy layer is high, 1
Even with a low rolling reduction of about 10%, the alloy packing density in the hydrogen storage alloy layer after pressurization becomes a higher value, the porosity of the hydrogen storage alloy electrode becomes sufficiently low, and the dryout of the separator is suppressed. This is because that.

However, in the electrode 8 of the present invention, in which the rolling reduction exceeds 20%, as can be seen from the small average particle size, cracking of the alloy occurs due to pressure. For this reason, in a battery using this electrode (battery number B-8),
The tendency of the alloy to become finer with the repetition of the charge / discharge cycle is increased, and the cycle life is shortened due to oxidation of the alloy. Further, in Comparative Example Electrode 2 in which the rolling reduction exceeds 25%,
A battery using the electrode (Battery No. C
The cycle life of -1) is greatly reduced.

Regarding the internal pressure characteristics of the battery, the electrode 1 of the present invention was used.
Batteries (Battery Nos. B-1 to B-4) using No. to No. 4 are particularly excellent. By the way, when the battery reaches a full charge, oxygen gas is generated from the positive electrode, and this oxygen gas reacts with hydrogen gas generated from the negative electrode on the alloy surface of the negative electrode to generate water. This reaction is smooth. In order to be carried out, the gas-
It is necessary that a solid (hydrogen storage alloy) -liquid (electrolyte) three-phase interface exists on the alloy surface. Here, when the rolling ratio is high, for example, 10% or more, the amount of hydrogen supply from the negative electrode to the electrolyte decreases because the amount of retained alloy is small,
The amount of generated oxygen gas is relatively increased, and the internal pressure of the battery is increased. Therefore, the rolling reduction is preferably 9% or less.

As described above, the electrode using the atomized alloy powder as the material has a higher alloy packing density than the electrode using the pulverized alloy powder as the material, and the thickness of the alloy layer before rolling is small. Is lower than that of the pulverized alloy powder, that is, 1 to 25%. Further, in order to avoid the influence of the crack of the alloy on the cycle life, the rolling reduction is 1 to 20%.
It is effective to set it in the range. Furthermore, in order to improve the internal pressure characteristics of the battery, it can be said that it is desirable to set the rolling reduction in the range of 1 to 9%.

Experiment 2 Using an atomized alloy powder, the alloy packing density was 4.0 to 4.0.
A plurality of hydrogen-absorbing alloy electrodes of 7.0 g / cc and a rolling reduction of 10% were produced, a nickel-hydrogen secondary battery was assembled using each electrode, and the charge / discharge cycle life was measured.
The results are shown in Table 3 below.

[0032]

[Table 3]

As is evident from Table 3, in Comparative Examples 10 and 11 in which the alloy packing density of the electrode was less than 4.5 g / cc, the porosity of the electrode was large due to insufficient rolling. In the batteries using the electrodes (battery numbers E-1 and E-2), the electrolyte is taken into the electrodes as the charge / discharge cycle is repeated, and the electrodes expand to cause dryout of the separator. Therefore, the cycle life is shortened. In the comparative example battery 12 having an alloy packing density of more than 6.5 g / cc, the alloy is cracked by pressurization.
The repetition of the charge / discharge cycle promotes the pulverization of the alloy and shortens the cycle life. Therefore, in a battery using a hydrogen storage alloy electrode using an atomized alloy powder as a material, the rolling ratio of the electrode is set in the range of 1 to 25%, and the packing density of the alloy layer is 4.5 to 6.5 g /. It can be said that setting in the range of cc is optimal.

Experiment 3 In the same manner as in Experiment 1, after preparing an atomized alloy powder and a crushed alloy powder, a binder (polytetrafluoroethylene) was added to each powder under the conditions shown in Table 4 below to prepare a paste. . Then, as in Experiment 1, the paste was applied to both surfaces of the current collector to produce a plurality of types of hydrogen storage alloy electrodes. Here, the rolling reduction of the hydrogen storage alloy layer was set to 10%, and the packing density after pressurization was set to 4.5 to 6.5 g / cc.

[0035]

[Table 4]

Then, by using these electrodes, nickel-
A hydrogen secondary battery was assembled, and charge / discharge cycle characteristics and battery internal pressure characteristics of each battery were evaluated. The results are shown in Table 5 below.

[0037]

[Table 5]

As is clear from Table 5, in the electrode using the atomized alloy powder as the material, the addition ratio of the binder was 1.0.
%, The batteries using the electrodes 14 to 18 of the present invention (battery numbers I-1 to I-5) have a high cycle life. On the other hand, in the electrodes using the pulverized alloy powder as the material, batteries using the comparative electrodes 13 and 14 in which the addition ratio of the binder was less than 1.0% (battery numbers J-1 and J-2)
In this case, the cycle life is remarkably reduced, and in order to recover the cycle life, it is necessary to increase the amount of the binder added (Battery Nos. J-3 and J-4).

This is for the following reason. That is,
Since the atomized alloy powder has a spherical shape, the fluidity in the paste state is superior to that of the pulverized alloy powder, and the amount of water required for producing a homogeneous electrode is small. Therefore, in the case of the atomized alloy powder, since the liquid content of the paste is low and the gap between the alloy particles in the dried alloy layer is small, the binding necessary for maintaining the alloy particles and maintaining the strength of the electrode. The amount of the agent is smaller than in the case of the pulverized alloy powder. If the amount of the binder is small, the gas absorption reaction in the battery is less likely to be inhibited by the binder, and the gas absorption reaction is promoted, so that an increase in the battery internal pressure is suppressed.
On the other hand, if the amount of the binder is small, the amount of liquid retained by the binder is reduced, so that the amount of liquid retained in the entire electrode is reduced and the cycle life is improved.

Further, when the addition ratio of the binder is less than 0.8%, the charge / discharge cycle life is further improved (battery No. I-
2, I-3). This is because, due to the decrease in the binder, the contact between the alloy particles is further improved, and the charge and discharge efficiency is improved, and the gas absorption during charging is improved. This is because the leakage of the electrolyte from the substrate is greatly reduced. However, in the electrode 14 of the present invention in which the addition ratio of the binder was less than 0.2%, the strength of the electrode was reduced. Therefore, in the battery using this electrode (battery No. I-1), the charge and discharge cycle was repeated. With this, the alloy particles easily fall off from the electrode, and the cycle life tends to decrease. Therefore, in a hydrogen storage alloy electrode using an atomized alloy powder as a material, the amount of the binder added is desirably 0.9% or less, and is most preferably set in the range of 0.2 to 0.8%. It can be said.

The description of the above embodiment 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.
In addition, the configuration of each part of the present invention is not limited to the above-described embodiment, and it goes without saying that various modifications can be made within the technical scope described in the claims.

[Brief description of the drawings]

FIG. 1 is a process chart showing a method for producing a hydrogen storage alloy electrode according to the present invention.

FIG. 2 is a cross-sectional view illustrating a pressing step.

FIG. 3 is a sectional view of a nickel-hydrogen secondary battery.

[Explanation of symbols]

 (1) Current collector (2) Hydrogen storage alloy layer (3) Hydrogen storage alloy layer

Continuation of the front page (72) Nobuyuki Higashiyama 2-5-5 Keihanhondori, Moriguchi-shi, Osaka Inside Sanyo Electric Co., Ltd. (72) Inventor Kozo Nogami 2-5-5 Keihanhondori, Moriguchi-shi, Osaka Within Sanyo Electric Co., Ltd. (72) Inventor Ikuro Yonezu 2-5-5 Keihanhondori, Moriguchi-shi, Osaka Prefecture Inside Sanyo Electric Co., Ltd. (72) Koji Nishio 2-5-2 Keihanhondori, Moriguchi-shi, Osaka No. 5 Sanyo Electric Co., Ltd.

Claims (4)

[Claims] 1. a step P1 of preparing a hydrogen storage alloy powder by an atomizing method; a step P2 of adding a binder and water to the prepared hydrogen storage alloy powder to prepare a paste;
A step P3 of applying the prepared paste to the surface of the current collector and drying the paste to form a hydrogen storage alloy layer on the surface of the current collector, and pressing the formed hydrogen storage alloy layer, with the thickness of the hydrogen storage alloy layer after pressing is 1% to 25% thinner relative to the thickness of the hydrogen storage alloy layer before pressurization, the hydrogen storage alloy layer per 1 cm ³ after pressurization 4.5 to Forming a hydrogen storage alloy layer so as to include 6.5 g of the hydrogen storage alloy layer. P4. 2. In the step P4, the thickness of the hydrogen storage alloy layer after pressurization is 1% of the thickness of the hydrogen storage alloy layer before pressurization.
2. The hydrogen storage alloy layer is pressurized so as to be thinner by 9%.
3. The method for producing a hydrogen storage alloy electrode according to item 1. 3. The hydrogen storage alloy powder according to claim 1, wherein an addition ratio of the binder is not more than 0.9%.
3. The method for producing a hydrogen storage alloy electrode according to item 1. 4. The method for producing a hydrogen storage alloy electrode according to claim 3, wherein an addition ratio of the binder is 0.2 to 0.8% based on the hydrogen storage alloy powder.