JP2002124253A - Nickel-hydrogen storage battery and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To further enhance initial service capacity, a high-rate discharging characteristic, and cycle life, in the case of a nickel-hydrogen storage battery. SOLUTION: A negative electrode is formed of a negative electrode core made of a ferromagnetic substance and/or a negative electrode paste (a hydrogen storage alloy powder or with an addition of a ferromagnetic powder). The negative electrode is given magnetism of 2 Ga or more by magnetizing it in the width or thickness direction of the electrode to strengthen a current collecting network between the core and the alloy powder, thereby improving charging/discharging characteristics. A method wherein a previously magnetized core is used or a method wherein the core is magnetized in a subsequent process can be employed as the magnetizing process.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a nickel-hydrogen storage battery using mainly a nickel hydroxide as a positive electrode and a hydrogen storage alloy capable of electrochemically storing and releasing hydrogen as a negative electrode and a method of manufacturing the same. It is.

[0002]

2. Description of the Related Art In recent years, with the development of portable devices and cordless devices, batteries as power sources thereof are required to have higher energy density and higher performance. To meet this demand, nickel-metal hydride storage batteries having a negative electrode of a hydrogen storage alloy, which has a volume energy density substantially equal to that of a lithium ion battery and is inexpensive, are used in many devices.

[0003] Such a negative electrode plate for a nickel-hydrogen storage battery is prepared by applying a paste comprising a hydrogen storage alloy powder, a binder, a thickener, etc. on a negative electrode core material as a current collector, drying and pressing. It is made. As the negative electrode core material, two types of foamed metal core material (SME), which is a porous body of nickel, and a punched metal core material (PME) obtained by plating nickel on the surface of a thin punched metal sheet made of iron are mainly used.

[0004] As the hydrogen storage alloy is a mainstream multicomponent alloy of MmNi ₅ system based on nickel. With higher performance of equipment, higher capacity and superior high rate discharge characteristics,
A long-life nickel-metal hydride storage battery is desired.

[0005]

On the other hand, a body-centered cubic lattice (bcc) type TiV-based hydrogen storage alloy having a large hydrogen storage amount, for example, a Ti _x V _y Ni _z alloy (Japanese Unexamined Patent Publication No.
228699) has been mainly developed.

However, when these hydrogen storage alloys are used, any one of the above-mentioned characteristics can be improved, but there is a problem that other characteristics are reduced or the cost is increased.

As a result of extensive studies, we have magnetized the negative electrode plate from the battery construction side and constructed a strong current collection network by magnetic attraction, thereby providing a high-capacity, high-rate discharge characteristic and an inexpensive. A long-life nickel-metal hydride storage battery has been realized.

[0008]

According to the present invention, the magnetic attraction force between the hydrogen storage alloy powder and between the negative electrode core material and the hydrogen storage alloy powder is increased by imparting magnetism (preferably 2 Ga or more) to the negative electrode plate. It is an object of the present invention to provide a long-life nickel-metal hydride storage battery that can work and strengthen the current collection network, and has high capacity and excellent high-rate discharge characteristics.

In a negative electrode plate composed of a negative electrode core material and a negative electrode paste (comprising a hydrogen storage alloy powder, a binder, a thickener, etc.), the negative electrode core material and / or the negative electrode paste are magnetized to be magnetically attracted. A force is generated to improve the current collection of the negative electrode plate. In order for the negative electrode plate to have magnetism, the negative electrode core material and / or the negative electrode paste must have a ferromagnetic material and be magnetized. To make the negative electrode paste magnetic,
A method is possible in which the hydrogen storage alloy powder itself is a ferromagnetic substance or a ferromagnetic powder having no hydrogen storage ability is added separately from the hydrogen storage alloy powder. However, in the latter case, the addition amount of the ferromagnetic powder should be 1 in consideration of the discharge capacity.
More than 5% by weight is effective.

The timing of the magnetization of the negative electrode plate is as follows: (1) The negative electrode core material is preliminarily magnetized, and then the negative electrode paste is applied to the negative electrode core material, dried and pressed to produce the negative electrode plate. (2) When applying the negative electrode paste to the negative electrode core material, a magnetic field is applied to the negative electrode paste, followed by drying and pressing to produce a negative electrode. (3) Applying the negative electrode paste to the negative electrode core material Thereafter, the paste is magnetized before or during drying of the paste. (4) The paste is applied to the anode core material, dried and pressed to produce the anode plate, and then magnetized. (5) The electrode is formed from the anode, the cathode and the separator. After the unit is manufactured, it is effective to magnetize the electrode unit. The direction of application of the magnetic field at the time of magnetization is preferably along the width direction or the thickness direction of the negative electrode plate in terms of the magnitude of the leakage magnetic field.

Few hydrogen storage alloy powders themselves have large remanent magnetization, and can be magnetized by providing a nickel layer on the surface. The strength of the magnetic field due to the residual magnetization of the negative electrode plate is desirably 2 Ga or more in order to form an effective current collection network.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In a nickel-metal hydride storage battery,
The cycle life is caused by a decrease in capacity (deterioration) of the negative electrode at the end of the cycle. At the beginning of the cycle, the capacity of the positive electrode dominate the battery capacity, but as the charge / discharge cycle is repeated, the hydrogen storage alloy is pulverized and partially departs from the current collection network. The powder that does not contribute to the battery reaction gradually increases, and the actual negative electrode capacity decreases, and the negative electrode capacity starts to dominate the battery capacity. It is considered that since the load on the negative electrode is further increased from this point, the hydrogen storage alloy powder is further reduced in size, the battery capacity is rapidly reduced, and the cycle life is extended. Therefore, by restraining the hydrogen storage alloy powder in the current collecting network by the magnetic attraction force, it is possible to suppress a decrease in the discharge capacity. In addition, since the current collection network is strong, the high-rate discharge characteristics are greatly improved.

Hereinafter, embodiments of the present invention will be described in detail.

(Embodiment 1) A predetermined amount of Mm (mixed rare earth),
An Mmmn _0.4 Al _0.3 Co _0.8 Ni _3.9 alloy was prepared from Mn, Al, Co, and Ni using a high-frequency melting furnace.
After annealing in vacuum at 1000 ° C. for 4 hours, alloy powder having an average particle size of 25 μm was obtained by mechanical pulverization and classification.
This powder was further immersed (alkali treatment) in 110 ° C. 5N potassium hydroxide solution for 1 hour, washed with water and dried to obtain a negative electrode hydrogen storage alloy powder.

Next, carboxymethyl cellulose (CMC) was used as a binder for 100 parts by weight of the alloy powder.
0.2 parts by weight, 1 part by weight of SBR as a thickener is added,
A small amount of water was added to form a paste, which was applied to both surfaces of a magnetized punched metal core (PME), dried and pressed to produce a negative electrode. Here, Cunico (alloy composition: 29Co.21Ni.50Cu) was used as the PME.
Thickness 60μm, punch hole diameter 2mm, punch hole interval 6mm
And magnetized using an electromagnet along the width direction (axial direction at the time of winding). When the magnetism of the produced negative electrode plate was measured with a Gauss meter, it varied depending on the location, but showed 3.2 Ga at the weakest point.

As the positive electrode, a foamed metal core material (SME) filled with spherical nickel hydroxide coated with cobalt oxyhydroxide was used. A positive electrode and a negative electrode are wound through a sulfonated olefin-based separator to produce an electrode unit, which is incorporated in a cylindrical battery case, and an electrolyte is injected under vacuum to regulate the positive electrode (positive / negative electrode capacity ratio 1: 1). 1.5) A sealed nickel-metal hydride battery (calculated capacity 1500 mAh) was produced.

Next, the first charge is performed at a current of 300 mA for 5 minutes.
Performed for 30 minutes and discharged at 300 mA (0.2 C discharge,
C: time rate discharge current), and a 1.0 V cut was performed, and the initial discharge capacity was measured. The second charging was performed under the same conditions as the first, the discharging was performed at 3 A (2 C), and the voltage was cut at 1 V. The ratio (%) of the second discharging capacity to the first discharging capacity was defined as high-rate discharging characteristics. 750 mA for the third and subsequent times, 2 hours 15
The charge / discharge cycle of minute charging, 750 mA, and 1 V cut was repeated, and the number of times the discharge capacity reached 70% of the third discharge capacity was defined as the cycle life of the battery. Table 1 shows the initial discharge capacity, high-rate discharge characteristics, and cycle life of this example. For comparison, a case where non-magnetized PME plated with nickel on a normal iron punching metal was used (Comparative Example 1)
The results are also shown. When the magnetism of the negative electrode plate was measured, it was 0.1 Ga or less. In this example, all the characteristics were improved as compared with the conventional one, and the effect was recognized. The reason for this is that, because the core material is magnetized, the hydrogen storage alloy powder (ferromagnetic nickel component on the alloy surface generated by the alkali treatment) that exhibits ferromagnetism is magnetically attracted to the core material and the hydrogen storage alloy It is considered that the magnetic attraction force acted between the powders and the current collecting property was improved. By repeating the charge and discharge in the battery, the pulverization of the hydrogen storage alloy powder proceeds, but since there is a strong current collection network by the magnetic field, the generation of the hydrogen storage alloy powder that is free and does not contribute to the battery reaction is suppressed, It is thought that the cycle life was also improved. As the negative electrode core material used in the cylindrical battery, a material having ductility to be wound is desirable.

[0018]

[Table 1]

(Embodiment 2) With the same material composition as in Embodiment 1,
A negative electrode paste was applied on both sides of the unpolarized negative electrode core material. During coating, a magnetic field was applied between discharge nozzles for coating to magnetize the negative electrode plate in the thickness direction. Thereafter, the battery was dried and pressed to produce a negative electrode plate, and a sealed nickel-hydrogen storage battery was assembled in the same manner as in Example 1. When the magnetism of this negative electrode plate was measured, it showed 4.0 Ga at the weakest point.

Table 1 shows the results of a charge / discharge test performed under the same conditions as in Example 1. All the characteristics were improved as compared with the conventional one (Comparative Example 1).

The magnetization in the longitudinal direction of the negative electrode plate has a low applied magnetic field strength due to the large gap between the magnetic poles, and further has a small leakage magnetic field from the negative electrode plate after the magnetization. Not suitable.

Example 3 The same hydrogen storage alloy powder as in Example 1 was used. 0.2 parts by weight of carboxymethyl cellulose (CMC) as a binder and 1 part by weight of SBR as a thickener were used for 100 parts by weight of the alloy powder. Parts, and 2 parts by weight (1.9% by weight in weight fraction) of cobalt steel powder (particle size: 20 μm), which is a ferromagnetic substance, is added to form a paste by adding a small amount of water. It was applied to nickel-plated PME, and before drying, a magnetic field was applied from both sides of the coated electrode plate in the thickness direction to perform magnetization. Thereafter, drying and pressing were performed to produce a negative electrode plate. When the magnetism of the negative electrode plate was measured, it showed 5.4 Ga at the weakest point. Next, a cylindrical sealed nickel-metal hydride storage battery was manufactured using the positive electrode and the separator manufactured in the same manner as in Example 1.

Table 1 shows the results of the same charge / discharge test as in Example 1. Although the initial discharge capacity was equal to that of Comparative Example 1, other characteristics were significantly improved.

(Example 4) In the same configuration as in Example 3, 1.1 parts by weight (1.1% by weight) of cobalt steel powder was added to form a paste, which was applied to a normal PME as in Example 3. It was then dried and pressed to produce a negative electrode plate. Magnetization was performed by applying a magnetic field in the thickness direction of the negative electrode plate. When the magnetism of the negative electrode plate was measured, the weakest point was 2.0 G
a.

Next, a sealed nickel-metal hydride storage battery was manufactured using the positive electrode and the separator manufactured in the same manner as in Example 1. For comparison, a negative electrode plate to which 0.9 parts by weight (0.9% by weight) and 6 parts by weight (5.6% by weight) of cobalt steel powder were added (magnetic field strengths of 1.8 Ga and 19 Ga, respectively)
Ga) was used to produce a sealed nickel-metal hydride battery (Comparative Example 2 and Comparative Example 3) similar to that of this example. Table 1 shows the results of the same charge / discharge test as in Example 1. In Comparative Example 2, none of the battery characteristics was significantly improved, and in Comparative Example 3, the initial discharge capacity was significantly reduced. On the other hand, in this example, the initial discharge capacity and the high-rate discharge characteristics were not significantly improved, but the cycle life was greatly improved.

From this, it was found that the addition amount of the cobalt steel powder is effective at 1% by weight or more from the viewpoint of high rate discharge characteristics and cycle life and at most 5% by weight from the viewpoint of initial discharge capacity.

(Example 5) Composition MmM as in Example 3.
Carboxymethylcellulose (CM) was used as a binder with respect to 100 parts by weight of n _0.4 Al _0.3 Co _0.8 Ni _3.9 alloy powder.
C) 0.2 parts by weight, 1 part by weight of SBR as a thickener, and 5 parts by weight (4.7% by weight) of cobalt steel powder (particle diameter: 20 μm) which is a ferromagnetic substance were added, and a small amount of water was added. To form a negative electrode plate. After using the negative electrode plate to form an electrode unit in the same manner as in Example 1, a magnetic field was applied in the width direction (axial direction of the cylinder) to perform magnetization. When the magnetism was measured at the outermost periphery, the minimum value showed 8.0 Ga.

Using the positive electrode and the separator produced in the same manner as in Example 1, a sealed nickel-metal hydride storage battery was produced. Table 1 shows the results of the same charge / discharge test as in Example 1. Although the initial discharge capacity was equal to that of Comparative Example 1, the high rate discharge characteristics and the cycle life characteristics were improved.

(Example 6) The alloys are Ti, V, La, and Cr.
Using a metal as a raw material, a body-centered cubic (bcc) hydrogen storage alloy powder (average particle size: 45 μm) having a composition of Ti _0.3 V _0.5 La _0.05 Cr _0.1 was prepared by a gas atomization method using argon gas. Next, after a nickel layer (about 1 μm thick) was formed on the surface of the hydrogen storage alloy powder by electroless plating,
Heat treatment was performed at 00 ° C. to obtain a hydrogen storage alloy powder for a negative electrode.

Next, samarium Sm-cobalt Co ₅ powder (particle size: 25 μm) was added to 100 parts by weight of the alloy powder.
m) 5 parts by weight (4.7% by weight), 0.2 parts by weight of carboxymethylcellulose (CMC) as a binder, 1 part by weight of SBR as a thickener, and a small amount of water were added to form a paste. It was coated on the same Cunico PME as in Example 1 and was magnetized during drying to produce a rectangular negative electrode plate.
This negative electrode plate was magnetized in the thickness direction with an electromagnet. When the magnetism of the produced negative electrode plate was measured, it showed 28Ga at the minimum.

As the positive electrode and the separator, the same material as in Example 1 was used, and a rectangular one was used. Five positive electrodes and six negative electrodes were laminated between the positive electrode and the negative electrode with a separator interposed therebetween (the positive electrode has slightly larger dimensions than the negative electrode). The electrode unit is made smaller, the separator size is larger than the negative electrode), and an electrode unit is manufactured and assembled in a rectangular battery case.
5) Square sealed nickel-metal hydride battery (calculated capacity 3)
000 mAh).

The first charge is performed at a current of 600 mA for 5 hours and 30 minutes, and discharge is performed at 600 mA (0.2 C) and 1.0 V
The cutting was performed, and the initial discharge capacity was measured. The second charge was performed under the same conditions as the first charge, and the discharge was performed at 6 A (2 C), 1 V
The cutting was performed, and the ratio of the second discharge capacity to the first discharge capacity was defined as high-rate discharge characteristics. 1.5 after the third
A, charge and discharge cycles of 1.5 hours and 1 V cut, charging for 2 hours and 15 minutes were repeated, and the number of times the discharge capacity reached 70% of the third discharge capacity was defined as the cycle life. Table 1 shows the results of the charge / discharge test.

For comparison, a negative electrode plate having the same shape as that of the present embodiment and the same PME as that of Comparative Example 1 was prepared using a structure in which SmCo ₅ powder was not added to the negative electrode paste. Using this negative electrode plate, a prismatic nickel-metal hydride storage battery (Comparative Example 4) was produced in the same configuration as in this example, and a charge / discharge test was performed. In addition, a battery (Comparative Example 5) having exactly the same configuration as that of the present example and without magnetizing the negative electrode plate and having no magnetism was produced. Although the results are also shown in Table 1, this example is superior to Comparative Example 4 in high-rate discharge characteristics and cycle life characteristics.
Outperformed in all properties.

As described above, it was found that the charge and discharge characteristics were greatly improved by magnetizing the negative electrode to 2 Ga or more. The upper limit of the magnetic strength is preferably as large as possible as long as the initial discharge capacity does not decrease, but the value varies depending on the ferromagnetic material used.

The timing of the magnetization is as follows: (1) magnetizing the negative electrode core material in advance, (2) coating, (3) before or during drying of the coating paste, and (4) after the preparation of the negative electrode plate. It was effective to magnetize the plate and (5) magnetize the electrode unit after producing the electrode unit. In particular, when the paste is magnetized before drying, a strong current collecting network is formed between the hydrogen storage alloy powders, and the initial discharge capacity and the high rate discharge characteristics can be improved.

[0036]

As is evident from the above embodiment, magnetism is given to the negative electrode plate by magnetization, and a strong current collection network is formed in the negative electrode plate. And a nickel-hydrogen storage battery having excellent cycle life.

The present manufacturing method has an advantage that a strong current collecting network can be formed at low cost and the overall charge / discharge characteristics can be improved.

 ──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Hiroshi Sato 1006 Kazuma Kadoma, Kadoma City, Osaka Prefecture F-term (reference) in Matsushita Electric Industrial Co., Ltd. FF02 FF04 HH01 5H050 AA02 AA07 AA08 BA14 CA03 CB17 CB18 DA03 DA04 DA09 EA02 FA17 GA01 GA02 GA03 GA10 GA22 GA27 HA01 HA16

Claims (12)

[Claims] 1. A nickel-hydrogen storage battery comprising a positive electrode made of nickel hydroxide and a negative electrode made of a hydrogen storage alloy, wherein the negative electrode plate has magnetism. 2. A nickel-metal hydride storage battery according to claim 1, wherein said negative electrode plate has a magnetism of 2 Ga or more. 3. The nickel-metal hydride storage battery according to claim 1, wherein the negative electrode comprises a negative electrode core material and a negative electrode paste, and the negative electrode core material and / or the negative electrode paste has magnetism. 4. The nickel-metal hydride storage battery according to claim 3, wherein the negative electrode paste has a ferromagnetic powder having no hydrogen absorbing ability. 5. The nickel-hydrogen storage battery according to claim 4, wherein the content of the ferromagnetic powder is 1% by weight or more and 5% by weight or less. 6. A nickel-hydrogen battery in which a negative electrode core material is preliminarily magnetized, and a negative electrode paste is applied on the magnetized negative electrode core material, dried and pressed to produce a negative electrode plate having magnetism. Manufacturing method of storage battery. 7. The method of applying a negative electrode paste to a negative electrode core material,
A method for producing a nickel-metal hydride storage battery in which a magnetic field is applied to magnetize, and then dried and pressed to produce a negative electrode plate having magnetism. 8. A method for producing a nickel-metal hydride storage battery, wherein a negative electrode plate having magnetism is produced by applying a negative electrode paste to a negative electrode core material, prior to or during drying of the paste, and then pressing. 9. A negative electrode plate is prepared by applying a negative electrode paste to a negative electrode core material, drying and pressing, and then magnetizing the negative electrode plate to prepare a negative electrode plate having magnetism. Manufacturing method of hydrogen storage battery. 10. A method for producing a nickel-metal hydride storage battery, comprising: producing an electrode unit from a negative electrode, a positive electrode and a separator, and magnetizing the electrode unit to produce a negative electrode plate having magnetism. 11. The nickel-hydrogen storage battery according to claim 6, wherein the magnetic field is applied along a width direction of the negative electrode plate by applying a magnetic field. Production method. 12. A method for manufacturing a nickel-metal hydride storage battery according to claim 6, wherein the magnetization is performed by applying a magnetic field in the thickness direction of the negative electrode plate. .