JP2002015732A - Secondary cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a secondary cell which has a better high-rate discharging characteristic than conventional ones. SOLUTION: A core material 2 which consists of porous nickel foil given a punching process so as to have burrs 2a intentionally formed, is adopted, and hydrogen storing alloy powder 4 which contains nickel powder 3 having a ratio of 2 to 10 wt.% as metal powder having ductility and conductivity is fixed at void ratio 18 to 24% by a current-carrying rolling (or warm rolling) to make up a negative electrode board 1, to be equipped for the secondary cell.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a secondary battery, and more particularly to a secondary battery such as a nickel battery or a nickel cadmium battery used for an electric vehicle or the like, which can improve the basic performance thereof.

[0002]

2. Description of the Related Art Conventionally, an electrode on the negative electrode side of a secondary battery such as a nickel-metal hydride battery or a nickel-cadmium hydrogen battery has a negative electrode made of a hydrogen storage plate formed of a hydrogen storage alloy powder such as a lanthanum-nickel system. A plate is used.

FIG. 7 is a diagram showing the structure of a secondary battery exemplified in the case of a nickel-metal hydride battery. The nickel-metal hydride battery shown here has a case b having a bottom a and an opening at the top. A positive electrode plate c in which a paste-like substance obtained by mixing nickel hydroxide: Ni (OH) ₂ and an organic binder containing a conductive agent is injected into sintered nickel, and a hydrogen storage alloy A negative electrode plate d, and a separator e having a cloth shape interposed between the positive electrode plate c and the negative electrode plate d and impregnated with an electrolytic solution, which is wound in a shape of "Naruto Maki". Accommodating.

A positive electrode current collector f connected to the positive electrode plate c is provided at an opening of the case b. Further, an upper portion of the positive electrode current collector f is closed with an insulating gasket g so as to close the opening. A sealing plate h is provided. At the center of the sealing plate h, a cap j is provided via a safety valve i.

[0005] The negative electrode plate d repeats charging and discharging by absorbing and releasing hydrogen. Therefore, such a negative electrode plate d
The porous body needs to be a porous body having an appropriate liquid or gas permeability through which an electrolytic solution or gas containing hydrogen atoms, molecules, or ions can pass, and have a required strength.

For this reason, as shown in a partially enlarged view in FIG. 8, a conventional negative electrode plate d is formed into a perforated plate by punching a through hole 1 in a steel plate k thinly extended to about 20 to 60 μm. A core material n is formed by performing nickel plating m on the surface of the perforated plate. For example, a hydrogen storage alloy powder o such as a lanthanum-nickel (La-Ni) system and a resin A slurry q mixed with a conductive organic binder obtained by adding conductive fine particles to the adhesive p is applied, dried, and then pressed with a press to obtain, for example, 2.
The negative electrode plate d had a thickness accuracy of about 50 to 450 μm.

[0007]

However, in the case where the negative electrode plate d is formed by applying the slurry q to the core material n and drying the same as described above, the hydrogen storage alloy powder o is used for the core material n. , And the powder particles are hardly electrically connected to each other due to the interposition of the organic binder, so that the electric bonding force between the hydrogen storage alloy powders o decreases, and the hydrogen storage alloy powder o A high conductive network cannot be formed, and an electrolyte such as potassium hydroxide is blocked by the organic binder in the gaps between the particles of the hydrogen storage alloy powder o, and does not spread well. There was a problem that the diffusion rate of hydrogen ions also decreased, and it was difficult to obtain good high-rate discharge characteristics.

The present invention has been made in view of the above circumstances, and has as its object to provide a secondary battery having excellent high-rate discharge characteristics.

[0009]

According to the present invention, a metal powder having ductility and conductivity is provided on both sides of a core material of a porous metal foil which has been subjected to a punching process so that burrs are formed actively. The present invention relates to a secondary battery comprising a negative electrode plate provided with a hydrogen storage alloy powder containing 10% by weight and fixed at a porosity of 18 to 24% by current rolling or warm rolling. .

According to such a secondary battery, the metal powder connects the particles of the hydrogen-absorbing alloy powder and between the particles and the core material, and furthermore, punches the surface of the core material by punching. The burrs penetrate the hydrogen-absorbing alloy powder and the contact area between the core material and the hydrogen-absorbing alloy powder is increased by forming a large number of burrs, so that the hydrogen-absorbing alloy powder is firmly fixed to both surfaces of the core material. Hard to peel off from the core material.

In addition, since the conductive metal powder electrically connects the particles of the hydrogen-absorbing alloy powder to form a good conductive network, high-rate discharge characteristics can be obtained, and the same output as the conventional one can be obtained. In obtaining this, it is possible to achieve a significant reduction in size.

Incidentally, in fixing the hydrogen storage alloy powder to the core material without using the organic binder as described above, the metal powder may be contained at a ratio of 2 to 10% by weight with respect to the hydrogen storage alloy powder. It is effective, and with this ratio, the connection between the particles of the hydrogen storage alloy powder and the connection between the particles and the core material can be performed without any trouble, and the ratio of the metal powder that is not an active material is mischievous. It is possible to maintain a high performance aspect by not increasing the number.

The reason why the porosity of the negative electrode plate is set to 18 to 24% is that when the porosity is made smaller than 18%, ion migration in the electrolyte solution filled in the voids of the negative electrode plate is hindered, resulting in a high porosity. When the discharge characteristics are deteriorated, and when the porosity is larger than 24%, the ratio of the hydrogen storage alloy powder occupying in the negative electrode plate becomes a predetermined level or less, and a practically necessary electric energy storage capacity cannot be obtained. Since the negative electrode plate is configured with such a porosity, the maximum effect of not using an organic binder can be obtained and extremely excellent high-rate discharge characteristics can be obtained. is there.

Further, in the present invention, the uncoated part of the core material, on which the hydrogen-absorbing alloy powder is not fixed, is left unprocessed on the long side portion of the negative electrode plate facing the negative electrode current collector plate side. In this case, the contact between the uncoated portion of the negative electrode plate and the negative electrode current collector plate is prevented from being impaired by the hydrogen storage alloy powder or punching, and the uncoated portion of the negative electrode plate and the negative electrode current collector plate are removed. It is possible to perform reliable welding by electric welding in a state of good contact.

Further, in the present invention, it is possible to form a burr on the edge of the slit by punching a radially extending slit toward the electrode housing side at a plurality of circumferential positions of the negative electrode current collector plate. Preferably, in this case, by welding the negative electrode plate and the negative electrode current collector plate in a state where the burr at the edge of the slit is pressed, the welding current is concentrated on the burr and the weldability is greatly improved. It is possible to more reliably join the negative electrode plate and the negative electrode current collector plate.

[0016]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows an example of a negative electrode plate provided in a secondary battery of the present invention. The negative electrode plate 1 shown here is punched so that burrs 2a are positively formed. Lanthanum-nickel containing a nickel powder 3 (a metal powder having ductility and conductivity) on both sides of the core material 2 in a ratio of 2 to 10% by weight. A hydrogen-absorbing alloy powder 4 of a metal or misch metal type is fixed at a porosity of 18 to 24% by electric current rolling.

The porosity referred to in the present invention refers to the volume ratio of voids in the total volume of the negative electrode plate 1, and the volume of the voids is defined as the hydrogen storage alloy powder 4 and the nickel powder. 3 is obtained by subtracting the volume occupied by the core material 2 from the total volume of the negative electrode plate 1.

Here, the punching of the core 2 is performed, for example, so that the through holes 2b are simultaneously punched in the opposite direction to the core 2 so that burrs 2a are formed alternately on both surfaces of the core 2. To be done.

When the negative electrode plate 1 of FIG. 1 is specifically manufactured, the hydrogen storage alloy powder 4 mixed with the nickel powder 3 is, as schematically shown in FIG. The negative electrode plate 1 may be completed by supplying the material to both surfaces of the core material 2 while passing the core material 2 therebetween, and conducting and rolling the resultant material on the both surfaces of the core material 2 by sintering.

That is, each of the rolling rolls 5 and 6 is made of a conductive material and has an AC or DC power supply device 7.
And the power supply device 7 allows current to flow between the rolling rolls 5 and 6. The hydrogen storage alloy powder 4 is instantaneously heated by energization to change the structure of the hydrogen storage alloy powder 4 (hydrogen storage alloy 4). If the powder 4 is exposed to a high temperature for a long time, the metal structure is not changed, and the hydrogen storage capacity is lost.

Here, the rolling portions of the rolling rolls 5 and 6 are N
_2. It is preferable that an inert gas atmosphere such as Ar, a reducing gas atmosphere such as H ₂ , a vacuum atmosphere, or the like is provided so as to prevent oxidation during energization rolling. The rolling section 6 is surrounded by an antioxidant chamber 8 so that the inside of the antioxidant chamber 8 is maintained in a non-oxidizing atmosphere.

In the example shown here, the case where the hydrogen-absorbing alloy powder 4 is fixed to both surfaces of the core material 2 by energizing rolling is exemplified. Alternatively, the core 4 may be fixed to the core material 2 by hot rolling at a high temperature.

Further, in this embodiment, as shown in FIG. 3, the long side (lower end in FIG. 3) of the negative electrode plate 1 facing the negative electrode current collector plate 9 is provided with a hydrogen storage alloy. Powder 4
The uncoated portion 10 of the core material 2 where the base material is not fixed is left unprocessed, and slits 11 extending in the radial direction are provided on the electrode housing side with respect to a plurality of circumferential positions of the negative electrode current collector plate 9. The burrs 11a (see FIG. 4) are formed at the edges of the slits 11 by punching (upward in FIG. 3).

The positive electrode plate 12 also uses the same core material 13 as the negative electrode plate 1, and applies nickel hydroxide powder 14 to both surfaces of the core material 13 with nickel powder 15 (a metal powder having ductility and conductivity). And then fixed by energizing rolling. Water is also applied to the long side (upper end in FIG. 3) of the positive electrode plate 12 thus configured, which faces the positive electrode current collector plate 16 side. The uncoated portion 17 of the core 13 to which the nickel oxide powder 14 is not fixed is left unprocessed,
At a plurality of locations in the circumferential direction of the positive electrode current collector plate 16, radially extending slits 18 are punched toward the electrode housing side (downward in FIG. 3), and burrs 18 a (FIG. Reference).

Then, the negative electrode plate 1 and the positive electrode plate 12 are wound in a shape of a “slipper” with a separator 19 interposed therebetween, and the uncoated portion 10 at the lower end of the negative electrode plate 1 is placed on the inner surface of the negative electrode current collector plate 9 (in FIG. In contact with the upper surface), and electric welding is performed.
2 is connected to the inner surface of the positive current collector 16 (FIG. 3).
(The lower surface in the inside), and they are electrically welded. These are housed in a case (not shown), the inside of the case is filled with an electrolytic solution, and the opening is finally sealed with a cap or the like to complete the secondary battery. I have to.

According to the secondary battery constructed as described above, with respect to the negative electrode plate 1 mounted inside the secondary battery, the nickel powder 3 causes the particles of the hydrogen storage alloy powder 4 to inter-between the particles and the core material 2 And the burr 2a punched on the surface of the core material 2 penetrates the hydrogen storage alloy powder 4 and forms a large number of burrs 2a to form the core material 2 and the hydrogen storage alloy powder 4. Since the contact area is increased, the hydrogen-absorbing alloy powder 4 is firmly fixed to both surfaces of the core material 2, and it is difficult to peel off the hydrogen storage alloy powder 4 from the core material 2.

Further, since the conductive nickel powder 3 electrically connects the particles of the hydrogen storage alloy powder 4 to form a good conductive network, a high rate discharge characteristic is obtained. When obtaining an output, it is possible to greatly reduce the size.

As described above, when the negative electrode plate 1 is formed by fixing the hydrogen storage alloy powder 4 to the core material 2 without using an organic binder, the hydrogen storage alloy powder
It is effective to include the nickel powder 3 at a ratio of 0% by weight. With this ratio, the connection between the particles of the hydrogen storage alloy powder 4 and the connection between the particles and the core material 2 can be performed without any trouble. It is possible to maintain high performance by not unnecessarily increasing the ratio of the metal powder that is not an active material.

Here, the content ratio of the nickel powder 3 is 2%
It should be added that the nickel-rich layer can be formed by subjecting the hydrogen-absorbing alloy powder 4 to an alkaline boiling treatment. 3
Can be reduced to 2%.

The reason why the porosity of the negative electrode plate 1 is set to 18 to 24% is that when the porosity is smaller than 18%, ion migration in the electrolyte filled in the voids of the negative electrode plate 1 is hindered. The high-rate discharge characteristics deteriorate, and the porosity is 24
%, The ratio of the hydrogen-absorbing alloy powder 4 in the negative electrode plate 1 falls below a predetermined level, which makes it impossible to obtain a practically necessary electric energy storage capacity. Since the negative electrode plate 1 is configured with such a porosity, it is possible to obtain the maximum effect of not using an organic binder and obtain extremely excellent high-rate discharge characteristics.

For example, according to a verification experiment by the present inventors, as shown in FIG. 6 as an example, when the performance of a negative electrode plate having a porosity of 20% is compared with that of a negative electrode plate having a porosity of 17%, discharge is particularly high. In the high capacity region, it has been found that the battery voltage of the negative electrode plate having a porosity of 17% is much lower than that of the negative electrode plate having a porosity of 20%. However, it has been confirmed that this appears remarkably in the case where the porosity of the negative electrode plate is lower than 20%.

On the other hand, in the secondary battery, it is necessary to increase the electric energy storage capacity by securing the volume occupied by the hydrogen storage alloy powder 4 as the active material as much as possible with respect to the determined volume. The volume occupied by the hydrogen storage alloy powder 4 in the current nickel-metal hydride secondary battery is about 60%
In consideration of this, in order to secure about 60%, the thickness of the negative electrode plate 1, the amount of the nickel powder 3, and the thickness of the core material 2 are adjusted as parameters within a range that does not impair the high-rate discharge characteristics. Is performed, the porosity of the negative electrode
%, It is extremely difficult to secure the volume occupied by the hydrogen storage alloy powder 4 to about 60%.

In order to further increase the electric energy storage capacity over conventional products, it is considered that the volume occupied by the hydrogen storage alloy powder 4 in the nickel-metal hydride secondary battery should be increased to about 68 to 71%. Preferably, the porosity of the negative electrode plate 1 is reduced to 18 to 22%.

Therefore, according to the above-described embodiment, the hydrogen storage alloy powder 4 is firmly fixed to both surfaces of the core material 2 without using an organic binder as in the related art for the negative electrode plate 1 of the secondary battery. In addition, the particles of the hydrogen storage alloy powder 4 can be electrically connected to each other, and a large contact area between the core material 2 and the hydrogen storage alloy powder 4 can be ensured to form a good conductive network. Further, an electrolyte such as potassium hydroxide can be spread well in the gaps between the particles of the hydrogen storage alloy powder 4 to greatly improve the diffusion rate of hydrogen ions. Due to the synergistic action, extremely excellent high-rate discharge characteristics can be obtained.

Further, as shown particularly in the present embodiment, the negative electrode plate 1 and the positive electrode plate 12 on the side of the negative electrode current collector 9 and the positive electrode current collector 1
6, the uncoated portions 10 and 17 where the hydrogen storage alloy powder 4 and the nickel hydroxide powder 14 are not fixed.
Is left unprocessed, the uncoated portions 10 and 17 of the negative electrode plate 1 and the positive electrode plate 12, the negative current collector 9 and the positive current collector The uncontacted portion 10 of the negative electrode plate 1, the negative electrode current collector 9, and the positive electrode 12
In this state, the uncoated portion 17 and the positive electrode current collector plate 16 are satisfactorily contacted with each other, and can be reliably joined by electric welding.

The slits 1 extending in the radial direction are provided at a plurality of locations in the circumferential direction of the negative electrode current collector plate 9 and the positive electrode current collector plate 16.
If the burrs 11a and 18a are formed at the edges of the slits 11 and 18 by punching the electrodes 1 and 18 toward the electrode housing side, the burrs 11a and 18 at the edges of the slits 11 and 18 are formed.
By welding the negative electrode plate 1 and the negative electrode current collector plate 9 and the positive electrode plate 12 and the positive electrode current collector plate 16 in a state where the pressure a is sandwiched, the welding current is concentrated on the burrs 11a and 18a, thereby greatly improving the weldability. Thus, the negative electrode plate 1 and the negative electrode current collector 9 and the positive electrode plate 12 and the positive electrode current collector 16 can be more reliably bonded.

It should be noted that the present invention is not limited only to the above-described embodiment, and the same structure except for the definition of the porosity is applied to the positive electrode plate of a nickel hydride battery and the positive and negative electrode plates of a lithium ion battery. Applicability, with regard to specific materials for hydrogen storage alloy powder, core material, metal powder having ductility and conductivity, materials other than those specifically described in the specification may be selected Of course, various changes can be made without departing from the spirit of the present invention.

[0039]

According to the above-mentioned secondary battery of the present invention, various excellent effects as described below can be obtained.

(I) According to the first aspect of the present invention, with respect to the negative electrode plate of the secondary battery, the hydrogen storage alloy powder is applied to both surfaces of the core material without using the conventional organic binder. In addition, it can be firmly fixed, and furthermore, electrically connects the particles of the hydrogen storage alloy powder and secures a large contact area between the core material and the hydrogen storage alloy powder to form a good conductive network. In addition, since the electrolyte such as potassium hydroxide can be spread well in the gaps between the particles of the hydrogen storage alloy powder, the diffusion rate of hydrogen ions can be greatly improved. By the synergistic action of the above, extremely excellent high rate discharge characteristics can be obtained.

(II) According to the second aspect of the present invention, the contact between the uncoated portion of the negative electrode plate and the negative electrode current collector plate is not impaired by the hydrogen storage alloy powder or punching, and the negative electrode The solid part of the plate and the negative electrode current collector plate can be securely joined by electric welding in a state where they are in good contact with each other.

(III) According to the third aspect of the present invention, the welding current is obtained by electrically welding the negative electrode plate and the negative electrode current collector plate with the burrs at the edges of the slit being pressed. Is concentrated on the burrs, the weldability is greatly improved, and the negative electrode plate and the negative electrode current collector plate can be more reliably joined.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view schematically showing one example of an embodiment of the present invention.

FIG. 2 is a schematic diagram showing a state in which hydrogen storage alloy powder is electrically rolled on both surfaces of a core material.

FIG. 3 is a perspective view showing details of an internal structure of a secondary battery equipped with the negative electrode plate of FIG. 1;

FIG. 4 is a cross-sectional view of a slit punched portion of the negative electrode current collector plate of FIG.

FIG. 5 is a sectional view of a slit punched portion of the positive electrode current collector plate of FIG. 3;

FIG. 6 is a graph showing an example of test data of a high-rate discharge characteristic of a nickel-hydrogen secondary battery.

FIG. 7 is an exploded perspective view showing a part of an example of the secondary battery in a broken state.

FIG. 8 is a cross-sectional view schematically showing one example of a conventional negative electrode plate.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Negative electrode plate 2 Core material 2a Burr 3 Nickel powder (metal powder) 4 Hydrogen storage alloy powder 9 Negative current collector plate 10 Solid part 11 Slit 11a Burr

Continued on the front page F term (reference) 5H017 AA02 CC01 DD08 5H022 AA04 BB02 CC22 5H028 AA05 BB15 CC12 5H050 AA02 BA14 CA03 CB16 DA03 DA10 EA02 FA05 HA01

Claims (3)

[Claims] 1. A metal powder having ductility and conductivity is contained at a ratio of 2 to 10% by weight on both sides of a core material of a porous metal foil subjected to a punching process so that burrs are formed actively. A secondary battery comprising a negative electrode plate formed by fixing a hydrogen storage alloy powder at a porosity of 18 to 24% by current rolling or warm rolling. 2. A non-processed portion of a core material on which the hydrogen-absorbing alloy powder is not fixed is left unprocessed on a long side portion of the negative electrode plate facing the negative electrode current collector plate side. 2. The secondary battery according to 1. 3. The method according to claim 1, wherein a plurality of positions on the negative electrode current collector plate in the circumferential direction are provided.
The secondary battery according to claim 1, wherein a slit extending in a radial direction is punched toward the electrode housing side to form a burr at an edge of the slit.