JPH09204911A - Manufacture of positive electrode plate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To minimize the occurrence of a welding failure by the residual nonconductive active material by compressing a prescribed position of a current collector to provide a tab mounting position, and continuously patting the tab mounting position after filling an active material paste. SOLUTION: A nickel porous sheet is pressed in the thickness direction by use of a press machine to form a recessed part 2, and a tab 2a is mounted thereon. A paste-like active material mix is applied onto the sheet followed by drying, and the whole sheet is rolled to regulate the thickness, and then cut into a prescribed dimension to form a positive electrode plate precursor 1a. The tab 2b of the precursor 1a is subjected to nickel hydroxide removing work. This removing work is performed by continuously patting the tab mounting position by an impact imparting means 4. As the imparting means 4, a member formed of a bundle of a plurality of needles 4a is used, and the nickel hydroxide exposed to the surface of the mounting position 2a is scraped to the needle tips, and the nickel hydroxide is peeled off from the communicating holes within the mounting position 2a.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a nickel positive electrode plate for an alkaline secondary battery.
The present invention relates to a method for producing a positive electrode plate in which a tab is spot-welded in a stable state to a positive electrode plate in which a current collector having a three-dimensional network structure carries an active material mixture.

[0002]

2. Description of the Related Art Nickel / cadmium batteries and nickel /
The nickel positive electrode plate incorporated as the positive electrode of the hydrogen battery is
The positive electrode active material mixture is carried on the current collector, and a tab for current collection is spot welded to a part of the positive electrode active material mixture.
As the current collector used for the nickel positive electrode plate, for example,
A foamed nickel porous body having a three-dimensional network structure is generally used.

Further, as the positive electrode active material mixture supported on the nickel porous body, a mixed powder containing nickel hydroxide as a main component and, if necessary, powder of a cobalt compound such as cobalt oxide is mixed. Used. here,
The particle size of the powder constituting the active material mixture is usually 1 to 100.
It is about μm. A sheet made of nickel foil or the like is generally used as the current collecting tab attached to the nickel porous body.

The nickel positive electrode plate having the above structure is
Usually, it is manufactured as follows. That is, first, an aqueous solution of a thickener prepared by dissolving carboxymethyl cellulose or methyl cellulose is added to the mixed powder of the positive electrode active material, and the whole is stirred to obtain a viscous paste-like active material mixture. Then, the sheet-like nickel porous body is filled and coated with the paste-like active material mixture, and then dried. As shown in FIG. 1, in the sheet-shaped nickel porous body 1, a recess 2 is formed in advance by crushing a predetermined range of a predetermined position in the thickness direction. The concave portion 2 will be a tab attachment point described later.

Thereafter, the entire sheet-shaped nickel porous body is rolled to adjust the thickness, and a predetermined portion indicated by a chain double-dashed line in FIG. 1 is cut by a cutter, and as shown in FIG. A strip-shaped nickel positive electrode plate precursor 1a having tab attachment points 2a at predetermined positions is obtained. The tab attachment portion 2a has a higher density than the other portions, so that a good nugget portion can be formed at the time of spot welding performed in the subsequent stage.

Finally, after the tab sheet ends of the strip precursor 1a are overlapped with the tab sheet ends to form a welded portion, the welded portion is attached to the upper electrode of the spot welding machine and the lower electrode. Electric current is applied while applying pressure to the electrode, and the tab 3 is spot-welded to the precursor to form a nickel positive electrode plate 1A as shown in FIG. The nickel positive electrode plate manufactured in this manner is incorporated into a battery outer can together with a negative electrode plate, a separator, an electrolytic solution and the like to form a battery.

[0007]

By the way, since nickel hydroxide used as the positive electrode active material is non-conductive, if the nickel hydroxide is present in the above-mentioned welded portion, energization will occur during spot welding. It may be hindered and good welding condition may not be obtained. In other words, in the nickel positive electrode plate, it is desirable to maximize the filling amount of nickel hydroxide in order to increase the capacity of the battery except for the welded portion of the tab, but at the tab attachment location, to eliminate welding defects. In addition, it is desirable to avoid the presence of nickel hydroxide at the mounting location as much as possible.

Therefore, usually, the active material is scraped off from the surface of the mounting portion of the tab to remove the nickel hydroxide on the surface layer, and then spot welding is performed. However, at the tab attachment location, even if the nickel hydroxide on the surface layer is removed, the nickel hydroxide still remains inside, so during the spot welding, the nickel hydroxide exists. Sparking is likely to occur due to poor electrical conduction resulting in poor welding.

It has been attempted to utilize ultrasonic vibration in order to remove such nickel hydroxide inside the nickel porous body, but in that case, ultrasonic vibration has high vibration energy, and therefore, It may damage the electrode plate itself and is not preferable as a means for removing nickel hydroxide in the porous nickel body. The present invention solves the above-mentioned problems in the nickel positive electrode plate of the alkaline secondary battery, and can reduce the occurrence of welding defects due to the non-conductive active material remaining at the tab attachment point. An object of the present invention is to provide a manufacturing method of.

[0010]

In order to achieve the above object, in the present invention, a tab is spot-welded to a current collector having a three-dimensional network structure carrying an active material mixture mainly composed of nickel hydroxide. In this case, a predetermined part of the current collector is compressed to provide a tab attachment part, and then the current collector is filled with an active material paste and then dried, and the tab attachment part is given an impact by bundling a plurality of needles. A method for manufacturing a positive electrode plate is provided, which comprises continuously hitting with a means.

In the method for producing a positive electrode plate of the present invention, the impact density of the needles is 400 needles / cm ² or more, and a force of 0.8 to 2.4 kgf is applied to the positive electrode plate at a rate of 6 per second.
It is preferable to continuously tap the tab attachment portion at a rate of -18 times. The method for manufacturing a positive electrode plate according to the present invention is an impact imparting means in which a plurality of needles are bundled, and by continuously striking the tab attachment point, the impact is applied to the point, and this impact causes the inside of the current collector to be damaged. The active material that has been filled up to the end, namely nickel hydroxide, is removed.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION In the method for producing a positive electrode plate according to the present invention, the step of producing a precursor for a positive electrode plate (hereinafter referred to as step A) and the nickel hydroxide present at the tab attachment portion of the precursor are removed. The process (hereinafter, referred to as process B) is included as an essential process. Process A and process B described above
In the present invention, the active material existing in the tab attachment portion is removed from the active material filled in the current collector by sequentially performing the above. As a result, spot weldability at the tab attachment point is improved.

First, in step A, a current collector having a three-dimensional network structure is prepared. Here, 3 used in the present invention
The current collector having a three-dimensional network structure is not particularly limited as long as it is a conventionally used one, but it is possible to increase the filling amount of the paste-like active material mixture. And, for example, a porosity of 94 to 97% and a pore size of 5
A sheet of a foamed nickel porous body having a communication hole of 0 to 500 μm can be mentioned as a preferable example.

Then, by using, for example, a pressing machine, the nickel porous sheet 1 is crushed at a predetermined position in the thickness direction to be densified and the recess 2 is formed. Here, when the concave portion 2 is provided in the nickel porous body sheet 1 by press molding, the nickel porous body sheet is crushed to increase the density, and the weldability in the spot welding performed in the subsequent stage is improved. However, if the rolling reduction during press molding exceeds 91%, the sponge-like nickel sheet becomes very dense and the weldability is improved, but on the other hand, the metal becomes brittle and the mechanical strength decreases. . On the other hand, if the rolling reduction is less than 83%, the work of removing nickel hydroxide becomes relatively easy, but the nickel sheet is not densified and spot weldability is impaired. Therefore, it is preferable to set the reduction rate when forming the tab attachment portion in the range of 83% or more and 91% or less.

Then, the paste-like active material mixture prepared by a predetermined method as conventionally used is filled and applied to the nickel porous body sheet, and then dried. Next, the whole of the nickel porous body sheet is roll-rolled to adjust the thickness, and thereafter, as shown by a chain double-dashed line in FIG.
The nickel sheet is cut into a predetermined size to obtain a strip-shaped positive electrode plate precursor 1a (see FIG. 2).

After the above step A is completed, in step B, the work of removing nickel hydroxide is performed on the tab attachment portion 2a of the positive electrode plate precursor 1a as shown in FIG. In this removing operation, the tab attaching portion is continuously hit by an impact applying means to be described later to give an impact, and the nickel hydroxide on the surface and the inside of the tab attaching portion is removed by the impact.

At this time, a so-called sword-shaped member in which a plurality of needles 4a are bundled is used as the impact applying means, as shown in FIG. The main function of the sword-shaped member 4 is to scrape out the nickel hydroxide exposed on the surface of the tab mounting portion 2a with a needle tip and to give an impact to the inside of the tab mounting portion 2a, thereby communicating holes inside. Is to strip nickel hydroxide from. Here, the diameter of the communication hole of the sponge-like nickel sheet is usually 50 to 50.
The diameter of the needle tip of the needle 4a is about 0 μm, and considering that nickel hydroxide is scratched out from the communication hole,
It is preferably about 0.01 to 0.05 mm. The shape of the needle tip may be sharp,
The tip of the needle is preferably spherical so as not to damage the surface of the tab mounting portion 2a as much as possible.

Further, when bundling a plurality of needles 4a, if the number of needles 4a to be planted per unit area, that is, the density of implantation is too low, the work efficiency of removing nickel hydroxide is lowered and the number of needles is also reduced. Since the stress is too small, the stress is excessively concentrated on the tip of the needle, and the pressure at the time of hitting the nickel porous body sheet is locally increased, which may damage the nickel porous body sheet. Therefore, the needle implantation density is preferably set to 400 needles / cm ² or more.

The shape of the sword-shaped member 4 is not particularly limited, but is a cubical base 4 as shown in FIG.
In addition to implanting a plurality of needles on the bottom surface of b, a needle having the needles implanted on the bottom surface of a cylindrical base may be used. At this time, the implantation density of the needles is within the above range, and the cross-sectional area of the contact portion with the tab attachment portion formed by the tips of the plurality of needles is substantially the same as or larger than the area of the tab attachment portion 2a. Also make it smaller.

Further, if the force for hitting the tab mounting portion 2a is too small, or if the number of hits per unit time is too small, the effect of removing nickel hydroxide decreases. On the contrary, if the force for hitting the tab attaching portion 2a is too large, or the number of hits per unit time is too large, the impact applied to the tab attaching portion 2a becomes too strong, and it is not the tab attaching portion. There is a risk that the nickel hydroxide in the part will drop off or the electrode plate itself will be damaged. Therefore, the force of hitting the tab attaching portion 2a with the sword-shaped member which is the impact applying means is 0.8.
It is preferable to be in the range of up to 2.4 kgf, and it is preferable to set the number of times to hit the tab attaching portion 2a per unit time when continuously hitting to 6 to 18 times (6 to 18 Hz) per second. Under the above conditions, the impact is applied for the required time, and the work of removing nickel hydroxide is performed.

In the above description, the nickel porous sheet is cut into strips and then the nickel hydroxide is removed from the tab-attached portions. However, in the continuous sheet state as shown in FIG. Alternatively, the recess 2 may be hit with an impact applying means to remove nickel hydroxide. As described above, after the steps A and B are completed, the ends of the tab sheet are superposed on the tab attachment portions of the positive electrode plate precursor to form a welded portion, and the welded portion is used as the upper electrode of the spot welding machine. While maintaining pressure under the lower electrode, electricity is applied to spot-weld the end portion of the tab to the precursor of the positive electrode plate to form a positive electrode plate.

[0022]

【Example】

Examples 1 to 5 A continuous sheet of sponge-like nickel porous body having a pore diameter of 470 to 500 μm, a porosity of 96 to 97%, a thickness of 1.1 mm and a width of 80 mm was prepared. And the long side dimension 18 mm,
A rectangular die having a short side dimension of 8 mm is pressed at 80 mm intervals so that the longitudinal direction of the sheet and the long side of the die are parallel to each other on the center line in the width direction of the nickel sheet, as shown in FIG. Compress the specified part of the sheet to
A plurality of rectangular recesses 2 were formed. The rolling reduction at this time was 83%.

Next, 70 parts by weight of spherical nickel hydroxide powder, 5 parts by weight of CoO powder, and 25 parts by weight of a 1% aqueous solution of carboxymethyl cellulose were mixed to prepare a paste-like positive electrode active material mixture. Then, the nickel porous sheet was filled with the paste-like positive electrode active material mixture by a vacuum impregnation method, and then dried at 80 ° C. for 1 hour. Then, in order to adjust the thickness of the nickel porous body sheet to 0.6 mm, roll rolling was performed on the entire sheet at a reduction rate of 45%.

Next, the nickel porous body sheet whose thickness has been adjusted as described above is cut from the end portion at intervals of 40 mm. At this time, as shown in FIG. 1, the cutting point is set so as to always include the middle of the long sides of the rectangular concave portion 2. In this way, as shown in FIG. 2, a strip-shaped positive electrode plate precursor having tab attachment points 2a is formed.

Next, as shown in FIG. 2, the long side dimension is 9 m.
m, a short side dimension of 8 mm, and a height of 8 mm, the bottom surface of the metal base 4b has a spherical tip shape and the tip has a diameter of 0.
An impact imparting device (not shown) is provided with a blade-like impact imparting means 4 in which stainless steel needles 4a having a diameter of 05 mm, a root diameter of 0.4 mm, and a length of 5 mm are implanted at an implantation density of 600 needles / cm ^2. Then, the positive electrode plate precursor 1a was attached to the tab mounting portion 2a with an impact to remove nickel hydroxide. At this time, in the removing work, the number of times the tab attachment portion 2a is hit per second is 10 times, and the tab attachment portion 2a is continuously hit by the sword-shaped member with the force (kgf) shown in Table 1. Went by. The working time at this time was constant for 1 minute. The removal work was performed on both the front and back surfaces of the tab attachment portion 2a.

The surface of the positive electrode plate precursor thus obtained was observed and inspected for damage. The results are shown in Table 1. Then, a nickel sheet for a tab was spot-welded to the positive electrode plate precursor manufactured under the above-mentioned conditions, and 2000 positive electrode plates were manufactured under each condition. The defective welding rate was calculated for the obtained positive electrode plate. The obtained results are also shown in Table 1. The welding defect rate was determined as follows.

That is, first, the welded portions were visually observed, and those having holes due to sparks, damage, defects, etc. were counted as defective welding products. Then, the ratio of the number of defective welding products to the total number of manufactured positive electrode plates (2000 sheets) was determined as a defective welding ratio (%). Next, a positive electrode plate was manufactured in the same manner as the above procedure, and the positive electrode plate was combined with a known separator, a hydrogen storage alloy electrode, and an alkaline electrolyte to obtain an AA size nickel-hydrogen battery with a rated capacity of 1100 mAh under each condition. 100 pieces were assembled for each.

After performing initial activation treatment on these batteries, charging / discharging was repeated at a temperature of 20 ° C. and 0.2 C, the discharge capacity after 7 cycles was measured, and the average value thereof is also shown in Table 1. . As is clear from the results of Examples 1 to 5, the force for hitting the tab attachment portion as in Example 3 was 1.
It can be seen that when the weight is 6 kgf, the defective welding rate is low and a good positive electrode plate can be obtained.

Examples 6 to 8 Example 1 was repeated except that the force for hitting the tab mounting portion was kept constant at 1.6 kgf, and the needle densities of the sword-like members were changed as shown in Table 1. A positive electrode plate was manufactured in the same manner as in, and a battery was manufactured in the same manner as in Example 1 using the positive electrode plate. Incidentally, the number of times the tab attachment part is hit per second is constant.

With respect to the positive electrode plate and the battery incorporating the same, the presence / absence of breakage, welding failure rate and discharge capacity were measured in the same manner as in Example 1, and the results are also shown in Table 1. As is clear from the results of Examples 6 to 8, when the implantation density is 800 lines / cm ² as in Example 8, the defective welding rate is low and a good positive electrode plate can be obtained.

Examples 9 to 13 The densities of the needles of the sword-shaped member were fixed at 800 needles / cm ² and the force for hitting the tab attachment point was constant at 1.6 kgf, and the number of times the tab attachment point was tapped per second was shown. A positive electrode plate was manufactured in the same manner as in Example 1 except that the changes were made as shown in Example 1, and a battery was manufactured in the same manner as in Example 1 using the positive electrode plate.

With respect to the positive electrode plate and the battery incorporating the same, the presence / absence of damage, the defective welding rate and the discharge capacity were measured in the same manner as in Example 1, and the results are also shown in Table 1. As is clear from the results of Examples 9 to 13, as in Example 11, the number of times the tab attachment point was hit per second was 1.
It can be seen that when the number of times is two, the defective welding rate is low and a good positive electrode plate can be obtained.

Comparative Example 1 A positive electrode plate was produced in the same manner as in Example 1 except that nickel hydroxide was not removed, and a battery was prepared in the same manner as in Example 1 using the positive electrode plate. Manufactured.

With respect to this positive electrode plate and the battery incorporating the same, the presence or absence of damage, the defective welding rate and the discharge capacity were measured in the same manner as in Example 1, and the results are also shown in Table 1.

[0035]

[Table 1]

As is clear from the results shown in Table 1, the positive electrode plate produced by the method of the present invention is
Low welding defect rate. In the case of the embodiment, the tab attaching portion is continuously hit by the impact applying means in which a plurality of needles are bundled to remove nickel hydroxide, and in the case of the comparative example 1, the tab attaching is performed as usual. This is the result of not performing the work of removing nickel hydroxide at the location. That is, in the case of Comparative Example 1, nickel hydroxide remained at the relevant portion, sparks were generated due to poor conductivity due to it, and good spot welding was not performed, so the welding defect rate was as high as 2.1%. It has become.

In particular, Examples 2 to 4, 7, 8, 10 to 12
The positive electrode plate of No. 1 was not damaged at all and had a poor welding defect rate of 0.3% or less. Further, the discharge capacity of each of the batteries incorporating these positive electrode plates is not less than the rated capacity. This is because the density of implanting the needles of the sword-shaped member, the force for hitting the tab attachment portion, and the number of times the tab attachment portion is tapped per second are all set to the above-mentioned preferable values.

In the case of Example 1, the defective welding rate is high. This is because the force at the time of hitting the tab attachment portion was weaker than 0.6 kgf as compared with the positive electrode plates of Examples 2 to 4, and nickel hydroxide at the tab attachment portion was not sufficiently removed. It is considered to be a thing. In addition, in the case of Example 5, breakage was observed at the tab attachment portion of the positive electrode plate, and the discharge capacity of the obtained battery was lower than the rated capacity. This is because the force when hitting the tab attachment point is as strong as 2.8 kgf, so the impact on the point is too strong, resulting in damage and removal of the positive electrode active material from the portion other than the tab attachment point. It is considered that this is because the required filling amount of the positive electrode active material could not be secured.

Further, in the case of Example 6, breakage of the positive electrode plate is recognized. It is considered that this is because the density of the needles of the sword-shaped member was low, so that the pressure was concentrated on the tips of the few needles and the positive electrode plate was damaged. Further, in the case of Example 9, the defective welding rate is high. This is because the number of hits per second at the tab attachment point was small, so the impact was weakened and nickel hydroxide at the tab attachment point was not sufficiently removed as compared with the positive electrode plates of Examples 10 to 12. It is believed that there is.

In the case of Example 13, the positive electrode plate was found to be damaged, and the discharge capacity of the battery obtained in the same manner as in Example 9 was lower than the rated capacity.
This is because the impact is too strong because the number of hits at the tab attachment point is large per second, and as a result, the positive electrode plate is damaged, and the positive electrode active material in the portion other than the tab attachment point is also removed. This is probably because the required filling amount of the positive electrode active material could not be secured.

[0041]

As is apparent from the above description, the method of manufacturing a positive electrode plate according to the present invention comprises continuously striking the tab attachment points of the positive electrode plate precursor with an impact applying means in which a plurality of needles are bundled. A shock is applied to the relevant part, and the nickel hydroxide inside the nickel porous body is removed by this shock. Therefore, when the tab is spot-welded to the tab-attached portion, conductive failure due to the presence of non-conductive nickel hydroxide is suppressed, and good welding can be performed. Therefore, when the method for manufacturing a positive electrode plate according to the present invention is adopted, the defective welding rate of the positive electrode plate is reduced, and the yield in battery manufacturing is improved.

[Brief description of drawings]

FIG. 1 is a perspective view showing a structure of a continuous sheet-shaped current collector.

FIG. 2 is a perspective view showing a structure of a precursor of a positive electrode plate.

FIG. 3 is a perspective view showing a structure of a positive electrode plate.

[Explanation of symbols]

 1 Continuous sheet of current collector 1a Strip-shaped positive electrode plate precursor 2a Tab attachment point 3 Tab 4 Impact imparting means (Kenyama member) 4a Needle

Claims (2)

[Claims] 1. When spot welding a tab to a current collector having a three-dimensional network structure carrying an active material mixture mainly composed of nickel hydroxide, the tab is formed by compressing a predetermined portion of the current collector. A method of manufacturing a positive electrode plate, characterized in that a mounting portion is provided, and then the current collector is filled with an active material paste and then dried, and the tab mounting portion is continuously beaten by an impact applying means in which a plurality of needles are bundled. . 2. The tab attaching portion is applied at a rate of 6 to 18 times per second with a force of 0.8 to 2.4 kgf by an impact imparting means having an implantation density of the needles of 400 needles / cm ² or more. The method for producing a positive electrode plate according to claim 1, wherein the positive electrode plate is continuously hit.