JPH09213300A - Tab mounting method for positive electrode plate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To lessen the occurrence of faulty welding caused by weaviness developed at a tab mounting spot. SOLUTION: A tab mounting spot is provided by compressing the specified spot of a current collector continuous sheet in a three dimensional reticulate structure, concurrently pasty active material mix is filled in the current collector continuous sheet, and the sheet is dried thereafter, subsequently the current collector continuous sheet is rolled, the current collector continuous sheet is curt off in a strip shape at the end part of which the tab mounting stop 2a is located, so as to be formed into a positive electrode plate precursor 1a thereafter, the tab mounting spot 1a of the positive electrode plate is then molded flat under pressure, and a tab is spot welded to the tab mounting spot 2a thereafter.

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 of attaching a tab to a positive electrode plate, which enables stable spot welding of the tab to the positive electrode plate when producing 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,
Those having a three-dimensional network structure such as a foamed nickel porous body are widely 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, a sheet-shaped nickel porous body is prepared, and a predetermined range of a predetermined position of the sheet-shaped nickel porous body 1 is crushed in the thickness direction to form the recess 2 (see FIG. 1). The concave portion 2 will be a tab attachment point described later. Here, in the sheet-shaped nickel porous body 1, the flat surface portion other than the concave portion 2 is referred to as an electrode plate flat surface portion 11 in the present invention.

Then, a viscous paste-like active material mixture is prepared by adding an aqueous solution of a thickener prepared by dissolving carboxymethyl cellulose or methyl cellulose to the mixed powder of the positive electrode active material and stirring the whole. Then, the paste-like active material mixture is filled and applied to the sheet-like nickel porous body, and then dried. After that, the entire sheet-shaped nickel porous body is roll-rolled to adjust the thickness, and a predetermined portion indicated by a chain double-dashed line in FIG. 1 is cut with a cutter, and as shown in FIG. Precursor 1 of a strip-shaped nickel positive electrode plate having tab attachment points 2a at predetermined positions
Obtain a. 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 ends of the tab sheet are superposed on the tab attachment points 2a of the strip-shaped precursor 1a to form welds, the welds are connected to the upper electrode and the lower electrode of the spot welding machine. While pressurizing, the electric current is applied, and the tab 3 is spot-welded to the tab mounting portion 2a to form the nickel positive electrode plate 1A as shown in FIG. The nickel positive electrode plate manufactured in this manner is a negative electrode plate, a separator,
The battery is formed by incorporating it into an outer can of the battery together with the electrolytic solution and the like.

[0007]

By the way, at the time of roll rolling performed by adjusting the thickness of the nickel porous body sheet, the sheet is compressed in its thickness direction, and by that amount, in the direction orthogonal to the thickness direction. Spread two-dimensionally. At this time, FIG.
As shown in, the outer edge portion 11a of the electrode plate flat surface portion 11a extends in the outer direction (direction of arrow A) orthogonal to the thickness direction, and the end portion 11b of the electrode plate flat surface portion which is in contact with the concave portion 2 is inside the concave portion. It extends in the direction (arrow B direction). Here, in the concave portion 2, when the end portion 11b of the electrode plate flat portion extends, the concave portion 2
The compressive force also acts on the flat part of the plate in the direction perpendicular to the thickness direction. However, the concave portion 2 is in a highly densified state, has a different degree of extension from the electrode plate flat portion, and is in a state in which planar deformation in four directions is limited. Therefore, when the end portion 11b of the electrode plate flat portion extends inward, the concave portion 2 is distorted. When the continuous sheet 1 in such a state is cut into a strip-shaped positive electrode plate precursor 1a, the tab attachment portion 2a has a wavy state as shown in FIG. When the spot welding of the tab is performed at the location, the tab and the tab attachment location are not in close contact with each other over the entire surface, and as a result, good spot welding may not be performed.

As described above, when welding failure occurs between the tab attachment point and the tab, the current does not flow evenly across the entire surface of the tab attachment point and the tab, and the current flows only at the contact points that are unevenly distributed. Therefore, as a result, a large current may flow in the contact portion, and the contact portion may generate heat by resistance to generate heat in the battery incorporating the positive electrode plate. Further, if the tab comes off from the positive electrode plate during use of the battery, there is a possibility that electricity may not be supplied or that the tab removed from the positive electrode plate may come into contact with a member on the negative electrode side to cause a short circuit.

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 undulation generated at the tab mounting position. For the purpose of providing.

[0010]

In order to achieve the above object, in the present invention, a predetermined position of a current collector continuous sheet having a three-dimensional network structure is compressed to provide a tab attachment position, and the current collector connection is continuous. The sheet is filled with the paste-like active material mixture and then dried, and then the current collector continuous sheet is roll-rolled, and then the current collector continuous sheet is cut into strips having tab attachment points at the ends. As a positive electrode plate precursor,
There is provided a method of attaching a tab to a positive electrode plate, which comprises press-molding a tab attachment portion of the positive electrode plate precursor to make it flat and then spot welding the tab to the tab attachment portion.

In the method of attaching a tab to a positive electrode plate of the present invention, it is preferable that the pressure at the time of press forming the tab attachment portion of the positive electrode plate precursor is 200 to 250 kgf / cm ² . The method for attaching a tab to a positive electrode plate according to the present invention is such that, after roll rolling, when pressure forming is performed on the tab attachment portion of the positive electrode plate precursor cut into strips, it occurs due to roll rolling performed by adjusting the thickness. The waviness of the tab attachment point is corrected and the point is flattened.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION In the method of attaching a tab to a positive electrode plate of the present invention, a step of producing a precursor of the positive electrode plate (hereinafter, referred to as
An essential step includes a step A) and a step of press-molding the tab attachment portion of the precursor thereof (hereinafter referred to as step B). In the present invention, the undulation of the tab attachment portion of the positive electrode plate precursor is corrected and the flat tab attachment portion is obtained by sequentially performing the above-described step A and step B. As a result, the tabs come into contact with each other in a state where the tabs and the tab attachment points are in close contact with each other, and the spot weldability at the tab attachment points is improved.

First, in step A, a current collector continuous sheet having a three-dimensional network structure is prepared. Here, the current collector having a three-dimensional network structure used in the present invention may be any one that has been conventionally used, and is not particularly limited, and may be a paste-like active material mixture. In terms of being able to increase the filling amount, for example, a porosity of 94-9
A preferable example is a continuous sheet of a foamed nickel porous body having 7% and continuous pores having a pore size of 50 to 500 μm.

Then, a predetermined position of the nickel porous body sheet 1 is crushed in the thickness direction with a predetermined area by using, for example, a pressing machine to densify the position to form a recess 2 (FIG. 1). Here, when the recessed 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.

Next, 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. After that, the entire thickness of the nickel porous body sheet was roll-rolled to adjust the thickness, and then the nickel porous body sheet was cut into a predetermined size as shown by a chain double-dashed line in FIG. The positive electrode plate precursor 1a (see FIG. 2) is used.

After the above step A is completed, in step B, as shown in FIG. 2, the tab attachment portion 2a having the waviness caused by the roll rolling in step A is attached to the positive electrode plate precursor.
Is pressure-molded and straightened to a flat surface. In this correction work, for example,
A method of sandwiching the upper mold 4 having a flat surface and the lower mold 5 from above and below and performing pressure molding is adopted.

The surfaces 4a, 5a of the upper die 4 and the lower die 5 are
It has a shape similar to that of the tab attachment portion 2a and has an area that is approximately the same as or smaller than the tab attachment portion. At this time, the pressure when pressurizing the tab mounting location is 200k.
If it is less than gf / cm ² , it is difficult to correct the waviness at the location to form a flat surface, and conversely, if the pressure exceeds 250 kgf / cm ² , the ability to correct the waviness is improved. May damage the location. Therefore, the pressure at the time of press forming the tab attachment location is 20
It is preferably set to 0 to 250 kgf / cm ² .
The more preferable range of the pressure is 220 to 230 kg.
f / cm ² , especially when pressure molding is performed at a pressure of 225 kgf / cm ² , without damaging the tab mounting location,
It is preferable because it can be sufficiently flattened.

After the steps A and B are completed as described above, the ends of the tab sheet are overlapped with the tab attachment points of the positive electrode plate precursor to form a welded portion, and the welded portion is spot welded. While maintaining pressure, the upper electrode and the lower electrode are energized to carry out spot welding of the end portions of the tabs to the tab attachment points of the positive electrode plate precursor to form a positive electrode plate.

[0019]

【Example】

Examples 1 to 7 A continuous sheet of sponge-like nickel porous body having a pore diameter of 100 to 500 μm, a porosity of 85 to 95%, a thickness of 1.1 mm and a width of 20 mm was prepared. Then, the long side dimension is 20 mm,
A rectangular die having a short side dimension of 5 mm was pressed at 90 mm intervals so that the longitudinal direction of the sheet and the long side of the die were parallel to each other on the center line in the width direction of the nickel porous body sheet, as shown in FIG. As shown, the sheet was compressed at a predetermined position to form a plurality of rectangular recesses 2. The reduction rate at this time was 80%.

Next, 70 parts by weight of spherical nickel hydroxide powder, 10 parts by weight of CoO powder, and 20 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 paste-like positive electrode active material mixture was filled in the nickel porous body sheet by a vacuum impregnation method, and then dried at 100 ° C. for 0.5 hour. afterwards,
Rolling is performed on the entire sheet 1 at a rolling reduction of 50% to reduce the thickness of the nickel porous body sheet 1 to 0.5.
mm.

Next, after the active material in the recesses 2 is removed from the nickel porous body sheet 1 whose thickness has been adjusted as described above, the nickel porous body sheet 1 is 50 m from the end.
By cutting at m intervals, as shown in FIG. 2, a strip-shaped positive electrode plate precursor 1a having tab attachment points 2a was formed.
At this time, the cross-sectional shape of the tab attachment portion 2a is as shown in FIG.
It was in a state where swells occurred like. The cutting location of the nickel porous body sheet 1 was set so as to include, for example, the center of the long side of the rectangular recess 2 as shown in FIG.

Next, the positive electrode plate precursors 1a were prepared in the numbers shown in Table 1, respectively. Then, as shown in FIG. 2, with a pressing machine having an upper mold 4 and a lower mold 5 each having a rectangular surface 4a, 5a having a length of 10 mm and a width of 5 mm, the positive electrode plate precursor 1a is attached to the tab attachment location 2a. Pressure molding was performed at the pressures shown in Table 1. The surface of the positive electrode plate precursor thus obtained was observed and inspected for damage, and the number of damaged positive electrode plate precursors is also shown in Table 1. Further, the ratio of the number of positive electrode plate precursors damaged during pressure molding to the number of all manufactured positive electrode plate precursors was determined, and this ratio is also shown in Table 1 as the non-defective rate (%) during pressure molding. . The damaged positive electrode plate precursor was removed at this point and was not sent to the subsequent tab spot welding step.

Then, the pressure forming of the tab mounting portion was completed, and a nickel sheet for a tab was spot-welded to the precursor 1a which was not damaged to manufacture a positive electrode plate 1A as shown in FIG. With respect to the obtained positive electrode plate 1A, it was determined whether or not welding failure occurred, and the number of positive electrode plates having welding failure was counted. Then, the ratio of the number of positive electrode plates having welding defects to the number of positive electrode plates subjected to tab welding is obtained, and this ratio is taken as the welding defect rate (%),
The obtained results are also shown in Table 1.

Here, the welding failure was judged as follows. First, the positive electrode plate 1 is attached to the upper and lower chucks of the peeling tester.
The electrode plate portion of A and the tab were attached, respectively, and pulled along the longitudinal direction of the positive electrode plate until the pulling force became 1 kgf. Then, when the pulling force was less than 1 kgf and the tab was peeled off, it was determined as a defective welding product, and when it was not peeled off, it was determined as a good product.

Next, the obtained positive electrode plate 1A was combined with a known separator, a hydrogen storage alloy electrode, and an alkaline electrolyte to assemble a nickel-hydrogen battery having a rated capacity of 500 mAh. It should be noted that three positive electrode plates are incorporated for each battery. The occurrence rate of short circuits was determined for the obtained batteries. The results are shown in Table 1. Here, the occurrence rate of the short circuit was determined as follows.

First, after charging, discharging and aging the obtained battery to activate the battery, the open circuit voltage is obtained for each battery, and the battery whose voltage value is below the standard voltage is determined. I pulled it out. Then, the extracted battery was disassembled, the state of the positive electrode tab was observed, and the battery in which the positive electrode tab came off the positive electrode plate and was in contact with the member on the negative electrode side was counted as a battery in which a short circuit occurred. Then, the ratio of the number of short-circuited batteries to the total number of manufactured batteries was determined, and this ratio is also shown in Table 1 as the short-circuit occurrence rate (%).

The ratio of the number of non-defective positive electrode plates which did not cause damage or welding defects and were not incorporated in the short circuit battery to the total number of manufactured positive electrode plate precursors was determined, and this ratio was calculated. The yield rate (%) of the whole positive electrode plate in the production is also shown in Table 1. Comparative Example 1 A positive electrode plate was manufactured in the same manner as in Example 1 except that the tab attachment location was not pressure-molded, and a battery was manufactured in the same manner as in Example 1 using the positive electrode plate. .

For this positive electrode plate and the battery incorporating the same, the good product rate at the time of pressure molding, the defective welding rate, the occurrence rate of short circuit, and the good product rate of the whole positive electrode plate were obtained in the same manner as in Example 1.
The results are shown in Table 1.

[0029]

[Table 1]

From the results shown in Table 1, the following is clear.
That is, when the tab mounting portion is pressure-molded and then the tab is mounted, as is apparent from Comparative Example 1, the welding defect rate is significantly reduced, and almost 100% can be incorporated into the battery as a positive electrode plate. Further, in the battery incorporating the positive electrode plate, the occurrence rate of the short circuit accident is about 1.2% at the maximum (Example 1). However, if the pressure at the time of pressure molding is increased, the tab attachment location may be damaged (Example 7).

Particularly, the pressure at the time of pressure molding is 200 to 250.
The positive electrode plates of Examples 2 to 6 set in the range of kgf / cm ² did not cause damage during pressure forming, and had a defective welding rate of 0.2.
% Or less. The short-circuit occurrence rate of the battery incorporating the positive electrode plate was 0%, and the good product rate of the whole positive electrode plate was 9%.
It turns out that it is as high as 9.8% or more. This is because the electrode plate is damaged when the tab attachment location where undulation occurs during roll rolling performed for thickness adjustment is pressure-molded at a pressure within the range specified in the present invention. This is because the undulations are eliminated and the tab attachment points are flattened, and as a result, good welding is performed in spot welding of tabs.

It can be seen that in Comparative Example 1, the defective welding rate was 40.4% and the short circuit occurrence rate was 2.5%.
This is because, as in the past, pressure forming was not performed at the tab attachment location, so undulations remain at that location, which prevents uniform contact between the tab and the tab attachment location, and good spot welding. Because it was not done.
For this reason, in the battery in which the positive electrode plate is incorporated, the tab may be disengaged from the positive electrode plate to cause a short circuit, and the occurrence rate of the short circuit is high, which reduces the non-defective rate of the entire positive electrode plate.

[0033]

As is apparent from the above description, according to the method of attaching a tab to a positive electrode plate of the present invention, the tab attachment portion of the positive electrode plate precursor is pressure-molded to correct the undulation at that portion. Can be flattened. For this reason, when the tab is spot-welded to the tab mounting portion, the tab and the tab mounting portion are in close contact with each other and are in full contact with each other, so that good spot welding can be performed. Therefore, when the method of attaching the tab to the positive electrode plate according to the present invention is adopted, when welding the tab to the positive electrode plate, the occurrence of welding defects is reduced, and the yield in battery production is improved.

[Brief description of drawings]

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

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.

FIG. 4 is a top plan view of a continuous sheet-shaped current collector (nickel porous sheet).

5 is a cross-sectional view taken along the line VV of FIG.

[Explanation of symbols]

1 Continuous sheet of current collector (nickel porous sheet) 1a Strip-shaped positive electrode plate precursor 2a Tab attachment point 3 Tab 4 Upper mold 5 Lower mold

Claims (2)

[Claims] 1. A current collector continuous sheet having a three-dimensional network structure is compressed at predetermined locations to provide tab attachment locations, and the current collector continuous sheet is filled with a paste-like active material mixture and then dried, and The current collector continuous sheet is rolled, then, the current collector continuous sheet is cut into a strip shape in which the tab attachment location is located at the end, as a positive electrode plate precursor,
A method of attaching a tab to a positive electrode plate, which comprises press-molding and flattening a tab attaching portion of the positive electrode plate precursor, and then spot welding the tab to the tab attaching portion. 2. The pressure during the pressure molding is 200 to 250.
The method for attaching a tab to a positive electrode plate according to claim 1, wherein the tab is kgf / cm ² .