JPH11307078A - Battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stabilize welding capability of resistance welding of a current collecting tab to a positive electrode plate and a sealing plate, and provide a battery having the current collecting tab capable of realizing high welding reliability in the positive electrode plate and the sealing plate by specifying the surface roughness of the current collecting tab of the battery. SOLUTION: A current collecting tab 2 used for this battery has a surface roughness of 0.1-4 μm, and can use the conventional material. The specified surface roughness is formed on the whole surfaces of both sides of the current collecting tab 2 or on only the one side. Only the portion for being welded to a current collecting substrate or a sealing plate may be formed so as to have the specified surface roughness. If the surface roughness is smaller than 0.1 μm, the surface state becomes a smooth surface similar to a bright finishing surface, the contact resistance with a mix non-coating part of the current collecting substrate or the sealing plate is decreased, the generation of Joule heat is decreased, and usable nugget formation is made difficult.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a battery, and more particularly, to a battery collecting tab used for electrically connecting a positive electrode plate and a sealing plate in an alkaline secondary battery.

[0002]

2. Description of the Related Art For example, a cylindrical nickel-hydrogen secondary battery has a positive electrode plate having a positive electrode active material typified by nickel hydroxide supported on a current collecting substrate and a hydrogen absorbing alloy supported on a current collecting substrate. The negative electrode plate and the negative electrode plate are stacked with an electrically insulating and liquid-retaining separator interposed between them, and the laminated sheet is wound with the negative electrode plate facing up to form a cylindrical power generating element. The power generating element is housed in a battery can also serving as a negative electrode terminal together with an alkaline electrolyte, and the upper opening of the battery can is sealed with a sealing plate also serving as a positive electrode terminal via an electrically insulating gasket.

In this structure, a negative electrode plate is in contact with a battery can, and a positive electrode plate and a sealing plate are connected by a current collecting tab to form a battery circuit.

By the way, with the spread of various electric and electronic devices in recent years, nickel and nickel, which are widely used as a driving source thereof, have been developed.
There is an increasing demand for higher capacity hydrogen rechargeable batteries.

In order to meet the demand, for example, a nickel fiber substrate or a nickel foam sheet having a three-dimensional network structure has been awarded as a current collecting substrate of a positive electrode plate. This is because the nickel fiber substrate or the nickel foam sheet has a porous structure, so that the amount of the positive electrode active material filled and supported therein increases, and the discharge capacity increases.

[0006] Such a positive electrode plate is generally manufactured as follows.

First, a mixture paste is prepared by kneading nickel hydroxide powder functioning as an active material, carboxymethyl cellulose as a thickener, a cobalt compound as a conductive auxiliary, and water. On the other hand, a nickel foam sheet having a predetermined porosity is prepared.

[0008] A predetermined amount of the mixture paste is applied to a nickel foam sheet, and the mixture paste is filled into the voids inside the sheet and simultaneously applied in layers to the sheet surface. At this time, the mixture paste is not filled and applied to the portion where the current collecting tab to be described later is attached, and the background of the nickel foam sheet is exposed as it is.

Next, the mixture paste is dried, and thereafter, the whole mixture is rolled, for example, to adjust the thickness, and the dried mixture is supported on the nickel foam sheet.

Finally, as shown in FIG. 1, one end 2A of the current collecting tab 2 is joined to a portion 1A of the surface of the nickel foam sheet 1 where the mixture paste is not applied. Thus, a positive electrode plate is manufactured. The other end 2B of the current collecting tab 2 is joined to a not-shown battery sealing plate. Note that, as the current collecting tab, a pure Ni piece or a Ni-plated steel sheet has been conventionally used, and the surface thereof is usually a bright finished surface.

[0011] The current collecting tab 2 is applied to the non-application portion 1 of the mixture paste.
The following method has been conventionally employed as a method of joining to A.

First, there is a method of crimping and joining the current collecting tab 2 and the non-coated portion 1A. However, in this method, there is a problem that the nickel foam sheet is crushed and its mechanical strength cannot be secured.

[0013] Laser welding has also been applied. This method can achieve strong welding, but has the problem that the equipment is very expensive and is not economically favorable.

[0014] Further, welding of the current collecting tab by application of ultrasonic waves is also performed, but in this case, the dry mixture carried on the nickel foam sheet is dropped by the applied vibration and the electrode is removed. It is not preferable because the capacity is reduced.

Finally, there is resistance welding. This method is illustrated in FIG.
As shown in the figure, the current collecting tab 2 is arranged at the location 1A where the dry mixture is not applied, and a pair of welding electrodes 3 are arranged from above and below.
In this method, a welding current is applied while being pressed by a and 3b, Joule heat is generated at a contact interface between the portion 1A and the current collecting tab 2, and a nugget is formed at the contact interface with the heat to perform welding. This method is widely used at present instead of the above three methods because the cost required for welding is small and maintenance is easy.

[0016]

However, the above-described resistance welding also has the following problems.

First, the current-collecting tab used conventionally has a surface which is usually a smooth bright surface and the contact resistance at the contact interface with the mating material tends to be low. The problem is that the Joule heat is also reduced, and it is difficult to form a large nugget. This problem is a factor that reduces the welding strength between the current collecting tab and the counterpart material and increases the variation in strength, thereby lowering the welding reliability.

In FIG. 1, one end 2A of the current collecting tab is shown.
When resistance welding is performed on the portion 1A, since the surface of the portion 1A is a surface on which the porous structure is roll-rolled, although a slight unevenness is present, the surface is a dense and smooth surface as a whole. . The contact resistance between the end portion 2A of the current collecting tab and the end portion 2A of the current collecting tab becomes substantially the same as when both are bright finished surfaces, so that the welding strength between the end portion 2A of the current collecting tab and the location 1A is reduced. come.

If the other end 2B of the current collecting tab has a bright finish, the following inconvenience occurs.

That is, when the end 2B is resistance-welded to a sealing plate (not shown), the sealing plate is generally made of a Ni-plated steel plate having a bright-finished surface.
This is because the welding strength between the sealing plate and the sealing plate is small, and the variation is large, and the welding reliability between the two is reduced.

In order to solve such a problem, for example, a method is known in which a projection is formed on a current collecting tab, and the projection is bitten into a counterpart material such as the location 1A, and the welding current is concentrated at the location. Have been. However, in the case of this method, the process cost is increased due to the formation of the projections on the current collecting tabs, and the welding current is applied only to the projections. There is difficulty in doing so.

The present invention can solve the above-mentioned problem when the current collecting tab is resistance-welded to both the positive electrode plate and the sealing plate, and can realize high welding reliability in both the positive electrode plate and the sealing plate. An object of the present invention is to provide a battery including a current collecting tab.

[0023]

In order to achieve the above object, according to the present invention, the surface roughness (Ra) is 0.1.
A battery is provided that includes a current collection tab that is ４4 μm.

[0024]

BEST MODE FOR CARRYING OUT THE INVENTION The current collecting tab used in the battery of the present invention is characterized in that its surface roughness (Ra) is 0.1 to 4 μm, and its material is conventionally used. Anything is acceptable.

The surface roughness (Ra) may be the entire front and back surfaces of the current collecting tab, or may be only one surface. In short, at least the current collecting substrate or the sealing plate may be used. It is sufficient that the portion to be welded has the surface roughness (Ra).

When the surface roughness (Ra) is smaller than 0.1 μm, the surface condition becomes a smooth surface similar to a bright finished surface. In such a case, the contact resistance becomes low, the generated Joule heat decreases, and it becomes difficult to form a good nugget, and the size of the formed nugget varies. As a result, a decrease in welding strength and an increase in its variation occur, and welding reliability decreases.

On the other hand, if the surface roughness (Ra) is larger than 4 μm, the contact resistance with the counterpart material becomes too large, making it difficult to smoothly carry out resistance welding and increasing the cost required for roughening. It is economically disadvantageous.

This current collecting tab is formed by, for example, subjecting a steel plate to Ni plating, and then rolling the obtained plate material cold using a roll having a roll surface roughness of the above Ra value. It can be manufactured by processing the processing material. Further, the steel sheet may be manufactured by a method in which the surface of the steel sheet is roughly plated.

[0029]

EXAMPLES Examples 1 to 8 and Comparative Examples 1 to 4 Nickel hydroxide powder 90% by weight and cobalt monoxide powder 1
0.2 parts by weight of carboxymethylcellulose and 40 parts by weight of water were kneaded with 100 parts by weight of a mixed powder of 0% by weight to prepare a mixture paste for a positive electrode.

A sponge-like Ni sheet (a current collecting substrate) having a porosity of 95% was prepared, and the mixture paste was filled in a portion except for a portion where a current collecting tab was welded, followed by drying at a temperature of 100 ° C. Roll rolling was performed at a pressure of 5 tons.

On the other hand, pure Ni pieces (0.15 mm thick) having different surface roughness (Ra) as shown in Table 1 were prepared as current collecting tabs.

Next, as shown in FIG. 2, one end of the current collecting tab 2 is arranged at a position 1A of the sheet 1, and the current collecting tab ² is pressed by welding electrodes 3a and 3b at a pressure of ² kg / cm ^2. A current of 1.5 kA was applied for 0.5 seconds while the current collector tab 2 was two-point resistance welded to the location 1A. The number of welds is 100. Then, the current-collecting tab was pulled using a push-pull gauge, and the strength at the time when the location 1A was broken was measured. The results are shown in Table 1 as average values. Also, during this tensile test, two nuggets remain on the current collection tab, ie,
The frequency at which the portion 1A of the current collecting substrate 1 was torn was measured and calculated as a tearing occurrence rate (%). The results are also shown in Table 1.

[0033]

[Table 1] The following is clear from Table 1.

Although the breaking strength increases as the surface roughness of the current collecting tab increases, the surface roughness is 0.5 μm.
When it becomes larger, the breaking strength becomes a substantially constant value, and the occurrence of tearing becomes 100%.

This means that the strength of the formed nugget is larger than the strength of the current collecting substrate, and proves the effectiveness of the roughened surface of the current collecting tab. is there.

Examples 9 to 15 and Comparative Examples 5 to 9 As mating materials for resistance welding, the surface roughness (Ra) was 0.05.
A sealing plate made of a Ni-plated steel sheet having a bright finish surface of .about.0.08 .mu.m was selected, and a current collecting tab was resistance-welded thereto under the same conditions as in Examples 1 to 8.

Table 2 shows the breaking strength and the rate of occurrence of tearing at that time.
It was shown to.

In this case, since the sealing plate has higher strength than the current collecting tab, at the time of the tensile test, the current collecting tab is torn and broken, and the two nuggets are closer to the sealing plate. Will be left. Therefore, the breaking strength and the tear generation rate in Table 2 are the measurement results for the current collecting tab.

[0039]

[Table 2]

[0040]

As is apparent from the above description, the current collecting tab of the present invention has a surface roughness (Ra) of 0.1 to 4 μm, and thus is resistance-welded to the current collecting substrate and the sealing plate. Then
The welding strength is much higher than before and the variation is small, so that the welding reliability can be improved.

[Brief description of the drawings]

FIG. 1 is a schematic view showing a state where a current collecting tab is welded to a current collecting substrate on which an active material mixture is carried.

FIG. 2 is a schematic view showing a state in which a current collecting tab is resistance-welded to a current collecting board.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Nickel foam sheet (current collector board) 1A Non-coating part of active material mixture 2 Current collector tab 2A One end of current collector tab 2 2B The other end of current collector tab 2 3a, 3b Welding electrode

Claims (1)

[Claims] 1. A battery comprising a current collecting tab having a surface roughness (Ra) of 0.1 to 4 μm.