JPH097560A - Sealed welding method for sealed batteries - Google Patents

Abstract

(57) [Summary] [Purpose] A prismatic sealed battery that can reduce the welding failure due to reheating in the overlapping part at the final stage of the sealing welding and can improve the yield of the prismatic sealed battery produced in this way. A manufacturing method is provided. [Constitution] At the open end of the outer can containing the electrode group,
When the lid plate on which the positive electrode is disposed is fitted and mounted, and the lid plate is laser-welded to the outer can by scanning the laser light along the fitting portion between the opening end of the outer can and the lid plate. The laser beam makes a round around the fitting portion, and the energy input per unit area of the laser beam is gradually reduced from the time when the laser beam returns to the welding start point, and the laser welding is completed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for sealing and welding a sealed battery, and more specifically, to a sealed battery which can suppress the occurrence of welding defects such as weld cracks at the welded portion between an outer can and a cover plate. The present invention relates to a sealing welding method.

[0002]

2. Description of the Related Art Alkaline secondary batteries such as nickel-hydrogen secondary batteries and nickel-cadmium batteries have a hermetically sealed structure as a whole, and their shapes are cylindrical and prismatic. Here, for example, the structure of a prismatic sealed type nickel-hydrogen secondary battery will be described with reference to FIG.

As shown in the exploded perspective view of FIG. 1, a prismatic nickel-hydrogen secondary battery has a rectangular parallelepiped outer can 1 in which an electrode plate group 2 is housed, and an open end 1 a of the outer can 1. A lid plate 3 that is fitted and mounted to seal the opening end 1a is provided. The outer can 1 is a nickel-plated steel rectangular parallelepiped bottomed can, and has an opening having a rectangular shape in a plan view at the top and also serves as an external terminal of the negative electrode. .

The electrode plate group 2 is a positive electrode sheet (nickel electrode) 2
1 and a negative electrode sheet (hydrogen storage alloy electrode) 22 are laminated with a plurality of electrically insulating separators 23 interposed therebetween. Each positive electrode sheet 21 is connected to a positive electrode 31 described later via the positive electrode current collector 4 and the lead plate 31a, and the negative electrode sheet 22 is connected to the outer can 1 also serving as a negative electrode.

The cover plate 3 is a rectangular plate that fits the opening of the outer can 1 so as to close the opening end 1a of the outer can 1, and has a positive electrode 31 in the center thereof. The lid plate 3 is
Like the outer can 1, it is made of nickel-plated steel.
The sealed nickel-hydrogen secondary battery having the above structure is
First, after the electrode plate group 2 is housed in the outer can 1, and the alkaline electrolyte is injected, the lid plate 3 is fitted and attached to the opening end 1a of the outer can 1, and the fitting portion is sealed over the entire circumference. By welding, a battery having a closed structure is obtained.

As a welding method for the fitting portion, a pulse type laser welding method suitable for fine processing is usually adopted. Here, a method of sealing and welding the outer can 1 and the cover plate 3 by the pulsed laser welding method will be described below. First, as shown in FIG. 2, a laser beam is applied from above to a boundary portion between the lid plate 3 fitted and mounted on the outer can 1 and the outer can 1, that is, the fitting portion J. Then, the laser beam is scanned at a predetermined speed along the fitting portion J as the laser spot s ₀ thereof is shown by the dotted line. Here, the laser light is usually a pulsed laser light generated with a pulse signal of a pulse oscillator,
The light collecting system collects light so that a predetermined spot diameter can be obtained at the welded portion (fitting portion J).

A laser spot s _{0 of the} laser light L
In, very strong energy is concentrated,
At the fitting portion J irradiated with this laser spot s ₀ ,
As shown in FIG. 3, a predetermined region W ₀ between the outer can 1 and the lid plate 3
Melts. When the laser spot s ₀ is scanned along the fitting portion J, the laser spot s ₀ and a certain area s ₁ behind it are melted in the fitting portion J as shown in FIG. State, a kind of melting zone S
And the melting zone S moves in the scanning direction of the laser light L. Then, after the melting zone S has passed, behind the melting zone S, cooling gradually progresses, and the predetermined region W ₀ between the outer can 1 and the lid plate 3 is changed from the molten state to the solid state, and the fitting is performed. Welding is performed at the joint. That is,
At the fitting portion J, the predetermined region W ₀ shown in FIG. 3 is solidified and the welding bead W ₁ is formed.

As described above, by sealing the laser light around the fitting portion, the outer can and the cover plate are welded to each other. By the way, when the laser light L is scanned along the fitting portion J to perform the sealing welding of the outer can 1, as shown in FIG. 5, when the irradiation of the laser light L is stopped immediately before the welding start point A, In some cases, the portion surrounded by the dotted circle in the figure is insufficiently welded, and a good weld bead may not be formed. Therefore, in order to ensure sealing welded to closed structure the entire circumference of the fitting portion, as shown in FIG. 6, the laser spot s ₀ that has returned after circling the fitting portion than the welding start point A Also, irradiation of the laser beam L is continued to a slightly advanced position and then stopped, and welding is completed. In other words, the entire circumference of the fitting portion is welded by slightly overlapping the final welding portion with the once-welded portion.

In this way, the outer can and the lid plate are sealed and welded to form a battery having a sealed structure.

[0010]

By the way, in the above laser welding method, the energy input per unit area of laser light from the start to the end of welding is
It is constant. That is, as shown in the graph of FIG. 6, the laser beam L having the constant energy E ₁ is scanned from the welding start point A to the welding end point B while being radiated to the fitting portion J.

Therefore, in the overlap portion O which is the final portion of the welding, the laser light L is irradiated again to the portion where the welding is once performed and the welding bead is formed. That is, the overlapping portion O is reheated and melted again. As described above, when the once welded portion is reheated, the amount of the melted portion increases, a part of the overlapping portion O flows into the battery, and a good weld bead is formed in the overlapping portion O. However, a through hole may occur.

In addition, in the weld bead once formed, the vicinity of the boundary with the base material (the outer can and the lid plate) (the portion surrounded by the dotted line in FIG. 7) p is affected by the heat during welding. , The crystal grains are coarsened and the structure is changed, resulting in embrittlement. In this way, the laser beam L
When is re-irradiated, a crack is generated at the boundary portion due to thermal shock due to reheating, and cracks from the outside to the inside of the battery may be generated from this crack as a starting point, resulting in poor welding.

In the sealed battery, if the above-mentioned through-holes or cracks occur, the sealed structure will be damaged, and problems such as leakage of alkaline electrolyte will occur, and the rate of defective batteries will increase, resulting in battery manufacturing. Yields at. The present invention solves the above-mentioned problems in manufacturing a sealed battery, reduces the welding failure due to reheating in the overlap portion at the final stage of the sealing welding, and improves the yield of the prismatic sealed battery manufactured in this way. An object of the present invention is to provide a method for manufacturing a prismatic sealed battery that can be improved.

[0014]

In order to achieve the above object, according to the present invention, a lid plate having a positive electrode is fitted and attached to the opening end of an outer can containing a group of electrode plates. By scanning laser light along the fitting portion between the opening end of the outer can and the lid plate, when the lid plate is laser-welded to the outer can, the laser light goes around the fitting portion. A method for sealing and welding a sealed battery is characterized in that the energy input per unit area of laser light is gradually reduced from the time of returning to the welding start point and the laser welding is completed.

In the present invention, the lid plate 3 having the positive electrode 31 arranged at the center is fitted and attached to the outer can 1 accommodating the electrode plate group 2, and the fitting portion J is laser-welded. A battery having a sealed structure is obtained by. At this time, laser welding
The fitting portion J is irradiated with a laser beam L whose input energy per unit area is, for example, E ₁ from the welding start point A, and the laser beam L is fed along the fitting portion J at a predetermined speed.
To scan.

Then, when the laser beam L goes around the fitting portion J and the laser spot returns to the welding start point A, as shown in FIG. The input energy per unit area is gradually decreased from E ₁ , and the welding is completed at 0 at the welding end point B to end the welding. In this way, when the input energy per unit area of the laser light L is gradually reduced, the remelting region of the fitting portion J (melting zone S in the overlapping portion O) gradually increases as shown in FIG. Becoming smaller,
At the welding end point B, the formation of the molten zone S stops. That is, in the method of the present invention, the laser spot s ₀ is the welding start point A.
Since welding is performed with a constant level of input energy until the point where the input energy overlaps, the fitting part is reliably sealed and welded over the entire circumference, but after that, the input energy is gradually reduced, so that the welding energy is gradually reduced after the welding start point A. In the overlap portion O, the area to be reheated becomes small. Therefore, the overlapping part O is less affected by reheating, and a good sealed battery with few welding defects can be obtained.

In the present invention, as a means for gradually reducing the energy input per unit area of the laser beam, it is preferable to gradually reduce the power energy from the power source. Further, since the laser light is focused to increase the energy at the focus (laser spot), conversely, if the focus is shifted from the fitting portion, the energy concentration is reduced. Therefore, it is also possible to gradually shift the focus of the laser light by adjusting the focusing system to gradually reduce the input energy per unit area of the laser light.

In the present invention, as the laser beam for laser welding, only the pulsed laser has been described, but it is also possible to use a laser beam which is continuously irradiated instead of pulsed. Further, the sealing welding method of the present invention is not limited to the rectangular sealed battery, and may be applied to a cylindrical sealed battery or the like. That is, the method of the present invention can be widely used for sealing welding of sealed batteries.

[0019]

In the method of sealing and welding the sealed battery according to the present invention, since the input energy per unit area is gradually reduced from the time when the laser beam returns to the welding start point, the reheated area becomes smaller and the amount of penetration increases. In addition to being suppressed, the effect of thermal shock is reduced.

[0020]

【Example】

Example 1 As shown in FIG. 2, the upper part is made of a nickel-plated steel plate having a thickness of 0.4 mm, and the upper part has a length of 4.8 mm and the width of 15.
A positive electrode sheet (nickel electrode) and a negative electrode (hydrogen storage alloy electrode) are electrically insulated from each other in an outer can 1 having a rectangular bottomed can body having a rectangular opening of 6 mm and a height of 45 mm. An electrode plate group formed by stacking the separators interposed between each other was inserted. The electrode plate group is shaped into a rectangular parallelepiped having a length of 4.5 mm, a width of 15.4 mm, and a height of 40 mm so as to fit inside the outer can.

Next, 1.0 cc of an alkaline aqueous solution containing KOH as a main component was injected into the outer can 1 as an electrolytic solution. Next, length 4.8 mm, width 15.6 mm, thickness 0.4 mm
The lid 3 having the positive electrode 31 in the center is used as the outer can 1.
It was fitted and attached to the opening of the. Then, using a pulse-type laser welding machine, the laser spot diameter is 0.4 mm, and the input energy per unit area is 100, with respect to the fitting portion J.
While irradiating the pulsed laser light of 60 kHz, which is 00 (W / mm ² ), the laser light L is 8 (mm / mm ² ).
sec) at the mating part J as shown by the dotted line in FIG.
Sealing welding was performed by scanning the top. In the final portion of the welding, from the time when the laser spot returned to the welding start point A, as shown in FIG. 8, the input energy per unit area was gradually reduced to 0 and the welding was completed.

In this way, laser sealing welding was carried out over the entire circumference of the fitting portion, and 1000 rectangular sealed type nickel-hydrogen secondary batteries were manufactured. The occurrence rate of laser welding failure was determined for the obtained battery. The results are shown in Table 1. Here, the incidence of laser welding failure was determined as follows.

First, the battery manufactured as described above is
Keep in an atmosphere of temperature 60 ℃, humidity 80% RH, 30
Left for days. Then, for the battery after 30 days,
The presence or absence of liquid leakage was confirmed. Then, the ratio of the battery in which the liquid leakage occurred to the whole of the manufactured batteries was obtained, and this ratio was taken as the incidence of laser welding failure. Comparative Example 1 In the final portion of welding, laser welding was performed at a constant level of input energy as in the conventional case without gradually reducing the input energy of laser light per unit area, and the laser spot s ₀ reached the welding end point B. By the way, turn off the power,
1000 nickel-hydrogen secondary batteries were manufactured in the same manner as in Example 1 except that the welding was completed.

For the battery thus obtained, the incidence of laser welding defects was determined in the same manner as in Example 1. The results are also shown in Table 1.

[0025]

[Table 1]

As is clear from the results in Table 1, Example 1
The battery has a laser welding defect occurrence rate of 0%. That is, when the cover plate is sealed and welded to the upper open end of the outer can, it is possible to suppress an increase in the amount of penetration and the occurrence of cracks in the overlap portion O at the final stage of welding,
Since good welding could be performed, it shows that a good product without welding defects was obtained. This is because, at the final portion of laser welding, the energy input per unit area was gradually reduced and the welding was completed, so the overlap portion was less affected by reheating.

On the other hand, the battery of Comparative Example 1 has a higher incidence of laser welding defects than the battery of the present invention. This is because in the battery of Comparative Example 1, the input energy per unit area is kept constant from beginning to end, so that the overlap portion O at the final stage of welding is reheated at the same input energy level as that at the beginning and the amount of penetration is This is because cracks were generated due to increase or thermal shock, and through holes and cracks which impair the hermeticity of the battery were generated.

[0028]

The method of sealing and welding the sealed battery according to claim 1 is
During laser welding, the input energy per unit area is gradually reduced from the time when the laser light returns to the welding start point,
Since the welding is completed, the influence of reheating on the overlap portion in the final stage of welding is extremely small. Therefore, in the overlapping portion, it is possible to suppress the generation of holes or cracks penetrating inside the battery due to an increase in the amount of melting and the generation of cracks. As a result, the number of defective products due to defective sealing is extremely reduced, and the yield in battery manufacturing is improved.

[Brief description of drawings]

FIG. 1 is an exploded perspective view showing the configuration of a prismatic sealed battery.

FIG. 2 is a top plan view showing a configuration when a lid plate is fitted in the opening of the outer can.

FIG. 3 is a sectional view taken along line III-III in FIG. 2;

FIG. 4 is a top plan view showing a state immediately after the start of welding of the laser spot scanned on the fitting portion.

FIG. 5 is a plan view of the laser spot scanned on the fitting portion as seen from the vicinity of the end of welding.

FIG. 6 is a top plan view showing a state of a laser spot in an overlapping portion at the final stage of welding in a conventional welding method, and a graph showing a relationship between input energy of laser light and time at that time. is there.

FIG. 7 is a cross-sectional view showing a state of a weld bead in a fitting portion.

FIG. 8 is a top plan view showing a state of a laser spot in an overlapping portion at the final stage of welding in the welding method of the present invention, and a graph showing a relationship between input energy of laser light and time at that time. Is.

[Explanation of symbols]

1 Outer can 1a Upper open end 2 Electrode plate group 3 Lid plate 31 Positive electrode A Welding start point B Welding end point J Fitting part O Overlap part s ₀ Laser spot S Melting zone W ₁ Welding bead

Claims (1)

[Claims] 1. A cover plate on which a positive electrode is arranged is fitted and attached to an open end of an outer can containing the electrode plate group, and a fitting portion between the open end of the outer can and the cover plate. By scanning the laser light along the, when laser welding the lid plate to the outer can, the laser light goes around the fitting portion, from the time of returning to the welding start point per unit area of the laser light. A method for sealing and welding a sealed battery, which comprises gradually reducing input energy and terminating laser welding.