JP6986672B2 - Manufacturing method of sealed battery - Google Patents

Description

The present invention relates to a method for manufacturing a sealed battery in which an opening of a battery case is sealed with a sealing plate.

As the material of the battery case, austenitic stainless steel having excellent corrosion resistance, high ductility, and good drawability is used.

However, austenitic stainless steel has the property of being cured when it is formed into a bottomed cylindrical battery case by drawing. Further, since residual stress exists in the battery case due to drawing processing, there is a possibility that aging cracking may occur in the battery case.

In order to remove the hardening due to the drawing process, the battery case formed by the drawing process is heat-treated at a high temperature (for example, Patent Document 1 and the like).

Japanese Unexamined Patent Publication No. 58-78364

However, when the battery case formed into a bottomed tubular shape by drawing is heat-treated at a high temperature in order to remove the hardening due to drawing, the battery case may be deformed by stress relaxation or recrystallization. If the shape of the opening of the battery case is deformed, a gap may be formed between the peripheral edge of the sealing plate and the peripheral edge of the opening of the battery case. As a result, when laser welding the peripheral edge of the sealing plate and the peripheral edge of the opening of the battery case, welding defects may occur at a portion having a large gap. Then, such welding defects become apparent when the thickness of the side portion of the battery case is reduced or the outer diameter of the battery case is increased in order to increase the capacity of the battery.

The present invention has been made in view of the above problems, and a main object thereof is to provide a method for manufacturing a sealed battery capable of preventing the occurrence of welding defects between a battery case and a sealing plate.

The method for manufacturing a closed-type battery according to the present invention is a method for manufacturing a closed-type battery in which the opening of the battery case is sealed with a sealing plate. The battery case is made of austenite-based stainless steel and is drawn by drawing. The process of preparing a battery case molded into a bottomed cylinder and the sealing plate are press-fitted into the opening of the battery case without subjecting the battery case to a heat treatment for removing processing and hardening, and the peripheral edge of the sealing plate and the battery are used. It is characterized by including a step of laser welding the peripheral edge of the opening of the case.

INDUSTRIAL APPLICABILITY According to the present invention, it is possible to provide a method for manufacturing a sealed battery capable of preventing the occurrence of welding defects between the battery case and the sealing plate.

It is sectional drawing which shows typically the structure of the closed type battery to which this invention is applied. It is a partially enlarged view which magnified the vicinity of the opening peripheral edge of a battery case.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The present invention is not limited to the following embodiments. Further, it can be appropriately changed as long as it does not deviate from the range in which the effect of the present invention is exhibited.

FIG. 1 is a cross-sectional view schematically showing the configuration of a closed-type battery to which the present invention is applied. Here, a lithium primary battery will be described as an example, but the present invention is not limited to this.

As shown in FIG. 1, in a lithium primary battery, a electrode plate group 4 in which a negative electrode 1 and a positive electrode 2 are wound via a separator 3 in a bottomed tubular battery case 9 is a non-aqueous electrolytic solution (non-aqueous electrolyte solution). (Illustrated) is housed together. Here, the battery case 9 is made of austenitic stainless steel. The negative electrode 1 is made of a lithium metal foil or a lithium alloy foil. Further, in the positive electrode 2, a core material such as stainless steel is filled with a positive electrode mixture containing a positive electrode active material. As the positive electrode active material, for example, manganese dioxide, iron sulfide, or the like can be used.

The opening of the battery case 9 is sealed by laser welding the peripheral edge portion 10a of the sealing plate 10 and the peripheral edge portion 9a of the opening portion of the battery case 9. Further, the positive electrode terminal 11 is caulked and fixed to the central opening of the sealing plate 10 via the gasket 12. A positive electrode lead 5 connected to the core material of the positive electrode 2 is connected to the positive electrode terminal 11, and a negative electrode lead 6 connected to the negative electrode 1 is connected to the bottom 9b of the battery case 9. Here, the bottom portion 9b of the battery case 9 also serves as a negative electrode terminal. Further, an upper insulating plate 7 and a lower insulating plate 8 are arranged on the upper part and the lower part of the electrode plate group 4 to prevent an internal short circuit, respectively.

By the way, austenitic stainless steel is usually non-magnetic, but when it is drawn, it hardens and becomes magnetic.

The inventor of the present application measured the magnetic permeability of the battery case after drawing the austenitic stainless steel to form a bottomed tubular battery case. The relative magnetic permeability was measured 1.14), but the relative magnetic permeability was as low as 1.01 to 1.03 except in the vicinity of the opening, and it was not magnetized. This means that in the battery case formed by drawing, there is almost no residual stress except in the vicinity of the opening. It is considered that such a result is due to the concentration of stress in the vicinity of the opening of the battery case when the battery case is formed by drawing.

Focusing on such a result, the inventor of the present application can seal the battery case formed by drawing with a sealing plate by laser welding without performing a heat treatment for removing work hardening. It was considered that a heat treatment equivalent to a heat treatment for removing work hardening could be applied to the vicinity of the opening of the battery case.

Table 1 shows the results of measuring the relative permeability near the opening of the battery case after performing three treatments 1 to 3 in the battery case formed by drawing austenitic stainless steel into a bottomed tubular shape. It is a table shown. Here, the process 1 is the specific magnetic permeability measured after the battery case is formed by drawing (without heat treatment), and the process 2 is the opening of the battery case after forming the battery case by drawing and without heat treatment. The specific magnetic permeability measured after laser welding with the sealing plate, and the treatment 3 indicate the specific magnetic permeability measured after the battery case is formed by drawing and then heat-treated. The heat treatment was performed at 1050 ° C. for 60 minutes in an argon atmosphere.

As shown in Table 1, the relative magnetic permeability after the treatment 1 is as high as 1.14, and it is considered that residual stress exists in the vicinity of the opening. On the other hand, the relative magnetic permeability after the treatment 2 has dropped to 1.06, and it is considered that the residual stress in the vicinity of the opening is considerably eliminated. Further, the relative magnetic permeability after the treatment 3 is very low at 1.01, and it is considered that the residual stress in the vicinity of the opening is almost eliminated.

From this, it is almost the same as the heat treatment for removing the work hardening by laser welding the opening of the battery case with the sealing plate without performing the heat treatment for removing the work hardening on the battery case formed by drawing. It can be said that the effect can be obtained.

That is, the residual stress existing in the vicinity of the opening of the battery case formed by drawing is removed in the process of laser welding. On the other hand, there is almost no residual stress except near the opening of the battery case. Therefore, it is considered that the battery case after laser welding has almost no residual stress, so that there is no possibility that the battery case will be cracked by aging.

By the way, as described above, when the battery case 9 formed by drawing is heat-treated at a high temperature in order to remove the curing due to drawing, the battery case 9 may be deformed by stress relaxation or recrystallization. If the shape of the opening of the battery case 9 is deformed, a gap may be formed between the peripheral edge 10a of the sealing plate 10 and the opening peripheral edge 9a of the battery case 9. As a result, when laser welding the peripheral edge portion 10a of the sealing plate 10 and the opening peripheral edge 9a of the battery case 9, welding defects may occur at a portion having a large gap.

Therefore, the peripheral portion 10a of the sealing plate 10 is subjected to a heat treatment for removing the hardening due to the drawing process and a case where the heat treatment is not performed on the battery case formed by drawing the austenitic stainless steel. The difference in the gap generated between the battery case 9 and the peripheral edge 9a of the opening of the battery case 9 was evaluated by the following method.

Austenitic stainless steel (SUS316L) was formed into a bottomed cylindrical battery case 9 having an outer diameter of 17 mm, a side thickness of 0.2 mm, a bottom thickness of 0.2 mm, and a height of 50 mm by drawing. The heat treatment for removing the curing due to the drawing process was performed at 1050 ° C. for 60 minutes in an argon atmosphere. Then, the same sealing plate 10 is inserted into the opening of the battery case 9, and as shown in FIG. 2, a gap formed between the peripheral edge portion 10a of the sealing plate 10 and the opening peripheral edge 9a of the battery case 9 is formed. Of these, the maximum gap L on the circumference was measured.

Table 2 shows the number of battery cases with heat treatment and battery cases without heat treatment by measuring the maximum gap L between the case and the sealing plate for 20 batteries each.

As shown in Table 2, in the battery case with heat treatment, more than half (13 pieces) had a maximum gap L of 0.06 mm or more, whereas in the battery case without heat treatment, the maximum gap L was All were 0.06 mm or less.

As a result, when the battery case 9 formed by drawing is heat-treated at a high temperature in order to remove the curing due to drawing, the shape of the opening of the battery case 9 is deformed, which causes the peripheral portion 10a of the sealing plate 10 to be deformed. It can be seen that a large gap is formed between the battery case 9 and the peripheral edge 9a of the opening.

As described above, when a large gap is formed between the peripheral edge portion 10a of the sealing plate 10 and the opening peripheral edge 9a of the battery case 9, the peripheral edge portion 10a of the sealing plate 10 is laser welded to the opening peripheral edge 9a of the battery case 9. At that time, welding defects may occur in places where the gap is large.

Therefore, in order to verify this, the relationship between the maximum gap L generated between the peripheral edge 10a of the sealing plate 10 and the opening peripheral edge 9a of the battery case 9 and the welding defect in laser welding is determined by the following method. evaluated.

Two flat plates (thickness 0.2 mm) made of austenitic stainless steel (SUS316L) were prepared, and laser welding was performed on the mating surfaces with the two plates sandwiched between spacers to observe the presence or absence of welding defects. By changing the thickness of the spacer, the maximum gap L between the sealing plate 10 and the battery case 9 is simulated. also. Laser welding was performed under the following conditions.

Laser welding was performed with a fiber laser at a continuous oscillation operation, an output of 500 W, and an irradiation speed of 200 mm / s. The laser oscillation operation is roughly divided into two operations, a pulse oscillation operation and a continuous oscillation operation. In order to obtain a stable and uniform heat treatment effect, the continuous oscillation operation was selected.

Further, regarding the output and the speed, the range of the output of 400 W to 600 W and the speed of 100 to 300 mm / s is preferable. If the output is increased and the speed is decreased from this range, the amount of heat becomes too large, and the upper insulating plate 7 and the gasket 12 of the resin member arranged in the vicinity of the welded portion are likely to be deformed.

Further, if the output is lowered and the speed is increased from the above range, the amount of heat becomes too small, the case 9 and the sealing plate 10 are insufficiently melted, welding defects occur, and the effect of heat treatment is difficult to obtain.

Table 3 is a table showing the number of cases where welding defects occurred after laser welding was performed 10 times for each maximum gap L between the battery case and the sealing plate. By visual confirmation, it was determined that welding was defective when there was a gap between the two plates or when there was a hole in the molten portion.

As shown in Table 3, it can be seen that when the maximum gap L generated between the peripheral edge portion 10a of the sealing plate 10 and the opening peripheral edge 9a of the battery case 9 is 0.08 mm or more, welding defects occur.

By the way, welding defects caused by the gap between the battery case 9 and the sealing plate 10 become apparent when the thickness of the side portion of the battery case is reduced or the outer diameter of the battery case is increased.

Therefore, in order to verify this, the maximum gap L generated between the battery case 9 and the sealing plate 10 when the thickness of the side portion of the battery case 9 was changed was measured. The measurement was performed by the following method.

Austenitic stainless steel (SUS316L) is drawn to fix the outer diameter to 32 mm and the height to 50 mm, and the thickness of the side is changed to the range of 0.2 mm to 0.6 mm. It was molded into case 9. The thickness of the bottom was molded to be the same as the thickness of the sides. The heat treatment for removing the curing due to the drawing process was performed at 1050 ° C. for 60 minutes in an argon atmosphere. Then, a sealing plate 10 whose outer diameter is changed according to a change in the thickness of the case side is inserted into the opening of the battery case 9, and as shown in FIG. 2, the peripheral portion 10a of the sealing plate 10 and the battery case 9 are inserted. Of the gaps formed between the gap and the peripheral edge 9a of the opening, the largest gap L on the circumference was measured.

Table 4 shows the number of battery cases having different thicknesses on the sides by measuring the maximum gap L between the case and the sealing plate for 20 batteries each.

As shown in Table 4, when the thickness of the side portion of the battery case is 0.5 mm or less, the maximum gap L generated between the battery case 9 and the sealing plate 10 may be 0.08 mm or more, and the battery case Welding defects between 9 and the sealing plate 10 may become apparent. Therefore, when the thickness of the side portion of the battery case 9 is set to 0.5 mm or less, it cannot be adopted to perform a heat treatment for removing the curing due to the drawing process.

Next, the maximum gap L generated between the battery case 9 and the sealing plate 10 when the size of the outer diameter of the battery case 9 was changed was measured. The measurement was performed by the following method.

Austenitic stainless steel (SUS316L) with a bottomed cylinder whose side thickness is fixed to 0.2 mm and height is fixed to 50 mm by drawing, and the outer diameter is changed to the range of 10 mm to 32 mm. It was molded into a battery case 9. The heat treatment for removing the curing due to the drawing process was performed at 1050 ° C. for 60 minutes in an argon atmosphere. Then, a sealing plate 10 whose outer diameter is changed according to a change in the size of the outer diameter of the case is inserted into the opening of the battery case 9, and as shown in FIG. 2, the peripheral portion 10a of the sealing plate 10 and the battery case are inserted. Among the gaps formed between the gap 9a and the peripheral edge 9a of the opening of 9, the maximum gap L on the circumference was measured.

Table 5 shows the number of battery cases having different outer diameters by measuring the maximum gap L between the case and the sealing plate for 20 batteries each.

As shown in Table 5, when the size of the outer diameter of the battery case 9 is 14 mm or more, the maximum gap L generated between the battery case 9 and the sealing plate 10 may be 0.08 mm or more, and the battery Welding defects between the case 9 and the sealing plate 10 may become apparent. Therefore, when the size of the outer diameter of the battery case 9 is 14 mm or more, it cannot be adopted to perform a heat treatment for removing the curing due to the drawing process.

From the above results, when the battery case 9 is drawn so that the thickness of the side portion is 0.5 mm or less, or when the outer diameter is drawn so that the size is 14 mm or more, By laser welding the opening of the battery case 9 with the sealing plate 10 without performing a heat treatment for removing work hardening, it is possible to prevent the occurrence of welding defects between the battery case 9 and the sealing plate 10. In this case, since laser welding has almost the same effect as heat treatment for removing work hardening, residual stress existing in the vicinity of the opening of the battery case can be removed by laser welding. On the other hand, since there is almost no residual stress except in the vicinity of the opening of the battery case, there is no possibility that aging cracking due to the residual stress will occur in the battery case after laser welding.

According to the present embodiment, the sealing plate 10 is press-fitted into the opening of the battery case 9 without subjecting the battery case 9 made of austenitic stainless steel and formed by drawing to a heat treatment for removing the work hardening. By laser welding the peripheral edge portion 10a of the sealing plate 10 to the opening peripheral edge 9a of the battery case 9, it is possible to prevent the occurrence of welding defects between the battery case 9 and the sealing plate 10. In addition, aging cracking of the battery case due to residual stress generated by drawing can be suppressed.

In the present embodiment, the material of the sealing plate 10 is not particularly limited, but it is preferable to use austenitic stainless steel having excellent corrosion resistance. Further, as shown in FIG. 1, by processing the sealing plate 10 so that a peripheral wall is formed on the peripheral edge portion 10a, the peripheral edge portion 10a of the sealing plate 10 and the opening peripheral edge 9a of the battery case 9 are formed. Laser welding can be easily performed.

By the way, in order to prevent the battery case 9 from being destroyed when the pressure in the battery rises abnormally, an explosion-proof valve is formed on the sealing plate 10 as a safety measure. This explosion-proof valve is composed of a thin-walled portion formed by pressing the sealing plate 10, and when the pressure inside the battery rises, the thin-walled portion breaks and the gas inside the battery is discharged to the outside. ..

However, since the explosion-proof valve is deformed to a thin thickness by press working, residual stress is generated in the sealing plate 10. Therefore, in order to prevent aging cracking of the sealing plate 10 due to residual stress, it is preferable to perform stress relaxation heat treatment on the sealing plate 10 before pressing the sealing plate 10 into the opening of the battery case 9. ..

Further, the explosion-proof valve is required to break stably at a low pressure with little variation, but in order to realize this, it is preferable that the material hardness of the sealing plate 10 is low. This is because a soft material is more likely to be deformed and the thin-walled portion is more likely to break when the internal pressure rises. Therefore, by heat-treating the sealing plate 10 on which the thin-walled portion is formed, work hardening due to press working is removed, so that the working pressure of the explosion-proof valve can be made uniform at a low pressure.

Since the height of the sealing plate 10 is sufficiently lower than that of the battery case 9 (for example, 5 mm or less), deformation due to heat treatment hardly occurs.

Table 6 measures the operating pressure of the explosion-proof valve when the battery is manufactured by press-fitting the sealing plate 10 having the explosion-proof valve into the opening of the battery case 9 which has not been heat-treated to remove work hardening. It is a table showing the results. Here, an embodiment shows a case where the sealing plate 10 is heat-treated before the sealing plate 10 is press-fitted into the opening of the battery case 9, and a comparative example shows a case where the sealing plate 10 is not heat-treated. .. As a reference example, the result when the heat-treated sealing plate 10 is press-fitted into the opening of the battery case 9 which has been heat-treated to remove work hardening is also shown. As the sealing plate 10, a thin-walled portion was formed by press working under the same conditions. In addition, for the measurement of the working pressure, five batteries were manufactured under the same conditions, and the average value and standard deviation (σ) were obtained.

As shown in Table 6, a battery in which the sealing plate 10 is heat-treated before the sealing plate 10 is press-fitted into the opening of the battery case 9 (Example) is a battery in which the sealing plate 10 is not heat-treated (comparative). Compared to the example), the working pressure was low and the variation (σ) was small. In the battery (reference example) in which the heat-treated sealing plate 10 was press-fitted into the opening of the heat-treated battery case 9, the variation in operating pressure (σs) was larger than that in the example. This is because the heat-treated battery case 9 is likely to be deformed when the hardness is lowered and the internal pressure is increased, and the stress for breaking the thin portion is dispersed. Conceivable.

Therefore, by not heat-treating the battery case 9 and heat-treating the sealing plate 10, it is possible to obtain a stable explosion-proof valve with a low magnetic susceptibility, less aging cracking, and a low magnetic susceptibility with little variation. And a highly safe battery can be obtained.

Further, in order to increase the capacity of the battery, the battery case 9 may be drawn so that the thickness of the side portion of the battery case 9 is thinner than the thickness of the bottom portion 9b.

In Table 7, when the thickness of the side portion is t1 and the thickness of the bottom portion is t2, the conditions of the outer diameter of 17 mm and the height of 50 mm are fixed, the thickness ratio of the bottom portion and the side portion is t1 / t2, and after laser welding (after heat treatment). ) Shows the relationship between the relative permeability and aging cracking. The aging cracking was tested with 5 samples each according to JIS G 0576-2001 “Stress corrosion cracking test method for stainless steel”.

As shown in Table 7, when the value of t1 / t2 is 0.7 or more, it is preferable to perform drawing so that aging cracking does not occur and 0.7 ≦ t1 / t2 ≦ 1. More preferably, 0.8 ≦ t1 / t2 ≦ 1, and even more preferably 0.9 ≦ t1 / t2 ≦ 1. If t1 / t2 is less than 0.7, the amount of change in the thickness of the side portion becomes large, and as a result, the residual stress on the side portion of the case becomes large, and aging cracking is likely to occur, which is not preferable.

Although the present invention has been described above in terms of preferred embodiments, such a description is not a limitation, and of course, various modifications can be made. For example, in the above embodiment, the lithium primary battery has been described as an example as the sealed battery, but the present invention is not limited to this, and for example, it can be applied to a dry battery, a nickel hydrogen battery, a lithium ion battery, and the like.

Further, in the above embodiment, SUS316L has been described as an example of the austenitic stainless steel, but the present invention is not limited to this, and for example, SUS304, SUS304L, SUS305 and the like can be used.

1 Negative electrode
2 Positive electrode
3 Separator
4 electrode plate group
5 Positive electrode lead
6 Negative electrode lead
7 Upper insulation plate
8 Lower insulation plate
9 Battery case
9a Battery case opening margin
9b Bottom of battery case
10 Seal plate
10a Peripheral part of sealing plate
11 Positive electrode terminal
12 Gasket

Claims (4)

It is a method of manufacturing a sealed battery in which the opening of the battery case is sealed with a sealing plate.
The battery case is made of austenitic stainless steel made of SUS316L.
The process of preparing the battery case molded into a bottomed cylinder by drawing, and
The sealing plate is press-fitted into the opening of the battery case without subjecting the battery case to a heat treatment for removing work hardening, and the peripheral wall formed on the peripheral edge of the sealing plate and the peripheral edge of the opening of the battery case Including the process of laser welding
The battery case has a side thickness of 0.5 mm or less, and 0.7 ≦ t1 / t2 ≦ 1 when the side thickness is t1 and the bottom thickness is t2. A method for manufacturing a sealed battery that has been drawn. The sealing plate is made of austenitic stainless steel made of SUS316L.
The method for manufacturing a sealed battery according to claim 1, wherein the sealing plate is subjected to a heat treatment for removing work hardening before the sealing plate is press-fitted into the opening of the battery case. The method for manufacturing a sealed battery according to claim 1, wherein the battery case is drawn so that the outer diameter is 14 mm or more. The method for manufacturing a sealed battery according to any one of claims 1 to 3, wherein in the laser welding step, the relative magnetic permeability of the battery case after laser welding is 1.06 to 1.08.

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