JP5677130B2 - Exterior can for lithium ion secondary battery - Google Patents

Description

  The present invention relates to an outer can for a lithium ion secondary battery.

  Lithium ion rechargeable batteries are widely used as power sources for portable devices such as notebook personal computers and mobile phones. Due to their superior characteristics, eco-cars (ecologic cars) such as electric bicycles and electric bikes, It is expected as a power source for transportation equipment and as a storage power source for solar and wind power generation systems.

Lithium-ion secondary batteries usually have a rectangular or cylindrical metal can that is filled with an electrode body and electrolyte solution, and then a metal lid member is assembled, and the lid member is joined to the metal can and sealed. Manufactured by.
Here, for example, in the case of a small lithium ion secondary battery used in a mobile electronic device such as a mobile phone, a square can made of aluminum alloy manufactured by a multistage deep drawing method may be adopted as the battery can. Many. In this multi-stage deep drawing method, an aluminum alloy plate material is used as a raw material, and a square can is generally manufactured by multi-stage pressing using, for example, a drum press.

In addition, as a method of joining the lid member of the small lithium ion secondary battery, the lid member is fitted into the opening of the battery case of the metal can via the low melting point brazing material layer, and the joining interface of the brazing material layer is solid-phase diffused. A method of joining the lid member by brazing has been proposed. (See Patent Document 1)
Since the content pressure of a small lithium ion secondary battery is not so high, a large pressure resistance is not required at the joint between the metal can and the lid member, but the joint strength by brazing is insufficient, so recently by welding The metal can and the lid member are joined.
However, since a high welding strength is not required for the welded portion of the small lithium ion secondary battery, the average penetration depth in the welded portion is generally about 0.3 mm or less. For this reason, as a welding machine used for laser welding, a small YAG pulse laser having an average output of 500 to 600 W class is usually used.

  On the other hand, recently, in various fields such as electric bicycles / electric bikes, other transport machines, solar power / wind power generation systems, etc. In such a case, a large battery having a volume several times to a dozen times or more that of a small battery is used.

  Here, in the case of a large battery, even a single battery generates a large amount of heat, and the internal temperature greatly increases. Therefore, it is necessary to devise measures for releasing the heat behind the battery. For example, in the case of a prismatic secondary battery, it is desirable to make the battery can thinner (peripheral portion in the cross-sectional view) so as to increase the surface area. Moreover, in order to increase a capacity | capacitance further in a large sized battery, it is common to use as a module and a package which combined several batteries. In the case of such usage, it is required that the shape and size of the battery can be designed to some extent freely according to the required battery capacity and the space where it can be installed.

However, in the conventional multistage deep drawing method, only battery cans with a limited shape and size can be produced due to structural limitations of the press.
For example, when a square can is produced by a multistage deep drawing method, W / B, where W is the long side length and B is the short side length in the cross section of the square can, and H is the height of the square can. If the ratio exceeds 8, the defect rate greatly increases, and if it exceeds 10, cracks frequently occur and production is almost impossible.

  In addition, regarding the height H, the height by the multistage deep drawing method is generally less than 100 mm. This is because, in order to make the height H 100 mm or more, a large press having a stroke 3 to 4 times or more is required. Such large presses are special and difficult to obtain, and enormous capital investment is required for their introduction.

In addition, since large square cans are difficult to obtain by press molding, aluminum alloy plate materials that can be used are limited to those having relatively good press formability, and the battery cans are improved in strength and weight and weld strength. It is difficult.
That is, in the case of a small square can, it can be manufactured even from a hard material to which work hardening having a strength of 300 MPa or more is added if the press technique is devised. For this reason, it is possible to easily increase the strength of the thin battery can.
However, in order to produce a large square can, it is necessary to deeply press the aluminum alloy sheet, so that the material is limited to a relatively soft material (a material having good press formability), and the high capacity of the battery can. The demand for strength and weight reduction cannot be met.

  Furthermore, since the pressure inside the battery of the large battery is significantly higher than that of the small battery, it is required that the welded portion between the metal can and the lid member has a large welding strength, that is, a deep penetration amount. . Moreover, when the size of the battery can increases, the welding distance of the welded portion also increases. For this reason, from the viewpoint of ensuring both welding strength and productivity, a high-power fiber laser machine with a large power is often used as a welding machine.

  However, when a high-power fiber laser machine with high power is used, the heat input per unit time applied to the metal can becomes remarkably large, and therefore the metal can is required to withstand such heat input. However, aluminum alloy sheet materials with relatively good press formability used in the multistage deep drawing method cannot be said to have sufficiently high heat resistance, and may cause changes in properties such as deformation and mechanical properties due to the heat effect of laser welding. There is sex. For this reason, in a large metal can formed by the multistage deep drawing method, the increase in power and speed of the laser machine is limited, and it is difficult to improve the welding strength and welding efficiency.

JP 2000-11964 A

  The present invention was made to solve these problems, has a high degree of dimensional freedom, and can select an aluminum-based material used for a metal can from a wide range, and has excellent mechanical strength, An object of the present invention is to provide an outer can for a lithium ion secondary battery in which high weld strength is obtained at a welded portion between a metal can and a lid member.

As a result of repeated investigations by the present inventors to obtain a prismatic battery can having a high degree of freedom in dimensions and excellent in mechanical strength and welding strength, A battery can is formed by welding a pair of lid members to each end by a laser welding method, respectively, and the average maximum penetration depth and average for the welded portion between each end of the square pipe and each lid member By defining the bead width, the inventors have obtained knowledge that a battery can that satisfies these requirements can be obtained.
The present invention has been made based on such findings and has the following configuration.

An outer can for a lithium ion secondary battery according to the present invention includes a square pipe and a pair of lid members that respectively close both ends of the square pipe. Each of the lid members is welded to each end of the square pipe by a laser welding method, and the square pipe has a long side length in its transverse section. W, where B is the short side length, and T is the thickness of the side wall, the W / B ratio is 8 or more, the thickness T is 0.6 to 1.5 mm, and the lid member is in the shape of a rectangular plate, The long side length of the lid member is the same as the long side length of the square pipe, the short side length of the lid member is the same as the short side length of the square pipe, and each lid member and the square pipe welds, the squareness pipe end and the lid member in contact with the end portion, et al provided to surround one round And a welded portion which is composed of a plurality of beads, the average maximum penetration depth is 0.4mm or more state, and are the average bead width of 0.5mm or more, the tensile of the welded portion with respect to the tensile strength of the squared pipe sidewall joint efficiency is the ratio of the intensity and wherein the der Rukoto least 43%.

In the present invention, the square pipe has a W / B ratio of 10.8 to 16.4, a wall thickness of 0.9 to 1.5 mm, an average maximum penetration depth of the weld zone of 495 to 621 μm, and an average bead width. Is preferably in the range of 631 to 741 μm.
In the present invention, the aluminum-based material is preferably made of any one of JIS 1000, JIS 3000, JIS 5000, JIS 6000, and JIS 8000 aluminum alloys .
Further, in the present invention, the extrusion molded body formed by using the hot extrusion method is obtained by further performing a drawing process on the extrusion molded body formed by the hot extrusion method. And

According to the present invention, the battery can has a square pipe and a pair of lid members that respectively close the end portions of the square pipe, and the square pipe is molded using a hot extrusion method. By being constituted by the extruded body, the cross-sectional dimension and height of the square pipe can be set relatively freely. For this reason, the battery can of this invention can make the shape easily respond | correspond to various usage forms, such as a module and a package. It is also possible to set the W / B ratio in the cross section of the square pipe to be relatively large, and as a result, the battery can has a large surface area per volume. Heat can be dissipated efficiently.
Each lid member is welded to each end of the square pipe by a laser welding method, and the average maximum penetration depth and average bead width are specified to be equal to or greater than a predetermined value for the welded portion between each lid member and the square pipe. As a result, a battery can having a high weld strength at the welded portion and excellent pressure strength can be obtained.

When the aluminum alloy used for hot extrusion is selected from those having a predetermined composition, a moderate or higher workability can be obtained during extrusion regardless of the size and W / B ratio of the target battery can. In addition, the battery can can have necessary and sufficient mechanical strength and welding strength.
When the wall thickness T of the square pipe is within a predetermined range, a battery can excellent in pressure strength can be reliably obtained while suppressing the weight.
Further, when the W / B ratio of the square pipe is within a predetermined range, the battery can has a large surface area per volume, and the above-described effect of efficiently dissipating the heat inside the battery is ensured. Can be obtained.

  In addition, when the extruded product formed using the hot extrusion method is a product obtained by further drawing the extruded product formed by the hot extrusion method, the dimensions of the square pipe The accuracy is further increased, and the quality of the battery can can be further improved.

The exploded longitudinal cross-sectional view which shows one Embodiment of the exterior can for lithium ion secondary batteries of this invention. The cross-sectional view which shows an example of the square pipe with which the exterior can for lithium ion secondary batteries shown in FIG. The side view which shows the welding part of the exterior can for lithium ion secondary batteries shown in FIG.

Next, specific embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is an exploded longitudinal sectional view showing a first embodiment of an outer can for a lithium ion secondary battery of the present invention, and FIG. 2 shows a square pipe provided in the outer can for a lithium ion secondary battery shown in FIG. FIG. 3 is a side view showing a welded portion of the outer can for the lithium ion secondary battery shown in FIG.
In the following description, in the square pipe 2, a cross section along the direction orthogonal to the central axis is referred to as a “cross section”, and the long side length of the outer shape in the cross section of the square pipe 2 is “W”, The short side length is “B”, and the ratio of the long side length to the short side length is the W / B ratio. The length in the direction along the central axis of the square pipe 2 is defined as “height H”.

A lithium ion secondary battery outer can (hereinafter simply referred to as a “battery can”) 1 shown in FIG. 1 includes a square pipe 2 and a pair of rectangular plate lid members that close both ends of the square pipe 2. 3.
As shown in FIG. 2, the square pipe 2 is a rectangular tube having a substantially rectangular or substantially square cross section, and is formed by extrusion molding an aluminum alloy having a composition to be described later using a hot extrusion method. It is composed of the body. In addition, the corner | angular part of the square pipe 2 may have an appropriate curvature in an outer surface or an inner surface.

Examples of the aluminum alloy forming the square pipe 2 include (1) an aluminum alloy having an inevitable impurity content of 0.6% by weight or less, and (2) aluminum having a Mn content of 0.3 to 2.0% by weight. Alloy, (3) aluminum alloy with Mg content of 0.5-3.0 wt%, (4) aluminum alloy with Fe content of 0.3-1.8 wt%, (5) Mg content of 0 Extrusion and laser weldability (average maximum penetration depth, average bead width), mechanical among 3 to 1.5 wt% aluminum alloy with Si content of 0.3 to 1.2 wt%, mechanical It is preferable to select appropriately according to the characteristics required of the battery can 1 in consideration of strength and the like.
In hot extrusion processing, good workability can be obtained with a relatively wide range of aluminum-based materials as compared to the multistage deep drawing method. For this reason, the aluminum-based material can be selected with emphasis on mechanical strength and laser weldability, and the battery can 1 can have necessary and sufficient mechanical strength and welding strength.

Here, specific examples and characteristics of the aluminum alloys (1) to (5) are as follows.
First, examples of the aluminum alloy (1) include JIS (or AA) 1000 series alloys. While these have excellent extrudability, the strength is low and the laser weldability is not so good, they can be used as the constituent material of the battery can 1.
Examples of the aluminum alloy containing Mn (2) include JIS (or AA) 3000 series alloys. While these have excellent laser weldability, they have moderate extrudability and strength.
Examples of the aluminum alloy containing Mg of (3) include JIS (or AA) 5000 series alloys. While this aluminum alloy can meet the demand for high extrudability or high strength by selecting the Mg content, it may be slightly inferior in terms of laser weldability.
Examples of the aluminum alloy containing Fe in (4) include JIS (or AA) 8000 series alloys. These have the advantage that the strength and laser weldability can be improved without impairing formability as compared with the aluminum alloy of (1). However, (2), (3), or (5) described later. The strength is lower than the strength of each aluminum alloy.
Examples of the aluminum alloy containing Mg and Si in (5) include JIS (or AA) 6000 series alloys. Since these have age-hardening properties in addition to high extrudability and high strength, there is an advantage that the joint between the lid and the pipe softened by laser welding can be reinforced. On the other hand, the laser weldability tends to be slightly inferior to the aluminum alloy (4).

  In order to obtain these aluminum alloys, first, a target billet alloy is melted and component-adjusted, and a cylindrical billet whose diameter corresponds to 1.2 to 2.0 times the long side length W of the battery can 1. Casting. Next, the obtained billet is subjected to an appropriate homogenization process according to its components, and then cut into an appropriate length. Thereby, the short billet used as the raw material of a hot extrusion process is obtained.

The square pipe 2 is obtained by forming such a short billet of aluminum alloy using a hot extrusion method.
Here, the hot extrusion processing method applies a pressure while keeping the material at a temperature higher than the temperature at which the material is recrystallized, and extrudes the material from the hole of the die, so that the cross-sectional shape corresponding to the hole shape of the die is obtained. This is a method for obtaining a long extruded product. In the present embodiment, a die whose hole shape corresponds to the target cross-sectional shape of the rectangular pipe 2 is used, and an aluminum-based material is extruded so as to be a long rectangular pipe. Then, the obtained extruded product is cut to a length corresponding to the height of the intended battery can 1. In this case, the square pipe 2 is configured by cutting the extruded product.

In the hot extrusion method, the molding process is performed satisfactorily regardless of the cross-sectional dimension of the target square pipe 2, and the square pipe 2 having a relatively large size and W / B ratio can be obtained with certainty. . In addition, since the cutting length for cutting the long extruded product corresponds to the height of the square pipe 2, the square pipe 2 having a desired height (length) is adjusted by adjusting the cutting length. Can be easily obtained.
For this reason, the square pipe 2 formed using the hot extrusion method can easily correspond to the usage form of the battery such as a module or a package. Moreover, it is also possible to set the W / B ratio in the cross section to be relatively large, whereby the battery can 1 has a large surface area per volume, and when applied to a battery, the heat inside the battery can be efficiently generated. Can diverge.

  Here, the square pipe 2 may be constituted by a cut piece obtained by cutting a drawn pipe obtained by subjecting an extruded product obtained by hot extrusion to a target length. The drawing method is a processing method in which a die having a die hole size smaller than the cross section of the workpiece is used, and a square-shaped pipe is drawn through the die hole. Thereby, the cross-sectional dimension of the square pipe 2 and the dimensional accuracy of wall thickness can be controlled much higher, and the quality of the battery can 1 can be further improved.

The square pipe 2 preferably has a W / B ratio in the cross section of 8 or more and a thickness T in the range of 0.6 to 1.5 mm.
When the W / B ratio of the square pipe 2 is less than 8, depending on the applied battery, it is difficult to dissipate the heat inside the battery, and the temperature rise inside the battery may adversely affect external electronic devices. There is. Moreover, since the square pipe 2 having a W / B ratio of less than 8 can be easily manufactured by a multistage deep drawing method, when the manufacturing equipment and molding conditions are already established, hot extrusion is performed. The advantage of using the processing method is not recognized, and there is an inconvenience that the existing facilities are wasted.
On the other hand, when the thickness T of the square pipe 2 is less than 0.6 mm, the pressure resistance of the battery can 1 is insufficient. Moreover, when the wall thickness T exceeds 1.5 mm, it is difficult to reduce the weight of the battery can 1.

As shown in FIG. 3, each of the pair of lid members 3 is assembled to each end of the square pipe 2 and welded by a laser welding method.
Here, the laser welding method is a welding method in which laser light is used as a heat source to join materials to be joined made of metal or the like. In this laser welding method, the laser beam is condensed near the boundary between the materials to be joined (the square pipe 2 and the respective lid members 3), and the focused spot is scanned along the boundary to thereby detect the metal. The square pipe 2 and each lid member 3 are joined by melting and solidifying locally.

And in this invention, about the welding part 4 of this square pipe 2 and each cover member 3, the average maximum penetration depth is prescribed | regulated 0.4 mm or more, and an average bead width is prescribed | regulated to 0.5 mm or more.
Here, in this specification, “average maximum penetration depth” and “average bead width” are values measured as follows.

a. Average Maximum Penetration Depth Battery can 1 is broken at weld 4 and the fracture surface is observed at a magnification of 50 times. Then, from this observed enlarged image, the maximum penetration depth of the welded portion 4 is measured over the entire length of the battery can 1 to obtain an average value.
b. Average bead width The weld bead of the battery can 1 is observed at an enlargement ratio of 50 times from above. Then, from this observed enlarged image, the bead width a of the welded portion 4 is measured over the entire width of the battery can 1 and the average value is obtained.

The average maximum penetration depth and the average bead width are indicators of the welding strength of the welded portion 4. The larger these values, the greater the weld strength of the welded portion 4, and the battery can 1 has a higher pressure resistance.
And when the average maximum penetration depth of the weld part 4 is less than 0.4 mm, the weld strength of the weld part 4 is small, and the pressure resistance of the battery can 1 is insufficient. However, if the average maximum penetration depth is set larger than necessary, the penetration portion may exceed the plate thickness, which may damage the battery components. Moreover, since the average maximum penetration depth is set to a large value, a large amount of heat input is required, resulting in a disadvantage that the welding efficiency is lowered. From these points, the average maximum penetration depth is preferably 4/5 or less of the wall thickness T of the square pipe 2.

  Moreover, when the average bead width of the weld part 4 is less than 0.5 mm, the joint strength of the weld part 4 is small, and the pressure resistance of the battery can 1 is insufficient. However, if the average bead width is set to a value larger than necessary, a large amount of heat input is required, resulting in a disadvantage that the welding efficiency is lowered. For this reason, the average beat width is preferably 90% or less of the wall thickness T of the square pipe 2.

The average maximum penetration depth and the average bead width in the welded portion 4 can be controlled by the type of aluminum material used for the square pipe 2 and each lid member 3 and the conditions of the laser welding machine.
Here, as the laser welding machine used for the laser welding method, it is preferable to use a fiber laser welding machine having a maximum output of 2 kw or more. Thereby, even when the scanning speed of the focused spot is relatively high, the average maximum penetration depth of the rectangular pipe 2 and each lid member 3 is 0.4 mm or more and the average bead width is 0.5 mm or more. Thus, it becomes possible to perform high-speed welding with high welding strength. Here, the characteristics of the aluminum alloys (1) to (5) described above hardly change even when the laser beam is irradiated by a laser welding machine having such a large output. This can be done without impairing the mechanical strength.

  As described above, the battery can 1 of the present embodiment is configured such that the square pipe 2 is formed of an extruded body formed by a hot extrusion method, so that its cross-sectional dimensions and height can be freely set. It is possible to easily adapt to the usage form of the applied battery, and it is also possible to increase the surface area per volume and to form a shape that can efficiently dissipate internal heat.

Further, a pair of lid members 3 are joined to the square pipe 2 by a laser welding method, and the average maximum penetration depth and the average bead width of the welded portion 4 are specified to be equal to or greater than a predetermined value. A battery can 1 having a high joint strength of the welded portion 4 and excellent pressure strength can be obtained.
For this reason, the battery can 1 of this invention can be used suitably as a battery can of a large capacity | capacitance and a large sized lithium ion secondary battery.
As mentioned above, although embodiment of the exterior can for lithium ion secondary batteries of this invention was described, each part which comprises the said exterior can is an example, Comprising: It can change suitably in the range which does not deviate from the scope of the present invention.

Specific examples of the present invention will be described below, but the present invention is not limited to these examples.
Example 1
A billet with an outer diameter of 13 inches was cast by melting JIS 1050 alloy.
The billet was homogenized, cut, reheated, and molded by a porthole extrusion method to obtain a flat pipe (long square pipe). This flat pipe has an outer dimension in a cross section of a long side length W: 205 mm, a short side length B: 12.5 mm, and a wall thickness T of 1.2 mm. The flat pipe was cut so that the height H was 250 mm to obtain a square pipe.
Next, two lid members made of JIS-defined 3003 alloy were prepared. The dimension of the lid member in plan view is substantially the same as the dimension of the cross section of the square pipe, and the wall thickness is 1.3 mm. Then, both ends of the square pipe were closed by assembling each lid member, and both ends of the square pipe and each lid member were joined by laser welding. A battery can was produced by the above process.

(Examples 2 to 5)
A battery can was produced in the same manner as in Example 1 except that the alloy used for casting the billet, the outer diameter of the billet, and the dimensions of the square pipe were changed as shown in Table 1.

(Examples 6 to 8)
The alloy used for casting the billet, the outer diameter of the billet, and the dimensions of the square pipe are changed as shown in Table 1, and the flat pipe obtained by hot extrusion is cooled to a thickness of 0.8 mm. A battery can was produced in the same manner as in Example 1 except that a thin pipe was produced by performing a thinning process and cutting the drawn pipe.

(Comparative Example 1)
Using a soft material (O material) made of JIS standard 1050 alloy with a plate thickness of 1.4 mm, molding was performed with a 9-stage deep drawing press to obtain a flat tube. The dimensions of the target flat tube are a long side length of 168 mm, a short side length of 15.5 mm, and a side wall thickness of 1.2 mm.

(Comparative Examples 2 and 3)
Molding was performed by a nine-stage deep drawing press in the same manner as in Example 1 except that the dimensions of the alloy used as the soft material and the target flat tube were changed as shown in Table 1.
(Comparative Examples 4 and 5)
Except for changing the dimensions of the alloy used as the soft material and the target flat tube as shown in Table 1, molding was performed by a 9-stage deep drawing press in the same manner as in Comparative Example 1.

<Evaluation>
1. Table 1 shows whether or not a flat pipe or a flat tube having a target dimension could be formed for each example and each comparative example.
○: When a flat pipe or flat tube could be formed ×: When a flat pipe or flat tube could not be formed Note that the 4-digit number in the column describing the type of alloy in Table 1 is JIS-regulated aluminum The alloy number.

  As shown in Table 1, in each example in which a flat pipe was formed by an extrusion method, a flat pipe having a desired size could be obtained. On the other hand, in each comparative example using the 9-stage deep drawing method, the material was broken before the 6th stage deep drawing, and the target flat tube could not be formed.

2. About each Example, the extrusion property of the used billet, the mechanical property of the produced battery can, and the laser weldability of a square pipe and a cover member were evaluated. The evaluation conditions are as shown below.
(1) Evaluation of extrusion processability The external dimensions in the cross section are long side length W: 188 mm, short side length B: 12.5 mm, wall thickness T is 1.2 mm, and curvature R on the inner surface side of the corner is 3 mm. Each billet was formed into a flat pipe at various extrusion speeds using an extrusion die. Then, the maximum extrusion speed at which the dimensional and shape accuracy was good and the surface quality was stably obtained was investigated. The measurement results were evaluated according to the following criteria.
When the maximum extrusion speed is 15 m / min or more, it is indicated by a double circle, when the maximum extrusion speed is 5 m / min or more and less than 15 m / min, it is indicated by a circle, and when the maximum extrusion speed is less than 5 m / min. Are indicated by Δ.

(2) Mechanical properties of battery can For each battery can, a sample was cut out in a strip shape from the vicinity of the center of the side wall forming the long side. And it processed into the JIS regulation No. 5 test piece, the tensile test was done, and tensile strength, yield strength, and elongation were measured, respectively.

(3) Laser Weldability Evaluation Using a Yb-fiber laser welder with a maximum output of 2 kw, a battery can was obtained by welding lid members made of 3003 alloy to both ends of each square pipe. The dimension of the lid member in plan view is substantially the same as the dimension of the cross section of the flat pipe, and the wall thickness is 1.1 mm. The welding conditions are as follows. Comparative examples 4 and 5 were welded under welding condition 2, and the others were welded under welding condition 1.
Welding condition 1
Oscillation method: CW oscillation, condensing optical system: YW50 (fc = 125), fiber diameter: φ0.1,
Ar gas flow rate: 20 (l / min), nozzle type: φ10 center, output: 550 W,
Processing speed: 166 (mm / sec).
Welding condition 2
Oscillation method: CW oscillation, condensing optical system: YW50 (fc = 125), fiber diameter: φ0.1,
Ar gas flow rate: 20 (l / min), nozzle type: φ10 center, output: 450 W
Processing speed: 166 (mm / sec).
About the obtained battery can, the average maximum penetration depth and average bead width of the welded part were measured as follows.

a. Average maximum penetration depth Each battery can was broken at the welded portion, and the fracture surface was observed at a magnification of 50 times. And from this observed enlarged image, the maximum penetration depth of the welded portion was measured over the entire length of the battery can, and the average value was obtained.
b. Average bead width The weld bead of the battery can was observed at an enlargement ratio of 50 times from above. And from this observed enlarged image, the bead width a of the welded portion was measured over the entire width of the battery can, and the average value was obtained.
c. Sputtering traces On the outer peripheral surface of each battery can, the range of ± 1.0 mm from the weld bead was observed with a CCD camera, the number of occurrences of melt spatter of 50 μm or more was measured, and converted to the number in a unit length of 250 mm. When the number was 250 or more, it was evaluated as x, when it was less than 200 to 250, Δ, when it was less than 100 to 200, when it was less than 100, and when it was less than 100.
The welded part of the battery can is located at the corner of the can, and it is difficult to cut out a test piece and evaluate it by a tensile test. Instead, the following method was adopted and evaluated.
Two short rail samples having a width of 50 and a length of 100 are cut out from each pipe or plate material, and two samples are obtained according to the welding conditions 1 (Invention Examples 1 to 8) or the welding conditions 2 (Comparative Examples 4 and 5). The short sides of each other were welded together. Thereafter, a JIS No. 5 test piece was prepared by setting the weld bead to the center of the parallel part so as to be perpendicular to the longitudinal direction of the test piece. A tensile test is performed using this test piece, the tensile strength is measured, and this value is referred to as the welding material tensile strength. A ratio between the tensile strength of the welding material and the tensile strength obtained by measuring the mechanical properties of the battery can was obtained, and this was called the joint efficiency and used as an evaluation index of the welding strength. The measurement results are also shown in Table 2, and it was judged that there was no problem as the welding strength if it was 40% or more.
The above evaluation results are shown in Table 2.

  As shown in Table 2, the square pipe and the lid member of each example are welded with an average maximum penetration depth of 400 μm (0.4 mm) or more and an average bead width of 500 μm (0.5 mm) or more. And a large welding strength was obtained. In addition, it turned out that it is preferable to select an aluminum alloy according to the characteristic requested | required of a battery can, since extrusion processability, a mechanical property, and laser weldability differ with aluminum alloys to be used.

  DESCRIPTION OF SYMBOLS 1 ... Exterior can (battery can) for lithium ion secondary batteries, 2 ... Square pipe, 3 ... Lid member, 4 ... Welded part, W ... Long side length, B ... Short side length, T ... Thickness, H ... Height, a ... Bead width.

Claims (4)

A square pipe and a pair of lid members that respectively close both ends of the square pipe, and the square pipe is made of an extruded product formed by molding an aluminum-based material using a hot extrusion method. Each of the lid members is welded to each end of the square pipe by a laser welding method,
The square pipe has a W / B ratio of 8 or more and a wall thickness T of 0.6 to 1 when the long side length in the cross section is W, the short side length is B, and the side wall thickness is T. 5 mm, the lid member has a rectangular plate shape, the long side length of the lid member is the same as the long side length of the square pipe, and the short side length of the lid member is the short side length of the square pipe. Are the same,
The welded portion between each lid member and the square pipe is a weld formed by an end portion of the square pipe and a plurality of beads provided so as to surround the lid member covered around the end portion. a part, the average maximum penetration depth is 0.4mm or more, the average bead width of Ri der least 0.5 mm, joint efficiency is the ratio of the tensile strength of the welded portion with respect to the tensile strength of the squared pipe sidewall 43 outer can for a lithium ion secondary battery, characterized der Rukoto than%. The square pipe has a W / B ratio of 10.8 to 16.4, a wall thickness of 0.9 to 1.5 mm, an average maximum penetration depth of the weld zone of 495 to 621 μm, and an average bead width of 631 to 741 μm. The outer can for a lithium ion secondary battery according to claim 1, wherein: The aluminum-based material, JIS1000 series, JIS3000 series, JIS5000 series, JIS6000 series, JIS8000 series claim 1 or 2 lithium ion secondary battery outer cans according to, characterized in that consisting of either aluminum alloy. Extrusion moldings molded using an extrusion processing method between the heat to the extruded body which is formed by the hot extrusion method, according to claim 1, characterized in that and further subjected to drawing process - The outer can for a lithium ion secondary battery according to any one of 3 .

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