JP7078468B2 - Secondary battery, battery container inspection method, and secondary battery manufacturing method - Google Patents

Description

The present invention relates to a secondary battery in which a lid is laser-welded to a case, a method for inspecting a battery container, and a method for manufacturing a secondary battery.

Conventionally, there is a secondary battery provided with a battery container in which a metal lid is welded to a metal case by irradiation with laser light. In such a secondary battery, high-precision laser welding is performed between the metal lid and the case in order to maintain a high degree of airtightness so that the electrolyte in the battery container does not leak to the outside. It has been. For example, Patent Document 1 describes an example of a technique for evaluating the penetration depth as an example of a technique for evaluating the suitability of welding.

The evaluation method described in Patent Document 1 is a method of evaluating the welding penetration depth of a welded portion in a battery container (work) formed by laser welding a case (can body) and a lid body (cover member). .. In this method, an echo signal acquisition step of acquiring an echo signal by scanning while transmitting ultrasonic waves to a battery container and an echo signal corresponding to each of the surface of the lid and the interface between the case and the lid are imaged. It is provided with an imaging process to be converted. In addition, this method has a binarization step of converting an imaged surface echo image and an interface echo image into a binarized image, and a binarized interface echo image from the binarized surface echo image. It has a subtraction step of subtracting. Further, in this method, a contour extraction step of extracting the contour of the welded portion from the subtracted image and a determination step of calculating the weld penetration depth of the welded portion based on the contour and determining the quality of the welded portion are performed. Have.

Japanese Unexamined Patent Publication No. 2010-14554

According to the evaluation method described in Patent Document 1, it is possible to evaluate whether or not the welding penetration depth between the case of the battery container and the lid does not reach the inner peripheral side of the battery container over the entire circumference of the battery container. However, the reliability of the battery container is not determined only by the weld penetration depth. That is, there is room for improvement in the manufacture of a battery having a highly reliable welded portion in the battery container.

The present invention has been made in view of such circumstances, and an object thereof is a secondary battery, a method for inspecting a battery container, and a method for manufacturing a secondary battery, which can enhance the reliability of the welded portion of the battery. Is to provide.

The secondary battery for solving the above problems is a secondary battery including a battery container in which the opening of a metal case accommodating a power generation element is sealed with a metal lid, and the opening of the case. The circumferential contact portion between the lid and the outer peripheral portion thereof is provided with a molten portion melted in the circumferential direction in which the contact portion extends by laser welding, and the melted portion has a cross section orthogonal to the circumferential direction. The region melted by the laser welding is a convex region having a tip portion that shrinks inward from the outer surface of the battery container and faces inward, and the convex shape is a cross section orthogonal to the circumferential direction. In the above, the tip portion faces the contact portion inside the battery container, and the outer surface portion of the battery container extends to the left and right of the position irradiated with the laser beam for laser welding. The tip portion does not reach the inside of the battery container, and the surface portion reaches the side surface of the cross section with respect to the laser-welded plane surface on the outside of the battery container.

A method for inspecting a battery container that solves the above problems is a battery container for a secondary battery in which an opening of a metal case is sealed with a metal lid, and the opening and the lid of the case are used. This is an inspection method for inspecting a battery container having a molten portion in which a circumferential contact portion with an outer peripheral portion of the body is melted in the circumferential direction in which the contact portion extends by laser welding with a laser beam. An image including a region melted by the laser welding is acquired for the cross section orthogonal to the circumferential direction, and the region melted by the laser welding is the region of the battery container based on the acquired image. A convex region having a tip portion that shrinks inward from the outer surface and faces inward, wherein the tip portion is inside the battery container in a cross section orthogonal to the circumferential direction. While facing the contact portion, the outer surface portion of the battery container extends to the left and right of the position where the laser beam is irradiated, and the tip portion does not reach the inside of the battery container. The surface portion inspects that one of the left and right sides of the cross section reaches the side surface with respect to the laser-welded plane on the outside of the battery container.

The inventors have described that the boundary portion formed between the case of the secondary battery and the lid, in which the strength of the boundary portion including the boundary line between the molten portion and the non-melted portion is relatively low, is relatively low. Was found to be prone to cracking. In this regard, according to such a configuration or method, the fused portion has a convex shape, the tip portion thereof faces the contact portion inside the battery container, and the surface portion thereof is on the outside of the battery container. It will spread to either the plate thickness in the left-right direction. As a result, the boundary portion including the boundary line formed between the molten portion and the non-melted portion in the battery container becomes an arc shape having a length equal to or larger than the plate thickness and longer than a straight line. Therefore, even if the boundary portion has a low strength, the strength is increased by lengthening the boundary portion, and the force and time required for breaking are increased, so that the reliability of the molten portion is improved.

As a preferred configuration, the convex shape has a center line from the surface portion toward the tip portion passing within 0.3 mm from the contact portion inside the battery container.
According to such a configuration, since the center line passing through the convex tip portion is within 0.3 mm with respect to the contact portion inside the battery container, the welded portion from the tip portion to the side surface portion and the non-melting portion are not melted. The length of the boundary portion between the portions can be made longer.

As a preferable configuration, when the boundary portion of the molten portion from the tip portion of the convex shape to the non-melted portion reaching the side surface thereof is viewed from the contact portion inside the battery container, the surface portion thereof is viewed. It is arranged in a range of less than 90 degrees on the side surface side of the center line in the viewing direction.

As a preferred method, in the inspection, the convex boundary line reaching the side surface has a predetermined length or more, and the outside of the battery container is viewed from the contact portion inside the battery container. When viewed, it is inspected whether or not it is arranged in a range of less than 90 degrees from the center line of the convex shape to the side surface side in the viewed direction.

According to such a configuration or method, since the spread of the molten portion is less than 90 degrees with respect to the direction in which the outside of the battery container is viewed from the contact portion inside the battery container, the molten portion reaching the side surface from the tip portion. The boundary between the unmelted portion and the non-melted portion can be lengthened.

As a preferred method, an image including the region melted by the laser welding is acquired by an X-ray CT device.
According to this method, if the X-ray CT device is used, the restrictions on the imaging conditions are relaxed, and the tomographic image can be acquired in a form in which the time required for imaging is suppressed to the same level as before. For example, restrictions on the evaluation method described in Patent Document 1, for example, eliminating or simplifying the trouble of arranging the battery in the water of the water tank and having to bring the ultrasonic sensor close to the battery container. Can be done.

As a preferred method, the predetermined length is the shortest distance from the tip of the convex shape to the side surface of the battery container.
According to such a method, the length of the boundary portion between the welded portion and the non-melted portion from the tip portion to the side surface portion becomes long.

The method for manufacturing a secondary battery that solves the above problems is a method for manufacturing a secondary battery including a battery container that is laser-welded in such a manner that the energy intensity irradiated with the laser light can be changed. An image of the irradiated portion of the laser beam and its surroundings is acquired, a light emitting image of the image is extracted by an extraction unit, and a light emitting image of the image and a light / dark value and melting set in advance in a storage unit are extracted by a control unit. From the relationship of depth, the energy intensity irradiated with the laser beam is controlled so that the melting depth becomes a predetermined depth, and the light and dark values preset in the storage unit in the correction unit. And, the correction unit corrects the relationship between the melting depth and the melting depth of the irradiation point of the laser beam at the past correction timing, and compares the emission image of the image at the past correction timing. Therefore, the relationship between the light / dark value and the melting depth preset in the storage unit is corrected.

According to such a method, even if the relationship between the light / dark value and the melting depth changes depending on the state of the material, the shape and output of the laser beam, the relationship between the light / dark value and the melting depth is corrected by the comparison at the correction timing. Then, the energy intensity irradiated with the laser beam is controlled by the relationship between the corrected light and dark value and the melting depth, so that laser welding is preferably performed.

As a preferred method, the melting depth of the irradiation site of the laser beam is measured by a non-destructive inspection using an X-ray CT device.
According to such a method, the melting depth can be measured with high accuracy by non-destructive inspection without mechanical deformation. Further, if it is a non-destructive inspection that does not require a cutting interval or a cutting margin, the state of the molten portion can be continuously inspected in the extending direction. In particular, it has been newly found that an X-ray CT device can clearly measure the range in which the density change has changed due to recoagulation. With an X-ray CT device, it is possible to acquire a tomographic image in a form in which restrictions on imaging conditions are suppressed and the time required for imaging is suppressed to the same level as before.

As a preferred method, the relationship between the light / dark value and the melting depth is determined for each welding position or each welding section of the object to be welded.
According to such a method, even if the relationship between the light / dark value and the melting depth changes depending on the welding position and the welding section of the welding object, the relationship between the light / dark value and the melting depth is determined at those welding positions and the like. Therefore, appropriate welding can be performed at each welding position and the like.

As a preferred method, the laser beam irradiation site is the opening of the case in a secondary battery including a battery container in which the opening of the metal case containing the power generation element is sealed by a metal lid. It is a circumferential contact portion between the portion and the outer peripheral portion of the lid, and the light / dark value and the melting depth are based on the emission image of the image acquired over the entire circumference of the contact portion by the determination portion. Based on the acquisition of the melting depth over the entire circumference of the contact portion from the relationship of the laser, it is determined whether or not the melting depth over the entire circumference is appropriate.

According to such a method, the emission image of the image over the entire circumference of the contact portion is continuously monitored in the circumferential direction, which is a defect of the contact portion of the secondary battery and is overlooked by cutting at predetermined intervals. Even defects that may be damaged can be detected.

As a preferred method, the laser beam has a first laser beam having a Gaussian intensity distribution and a second laser beam having a larger irradiation diameter than the first laser beam and having a top hat intensity distribution. It is a laser beam generated by synthesizing light, and has a distribution in which the intensity of the generated laser beam becomes the maximum value in the central portion surrounded by the peripheral portion.

According to such a method, the laser beam applies energy to the corresponding irradiation range of the top hat type on average to enable stable welding, the control thereof is easy, and the Gauss type Reliable welding with high energy can be enabled at the center of the corresponding irradiation range.

According to the present invention, the reliability of the welded portion of the battery can be improved.

The block diagram which shows the schematic structure about one Embodiment of the secondary battery, the inspection method of a battery container, and the manufacturing method of a secondary battery. FIG. 5 is a cross-sectional view schematically showing a cross-sectional structure of a laser welded portion in the same embodiment. The schematic diagram which shows typically the state of the weld part at the time of welding in the laser welding apparatus in the same embodiment. In the same embodiment, it is a figure which shows the welding state, (a) is the sectional view which shows the good welding state, (b) is the sectional view which shows an example of the conventional welding state. The graph which shows the relationship between the weld shape and durability in the same embodiment. In the same embodiment, it is a figure which shows the relationship between the light emission image and the penetration depth at each welding position, (a) is the image which shows the light emission image, (b) is the sectional view which shows the melting depth. The graph which shows the relationship between the light-dark value and the melting depth, and the correction in the same embodiment. The flowchart which shows the procedure which inspects the molten state of a molten part in the same embodiment.

An embodiment of a method for inspecting a secondary battery and a battery container, and a method for manufacturing a secondary battery will be described with reference to FIGS. 1 to 8.
As shown in FIG. 1, a laser welding apparatus used for manufacturing a secondary battery irradiates a welding target with an irradiation laser beam L2 generated based on an oscillating laser beam L0 output from a laser oscillator 110 to perform laser welding. I do. The laser welding apparatus includes the laser oscillator 110 that oscillates and outputs a laser beam, and a laser output unit 200 that irradiates a welding target with an oscillating laser beam L0 output from the laser oscillator 110. The laser welding device is used for the welding control unit 500 that controls laser welding, the X-ray CT device 600 that measures the melting depth of the battery container 300 by non-destructive inspection, and the determination of the melting depth during laser welding. It is provided with a determination data management device 700 that manages determination data.

The laser oscillator 110 is a so-called semiconductor laser, and oscillates a laser diode to output an oscillating laser beam L0. The laser oscillator 110 outputs the oscillating laser beam L0 as a laser beam that can be used for laser welding, for example, a laser beam having a wavelength of 880 to 980 nanometers (nm). Further, the laser oscillator 110 outputs the intensity distribution of the energy of the oscillating laser beam L0 as a predetermined type, for example, a top hat type (rectangular distribution type). It is relatively easy to output a laser beam having a top hat type intensity distribution from a semiconductor laser.

The laser output unit 200 inputs the oscillating laser light L0 and generates and outputs the irradiation laser light L2 to irradiate the welding target. The laser output unit 200 irradiates the output irradiation laser beam L2 on the welding target portion of the battery container 300 to be welded.

The battery container 300 is a secondary battery in which a power generation element is housed. The battery container 300 is composed of a metal case 310 and a metal lid 320 that is fitted into the opening 310c of the case 310 to seal the case 310, and the case 310 and the lid 320 are peripheral to each other. A contact portion 330 having a shape is formed. The contact portion 330 is provided in a circumferential shape between the side surface end portion 310a of the case 310 and the outer peripheral portion 320b of the surface 320a of the lid 320. In the present embodiment, the surface 320a of the lid 320 constitutes a laser-welded flat surface, and the side surface 310b of the case 310 constitutes a side surface with respect to the laser-welded flat surface. In the battery container 300, the circumferential welding target portion set in the extending direction of the contact portion 330 is continuously laser welded by the irradiation laser beam L2 emitted from the laser output portion 200. In this embodiment, the metal constituting the case 310 and the lid 320 is aluminum or an aluminum alloy.

The laser output unit 200 includes an intensity distribution converter 261 to which the oscillating laser light L0 is incident, a collimating lens 260 to which the output of the intensity distribution converter 261 is input, and a condenser lens 250 to emit the irradiation laser light L2. Be prepared.

The intensity distribution converter 261 outputs the incident oscillating laser beam L0 as the converted laser beam L3 having an intensity distribution suitable for laser welding. The intensity distribution converter 261 converts the top hat type oscillating laser beam L0 into a conversion laser beam L3 having an appropriate energy intensity distribution (see, for example, the energy intensity distribution D6 in FIG. 2). The intensity distribution converter 261 is a known converter, which includes an optical fiber such as an optical lens, a process fiber, or a double core fiber, and can change the intensity distribution of the input laser light to a target intensity distribution.

The collimating lens 260 is a lens that converts the incident conversion laser light L3 into parallel light L1 and outputs the parallel light L1, and outputs the parallel light L1 to the condenser lens 250.
The condenser lens 250 emits the input parallel light L1 as irradiation laser light L2 that concentrates the input parallel light L1 on the irradiation site. The condenser lens 250 increases the energy intensity at the irradiation point of the irradiation laser beam L2 by narrowing the irradiation diameter (for example, the diameter L2D in FIG. 2) rather than the outer diameter of the parallel light L1. As a result, the irradiation laser beam L2 laser-welds the two metal members to be welded by melting the two metal members.

As shown in FIG. 2, the laser beam showing an example of the irradiation laser beam L2 has an irradiation diameter of L2D, and the energy intensity distribution D6 is surrounded by a top hat type intensity distribution D2 as a peripheral portion. It is a distribution having a Gaussian intensity distribution D1 in the central portion. The irradiation laser beam L2 irradiates the welding target portion including the contact portion 330 so that the contact portion 330 between the case 310 and the lid 320 is included in the irradiation diameter. Then, by applying high energy to the welding target portion, the contact portion 330 included in the laser irradiation portion is laser welded. If a long boundary line can be provided between the molten portion and the non-melted portion, the energy intensity distribution of the irradiation laser beam L2 is not limited to the energy intensity distribution D6 shown in FIG. 2, and is the top. It may be a hat-type intensity distribution, a Gaussian-type intensity distribution, or another intensity distribution.

As shown in FIG. 3, the irradiation laser beam L2 is relatively moved in the extending direction of the contact portion 330, so that the case 310 and the lid 320 are laser welded. At the irradiation location of the irradiation laser beam L2, the aluminum alloy is melted by the applied high energy, and a molten pool 350 made of the melted aluminum alloy is formed. On the other hand, the molten pool 350 solidifies in response to a decrease in temperature due to being deviated from the irradiation portion of the irradiation laser beam L2, and forms a molten portion 340 which is a welded portion.

The density of the aluminum alloy differs between before and after melting due to the solidification shrinkage that occurs after melting. The present inventors have found that the difference in density generated in the battery container 300 by laser welding can be obtained as a tomographic image by the X-ray CT apparatus 600 as the difference in the amount of X-ray transmission.

FIG. 4A is a cross-sectional image of the molten portion 340 formed in the abutting portion 330 laser-welded by the irradiation laser beam L2 of the present embodiment, which is orthogonal to the extending direction (circumferential direction) of the abutting portion 330. be. The irradiation laser beam L2 of the present embodiment has an energy intensity distribution (for example, the energy intensity distribution D6 of FIG. 2) adjusted so that the molten portion 340 has a cross-sectional image shown in FIG. 4 (a).

As shown in FIG. 4A, in the melting portion 340, the region melted by laser welding shrinks from the outside to the inside of the battery container 300 in the cross section orthogonal to the circumferential direction, and the battery container 300 It has a convex region with an inwardly facing tip 341. The surface 320a of the lid 320 and the side end 310a (see FIG. 2) of the case 310 form the outer surface of the battery container 300.

The tip portion 341 faces the direction of the remaining portion 331 of the contact portion 330, which is inside the battery container 300 and remains unmelted. The tip portion 341 has not reached the inside of the battery container 300 in order to prevent the molten metal or the like from entering the inside.

Further, in the convex region, the surface portion 342 of the molten portion 340 extends to the left and right with respect to the irradiation position LP of the irradiation laser beam L2 in the cross section orthogonal to the circumferential direction. In the cross section of the melting portion 340, the surface portion 342 on the outside of the battery container 300 is the flat surface of the battery container 300 (the surface 320a of the lid 320 and the side surface end portion 310a of the case 310, many of which include the contact portion 330. ), But a part of the right side reaches the side surface 310b of the case 310, which is the side surface of the battery container 300 with respect to the plane.

The convex region has a boundary portion including a boundary line L10 between the molten portion 340 and the non-melted portion in a cross section orthogonal to the circumferential direction. The boundary line L10 has the boundary line L1b on the lid 320 side (left side in the figure) from the branch point L1c, with the remaining portion 331 of the contact portion 330 as the branch point L1c, and the case 310 side (right side in the figure) of the branch point L1c. Each has a boundary line L1a. More specifically, the molten portion 340 is composed of a portion melted by laser welding of the lid body 320 and the case 310. The non-melting portion is a portion of the lid body 320 or the case 310 that has not been melted by laser welding. Therefore, the boundary line L1b is on the left side of the contact portion 330 and is a boundary line formed between the molten portion 340 and the non-melted portion of the lid 320, and the boundary line L1a is the boundary line L1a of the contact portion 330. On the right side, it is a boundary line formed between the molten portion 340 and the non-melted portion of the case 310. The convex region is deepest in the central portion corresponding to the irradiation position LP in the left-right direction of the cross section, and becomes shallower as it is separated from the central portion to the left and right. Therefore, the boundary line L10 is a curve corresponding to the shape of the convex region, and is configured as a convex curve from the outside to the inside of the battery container 300.

The melting portion 340 has a total width W11 as a width in the left-right direction orthogonal to the irradiation direction of the irradiation laser beam L2 in a cross section, and has a lid side width W13 on the lid 320 side and a lid side width W13 on the case 310 side of the total width W11. It has a case side width W. Since the boundary line L10 has a convex shape, it is longer than the total width W11. More specifically, since the boundary line L1b is a curve reaching the surface 320a of the lid 320 from the branch point L1c having a depth due to melting, its length is secured longer than the lid side width W13. Further, since the boundary line L1a is a curve reaching the side surface 310b of the case 310 from the branch point L1c having a depth due to melting, the length thereof is from the case side width W which is the shortest distance from the branch point L1c. Will be secured for a long time.

The convex tip portion 341 is formed on an extension of the optical axis LC (center line) of the irradiation laser beam L2. In other words, in the present embodiment, the optical axis LC of the irradiation laser beam L2 is arranged within a predetermined range LD with respect to the contact portion 330 at the time of laser welding. The predetermined range LD is a range that is less than the case side width W. For example, the predetermined range LD can be a range of 0.3 mm, more preferably a range of 0.2 mm.

From this, the angle α between the straight line LR connecting the branch point L1c and the position where the boundary line L1a appears on the side surface 310b of the case 310 and the straight line LH orthogonal to the optical axis LC (center line) of the irradiation laser light L2. Is greater than 0 degrees, in other words, the angle between the optical axis LC and the straight line LR is less than 90 degrees.

By the way, FIG. 4B is an example of a molten portion 340B formed in the abutting portion 330 by laser welding, which was conventionally performed unintentionally for the molten portion 340 to be a cross-sectional image shown in FIG. 4 (a). It is a cross-sectional image showing.

As shown in FIG. 4B, for example, in laser welding with a laser beam having an average energy intensity in the irradiation range, the depth of the melted portion is also average, so that the melt has a shallow melt depth as a whole. Part 340B is formed. Since the depth is shallow as a whole and the energy is average, the boundary line L20 formed between the molten portion 340 and the non-melted portion has a shape closer to a straight line than the above-mentioned boundary line L10. Become. The melting portion 340B has a total width W21 as a width in the left-right direction orthogonal to the irradiation direction of the irradiation laser light in the cross section, has a lid side width W23 on the lid 320 side of the total width W21, and has a case on the case 310 side. It has a side width W22. Since the boundary line L20 is linear, it has a length close to the total width W21. Since the boundary line L2b reaches the surface 320a of the lid 320 from the shallow branch point L2c, it is secured slightly longer than the lid side width W23. Further, since the boundary line L2a reaches the side surface 310b of the case 310 from the shallow branch point L2c, its length is substantially the same as the case side width W22.

Further, as shown in FIG. 1, the laser output unit 200 inputs light E1 which is the light observed in and around the irradiation point of the irradiation laser light L2 from the condenser lens 250, and parallel light is transmitted by the spectroscope 400. It is output separately from L1. That is, the laser output unit 200 causes the light E1 to be input to the condenser lens 250 from the direction opposite to the traveling direction of the irradiation laser light L2. The light E1 includes light emitted from the welding target according to the temperature mode and the melting state of the welding target portion including the molten pool 350. The spectroscope 400 transmits the parallel light L1 with respect to the traveling direction thereof, and transmits the light E1 incident from the direction opposite to the traveling direction of the parallel light L1 at a predetermined direction of 90 ° with respect to the opposite direction. Reflect in the direction.

The light E1 output from the laser output unit 200 in the direction of 90 ° with respect to the opposite direction is input to the image pickup unit 440.
The image pickup unit 440 includes at least one of a visible light wavelength region and an invisible light wavelength region in a wavelength region that can be imaged, and captures an image of light in the wavelength region that can be imaged. That is, the molten pool 350 and its surroundings are imaged as an image composed of visible light and invisible light. The image pickup unit 440 can photograph, for example, light emission (wavelength 400 to 500 nm) when the molten metal is vaporized (plasma) and light emission (wavelength 700 to 800 nm) of the metal generated by the melting.

The welding control unit 500 is connected to the image pickup unit 440 and inputs an captured image. The welding control unit 500 includes an image acquisition unit 510 that acquires an image, a light emission image extraction unit 520 that extracts a light emission image related to a molten state from the captured image, and a melt depth determination unit 530 that determines the melt depth. To prepare for. Further, the welding control unit 500 includes a storage unit 540 that stores data and the like necessary for determining the melting depth. The welding control unit 500 performs a welding process for joining the lid 320 to the case 310 by continuously laser welding the peripheral contact portion 330 of the battery container 300.

The storage unit 540 is a non-volatile storage unit such as a hard disk or a flash memory, and stores determination data 541 used for determining the melting depth and emission image data 542 including light and dark values of the emission image. There is.

Further, the welding control unit 500 outputs the determined melting depth to a display device or the like. Then, the determined melting depth is output via a display device or the like.
The image acquisition unit 510 acquires an image captured from the image pickup unit 440.

The luminescence image extraction unit 520 extracts a luminescence image (for example, see the luminescence image 350A in FIG. 6) from the image captured from the image pickup unit 440. The light emission image is an image showing a range in which light is emitted in response to melting of the welded object by laser welding. In the present embodiment, a state in which the temperature of the aluminum alloy rises, melts, or evaporates due to the energy from the laser beam is imaged in and around the laser irradiation site. When the aluminum alloy is irradiated with a laser, energy is diffused around the laser irradiation site, so that the range in which the applied energy intensity is the same tends to be a circular shape centered on the laser irradiation site. Therefore, the molten pool 350 is also formed in a substantially circular shape, and the light emission generated by the melting of the metal can also be obtained in a circular shape.

The melting depth determination unit 530 determines the melting depth of the laser-welded fusion unit 340 based on the emission image extracted by the emission image extraction unit 520 and the determination data 541. The determination data 541 is data showing the correlation between the light and dark value of the luminescent image and the melting depth, and can specify the melting depth corresponding to the light and dark value of the luminescent image.

Further, the melting depth determination unit 530 determines the melting depth based on the emission image data 542 and the determination data 541 stored in the storage unit 540. The melting depth determination unit 530 acquires the brightness value of the welding position of the contact portion 330 from the light emission image data 542, applies the acquired brightness / dark value to the determination data 541, and calculates the melting depth of the welding position. .. Then, it is determined whether or not the calculated melting depth is within an appropriate melting depth range.

As shown in FIG. 7, the determination data 541 is data showing the correlation between the light / dark value and the melting depth, and is data showing the correlation as shown in the graph L71, for example. The data showing the correlation may be list data, map data, functions, arithmetic expressions, or the like. Usually, the data showing the correlation tends to have a deeper melting depth as the light and dark values are brighter. The relationship between the light and dark values and the melting depth varies slightly depending on the material thickness, the type of material, the intensity distribution of the laser beam, the irradiation diameter of the laser beam, and the like. Therefore, in the present embodiment, the data showing the correlation between the light / dark value and the melting depth can be updated at any time.

As shown in FIG. 1, the X-ray CT apparatus 600 includes an imaging unit 610 that captures an X-ray CT image, an imaging control unit 620 that controls the entire X-ray CT apparatus 600, and a CT imaged by the imaging unit 610. A storage unit 630 for storing an image is provided. The X-ray CT device 600 is a well-known X-ray CT device, and takes a CT image which is a tomographic image of the molten portion 340 of the battery container 300. The X-ray CT apparatus 600 mounts a battery container 300 having a lid 320 laser-welded on a case 310 to be imaged on a sample table 611 of an imaging unit 610, and photographs a CT image on the mounted battery container 300. do. In the present embodiment, the X-ray CT apparatus 600 captures a CT image by the "1a-1a" cutting line set in the range including the melting portion 340 and a CT image by the "1b-1b" cutting line. For example, FIG. 4A is a CT image with a “1a-1a” cutting line, and FIG. 6B is a CT image with a “1b-1b” cutting line. The CT image is a CT image of the melting portion 340 in a direction orthogonal to the direction in which the melting portion 340 is continuously formed (“1a-1a” cutting line), and is predetermined in the direction in which the melting portion 340 is continuously formed. It is a CT image taken continuously at the slice pitch of. The slice thickness and slice pitch are set so that a clearer CT image of the molten portion 340 can be obtained.

The imaging control unit 620 captures a CT image over the entire circumference of the melting unit 340, and stores the CT image captured in a mode capable of specifying the imaging position in the circumferential direction in the storage unit 630.
By the way, the time required for the X-ray CT apparatus 600 to perform full-circle imaging of the molten portion 340 is longer than the time required for laser welding the entire circumference of the fused portion 340. Therefore, the number of batteries 30 in which the X-ray CT device 600 can capture a CT image of the entire circumference of the molten portion 340 during a certain period of time is smaller than the number of batteries 30 in which the entire circumference of the contact portion 330 is laser-welded. Therefore, only the battery 30 sampled from the plurality of laser-welded batteries 30 is photographed by the X-ray CT apparatus 600 in the CT image of the molten portion 340. For example, the X-ray CT apparatus 600 captures a CT image of the latest laser-welded battery 30 at the timing when the next CT image can be captured. Then, the determination data 541 is corrected based on the CT image and the light emission image of the battery 30 in which the CT image is taken. The correction timing is the timing at which the laser welding of the battery 30 from which the CT image is taken is performed.

Therefore, in the present embodiment, in the X-ray CT apparatus 600, the timing at which the battery 30 on which the CT image is taken is laser-welded is set as the past correction timing, and the CT image of the battery 30 laser-welded at the same correction timing is the past. It is a CT image of the correction timing of.

As shown in FIG. 1, the determination data management device 700 manages the update of the determination data 541 used by the welding control unit 500 to determine the melting depth based on the X-ray CT image taken by the X-ray CT apparatus 600. .. The determination data management device 700 can acquire CT image data stored in the storage unit 630 of the X-ray CT device 600. Further, the determination data management device 700 can acquire and update the determination data 541 stored in the storage unit 540 of the welding control unit 500, and can acquire the emission image data 542.

The determination data management device 700 includes a determination control unit 710 that performs arithmetic processing and the like, and a storage unit 720 that stores data and the like used for arithmetic processing.
The storage unit 720 stores the emission image data 721, the CT image data 722, and the reference data 723.

The light emission image data 721 is data of a light emission image corresponding to the correction timing, and is data acquired from the light emission image data 542 of the welding control unit 500 as corresponding to the correction timing.

The CT image data 722 is CT image data corresponding to the correction timing, and is acquired from the X-ray CT device 600 by the determination data management device 700 each time the X-ray CT device 600 completes capturing the CT image of the battery container 300. It is data.

The reference data 723 is CT image model data, emission image model data, determination data model data, determination data past data, and the like. The model data of the CT image can be used as an initial value when the CT image data is not acquired. Further, the model data of the emission image is data that can be used as an initial value of the emission image.

The determination control unit 710 includes a CT determination unit 711 that determines a CT image, and a determination data update unit 712 as a correction unit that updates the determination data.
The CT determination unit 711 acquires the welding positions 635A to 635D (see FIG. 6B) and the melting depth Dx (see FIG. 6B) from the CT image data 722. As for the melting depth Dx, the welding position 635A is the melting depth Da, the welding position 635B is the melting depth Db, the welding position 635C is the melting depth Dc, and the welding position 635D is the melting depth Dd. Is.

Further, the CT determination unit 711 determines whether the acquired melting depth Dx is in the NG region (see FIG. 7) or the OK region (see FIG. 7), and at the same time, the welding position which is an appropriate depth. To identify. The NG region shown in FIG. 7 is a region where the melting depth is too shallow and the melting is insufficient, or a region where the melting depth is too deep and the melting is excessive. The OK region, also shown in FIG. 7, is a region showing an appropriate melting depth.

Further, the CT determination unit 711 performs a fusion shape determination process for determining whether or not the boundary line L1a (see FIG. 4A) of the fusion unit 340 is long and has high reliability.
The melt shape determination process will be described with reference to FIG. The melting shape determination process is performed by the CT determination unit 711 of the determination data management device 700 on the CT determination unit 711 based on the X-ray CT image.

When the melting state determination process is started, the CT determination unit 711 acquires the angle α (see FIG. 4A) of the boundary line L1a of the melting unit 340 (step S10 in FIG. 8). Then, the CT determination unit 711 determines whether or not the acquired angle α is larger than 0 degrees (step S11 in FIG. 8). Since the distance from the tip portion 341 to the outer surface of the battery container 300 is shorter on the case 310 side of the melting portion 340 and cracks are more likely to occur, the case 310 side (right side) is particularly selected as the determination target.

Then, when it is determined that the angle α is 0 degree (NO in step S11 in FIG. 8), the CT determination unit 711 determines that the molten shape is inappropriate and makes an NG determination (step S17 in FIG. 8). The melting state determination process is terminated.

On the other hand, when it is determined that the angle α is larger than 0 degrees (YES in step S11 in FIG. 8), the CT determination unit 711 acquires the case side width W of the melting portion 340 on the right side of the contact portion 330 (FIG. Step S12 of 8. Then, the CT determination unit 711 determines whether or not the case side width W is equal to or greater than the plate thickness t of the case 310 (step S13 in FIG. 8). When it is determined that the case side width W is less than the plate thickness t of the case 310 (NO in step S13 of FIG. 8), the CT determination unit 711 makes an NG determination as the melt shape is inappropriate (FIG. 8). Step S17), the melting state determination process is completed.

On the other hand, when it is determined that the case side width W is equal to or larger than the plate thickness t of the case 310 (YES in step S13 in FIG. 8), the CT determination unit 711 is the boundary line of the melting portion 340 on the right side of the contact portion 330. The length D10 of L1a and the thickness D11 from the tip end portion 341 of the convex portion of the melting portion 340 to the surface 320a of the lid body 320 are acquired (step S14 in FIG. 8). Then, the CT determination unit 711 determines whether or not the length D10 has a value larger than the thickness D11 (step S15 in FIG. 8). When it is determined that the length D10 is a value equal to or less than the thickness D11 (NO in step S15 in FIG. 8), the CT determination unit 711 determines NG if the molten shape is inappropriate (step in FIG. 8). S17), the melting state determination process is completed.

On the other hand, when it is determined that the length D10 is larger than the thickness D11 (YES in step S15 in FIG. 8), the CT determination unit 711 determines that the melt shape is appropriate (FIG. 8). Step S16), the state determination process is completed.

As shown in FIG. 1, the determination data updating unit 712 acquires the light and dark values of the emission image data 721 and also acquires the welding position of the appropriate melting depth Dx specified by the CT determination unit 711. Then, the determination data updating unit 712 specifies the light / dark value corresponding to the appropriate melting depth, and also specifies and updates the graph L71 (see FIG. 7) of the “melting depth-light / dark value relationship curve”. Perform update processing.

(Melting depth-brightness value relationship curve)
Based on FIGS. 6A and 6B, the relationship between the melting depth Dx obtained by the X-ray CT image and the light and dark values of the emission images 350A to 350D can be obtained for each welding position 635A to 635D. 6 (a) and 6 (b) show that the darker the color, the brighter it is. For example, it corresponds to the melting depth Da corresponding to the light emitting image 350A, the melting depth Db corresponding to the light emitting image 350B, the melting depth Dc corresponding to the light emitting image 350C, and the light emitting image 350D. The melting depth Dd is obtained as a correlation. At this time, the brightness value of the light emitting image is "light emitting image 350A <light emitting image 350B <light emitting image 350C <light emitting image 350D", and the melting depth is "melting depth Da <melting depth Db <melting depth Dc". <Melting depth Dd ". Then, from this relationship, it is possible to obtain a light / dark value corresponding to an appropriate melting depth. For example, if the melting depth Dc is an appropriate melting depth, the light and dark values at that time can be obtained from the emission image 350C. At the same time, the light / dark value at the melting depth Da shallower than the melting depth Dc is obtained from the light emitting image 350A, and the light / dark value at the melting depth Dd deeper than the melting depth Dc is obtained from the light emitting image 350D. ..

As shown in FIG. 7, an appropriate melting depth Dx is set as the median Dm, and the melting depth is considered to be distributed between + 4σ and -4σ with respect to the median Dm. It should be noted that + 4σ is a value equal to or lower than the standard upper limit value DH which is the upper limit for maintaining reliability, and -4σ is a value equal to or higher than the standard lower limit value DL which is the lower limit value for maintaining reliability. And. Further, the light / dark value corresponding to + 4σ is calculated from the relationship between the light emitting image 350C and the light emitting image 350D, and the light / dark value corresponding to -4σ is calculated from the relationship between the light emitting image 350C and the light emitting image 350A. In this way, the graph L71 of the "melting depth-bright-dark value relationship curve" showing the correlation between the melting depth and the light-dark value is obtained. Further, from the graph L71, a light / dark value corresponding to the standard lower limit DL of the melting depth and a light / dark value corresponding to the standard upper limit DH of the melting depth are obtained, and an NG region with respect to the light / dark value is determined, in other words, an OK region. Is decided. According to FIG. 7, in laser welding around the entire circumference of the contact portion 330, it is preferable that the acquired light / dark value has a target normal distribution L72 centered on the target value of the light / dark value corresponding to the median Dm. When the normal distribution is biased toward the dark side or the bright side, it is preferable that the normal distribution approaches the target normal distribution L72.

(Welding process)
That is, as shown in FIG. 1, the welding control unit 500 determines the amount of energy applied to the abutting portion 330 so that laser welding with an appropriate melting depth Dx can be performed, depending on the brightness of the light emitting image of the molten pool 350. Feedback control is performed based on the value. For example, the welding control unit 500 is configured to be able to adjust the output of the laser oscillator 110. The welding control unit 500 feedback-controls the intensity of the output of the laser beam from the laser oscillator 110 whose output can be adjusted based on the brightness value of the light emission image.

When the light / dark value changes brighter than the target value at which an appropriate melting depth Dx is considered to be obtained (the melting depth Dx is considered to be deep), the welding control unit 500 applies energy to the welding target portion. In order to reduce the amount, the light / dark value is controlled to approach the target value by adjusting the output of the laser oscillator 110 to decrease. On the contrary, when the light / dark value changes darker than the target value (it is considered that the melting depth Dx becomes shallow), the welding control unit 500 increases the energy applied to the welding target portion, so that the output of the laser oscillator 110 is output. By adjusting so as to increase, the light and dark values are controlled to approach the target value.

That is, the welding control unit 500 controls the energy intensity of the laser beam so that the brightness and darkness values of the dynamically changing laser irradiation points approach the target value, so that the laser welding points have an appropriate melting depth Dx. I am trying to be.

That is, with reference to FIG. 6, in laser welding, if the light and dark values are bright, for example, as in the light emitting image 350D, the material is welded at a deep melting depth Dx as shown in the welding position 635D. However, since the case 310 and the lid 320 of the battery container 300 are thin, if the melting depth Dx becomes deeper than the standard upper limit value DH, a through hole may be formed. Further, it is not preferable that the melting range is widened and the scattering of spatters due to welding increases. On the other hand, if the light and dark values are dark as in the emission images 350A and 350B, the material is welded at a shallow melting depth Dx as shown in the welding positions 635A and 635B. However, there is a possibility that appropriate strength and stability may not be ensured for welding the case 310 and the lid 320. Therefore, in the present embodiment, the light-dark value of the light emission image extracted from the observed light E1 is applied to the contact portion 330 so that the light-dark value is expected to be an appropriate melting depth. The energy intensity is adjusted.

Further, as shown in FIG. 1, the brightness value of the entire circumference is stored as a part of the emission image data 542 based on the emission image of the entire circumference of the contact portion 330. This makes it possible to confirm after the fact whether or not the case 310 and the lid 320 are welded to an appropriate melting depth.

(Melting depth determination process)
As shown in FIG. 1, the welding control unit 500 arranges the irradiation energy of the irradiation laser beam L2 so that the emission image of the molten pool 350 (see FIG. 3) falls within the allowable range of the determination data 541, that is, the light / dark value OK region. Laser welding is performed while adjusting. By the way, the time required to acquire an X-ray CT image with the X-ray CT device 600 for one battery 30 is longer than the time required for laser welding. On the other hand, in the case of laser welding of the battery container 300 having the same member and the same shape, the graph L71 (see FIG. 7) of the “melting depth-brightness value relationship curve” does not change significantly.

Therefore, the welding control unit 500 performs laser welding by continuing to use the set determination data 541 until it is updated. As a result, the light and dark values of the emission image are expected to be distributed as in the target normal distribution L72 (see FIG. 7). Further, it is determined whether or not the entire circumference of the contact portion 330 is properly welded based on the light emitting image and the graph L71 (see FIG. 7) of the “melting depth-brightness value relationship curve”. If it is determined that the entire circumference is properly welded, the battery 30 is determined to be a non-defective product, and if it is determined that the entire circumference is not properly welded, the battery 30 is regarded as a product requiring re-inspection or a defective product. If the luminescent image is in the NG region on the dark side, it is determined that the melting depth (melting) is insufficient, and if the luminescent image is in the NG region on the bright side, it is determined that the melting depth (melting) is excessive.

Conventionally, when an NG product is simply found by sampling inspection, it is necessary to re-inspect or discard all the batteries 30 manufactured up to the previous sampling inspection. On the other hand, according to the present embodiment, the number of batteries 30 that need to be re-inspected and the number of batteries 30 that need to be discarded can be reduced, so-called narrowing down.

For example, as an example of narrowing down, when an NG product is found in an X-ray CT image, the emission image of this NG product and the emission image of a product laser-welded after the production of the product for which the previous X-ray CT image was acquired are obtained. By comparison, it is possible to extract a product having an emission image that matches the aspect of the emission image. A luminescence image that matches the mode of the luminescence image is one that has the same distribution of light and darkness around the entire circumference, or a luminescence image that matches the luminescence image of the part causing inconvenience in some part of the entire circumference. Identified based on having. According to this, only the extracted battery 30 can be subject to re-inspection, disposal, or the like.

For example, as another example of narrowing down, the determination data management device 700 has a graph L71 of the "melting depth-brightness value relation curve" before the update and a graph L71 of the "melting depth-brightness value relational curve" calculated this time. To determine whether or not the two relational curves match. If the two relational curves match, all the NG products after the previous X-ray CT image was taken will be specified in the above example. On the other hand, if the two relational curves do not match, the emission image of the battery 30 manufactured after the previous X-ray CT image was taken is inspected again with the graph L71 of the "melting depth-brightness value relational curve" calculated this time. .. Then, the product corresponding to the NG product is extracted by this re-inspection, and the extracted product is re-inspected. On the other hand, since the battery 30 which is determined to be a non-defective product in both the previous inspection by the graph L71 and the inspection by the current graph L71 is determined to be a non-defective product, it can be said that the re-inspection or the like is not performed. That is, the products to be re-inspected are limited to the products having the same emission image as the NG products and the products judged to be NG products in the graph L71 of the "melting depth-brightness value relationship curve" calculated this time. This can reduce the time and effort required for re-inspection.

(Judgment data update process)
Next, the operation of updating the determination data 541 will be described with reference to FIG. 1.
The emission image data 542 when the battery 30 for which the X-ray CT image is captured is laser welded (correction timing) is specified. Further, the position in the circumferential direction of the X-ray CT image and the position in the circumferential direction of the emission image are synchronized. Then, an appropriate melting depth Dx is set as the median Dm, and the light and dark values at the welding position corresponding to the median Dm are specified. The median Dm, the standard lower limit DL, and the standard upper limit DH, which are appropriate melting depths, are defined according to the structure, type, and the like of the battery container 300. As an example, the standard lower limit DL is 0.16 mm, and the slice interval in the circumferential direction is 5 μm at the minimum.

First, the X-ray CT apparatus 600 measures the melting depth Dx at each welding position in the circumferential direction of the battery 30 to be inspected from the X-ray CT image, and confirms that the entire circumference is equal to or higher than the standard lower limit DL. .. In addition, it is confirmed that the median value Dm and the variation (δ) of the melting depth Dx in the entire circumference are appropriate. As a result, it is first determined that the sampling inspection of the battery 30 to be inspected is OK. Such a determination result may be output as a status display signal or a display signal.

The determination data management device 700 has a melting depth Dx of -4σ with respect to the median Dm, a light / dark value corresponding to the melting depth Dx, and a melting depth of + 4σ obtained from the X-ray CT image obtained from the X-ray CT image for which the sampling inspection is determined to be OK. The light and dark values corresponding to Dx are calculated. Then, a “melting depth-bright / dark value relationship curve” graph L71 is generated by combining the light / dark values corresponding to the standard upper limit value DH and the standard lower limit value DL, and this is used as the determination data 541. Then, the determination data management device 700 updates the determination data 541 of the welding control unit 500 with the generated determination data 541.

It is assumed that the range from -4σ to + 4σ with respect to the median Dm is between the standard lower limit value DL and the standard upper limit value DH. Therefore, if it deviates, it is determined that the melting depth Dx obtained from the X-ray CT image is not suitable for updating the determination data 541. As described above, the determination data management device 700 does not update the determination data 541 of the welding control unit 500 when the graph L71 of the appropriate “melt depth-brightness value relationship curve” cannot be generated. Alternatively, the determination data management device 700 updates the determination data 541 of the welding control unit 500 with the determination data 541 set in the reference data 723 or the previously generated determination data 541.

The effect of this embodiment will be described.
Conventionally, it is possible to identify how the crack was generated in the welded portion after confirming the crack that was generated between the lid 320 and the case 310 and can be confirmed from the outside. could not. Further, it is difficult to confirm the crack in the middle of growing inside the battery 30 from the outside. In this regard, the inventors of the present application identify the location of the crack by taking an X-ray CT image of the molten portion 340 of the battery container 300 of the battery 30, and observe the crack over time to crack the crack. By investigating the relationship between the growth process of the battery 30 and the molten portion 340, it was found that the crack of the battery 30 is formed and grows along the boundary line L1a (see FIG. 4A). Further, the crack of the battery 30 is along the boundary line regardless of whether it is the long boundary line L1a (see FIG. 4A) or the short boundary line L2a (see FIG. 4B). Found to grow. If the crack growth rate is constant, the battery 30 having a long boundary line L1a has a higher probability of lasting longer than the battery 30 having a short boundary line L2a, and the reliability of the battery 30 is enhanced.

For example, FIG. 5 shows the relationship between the stress amplitude and the number of durability lines for each difference in the length of the boundary line. The graph of the melt shape L51 is a graph showing the case of the battery 30 having the boundary line L10 including the long boundary line L1a formed in the melt portion 340 of the present embodiment. On the other hand, the graph of the molten shape L52 is a graph in the case of the battery 30 having the boundary line L20 including the short boundary line L2a formed in the conventional melting portion 340B. For example, when the stress amplitude is 10 MPa, the number of cycles of the battery 30 of the molten shape L52 including the short boundary line L2a is about 20,000, while the number of cycles of the battery 30 of the molten shape L51 is about 1 million. That is, when the molten shape L51 is used, the number of cycles is increased by, for example, about 50 times as compared with the case where the molten shape L52 is used, and the durability is improved, so that the reliability of the battery 30 is improved. Further, for example, in order to secure 1 million cycles, the stress amplitude of the melt shape L51 needs to be limited to about 10 MPa, while the stress amplitude of the melt shape L52 needs to be limited to about 3.5 MPa. .. That is, when the molten shape L51 is used, the stress amplitude can be increased as compared with the case where the molten shape L52 is used, and the durability is improved, so that the reliability is improved.

As described above, according to the secondary battery, the battery container inspection method, and the secondary battery manufacturing method of the present embodiment, the effects listed below can be obtained.
(1) The molten portion 340 has a convex shape, the tip portion 341 thereof faces the contact portion 330 inside the battery container 300, and the surface portion 342 thereof is outside the battery container 300 and either in the left-right direction. It will spread to the plate thickness t. As a result, in the battery container 300, the boundary portion including the boundary line L1a formed between the molten portion 340 and the non-melted portion becomes an arc shape having a length equal to or more than the plate thickness t and longer than a straight line. Therefore, even if the boundary portion has a low strength, the strength is increased by lengthening the boundary portion, and the force and time required for breaking are increased, so that the reliability of the molten portion 340 is improved.

(2) Since the optical axis LC (center line) of the irradiation laser beam L2 passing through the convex tip portion 341 is within 0.3 mm with respect to the contact portion 330 inside the battery container 300, from the tip portion 341. The length of the boundary line L1a of the boundary portion between the molten portion 340 and the non-melted portion up to the side surface 310b as the side surface portion can be made longer.

(3) Since the spread of the molten portion 340 is less than 90 degrees with respect to the direction in which the outside of the battery container 300 is viewed from the contact portion 330 inside the battery container 300, the molten portion 340 reaching the side surface 310b from the tip portion 341. The boundary line L1a between the unmelted portion and the non-melted portion can be lengthened.

(4) With the X-ray CT device 600, the restrictions on the imaging conditions are relaxed, and the CT image can be acquired in a form in which the time required for imaging is suppressed to the same level as before. For example, restrictions on the evaluation method described in Patent Document 1, for example, eliminating or simplifying the trouble of arranging the battery in the water of the water tank and having to bring the ultrasonic sensor close to the battery container. be able to.

(5) The length of the boundary line L1a can be secured to be long. For example, the predetermined length can be the plate thickness t of the battery container 300 constituting the side surface or the plate thickness of the lid 320.
(6) Even if the relationship between the light / dark value and the melting depth changes depending on the state of the material, the shape and output of the laser beam, the relationship between the light / dark value and the melting depth is corrected by the comparison at the correction timing, and this correction is made. Since the energy intensity irradiated with the laser beam is controlled by the relationship between the light and dark values and the melting depth, laser welding is preferably performed.

(7) By using the X-ray CT device 600, the melting depth can be measured with high accuracy by non-destructive inspection without mechanical deformation. Further, if it is a non-destructive inspection that does not require a cutting interval or a cutting margin, the state of the molten portion 340 can be continuously inspected in the extending direction. In particular, it has been newly found that the range in which the density change has changed due to recoagulation can be clearly measured by the X-ray CT apparatus 600. With the X-ray CT apparatus 600, it is possible to acquire a CT image in a form in which restrictions on imaging conditions are suppressed and the time required for imaging is suppressed to the same level as before.

(8) By continuously monitoring the emission image of the image over the entire circumference of the contact portion 330 in the circumferential direction, the contact portion 330 of the battery container 300 may be defective and may be overlooked when cut at predetermined intervals. Even a certain defect can be detected.

(9) The laser beam applies energy to the corresponding irradiation range of the top hat type on average to enable stable welding, and its control is easy, and the corresponding irradiation range of the Gauss type It is possible to perform reliable welding with high energy in the central part.

(Other embodiments)
This embodiment can be modified and implemented as follows. The present embodiment and the following modified examples can be implemented in combination with each other within a technically consistent range.

-In the above embodiment, the case where one "melting depth-brightness value relationship curve" is provided for the battery 30 is illustrated. However, not limited to this, the "melting depth-brightness value relationship curve" is set for each welding position of the case, or the entire circumference of the contact portion is divided into several sections for each welding section. You may set it. Even if the relationship between the light / dark value and the melting depth changes depending on the welding position and the welding section of the battery container as the welding object, the relationship between the light / dark value and the melting depth is defined in those welding positions, etc., so that each welding Welding can be performed appropriately for the position.

-In the above embodiment, the case where the welding control unit 500 adjusts the output of the laser oscillator 110 has been exemplified. However, the present invention is not limited to this, and if the energy applied to the welding target portion can be adjusted, the welding control unit may adjust the applied energy in other embodiments. For example, the amount of energy may be adjusted by changing the irradiation range of the laser beam by controlling the optical system of the laser output unit or controlling the distance to the battery. Further, the amount of energy may be adjusted by changing the relative speed of the laser beam by controlling the relative speed between the laser output unit and the battery. That is, the melting depth is maintained or changed by adjusting the amount of energy applied to the laser irradiation site.

In the above configuration, the oscillating laser light L0 may be a laser light other than a semiconductor laser, for example, a laser light such as a high-brightness YAG laser.
-In the above embodiment, an example of the energy intensity distribution D6 of the irradiation laser beam L2 is an example of a top hat type + Gaussian type. However, the intensity distribution of the energy of the laser beam is not limited to this, and may be mainly a Gaussian type, a top hat type, or the like. When a Gaussian type laser is used, the irradiation range is narrowed and energy can be easily concentrated, so that the time required for forming a keyhole can be shortened, and the time required for laser welding can be shortened.

-In the above embodiment, the case where the case 310 and the lid 320 are made of aluminum (including an aluminum alloy) has been exemplified. However, the present invention is not limited to this, and the case and the lid may be made of a metal material other than aluminum such as iron, an alloy such as copper or stainless steel. The metal material other than aluminum may be any material that can be used as a container and can be welded by laser light. As a result, the degree of freedom in designing the battery case and lid can be improved.

-In the above embodiment, the welding control unit 500 adjusts the amount of energy applied while determining the brightness value of the laser irradiation portion dynamically changing in the welding process (indirectly determining the melting depth). The case was illustrated. However, the welding control unit is not limited to this, and after welding one battery or welding a predetermined section of the contact portion, the welding of the next battery or the next is based on the brightness value of the welded portion. Feedback control may be performed so as to adjust the energy intensity applied when welding the section. This makes it possible to reduce the load of acquiring and calculating the light and dark values.

In the above embodiment, a case where a contact portion 330 extending in the vertical direction is provided by fitting the lid 320 into the opening 310c of the case 310 has been illustrated. However, the present invention is not limited to this, and the contact portion 330 may be provided in the horizontal direction so as to cover the side surface end portion 310a around the opening 310c of the case 310 so as to cover the lid. At this time, in laser welding, the laser may be irradiated so that the extending direction of the contact portion is the irradiation direction of the laser. At this time, the side surface of the case constitutes a laser-welded flat surface, and the end portion of the outer peripheral portion of the lid constitutes a side surface with respect to the laser-welded flat surface.

-In the above embodiment, the timing at which the laser welding of the battery 30 is performed is set as the correction timing, but the correction timing may be after a predetermined time has elapsed after the laser welding of the battery is performed or at any timing.

-In the above embodiment, the case where the case 310 of the battery container 300 and the lid 320 are welded is exemplified, but the present invention is not limited to this, and if laser welding is required, the battery other than the case and the main body is a laser. It may be the object of welding.

30 ... Battery, 110 ... Laser oscillator, 200 ... Laser output unit, 250 ... Condensing lens, 260 ... Collimating lens, 261 ... Intensity distribution converter, 300 ... Battery container, 310 ... Case, 310a ... Side edge, 310b ... Side surface, 310c ... Opening, 320 ... Lid, 320a ... Surface, 320b ... Outer circumference, 330 ... Contact part, 331 ... Remaining part, 340 ... Welded part, 340B ... Melted part, 341 ... Tip part, 342 ... Surface Unit, 350 ... molten pond, 350A ... emission image, 350A-350D ... emission image, 350B ... emission image, 350C ... emission image, 350D ... emission image, 400 ... spectroscope, 440 ... image pickup unit, 500 ... welding control unit, 510 ... Image acquisition unit, 520 ... Emission image extraction unit, 530 ... Welding depth determination unit, 540 ... Storage unit, 541 ... Judgment data, 542 ... Emission image data, 600 ... X-ray CT device, 610 ... Imaging unit, 611. ... Sample stand, 620 ... Imaging control unit, 630 ... Storage unit, 635A ... Welding position, 635A-635D ... Welding position, 635B ... Welding position, 635D ... Welding position, 700 ... Judgment data management device, 710 ... Judgment control unit, 711 ... CT judgment unit, 712 ... Judgment data update unit, 720 ... Storage unit, 721 ... Light emission image data, 722 ... CT image data, 723 ... Reference data, α ... Angle, t ... Plate thickness, Da to Dd ... Weld depth Dx ... melting depth, E1 ... light, W ... case side width, L0 ... oscillating laser light, L1 ... parallel light, L2 ... irradiation laser light, L3 ... conversion laser light.

Claims (12)

A secondary battery comprising a battery container in which the opening of a metal case containing a power generation element is sealed by a metal lid.
A circumferential contact portion between the opening portion of the case and the outer peripheral portion of the lid body is provided with a melting portion melted in the circumferential direction in which the contact portion extends by laser welding.
The molten portion is a convex region having a tip portion in which the region melted by the laser welding is reduced inward from the outer surface of the battery container and faces inward in a cross section orthogonal to the circumferential direction. hand,
In the cross section orthogonal to the circumferential direction, the convex shape has the tip end facing the contact portion inside the battery container, and the outer surface portion of the battery container is a laser for laser welding. It spreads to the left and right of the position where the light was irradiated,
The tip portion has not reached the inside of the battery container and has not reached the inside.
The front surface portion has one of the left and right sides of the cross section reaching the side surface with respect to the laser-welded plane on the outside of the battery container .
The length of the boundary line of the molten portion outside the contact portion is a value larger than the thickness from the tip portion of the convex portion of the fused portion to the surface of the lid body.
Secondary battery. The secondary battery according to claim 1, wherein the convex shape is such that the center line from the surface portion to the tip portion passes within 0.3 mm from the contact portion inside the battery container. When the boundary portion of the molten portion from the tip portion of the convex shape to the non-melted portion reaching the side surface is viewed from the contact portion inside the battery container, the viewing direction thereof. The secondary battery according to claim 2, wherein the secondary battery is arranged in a range of less than 90 degrees on the side surface side of the center line. The opening of the metal case is a battery container for a secondary battery sealed by a metal lid, and a circumferential contact portion between the opening of the case and the outer peripheral portion of the lid. Is an inspection method for inspecting a battery container provided with a molten portion melted in the circumferential direction in which the contact portion extends by laser welding with a laser beam.
An image including a region melted by the laser welding is acquired for the cross section of the melted portion, which is orthogonal to the circumferential direction.
Based on the acquired image, the region melted by the laser welding is a convex region having a tip portion that shrinks inward from the outer surface of the battery container and faces inward, and the convex shape is In the cross section orthogonal to the circumferential direction, the tip portion faces the contact portion inside the battery container, and the outer surface portion of the battery container faces the left and right of the position where the laser beam is irradiated. The tip portion does not reach the inside of the battery container, and the surface portion reaches the side surface of the cross section with respect to the laser-welded plane surface on the outside of the battery container. And
Inspection of the battery container for inspecting that the length of the boundary line of the molten portion outside the contact portion is larger than the thickness from the tip portion of the convex portion of the fused portion to the surface of the lid body. Method. The method for inspecting a battery container according to claim 4, wherein an image including a region melted by laser welding is acquired by an X-ray CT apparatus. In the inspection, when the convex boundary line reaching the side surface is longer than a preset length and the outside of the battery container is viewed from the contact portion inside the battery container. The method for inspecting a battery container according to claim 5, wherein the battery container is inspected whether or not it is arranged in a range of less than 90 degrees from the center line of the convex shape to the side surface side in the viewed direction. The method for inspecting a battery container according to claim 6, wherein the preset length is the shortest distance from the tip portion of the convex shape to the side surface of the battery container. A method for manufacturing a secondary battery including a battery container that is laser-welded in such a manner that the energy intensity irradiated with the laser beam can be changed.
The image acquisition unit acquires an image of the irradiation point of the laser beam and its surroundings, and obtains an image.
The emission image of the image is extracted by the extraction unit, and the emission image is extracted.
The control unit irradiates the laser beam so that the melting depth becomes a predetermined depth based on the relationship between the light emission image of the image and the light / dark value and the melting depth preset in the storage unit. Control the energy intensity
The correction unit corrects the relationship between the light / dark value and the melting depth preset in the storage unit.
The correction unit compares the melting depth of the irradiation point of the laser beam at the past correction timing with the light emission image of the image at the past correction timing, and the light / dark value preset in the storage unit. A method for manufacturing a secondary battery that corrects the relationship between the melting depth and the melting depth. The method for manufacturing a secondary battery according to claim 8, wherein the melting depth of the irradiated portion of the laser beam is measured by a non-destructive inspection using an X-ray CT device. The method for manufacturing a secondary battery according to claim 8 or 9, wherein the relationship between the light and dark values and the melting depth is defined for each welding position or each welding section of the object to be welded. The irradiation point of the laser light is a secondary battery including a battery container in which the opening of a metal case accommodating a power generation element is sealed with a metal lid, and the opening and the lid of the case are provided. It is a circumferential contact part with the outer peripheral part of the body.
The determination unit acquires the melting depth over the entire circumference of the abutting portion from the relationship between the light and dark values and the melting depth based on the emission image of the image acquired over the entire circumference of the abutting portion. The method for manufacturing a secondary battery according to any one of claims 8 to 10, wherein it is determined whether or not the melting depth over the entire circumference is appropriate based on the above. The laser beam is a combination of a first laser beam having a Gaussian intensity distribution and a second laser beam having an irradiation diameter larger than that of the first laser beam and having a top hat type intensity distribution. Any of claims 8 to 11, wherein the laser beam is generated by the above-mentioned method and has a distribution in which the intensity of the generated laser beam has the maximum value in the central portion surrounded by the peripheral portion. The method for manufacturing a secondary battery according to item 1.

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